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™
Everything Easier!
Making

Biology
Learn to:
• Identify and dissect the many structures
and functions of plants and animals
• Grasp the latest discoveries in
evolutionary, reproductive, and
ecological biology
• Think like a biologist and use scientific
methods

Rene Fester Kratz, PhD
Author of Molecular and Cell Biology
For Dummies

Donna Rae Siegfried
Writer and former college professor

2nd Edition

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About the Authors
Rene Fester Kratz, PhD, teaches cellular biology and microbiology
...
Kratz is also
the author of Molecular and Cell Biology For Dummies and Microbiology The
Easy Way
...
She has taught anatomy and physiology at the
college level
...


Dedication
To the memory of Cindy Fuller Kratz Berdan, RN
...
—Rene Kratz

Author’s Acknowledgments
Thanks to Matt Wagner, of Fresh Books, Inc
...
And thanks to all the
great people at Wiley who made it happen: editors Tim Gallan and Jennifer
Tebbe, acquisitions editor Erin Calligan Mooney, art coordinator Alicia South,
and technical reviewers Michael Pratt and Medhane Cumbay
...
On the home front, thanks to my husband, Dan, and my
sons, Hueston and Dashiel, for all of their love and support
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custhelp
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For other comments, please contact our Customer
Care Department within the U
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at 877-762-2974, outside the U
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at 317-572-3993, or fax 317-572-4002
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Cumbay,
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Amick
Art Coordinator: Alicia B
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the5thwave
...
1
Part I: Biology Basics
...
9
Chapter 2: How Life Is Studied
...
27
Chapter 4: The Living Cell
...
65

Part II: Cell Reproduction and Genetics:
Let’s Talk about Sex, Baby
...
81
Chapter 7: Making Mendel Proud: Understanding Genetics
...
113
Chapter 9: Engineering the Code: DNA Technology
...
141
Chapter 10: Biodiversity and Classification
...
159
Chapter 12: Evolving Species in an Ever-Changing World
...
203
Chapter 13: Pondering the Principles of Physiology
...
211
Chapter 15: Going with the Flow: Respiratory and Circulatory Systems
...
241
Chapter 17: Fighting Back: Human Defenses
...
277
Chapter 19: Reproduction 101: Making More Animals
...
319
Chapter 20: Living the Life of a Plant
...
333

Part VI: The Par t of Tens
...
343
Chapter 23: Ten Ways Biology Affects Your Life
...
351

Table of Contents
Introduction
...
1
Conventions Used in This Book
...
2
Foolish Assumptions
...
3
Part I: Biology Basics
...
3
Part III: It’s a Small, Interconnected World
...
4
Part V: It’s Not Easy Being Green: Plant Structure and Function
...
5
Icons Used in This Book
...
5

Part I: Biology Basics
...
9
It All Starts with a Cell
...
10
Making the Connection between Ecosystems and Evolution
...
11
Comparing Plants to People
...
13
Living Things: Why Biologists Study Them and What Defines Them
...
15
Introducing the scientific method
...
18
Seeing Science as the Constant Sharing of New Ideas
...
24
Journals: Not just for recording dreams
...
25
The popular press: Not always accurate
...
25

x

Biology For Dummies, 2nd Edition
Chapter 3: The Chemistry of Life
...
27
Recognizing the Differences between Atoms,
Elements, and Isotopes
...
29
Elements of elements
...
32
Molecules, Compounds, and Bonds
...
33
“Ph”iguring out the pH scale
...
35
Carbon-Based Molecules: The Basis for All Life
...
36
Making life possible: Proteins
...
41
Supplying structure, energy, and more: Lipids
...
47
An Overview of Cells
...
49
Examining the Structure of Eukaryotic Cells
...
52
Holding it all together: The plasma membrane
...
57
Controlling the show: The nucleus
...
58
Serving as the cell’s factory: The endoplasmic reticulum
...
59
Cleaning up the trash: Lysosomes
...
59
Providing energy, ATP-style: Mitochondria
...
60
Presenting Enzymes, the Jump-Starters
...
62

...
62
Getting some help from cofactors and coenzymes
...
63

Chapter 5: Acquiring Energy to Run the Motor
...
65
Looking at the rules regarding energy
...
67
Transferring energy with ATP
...
68
Finding food versus producing your own
...
70
Transforming energy from the ultimate energy source
...
72
Cellular Respiration: Using Oxygen to Break Down Food for Energy
...
74
Transferring energy to ATP
...
76

Part II: Cell Reproduction and Genetics:
Let’s Talk about Sex, Baby:
...
81
Reproduction: Keep On Keepin’ On
...
82
Cell Division: Out with the Old, In with the New
...
87
Mitosis: One for you, and one for you
...
91
How Sexual Reproduction Creates Genetic Variation
...
96
Crossing-over
...
96
Fertilization
...
97
Pink and blue chromosomes
...
101
Why You’re Unique: Heritable Traits
and the Factors Affecting Them
...
103
Pure breeding the parentals
...
104
Reviewing Mendel’s results
...
105
Bearing Genetic Crosses
...
108
Creating pedigree charts
...
111
Drawing conclusions about traits
...
113
Proteins Make Traits Happen, and DNA Makes the Proteins
...
114
Rewriting DNA’s message: Transcription
...
118
Converting the code to the right language: Translation
...
124
Giving Cells Some Control: Gene Regulation
...
127
Becoming an expert through differentiation
...
129
Understanding Just What’s Involved in DNA Technology
...
130
Combining DNA from different sources
...
132
Copying a gene with PCR
...
135
Mapping the Genes of Humanity
...
138
Why GMOs are beneficial
...
139

Part III: It’s a Small, Interconnected World
...
143
Biodiversity: Recognizing How Our Differences Make Us Stronger
...
144
Surveying the threats posed by human actions
...
146
Protecting biodiversity
...
148
Unsung heroes: Bacteria
...
149
A taste of the familiar: Eukaryotes
...
152
Mastering the domains
...
154
Playing the name game
...
159
Ecosystems Bring It All Together
...
160
Why can’t we be friends: Interactions between species
...
163
Reviewing the basic concepts of population ecology
...
167
Taking a closer look at the human population
...
173
Going with the (energy) flow
...
178

Chapter 12: Evolving Species in an Ever-Changing World
...
183
How Charles Darwin Challenged Age-Old Beliefs
about Life on Earth
...
185
Darwin’s theory of biological evolution
...
186
The Evidence of Biological Evolution
...
190
Comparative anatomy
...
191
Molecular biology
...
193
Observable data
...
195
Why So Controversial? Evolution versus Creationism
...
197
Fossil finds
...
201
Check out the big brain on the Homo sapien
...
203
Chapter 13: Pondering the Principles of Physiology
...
205
Wrapping Your Head around the Big Physiological Ideas
...
207
Balancing the body to maintain homeostasis
...
209
Recognizing that what comes in, must go out
...
211
Doing the Locomotion, Animal-Style
...
212
Splitting apart vertebrate skeletons
...
213
Joining the movement fun
...
215
Muscle tissue and physiology
...
218

Chapter 15: Going with the Flow: Respiratory
and Circulatory Systems
...
221
Integumentary exchange
...
223
Tracheal exchange systems
...
224
Circulation: Nutrients In, Garbage Out
...
227
Closed circulatory systems
...
228
A worm’s heart and circulatory system
...
229
Exploring the Human Heart and Circulatory System
...
233
Navigating the path of blood through the body
...
236
A Bloody-Important Fluid
...
237
The plasma “stream” in your bloodstream
...
239

Chapter 16: Checking Out the Plumbing:
Animal Digestive and Excretory Systems
...
241
The Ins and Outs of Digestive Systems
...
243
Continuous versus discontinuous feeders
...
244
The busiest stop of all — your mouth
...
245
The long and winding road of your small intestine
...
247
How nutrients travel through your body
...
248

Table of Contents
What’s for Dinner? Making Wise, Nutritious Food Choices
...
250
Proteins: You break down their chains; they build yours
...
252
Minerals and vitamins: The fuel for your enzymes
...
254
Getting to know your large intestine and
how it eliminates solid wastes
...
255

Chapter 17: Fighting Back: Human Defenses
...
259
Good bacteria: Health helpers
...
260
Viruses: All bad, all the time
...
262
Your body’s best blockers: Skin and mucous membranes
...
264
Microbe seeker-outers: Dendritic cells
...
266
Damage control: Inflammation
...
267
Learning a Lesson: Adaptive Human Defenses
...
269
Soldiers on the march: B cells and antibodies
...
270
Giving Your Defenses a Helping Hand
...
271
Using viruses to kill bad bacteria
...
273
Getting ahead of the game with vaccines
...
275

Chapter 18: The Nervous and Endocrine Systems,
Messengers Extraordinaire
...
277
Distinguishing between the CNS and PNS
...
280
Processing signals with the three types of neurons
...
281
What a Sensation! The Brain and the Five Senses
...
283
Mmm, mmm, good: Taste
...
285
Seeing is believing: Sight
...
286

xv

xvi

Biology For Dummies, 2nd Edition
Following the Path of Nerve Impulses
...
287
Jumping the gap between neurons
...
291
Seeing how hormones work
...
293

Chapter 19: Reproduction 101: Making More Animals
...
295
The Ins and Outs of Sexual Reproduction
...
297
Mating rituals and other preparations for the big event
...
304
How Other Animals Do It
...
309
From single cells to blastocyst
...
311
Fetal development and birth
...
313
The ability to become any type of cell
...
315
Gender differentiation in humans
...
319
Chapter 20: Living the Life of a Plant
...
321
Plant tissues
...
322
Herbaceous versus woody stems
...
326
Going It Alone: Asexual Reproduction
...
328
The life of a plant
...
330
How pollination and fertilization occur
...
332
A little protection for the embryo: Seeds
...
333
How Nutrients, Fluids, and Sugars Move through Plants
...
334
Transporting water and other nutrients from the ground up
...
337
Controlling water loss
...
340

Part VI: The Par t of Tens
...
343
Seeing the Unseen
...
343
Protecting People from Smallpox
...
344
Finding and Fighting Defective Genes
...
345
Evolving the Theory of Natural Selection
...
345
Moving Energy through the Krebs Cycle
...
346

Chapter 23: Ten Ways Biology Affects Your Life
...
347
Putting Microbial Enzymes to Work
...
348
Obtaining Fossil Fuels for Energy
...
348
Staying Alive
...
349
Changing Physically and Mentally
...
350
Facing Extinction
...
351

xvii

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Biology For Dummies, 2nd Edition

Introduction

L

ife is all around you, from invisible microbes and green plants to the
other animals with whom you share the Earth
...
Plants make your food and provide you with oxygen, microbes
break down dead matter and recycle materials that all living things need, and
insects pollinate the plants you rely on for food
...

What makes biology so great is that it allows you to explore the interconnectedness of the world’s organisms and really understand that living beings are
works of art and machines rolled into one
...
And regardless of
whether they’re plants, animals, or microbes, all living things have numerous
working parts that contribute to the function of the whole being
...

Biology is the key you need to unlock the mysteries of life
...
Biology also helps you
realize what a truly miraculous machine your body is, with its many different
systems that work together to move materials, support your structure, send
signals, defend you from invaders, and obtain the matter and energy you
need for growth
...
It also provides an overview of the concepts and processes
that are fundamental to living things
...


2

Biology For Dummies, 2nd Edition

Conventions Used in This Book
To help you find your way through the subjects in this book, we use the following style conventions:
✓ Italics highlight new words or terms that are defined in the text
...

✓ Boldface indicates key words in bulleted lists or the action parts of numbered steps
...

✓ Sidebars are gray-shaded boxes that contain text that’s interesting to
know but not necessarily critical to your understanding of the chapter
or section topic
...


What You’re Not to Read
Throughout this book you’ll find paragraphs marked with a Technical Stuff
icon and sidebars (gray-shaded boxes)
...
They’re fun to read,
but they’re by no means necessary for a thorough understanding of biology
...
Here’s what we came up with:
✓ You’re a high school student taking biology, possibly in preparation for
an advanced placement test or college entrance examination
...

✓ You’re a college student who isn’t a science major but is taking a biology
class to help fulfill your degree requirements
...
If you need to fix a concept in your
brain, read the related section after class
...
Good news
...
We
include several examples of how biology impacts everyday life to help
keep your interest piqued
...
Like all For Dummies books, each
chapter is self-contained, so you can pick up this book whenever you need it
and jump straight into the topic you’re working on
...
If
you don’t read the book in order, you may occasionally have to refer back to
an earlier section for some background information
...


Part I: Biology Basics
If biology is the study of life and life is so complex, then you may be wondering where to even begin in your study of biology
...
This part breaks
down the all-encompassing field of biology into smaller, more palatable
chunks
...
Next, we give you
a review of the types of molecules that are important to a cell’s functioning
(yes, this means delving into some basic chemistry; sorry!)
...
Every organism, whether it’s a
human, a dog, a flower, a strep throat bacterium, or an amoeba, has at least
one cell (most actually have millions)
...


Part II: Cell Reproduction and Genetics:
Let’s Talk about Sex, Baby
How do you get a multicellular human from a one-celled embryo? Cellular
reproduction, of course! Cells can make exact copies of themselves in order

3

4

Biology For Dummies, 2nd Edition
to repair, grow, or produce offspring that are genetically identical to the
parent cell
...

Regardless of whether organisms reproduce asexually or sexually, the traits
of the parents are visible in the offspring because parents pass DNA on to
their offspring
...


Part III: It’s a Small, Interconnected World
All the amazingly diverse forms of life on Earth interact with each other (if
they didn’t, life on this planet would be in big trouble)
...
You also get to discover how yesterday’s living beings are
connected to today’s living beings through biological evolution
...
Animals have many different systems designed to support this struggle for balance
...
These systems
coordinate many functions in animals, such as digestion, movement, circulation, gas exchange, and defense
...
However, the importance of plants to life on Earth simply can’t
be overstated
...
When you
take the time to study plants, you find that they’re actually pretty interesting
...


Introduction

Part VI: The Part of Tens
No For Dummies book would be complete without The Part of Tens and its
chapters containing fun and interesting facts
...


Icons Used in This Book
We use some of the familiar For Dummies icons to help guide you and give you
new insights as you read the material
...

The information highlighted with this icon is stuff we think you should permanently store in your mental biology file
...

Next to these icons lie paragraphs that give you extra information but
aren’t necessary to understanding the material in the chapter
...
If you just want the basics and don’t want to bother
with nonessential information, skip them
...


Where to Go from Here
Where you start reading is up to you
...

✓ If you’re using this book as a companion to a biology class that’s just
beginning, you can follow along with the topics being discussed in class
with one small exception
...
We
prefer to start with cells to give you an idea of where everything is happening before moving on to the molecules
...


5

6

Biology For Dummies, 2nd Edition

Part I

Biology Basics

B

In this part
...
One goal of this part is to immerse you
in the world of biology so you can understand how biologists go about studying living things and know what chemical components make up all forms of life
...
Cells are the
smallest entities that show all the properties of life, so
that’s where we begin zeroing in on things
...


Chapter 1

Exploring the Living World
In This Chapter
▶ Seeing how cells are part of all living things
▶ Finding out the fundamentals of where babies come from and why you have the traits

you do
▶ Recognizing that all of Earth’s ecosystems are interconnected
▶ Surveying animal anatomy and physiology
▶ Exploring the similarities and differences between plants and people

B

iology is the study of life, as in the life that covers the surface of the
Earth like a living blanket, filling every nook and cranny from dark
caves and dry deserts to blue oceans and lush rain forests
...
For many people, a hike in the forest or a trip
to the beach is a chance to reconnect with the natural world and enjoy the
beauty of life
...
Our
goal is to show you how biology connects to your life and to give you a preview of the topics we explore in greater detail later in this book
...
What’s the smallest unit of life you can think of? (Here’s a hint: Try to
recall the basic properties of life; if you can’t, head to Chapter 2 to discover
what they are
...
The absolute smallest unit
of life is a single cell
...
coli bacteria or a
human being made up of approximately 10 trillion cells
...
coli
...
Yet you have some
distinct similarities as well
...
coli are made up of the same raw
materials (flip to Chapter 3 to find out what those are) and have DNA as your
genetic material (more on DNA in Chapter 8)
...


Life Begets Life: Reproduction
and Genetics
You began life as a single cell, when a sperm cell from your dad met an egg
cell from your mom
...
When their reproductive cells combined, your dad and mom each
donated half of your genetic information — 23 chromosomes from mom and
23 from dad — for a total of 46 chromosomes in each of your cells
...
The science of genetics tracks the
inheritance of genes and studies how they determine traits (see Chapter 7)
...

Your genes are found in your DNA, which is in turn found in your chromosomes
...
Each type of cell in your body uses the blueprints found in your
genes to build the proteins it needs to do its particular job
...

Scientists are discovering more and more about DNA; they’re also developing
tools to read and alter the DNA in cells (see Chapter 9)
...
Why? Because scientists use recombinant DNA technology to
alter organisms used in food and medicines
...
For example, scientists alter the cells of bacteria with human genes, turning them into tiny living
factories that produce human proteins needed to treat diseases
...
Each type of organism
plays a role in the environment, and each one is connected to the other
...
(For
more on the interconnectedness of all living things on Earth, head to Chapter 11
...
However, the human
species is unusual in its ability to use technology to extend its reach, drawing heavily on the natural resources of the Earth and changing environments
to suit its needs
...

Yet as humans draw more heavily upon the Earth’s resources, we’re putting
stress on many other species and possibly driving them to extinction
...
The challenge that humans face today is discovering ways to get
what we need but still live in balance with the Earth’s various ecosystems
...
In a complex, multicellular animal like you, all of your organ systems
must work together to maintain homeostasis
...
Made up of your bones (see Chapter 14)
...
Consists of your skeletal and
smooth muscles (see Chapter 14)
...
Made
up of your lungs and airways (see Chapter 15)
...
Consists
of your heart, blood, and blood vessels (see Chapter 15)
...

Made up of your stomach, intestines, liver, and pancreas (see Chapter 16)
...
Consists of your kidneys and bladder
(see Chapter 16)
...
Made up of your skin (see Chapter 17)
...
Consists of your
thymus, spleen, and lymph nodes (see Chapter 17)
...

Made up of your brain, spinal cord, and nerves (see Chapter 18)
...
Consists of your glands (see Chapter 18)
...
Made
up of ovaries, fallopian tubes, a uterus, a cervix, a vagina, and a vulva
if you’re female, and testes, a scrotum, vas deferens, a prostate gland,
seminal vesicles, and a penis if you’re male (see Chapter 19)
...
Both humans and
plants engage in sexual reproduction, meaning they produce new offspring
from the fusion of sperm and eggs that contain half the genetic material of
the parents (see Chapter 20 for more information on how plants reproduce)
...

Of course, plants also have major differences from humans
...
As a
byproduct of their food production, plants give off oxygen as waste
...


Chapter 2

How Life Is Studied
In This Chapter
▶ Studying life
▶ Using observations to solve the world’s mysteries
▶ Recognizing science as an always-changing thing
▶ Discovering where to find scientists’ research and conclusions

B

iology wouldn’t have gotten very far as a science if biologists hadn’t
used structured processes to conduct their research and hadn’t communicated the results of that research with others
...
It also introduces you to the methods scientists (whether
they’re biologists, physicists, or chemists) use to investigate the world around
them and the tools they use to communicate what they’ve discovered
...
Organisms are part of the
natural world — they’re made of the same chemicals studied in chemistry
and geology, and they follow the same laws of the universe as those studied
in physics
...
Granted, life is a little hard to define, but
biologists have found a way
...
A cell is the smallest
part of a living thing that retains all the properties of life
...
DNA, short for deoxyribonucleic acid, is the
genetic material, or instructions, for the structure and function of cells
...
)
✓ Living things maintain order inside their cells and bodies
...

According to this law, if you build a sand castle, it’ll crumble back into
sand over time
...
Living things, as long as they remain alive, don’t
crumble into little bits
...
(To find out how living things obtain
the energy they need to maintain themselves, turn to Chapter 5
...
Living things maintain their internal conditions in a way that supports life
...
Think about what happens when you go outside on a cool day
without wearing a coat
...
It may also trigger
shivering, which gets you moving and generates more body heat
...
(When living
things maintain their internal balance, that’s called homeostasis; you can
find out more about homeostasis in Chapter 13
...
If you pop up suddenly and say “Boo!” to a rock, it doesn’t do anything
...
That’s
because living things have systems to sense and respond to signals
...
(Have you ever seen a houseplant bend and
grow toward sunlight? Then you’ve seen one of the responses triggered
by a plant cell detecting the presence of light
...

✓ Living things transfer energy among themselves and between themselves and their environment
...
Organisms such as plants capture light energy from the Sun and use it to build food molecules that
contain chemical energy
...
As cellular processes occur, they transfer energy back to the
environment as heat
...
)
✓ Living things grow and develop
...
That
cell divided to form new cells, which divided again
...
As your body grew, your cells
received signals that told them to change and become special types of
cells: skin cells, heart cells, liver cells, brain cells, and so on
...

The DNA in your cells controlled all of these changes as your body
developed
...
)
✓ Living things reproduce
...
When organisms
reproduce, they pass copies of their DNA onto their offspring, ensuring
that the offspring have some of the traits of the parents
...
)
✓ Living things have traits that evolved over time
...
The oldest feathers seen in the fossil record are found on a feathered dinosaur called
Archaeopteryx
...
From observations like these, scientists can infer that having feathers is a trait that wasn’t always present
on Earth; rather, it’s a trait that developed at a certain point in time
...
(Ready to dig into the nitty-gritty details of evolution?
See Chapter 12
...
Science is about exploring the natural world,
making observations using the five senses, and attempting to make sense of

15

16

Part I: Biology Basics
those observations
...
If a biologist
doesn’t want to disturb an organism’s habitat, he or she may use observation to find out how a certain animal lives in its natural environment
...

Many of the animals and plants you’re familiar with were first identified
during a huge wave of discovery science that took place in the 1800s
...
Discovery science continues
today as biologists attempt to identify all the tiniest residents of planet
Earth (bacteria and viruses) and explore the oceans to see the strange
and fabulous creatures that lurk in its depths
...

Modern biologists are using hypothesis-based science to try and understand many things, including the causes and potential cures of human
diseases and how DNA controls the structure and function of living
things
...


Introducing the scientific method
The scientific method is basically a plan that scientists follow while performing scientific experiments and writing up the results
...
Here’s the general
process of the scientific method:
1
...

The scientific method starts when scientists notice something and ask
questions like “What’s that?” or “How does it work?” just like a child
might when he sees something new
...
Then form a hypothesis
...
This hypothesis represents scientists’ thinking about possible answers to their questions
...
His hypothesis is therefore that the
creature is some kind of worm
...
In other words, it has to be an idea that you can support or reject by exploring the situation further using your five senses
...
Next, make predictions and design experiments to test the idea(s)
...
then” statements
...

4
...

Scientists must design their experiments carefully in order to test just one
idea at a time (we explain how to set up a good experiment in the later
“Designing experiments” section)
...
Continuing with the worm example, the
marine biologist tests his hypothesis by dissecting the wormlike creature,
examining its internal parts carefully with the assistance of a microscope,
and making detailed drawings of its internal structures
...
One incredibly important project that employed modern discovery science is
the Human Genome Project, which set out to
map where each trait is found on the 46 human
chromosomes
...

Each of the 25,000 genes they located provides
information about inherited traits
...

By finding out where genes are located, scientists can turn their attention to using this newfound information to develop hypotheses about
cures and gene therapies
...
Then make conclusions about the findings
...
When making deductive conclusions, scientists consider their original hypothesis and ask whether it could still be true in light of the new
information gathered during the experiment
...
If not, scientists
reject the hypothesis and try to come up with an alternate explanation
(a new hypothesis) that could explain what they’ve seen
...
He can therefore conclude that the new animal is
likely a relative of that other type of worm
...
Finally, communicate the conclusions with other scientists
...
Without it, discoveries can’t be
passed on, and old conclusions can’t be tested with new experiments
...
Then
they submit that paper to a scientific journal in their field
...
In addition to sponsoring meetings,
these societies support their respective disciplines by printing scientific
journals and providing assistance to teachers and students in the field
...

When a scientist designs an experiment, he tries to develop a plan that
clearly shows the effect or importance of each factor tested by his experiment
...

Three kinds of variables are especially important to consider when designing
experiments:
✓ Experimental variables: The factor you want to test is an experimental
variable (also called an independent variable)
...

✓ Controlled variables: Any factors that you want to remain the same
between the treatments in your experiment are controlled variables
...

To design an experiment:
1
...

Inductive reasoning uses specific observations to generate general
principles
...
Think about how to test your hypothesis, creating a prediction about
it using an “if
...

3
...

The condition you alter in your experiment is your experimental variable
...

4
...

The experimental group receives the experimental treatment; in other
words, you vary one condition that might affect this group
...

5
...

6
...

Quantitative data is numerical data, such as height, weight, and number of
individuals who showed a change
...
Qualitative data is descriptive data, such as color,
health, and happiness
...

Be sure to date all of your observations
...
Analyze your data by comparing the differences between your experimental and control groups
...

8
...

9
...

As an example of how you design an experiment, imagine you’re a marathon
runner who trains with a group of friends
...
To answer your question, follow the scientific method and
design an experiment
...
Form your hypothesis
...
Translate that hunch into a proper
hypothesis, which looks something like this: The time it takes to run a
marathon is improved by consuming large quantities of carbohydrates
prerace
...
Treat one group with your experimental variable
...
Because the factor you want to test
is the effect of eating pasta, pasta consumption is your experimental
variable
...
Create a control group that doesn’t receive the experimental variable
...

For the best results in your experiment, this control group should be
as similar as possible to your experimental group so you can be pretty
sure that any effect you see is due to the pasta and not some other
factor
...
They’re also eating about the same
thing before the race — with the sole exception being the pasta
...

4
...

Race time is your responding variable because you determine the effect
of eating pasta by timing how long it takes each person in your group
to run the race
...

5
...

If your pasta-eating friends ran the marathon an average of two minutes
faster than your friends who didn’t eat pasta, you may conclude that
your hypothesis is supported and that eating pasta does in fact help
marathon runners run faster races
...
I
...
He found that the rabbits’ aortas developed the same kind of plaques that form in
people with atherosclerosis
...
He was wrong
...
Anichkov and some of his
colleagues repeated Ignatowski’s study with
one small change: They split the rabbits into

three different groups
...
Only the yolk-eating
rabbits developed plaques in their aortas
...
In 1913, Anichkov and his colleagues discovered that cholesterol in the egg
yolk was responsible for creating plaques in the
aorta
...


Before you can consider your research complete, you need to look at a few
more factors:
✓ Sample size: The number of individuals who receive each treatment
in an experiment is your sample size
...
If you had only
four friends participate in your experiment, you’d have to conduct your
experiment again on much larger groups of runners before you could
proudly proclaim that consuming large quantities of carbohydrates prerace helps marathon runners improve their speed
...
Suppose you have 60 marathon-running friends and you
break them into six groups of 10 runners each
...

(Your total sample size is therefore 30 for each treatment
...
Scientists analyze
their data with statistics in order to determine whether the differences
between groups are significant
...
In your experiment, if the race times for your friends were very
similar within each group, so that pretty much all of your pasta-eating
friends ran faster than your non-pasta-eating friends, then that twominute difference actually meant something
...

✓ Error: Science is done by people, and people make mistakes, which is
why scientists always include a statement of possible sources of error
when they report the results of their experiments
...
What if you didn’t specify anything about the
content of the normal meals to your non-pasta-eating friends? After the
race, you might find out that some of your friends ate large amounts of
other sources of carbohydrates, such as rice or bread
...

Whether the scientist is right or wrong isn’t as important as whether he or she
sets up an experiment that can be repeated by other scientists who expect to
get the same result
...
Scientists are continually poking and prodding at ideas, always
trying to get closer to “the truth
...
Scientists
also encourage argument and debate over ideas because the discussion
pushes them to test their ideas and ultimately adds to the strength of scientific knowledge
...
For instance,
a scientist working in a particular area of biology reads all the scientific
publications he can that relate to his work to be sure he has the best understanding possible of what has already been done and what’s already known
...

✓ Some scientific ideas are very old but still applicable today
...
Case
in point: Up until the 1970s, scientists looking through microscopes
thought only two main types of cells made up living things
...
Of course, old ideas aren’t always proved completely
wrong — for example, scientists still recognize the two structural types
of cells — but big ideas can shift slightly in the face of new information
...
A scientific theory is an idea
that’s supported by a great deal of evidence and hasn’t been proven
false despite repeated tests
...
Ideally, scientists always keep an open mind and look at new evidence objectively
...
For
example, when scientists figured out that high
cholesterol levels contributed to heart disease,
they correctly determined that a product created from vegetable oil rather than animal
fat — in other words, margarine rather than
butter — was a healthier choice if you were
trying to lower your cholesterol level
...

They keep wondering, questioning, and

pondering
...

Recently, they discovered that when margarine breaks down, it releases trans fatty acids,
which were found to be harmful to the heart
and blood vessels
...
Yes, this
can make decisions at the grocery store more
confusing, but it can also lead to better health
for everyone
...


23

24

Part I: Biology Basics

Tracking Down Scientific Information
Scientists publish their work in part because scientists in different areas of
the world may be trying to answer the same questions and could benefit from
seeing how someone else approached the problem
...
The sections that follow provide an overview
of the different sources scientists use to communicate with each other (and
the rest of the world)
...
They’re
published by numerous organizations, including professional groups, universities or medical centers, and medical and scientific publishing companies
...

Anyone researching a topic, whether he’s a student or a scientist, consults
the journals first
...
The
research papers are written following the scientific style of an abstract (summary)
...
Next come a description
of the materials used; a description of how the experiment was designed and
performed; and the results of the experiment, including raw data, graphs,
and tables
...

Scientific journals undergo a peer-review process to help ensure the reliability
of published scientific information
...
They’re tasked with making sure the science is thorough
and that the research adds to the scientific knowledge base
...
If the reviewers’ and editor’s stringent criteria aren’t meant, the
research paper can’t be published in the journal
...
However, if you’re a student at a college
or university, your school library may subscribe to various scientific journals
...


Chapter 2: How Life Is Studied

Textbooks: A student’s go-to source
Textbooks
...
Secondary
sources aren’t usually written by the original researchers
...


The popular press: Not always accurate
The popular press — regular ol’ newspapers, magazines, and television
and radio programs, are considered tertiary sources (meaning they’re twice
removed from the original source of information)
...
There’s always a chance that the journalist doing the reporting may
have misunderstood the scientist’s research or something he said
...

You’re always better off citing an article in a journal or textbook before one
from a major media outlet
...
The trick is distinguishing the good stuff from the bad
...
These Web sites end in
...
Some primary literature is available on government Web sites, but even the
secondary literature is usually of high quality
...

✓ Surf university Web sites
...
edu
...

(Better yet, if you’re a student at a college or university, access the
primary literature — scientific journals — through your school library’s
subscription service
...
These Web sites
end in
...
Large organizations with good reputations, such as the
American Heart Association, usually have good-quality secondary information on their sites; they may even post links to primary sources
...

Avoid commercial Web sites (those with
...
People and organizations operating commercial
sites are trying to sell you something
...
The information they present may be one-sided or not accepted as reliable by the scientific community
...
Atoms make up molecules, which
make up the substance of living things
...
In this chapter, we present a bit of
the basic chemistry that’s essential for understanding biology
...
Every living thing is made of matter
...

When living things die, be they plants or animals, microbes such as bacteria
and fungi digest the dead matter and recycle it so that other living things
can use it again
...
5 billion years ago; it has just been recycled since
then
...


28

Part I: Biology Basics

Invisible matter
What looks like nothing but is really something?
Air! Earth’s atmosphere may seem like nothing,
but it’s made of gases such as nitrogen, carbon
dioxide, and oxygen
...
Plants, for example,
take in carbon dioxide to make food and then
use that food to build their structures
...
Obviously the
redwood tree takes up space and has mass,
but those invisible carbon dioxide molecules
are matter too
...
Space is measured in volume, and volume is measured in liters (L)
...
Mass is the term for describing the amount of matter
that a substance has
...
Earth’s gravity pulls on
your mass, so the more mass you have, the more you weigh
...
The most familiar forms of matter are
solids, liquids, and gases
...
Liquids have a definite volume
...
Gases are
easy to compress and expand to fill a container
...
No matter where you are, your
body is made of the same amount of stuff, or matter
...
So, your
weight on the Moon would be just one-sixth of your weight on Earth, but your
mass would remain the same!

Recognizing the Differences between
Atoms, Elements, and Isotopes
All matter is composed of elements
...
And sometimes the number of those subatomic particles within a particular atom differs,

Chapter 3: The Chemistry of Life
creating isotopes
...
That’s a lot to take in, which is why we break the concepts of atoms, elements, and isotopes down for you in the sections that follow
...
It’s the smallest “piece” of matter that can be measured
...
These include protons, neutrons, and electrons (and
even quarks, mesons, leptons, and neutrinos)
...

Here’s the basic breakdown of an atom’s structure (see Figure 3-1):
✓ The core of an atom, called the nucleus, contains two kinds of subatomic
particles: protons and neutrons
...
Protons carry a positive charge, but neutrons have no charge
(they’re neutral)
...

✓ Clouds of electrons surround the nucleus
...

Atoms become ions when they gain or lose electrons
...
Positive (+) ions have more protons than electrons;
negative (–) ions have more electrons than protons
...


Elements of elements
An element is a substance made of atoms that have the same number of protons
...
All the
known elements are organized into the periodic table of elements (shown in
Figure 3-2), which has the following properties:
✓ Each row of the table is called a period
...

✓ Each column is called a family or group
...
The size of the atom increases
from top to bottom within each column
...
Bohr's model of an atom: carbon used as an example
...
Carbon has
six protons, six neutrons, and six
Also
electrons; two electrons are on the
6p
written
inner shell, four are on the
6n
as
outer shell
...
Sodium and chloride ions joining to form table salt
...
The chloride ion is negative because after it accepts the electron
from sodium, it then has one more electron than protons (18 versus 17), so the
overall charge is negative
...

Chloride
ion

Sodium
ion
11p

17p

Sodium has the right
number of electrons
to balance its protons,
but it donates the one
that’s alone in the
outer shell
...
Two atoms of oxygen joining to form oxygen gas
...


8p

Oxygen

Oxygen

8p

8p

Covalent bondshare electrons

Molecules of oxygen gas
(O2) formed by covalent
bond
...


Chapter 3: The Chemistry of Life
1

2

H

He

Hydrogen
1
...
00

3

4

5

6

7

8

9

10

Li

Be

B

C

N

O

F

Ne

Lithium
6
...
01

Boron
10
...
01

Nitrogen
14
...
00

Fluorine
19
...
18

11

12

13

14

15

16

17

18

Na

Mg

Al

Si

P

S

Cl

Ar

Sodium
22
...
31

Aluminum
26
...
09

Phosphorus
30
...
06

Chlorine
35
...
95

19

20

21

22

23

K

Ca

Sc

Ti

V

Potassium
39
...
08

Scandium
44
...
90

Vanadium
50
...
47

Strontium
87
...
91

Zirconium
91
...
91

55

56

57

72

73

24

25

Cr

Mn

Chromium Manganese
52
...
94

26

29

30

31

32

33

34

35

36

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

Nickel
58
...
55

Zinc
65
...
72

Germanium
72
...
92

Selenium
78
...
90

Krypton
83
...
93

Molybdenum Technetium Ruthenium
95
...
07
74

27

Fe
Iron
55
...
91

Palladium
106
...
87

Cadmium
112
...
82

Tin
118
...
75

Tellurium
127
...
90

Xenon
130
...
91

Barium
137
...
91

Hafnium
178
...
95

Tungsten
183
...
21

Osmium
190
...
22

Platinum
195
...
97

Mercury
200
...
37

Lead
207
...
98

Polonium
(210)

Astatine
(210)

Radon
(222)

87

88

89

104

105

106

107

108

109

Fr

Figure 3-2:
The periodic
table of
elements
...
12
90

Actinides

59

Pr

60

Nd

61

Pm

62

Sm

Praseodymium Neodymium Promethium Samarium

140
...
24
92

(147)
93

150
...
96

Gadolinium
157
...
93

Dysprosium
162
...
93

Erbium
167
...
93

Ytterbium
173
...
97

102

103

No

Lr

95

96

97

Th

Pa

U

Np

Pu

Am

Cm

Bk

Thorium
(232)

Protactinium
(231)

Uranium
(238)

Neptunium
(237)

Plutonium
(242)

Americium
(243)

Curium
(247)

Berkelium
(247)

98

99

Cf

Es

Californium Einsteinium
(251)
(254)

100

101

Fm

Md

Fermium
(257)

Mendelevium

(258)

Nobelium Lawrencium
(259)
(260)

Notice in Figure 3-2 how each element has a number associated with it? That
number is the atomic number — the number of protons in the nucleus of an atom
of a particular element
...
Periodic law
states that the properties of elements are a periodic function of their atomic numbers
...
The number of electrons in one atom of an
element is also equal to the atomic number because atoms are neutral (the positively charged particles are offset by the negatively charged particles one for one)
...
The
four most common elements found in living things are hydrogen, carbon,
nitrogen, and oxygen, all of which are found in air, plants, and water
...
)
Most often, the elements sodium, magnesium, chlorine, potassium, and calcium
circulate in the body as electrolytes, substances that release ions (described in
the preceding section) when they break apart in water
...


31

32

Part I: Biology Basics

I so dig isotopes
All atoms of an element have the same number of protons, but the number
of neutrons can change
...

For example, carbon-12 and carbon-14 are two isotopes of the element
carbon
...
These carbon
atoms have a mass number of 12 because their mass is equal to 12
...

The atomic mass of an element is the average mass of all the isotopes of that
element, taking into account their relative abundance
...
01
...
01
...
(When you average the mass of lots of atoms of carbon12 with some of carbon-14, you get a number slightly larger than 12
...
Molecules are made of two or
more atoms, and compounds are molecules that contain at least two different
elements
...
First, you need to mix
the wet ingredients: butter, sugar, eggs, and vanilla
...
You need two sticks of the element butter
...
Before
you add the element of eggs, you need to beat them
...
When all the wet ingredients are mixed together, the molecule of butter is combined with the molecule
of eggs, and you get a compound called “wet
...
Think of each of those ingredients as a separate element
...
” Only when the wet compound is mixed with
the dry compound is the reaction sufficiently ready for the most important
element: the chocolate chips
...
Two important types of bonds exist in living things:
✓ Ionic bonds hold ions joined together by their opposite electrical
charges
...
When sodium (Na) and chlorine (Cl) combine, for example,
sodium loses an electron to chlorine
...
These two oppositely charged ions are attracted to
each other, forming an ionic bond
...
When two oxygen atoms join together to form oxygen gas,
they share two pairs of electrons with each other
...
Covalent bonds are
extremely important in biology because they hold together the backbones of all biological molecules
...
Others, such as battery acid and ammonia, are so caustic you
don’t even want to get them on your skin
...

✓ Acids are molecules that can split apart in water and release hydrogen
ions (H+)
...
When HCl is
added to water, it splits apart into H+ and Cl–, increasing the number of
hydrogen ions in the water/HCl solution
...
The most common example is sodium hydroxide
(NaOH)
...

Charged particles, like hydrogen and hydroxide ions, can interfere with the chemical bonds that hold molecules together
...

Even water can split apart to create hydrogen and hydroxide ions
...
These ions can easily recombine to reform water molecules and will

33

34

Part I: Biology Basics
keep shifting back and forth between their molecular and ionized forms
...

The relative concentration of hydrogen to hydroxide ions is represented by
the pH scale
...


“Ph”iguring out the pH scale
In the early 1900s, scientists came up with the pH scale, a system of classifying how acidic or basic a solution is
...
The pH scale goes from 1 to 14
...

A solution that contains more hydrogen ions than hydroxide ions is acidic,
and the pH of the solution is less than 7
...
The more hydrogen ions it releases, the stronger the
acid, and the lower the pH value
...
Bases dissociate (break apart) into hydroxide ions
(OH–) and a positive ion
...
Because the hydrogen ions are used, the number of hydrogen ions in
the solution decreases, making the solution less acidic and therefore more
basic
...

Table 3-1 shows you the pH of some common substances
...


Table 3-1

The pH of Some Common Substances

Increasing pH

Substances

0 (most acidic)

Hydrochloric acid (HCl)

1

Battery acid

2

Lemon juice, vinegar, stomach acid

3

Cola, apples

4

Beer

4
...
5

Normal rainwater

6

Urine

6
...
5

Human blood

8

Seawater, eggs

9

Baking soda, antacids

10

Great Salt Lake

11

Ammonia

12

Bicarbonate of soda, soapy water

13

Oven cleaner, bleach

14 (most basic)

Sodium hydroxide (NaOH), liquid drain cleaner

Buffing up on buffers
In organisms, blood or cytoplasm are the “solutions” in which the required
ions (for example, electrolytes) are floating
...
However, nothing’s perfect, so
the human body has a backup system in case things go awry
...

Buffers keep solutions at a steady pH by combining with excess hydrogen (H+)
or hydroxide (OH–) ions
...
If a substance releases these ions into a buffered solution, the buffers
will “soak up” the extra ions
...
Bicarbonate ion carries carbon dioxide through
the bloodstream to the lungs to be exhaled (see Chapter 15 for more on the
respiratory system), but it also acts as a buffer
...
If the opposite situation occurs and the pH of the
blood gets too high, carbonic acid breaks apart to release some hydrogen
ions, which brings the pH back into balance
...
If the
reverse happens and the pH gets too high, an organism can develop alkalosis
(meaning the blood becomes too basic)
...
The little ol’ carbon atom, with its six protons and an outer shell of
four electrons, is the central focus of organic chemistry, which is the chemistry of living things
...
Molecules with lots of carbon-hydrogen
bonds are called hydrocarbons
...

So where do the carbon-containing molecules come from? The answer’s
simple: food
...

Regardless of the food source, all living things use food as a supply of carboncontaining molecules
...
The sections that follow describe the roles
of these materials
...

The basic formula for carbohydrates is CH2O, meaning the core structure of a
carbohydrate is one carbon atom, two hydrogen atoms, and one oxygen atom
...

But what is a carbohydrate? Well, carbohydrates are energy-packed compounds
...
However, the energy supplied by carbohydrates doesn’t last long
...
Although carbohydrates are a source of energy, they also
serve as structural elements (such as cell walls in plants)
...
In living things, monosaccharides form ring-shaped structures and can join together to form
longer sugars
...


Chapter 3: The Chemistry of Life
✓ Disaccharides: Two monosaccharide molecules joined together form a
disaccharide (see Figure 3-3b)
...

✓ Oligosaccharides: More than two but just a few monosaccharides joined
together are an oligosaccharide (see Figure 3-3c)
...

✓ Polysaccharides: Long chains of monosaccharide molecules linked
together form a polysaccharide (see Figure 3-3d)
...
Starch and
glycogen, which serve as a means of storing carbohydrates in plants and
animals, respectively, are examples of polysaccharides
...


HOCH2 O
HO CH2OH

HO

OH
OH

OH

glucose

fructose
H2O

HO

CH2OH
O
OH

HOCH2 O

O

OH

H

c Oligosaccharide

CH2OH
O
OH

HO CH OH
2
OH

sucrose
d Polysaccharide

glucose
unit

Note that most of the names of carbohydrates end in -ose
...
A sugar is a carbohydrate
that dissolves in water, tastes sweet, and can form crystals
...


37

38

Part I: Biology Basics

What’s the big deal about “natural” sugars?
Sugars are an important source of energy and
carbon for living things
...

Overconsumption of sugars such as sucrose
can lead to obesity, diabetes, and tooth decay,
so sometimes people perceive sugar as harmful
to the body
...
Some products advertise
themselves as healthier because they contain
“natural” sugars such as fructose (the sugar in
fruit)
...
Fructose

is a six-carbon sugar molecule that digests a
little more slowly than glucose and is sweeter
to the taste
...
However, the sweetening power of
fructose depends on the food it’s used in
...
Plus, much of the commercially available fructose is actually derived from
sucrose, not extracted from fruit
...


The next sections explain how sugars interact with one another and how the
human body stores a particular carbohydrate known as glucose
...
Figure 3-3b
shows the dehydration synthesis of glucose and fructose to form sucrose
...
Dehydration, as we’re sure you know,
is what happens when you don’t drink enough water
...
Synthesis means making something
...
That’s exactly what happens
...

The opposite of dehydration synthesis is hydrolysis
...
When
something undergoes hydrolysis, a water molecule splits a compound (hydro
means “water”; lysis means “break apart”)
...


Chapter 3: The Chemistry of Life
Converting glucose for storage purposes
Carbohydrates are found in nearly every food, not just bread and pasta
...
Basically, any food that contains sugar has carbohydrates,
and most foods are converted to sugars when they’re digested
...
Those glucose molecules are then absorbed from
your intestinal cells into your bloodstream, which carries the glucose molecules throughout your entire body
...

Because glucose provides a rapid source of energy, organisms often keep
some on hand
...
Consider the following list your primer
on the things glucose can be stored as:
✓ Glycogen: Animals, including people, store a polysaccharide of glucose
called glycogen
...
Your liver, in particular, keeps a large glycogen
reserve on hand for when you exercise
...
The leaves of
a plant produce sugar during the process of photosynthesis and then
store some of that sugar as starch
...

Plants also make a polysaccharide of glucose called cellulose
...
Most animals, including people, can’t digest cellulose because of
the type of bonds between the glucose molecules
...


Making life possible: Proteins
Without proteins, living things wouldn’t exist
...
Some proteins are involved in reactions in the body when they serve
as enzymes (see Chapter 4 for more on enzymes)
...
Proteins are so diverse that we
can’t possibly tell you about all of them
...


39

40

Part I: Biology Basics
The building blocks of proteins
Amino acids, of which there are 20, are the foundation of all proteins
...
Figure 3-4
shows what one amino acid looks like
...
Amino acids link
together by dehydration synthesis, just like sugars do (as explained in the
earlier “Making and breaking sugars” section), and each polypeptide chain is
made up of a unique number and order of amino acids
...

The name of the amino acid depends on which one of the 20 side-chain groups
is at R
...


O
O- was at R, the amino acid would be aspartic acid
...
Specific proteins are
created based on the order of amino acids connected together
...


The main functions of proteins
One or more polypeptide chains come together to form functional proteins
...

✓ Enzymes are proteins that speed up the rate of chemical reactions
...

For the full scoop on enzymes, head to Chapter 4
...
Collagen, a structural
protein found in connective tissue (the tissue that joins muscles to bones to
allow movement), is the most abundant protein in animals with a backbone
...
It provides support in the body,
and it has a great capability to be flexible and resistant to stretching
...

Hemoglobin is a transport protein found in red blood cells that carries
oxygen around the body
...
Each leaf of the clover
is a separate polypeptide chain
...
When gas exchange occurs between the lungs and a blood cell
(for more on respiration and circulation, see Chapter 15), the iron atom
attaches to the oxygen
...


Drawing the cellular road map:
Nucleic acids
Until as recently as the 1940s, scientists thought that genetic information was
carried in the proteins of the body
...
That all changed in 1953
when James Watson and Francis Crick figured out the structure of a nucleic
acid, proving things were the other way around: Nucleic acids created the
proteins!
Nucleic acids are large molecules that carry tons of small details, specifically
all the genetic information for an organism
...
Just think about that fact
for a moment
...

Nucleic acids are made up of strands of nucleotides
...
Your entire genetic composition, personality, and maybe even
your intelligence hinge on molecules containing a nitrogen compound, some
sugar, and a phosphate
...


41

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Part I: Biology Basics
Deoxyribonucleic acid (DNA)
You may have heard DNA (short for deoxyribonucleic acid) referred to as
“the double helix
...
See for yourself in
Figure 3-5
...


The sides of the ladder are made up of sugar and phosphate molecules,
hence the nickname “sugar-phosphate backbone
...
) The “rungs” on the ladder of DNA are made from pairs
of nitrogenous bases from the two strands
...
The order of these chemical letters
spells out your genetic code
...
These particular base pairs line up just right chemically so
that hydrogen bonds can form between them
...
A
gene is a unit that contains the genetic information or codes for a particular

Chapter 3: The Chemistry of Life
protein and transmits hereditary information to the next generation
...
(You can find details about this in Chapter 6
...

But genes aren’t found only in reproductive cells
...
Proteins control function and provide structure
...

The order of the nitrogenous bases on a strand of DNA (or in a section of the
DNA that makes up a gene) determines the order in which amino acids are
strung together to make a protein
...

Every cellular process and every aspect of metabolism is based on genetic
information stored in DNA and thus the production of the proper proteins
...


Ribonucleic acid (RNA)
RNA, short for ribonucleic acid, is a chain of nucleotides that serves as an
important information molecule
...
The structure of RNA is slightly
different from that of DNA
...

✓ The nitrogenous bases used are adenine, guanine, cytosine, and uracil
(rather than thymine)
...


Supplying structure, energy,
and more: Lipids
In addition to carbohydrates, proteins, and nucleic acids, your body needs
one more type of large molecule to survive
...
We’re talking about fats, which
can be both a blessing and a curse because of their incredible energy density
(the ability to store lots of calories in a small space)
...
But that same energy density makes
it really easy to pack in the calories when you eat fatty foods!

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Part I: Biology Basics
Fats are an example of a type of molecule called lipids
...
You’ve probably heard
the saying that “oil and water don’t mix
...
Butter and lard are examples
of solid lipids, as are waxes, which are valued for their water-repellent properties on snowboards, skis, and automobiles
...
Phospholipids aren’t the type of lipid floating around the
bloodstream clogging arteries
...
Cholesterol is a steroid molecule used to make testosterone and estrogen; it’s also found in the membranes of cells
...
If you have too much cholesterol floating in your bloodstream, then you have an excess of fats carrying it through your bloodstream
...

✓ Triglycerides: These fats and oils, which are made up of three fatty acid
molecules and a glycerol molecule, are important for energy storage and
insulation
...
After the liver
stores all the glucose it can as glycogen, whatever remains is turned into
triglycerides
...
) The triglycerides float through your bloodstream on their way
to be deposited into adipose tissue — the soft, squishy fat you can see
on your body
...

The more fat molecules that are added to the adipose tissue, the bigger
the adipose tissue (and the place on your body that contains it) gets
...

• Fats contain lots of single bonds between their carbon atoms
...

• Oils contain lots of double bonds between their carbon atoms
...


Chapter 3: The Chemistry of Life

Glycerol

Fatty acid
O

H
H

C

OH HO

H

C

OH

C

OH

H

C

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

H2O

H

H
H

C

O
O

C

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

O
H

Figure 3-6:
Saturated
and unsaturated bonds
in a typical
triglyceride
...
When you use up all of your
stored glucose (which doesn’t take long because sugars “burn” quickly in
aerobic conditions), your body starts breaking down glycogen, which is
stored primarily in the liver and muscle
...
After that, your body starts breaking down adipose
tissue to retrieve some stored energy
...
(Notice we didn’t say “pounds” here
...
)

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Part I: Biology Basics

Chapter 4

The Living Cell
In This Chapter
▶ Finding out what makes cells the basic units of life
▶ Taking a look at the structure of prokaryotic and eukaryotic cells
▶ Discovering how enzymes accelerate reactions

E

very living thing has cells
...
What exactly is a cell? In plain and simple
terms, it’s the smallest living piece of an organism — including you
...
And that is why the cell is the fundamental unit of life
...
And
because cells rely on chemical reactions to make things happen, you also
find out all about enzymes, which are proteins that help speed up the pace of
chemical reactions
...
Inside the fluid float chemicals and organelles, structures inside
cells that are used during metabolic processes
...
)
A cell is the smallest part of an organism that retains characteristics of the
entire organism
...
Because cells can perform all the functions of life (as shown in Figure 4-1), the cell is the smallest
unit of life
...


Lysosomes
Vacuoles

Chloroplasts

Cells can be categorized in different ways, according to structure or function,
or in terms of their evolutionary relationships
...
Nor do they have
organelles
...

✓ Eukaryotes have a nucleus in their cells that houses their genetic material
...
Plants, animals, algae, and fungi are all eukaryotes
...
Although viruses
make you sick, just like bacteria do, viruses and
bacteria are actually quite different
...
In fact, viruses have so few

parts that they can’t even grow and divide by
themselves (so they’re not considered to be
alive)
...


Chapter 4: The Living Cell

Peeking at Prokaryotes
Prokaryotes include cells you’ve probably heard of, such as the bacteria E
...

Whether you’ve heard of a specific prokaryote or not, you’re likely well aware
that bacteria have a pretty bad rap
...
Behind the scenes, though, bacteria are quietly performing many beneficial tasks for people and the rest of life
on planet Earth
...

✓ Bacteria can clean up our messes! Oil-eating bacteria help save
beaches, and other bacteria help clean up our sewage
...

✓ Bacteria are nature’s recyclers! Bacteria release nutrients from dead
matter during decomposition
...

The cells of prokaryotes are fairly simple in terms of structure because they
don’t have internal membranes or organelles like eukaryotic cells do (we
cover all the structures present in eukaryotic cells later in this chapter)
...

✓ DNA, the genetic material of prokaryotes, is located in the cytoplasm, in
an area called the nucleoid
...

✓ Prokaryotes break down food using cellular respiration (which requires
oxygen, as explained in Chapter 5) and another type of metabolism
called fermentation (which doesn’t require oxygen)
...


Examining the Structure
of Eukaryotic Cells
The living things you’re probably most familiar with — humans, animals,
plants, mushrooms, and molds — are all eukaryotes, but they’re not the only
members of the eukaryote family
...

Eukaryotes have the following characteristics (see Figures 4-3 and 4-4 for diagrams of eukaryotic cells):
✓ A nucleus that stores their genetic information
...

✓ Internal membranes, such as the endoplasmic reticulum and the Golgi
apparatus, that create specialized compartments inside the cells
...


Chapter 4: The Living Cell
✓ Organelles called mitochondria that combine oxygen and food to transfer the energy from food to a form that cells can use
...
(Chloroplasts are found only in
the cells of plants and algae
...
(This is found only in
the cells of plants, algae, and fungi; animal cells just have a plasma membrane, which is soft
...


Smooth
endoplasmic
reticulum
Golgi
apparatus

Rough
Ribosomes
endoplasmic
reticulum

Golgi
vesicles

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Part I: Biology Basics
Cytoplasm
Cilia
Vesicle formation
Nucleolus
Nucleus

Mitochondrion

Vacuole
Rough endoplasmic
reticulum

Ribosomes

Golgi apparatus
Smooth endoplasmic
reticulum
Lysosome
Figure 4-4: Plasma membrane
Structures
in a typical
animal cell
...
Just like you have organs that perform specific functions for your body,
cells have organelles that perform specific functions for the cell
...

The sections that follow highlight the organelles found in eukaryotic cells and
get you acquainted with their specific functions
...
Plant cells have chloroplasts, large central vacuoles,
and cell walls; animal cells don’t
...


Chapter 4: The Living Cell

Holding it all together:
The plasma membrane
The membrane that encloses and defines all cells as separate from their environment is called the plasma membrane, or the cell membrane
...

Thinking of the plasma membrane as an international border controlling what
enters and leaves a particular country is a good way of remembering the
plasma membrane’s function
...
(Cyto means “cell,” and
plasm means “shape
...
)
Animal cells are supported by a fluid protein-and-carbohydrate matrix called
the extracellular matrix
...
”) Plant cells are supported by a more solid structure, called a cell wall, that’s made of the carbohydrate cellulose
...


Deciphering the fluid-mosaic model
Plasma membranes are made of several different components, much like a
mosaic work of art
...
We’ve drawn the model for you in Figure 4-5 to help you
visualize all the parts that make up a plasma membrane
...
This serves as the foundation of the plasma membrane
...
At body temperature, phospholipids
have the consistency of thick vegetable oil, which allows plasma membranes
to be flexible and fluid
...
(Hydro

53

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Part I: Biology Basics
means “water,” phile means “love,” and phobia means “fear,” so hydrophilic
literally means “water-loving” and hydrophobic literally means “water-fearing
...
Phospholipid bilayer

Internal surface membrane
Hydrophobic tail

In each cell, the hydrophilic heads point toward the watery environments
outside and inside the cell, sandwiching the hydrophobic tails between them
to form the phospholipid bilayer (see Figure 4-5)
...

In addition to phospholipids, proteins are a major component of plasma
membranes
...

Cholesterol and carbohydrates are minor components of plasma membranes,
but they play fairly significant roles
...
(It keeps you from literally freezing when you’re “freezing
...
When carbohydrates attach to the phospholipids,
they form glycolipids (and when they attach to the proteins, they form
glycoproteins)
...


Chapter 4: The Living Cell
Transporting materials through the plasma membrane
Cells are busy places
...
These
important exchanges take place at the plasma membrane
...
Small, hydrophobic molecules such as oxygen and
carbon dioxide are compatible with the hydrophobic tails of the phosopholipid bilayer, so they can easily scoot across membranes
...
Larger molecules (think food and hormones) also need help,
which comes in the form of transport proteins
...

Small molecules such as hormones and ions may be allowed to pass through
these channel proteins
...

Other proteins in the membrane act as receptors that detect the presence of
molecules the cell needs
...

Because the plasma membrane is choosy about what substances can pass
through it, it’s said to be selectively permeable
...
Permeable means that most substances can easily pass through
...
Selectively permeable and
semipermeable mean that only certain substances are able to pass through
...


Passively moving along
Passive transport requires no energy on the part of the cell
...
In both cases, the molecules are moving from where they’re more concentrated to where they’re
less concentrated
...
) Here are the two methods of passive transport:
✓ Diffusion: The movement of molecules other than water from an area
where they’re highly concentrated to an area where they’re less concentrated is diffusion
...

✓ Osmosis: The diffusion of water across a membrane is osmosis
...
Basically, water moves from
areas where it’s more concentrated (more pure) to areas where it’s less
concentrated (where it has more solutes)
...
For example, the
blood in your body contains a certain amount of salt
...
On the other hand, if too much
fluid is in the bloodstream, the blood cells have too many molecules
of salt in comparison, so they take in water
...

The relative concentration of solutes on either side of a membrane is compared in terms of the tonicity of the solutions
...
If one solution is hypotonic, it has a lower concentration of substances (and more water) in it when compared to another solution
...


Actively helping molecules across
Active transport requires some energy from the cell to move molecules that
can’t cross the phospholipid bilayer on their own from where they’re less
concentrated to where they’re more concentrated
...

Active transport is a little like having to pay to take the Staten Island Ferry
...
The fee that you pay is equivalent to the energy molecules
expended by the cell
...
You breathe in air, and
oxygen gets into the tiniest air sacs of the lungs,
called the alveoli
...
The pulmonary capillaries contain the
lowest concentration of oxygen in the body
because by the time blood gets to them, most

of the oxygen has been used up by other organs
and tissues
...
Oxygen from the alveoli of the
lungs diffuses across the membrane between
the air sac and the capillary, getting into the
bloodstream so it can travel around the body
...
However, it provides that reinforcement in the form of protein cables rather than bones
...
They also run through the cell like railroad
tracks, helping vesicles and organelles circulate around the cell
...

Some cells have whiplike projections that help them swim or move fluids
...
If the projections are long, they’re called flagella
...
The proteins flex back and forth, making
the cilia and flagella beat like little whips
...
Flagella are present on human sperm cells; they’re what allow sperm to
swim rapidly toward an egg during sexual reproduction
...
In eukaryotic
cells, DNA is contained within a chamber called a nucleus that’s separated
from the cytoplasm by a membrane called the nuclear envelope (also known
as the nuclear membrane)
...
When
DNA is in this form, it’s called chromatin
...
Human cells have 46 chromosomes, each one of which is a separate piece of DNA
...
Cell function depends upon the action of these proteins,
and organism function depends on cell function
...

Consider the nucleus the library of the cell because it holds lots of information
...

Proteins in the nucleus copy the instructions from the DNA into molecules
that get shipped out to the cytoplasm, where they direct the behavior of the
cell
...


57

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Part I: Biology Basics
The nucleolus produces ribosomes, which move out to the cytoplasm to
help make proteins
...
So, the nucleus is the true control center
of the cell
...
The instructions for proteins are copied from the DNA into a new molecule called
messenger RNA (mRNA)
...
The ribosomes
then organize the mRNA and other molecules that are needed to build
proteins (for the full scoop on how proteins are made, flip to Chapter 8)
...


Serving as the cell’s factory:
The endoplasmic reticulum
The endoplasmic reticulum (ER) is a series of canals that connects the nucleus
to the cytoplasm of the cell
...
”) As you can see in Figure 4-4, part of the
ER is covered in dots, which are actually ribosomes that attach to it during
the synthesis of certain proteins
...
The
part of the ER without ribosomes is called the smooth ER (SER)
...
(Proteins that stay in the cell are put
together on ribosomes that float free in the cytoplasm
...
Proteins and lipids made at the ER get packaged up into little spheres of membrane called transport vesicles that carry
the molecules from the ER to the nearby Golgi apparatus
...


Chapter 4: The Living Cell

Preparing products for distribution:
The Golgi apparatus
The Golgi apparatus, which is located very close to the ER (as you can see
in Figure 4-4), looks like a maze with water droplets splashing off of it
...

Inside the Golgi apparatus, products produced by the cell, such as hormones
or enzymes, are chemically tagged and packaged for export either to other
organelles or to the outside of the cell
...
If the molecules are to be shipped out of the cell, the vesicle finds
its way to the plasma membrane, where certain proteins allow a channel to
be produced so that the products inside the vesicle can be secreted to the
outside of the cell
...

If it helps you remember, you can consider the Golgi apparatus the cell’s post
office because it receives molecular packages and tags them for shipping to
their proper destination
...

Lysosomes contain digestive enzymes, which are used to break down products
that may be harmful to the cell and “spit” them back out into the extracellular
fluid
...
) Lysosomes also remove dead organelles by surrounding them,
breaking down their proteins, and releasing them to construct a new organelle
...


Destroying toxins: Peroxisomes
Peroxisomes are little sacs of enzymes that break down many different types
of molecules and help protect the cell from toxic products
...


59

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Part I: Biology Basics
Some of the reactions that occur in peroxisomes produce hydrogen peroxide,
which is a dangerous molecule to cells
...

Peroxisomes are a little bit like food processors
...


Providing energy, ATP-style: Mitochondria
Mitochondria supply cells with the energy they need to move and grow by
breaking down food molecules, extracting their energy, and transferring it to
an energy-storing molecule that cells can easily use
...

Recall the role of mitochondria by thinking of them as the power plants of the
cell because they produce the energy the cell needs
...
What occurs during cellular respiration is like what occurs
when a campfire burns, just on a much smaller scale
...
In a mitochondrion, food
molecules break down, consuming oxygen and transferring energy to cells (to
be stored in ATP) and the environment (as heat)
...


Converting energy: Chloroplasts
Chloroplasts are organelles found solely in plants and algae
...
They
often have a distinctly green color because they contain chlorophyll, a green
pigment that can absorb sunlight
...
(Turn to
Chapter 5 for more on photosynthesis
...


Chapter 4: The Living Cell
A very common misconception is that plants have chloroplasts rather than
mitochondria
...
When
plants make food, they store matter and energy for later
...


Presenting Enzymes, the Jump-Starters
Chemical reactions occur whenever the molecules in cells change
...

Of course, because the pace of life in cells is so fast, cells can’t just wait
around for chemical reactions to happen — they have to make them happen
quickly
...

Each reaction of a pathway or cycle requires a specific enzyme to act as a
catalyst, something that speeds up the rate of chemical reactions
...
Enzymes also have
pockets, called active sites, that they use to attach to certain molecules
...

Enzyme
(lactase)
Active site

Substrate
(lactose)

Galactose
1
...
Products
are released
Figure 4-6:
Enzyme
catalysis
...
Enzyme
catalyzes reaction
H2O

2
...
The result of an uncompleted cycle or
pathway is the lack of what that cycle or pathway is supposed to produce
(a product)
...
For example, if people don’t get enough
vitamin C, the enzymes needed to make collagen can’t function, resulting in
a disease called scurvy
...

The sections that follow introduce you to how enzymes work, what they need
to get the job done, and how cells are able to keep them under control
...

Enzymes themselves are recycled
...
For example, the
first enzymatic reaction discovered was the one that breaks down urea into
products that can be excreted from the body
...

Urease
Urea + Water ↔ Carbon dioxide + Ammonia
In this reaction, the enzyme urease helps the reactants (molecules that enter
a chemical reaction), urea and water, combine with each other
...
When the reaction is over, urease is unchanged and can catalyze another
reaction between urea and water
...
For example, lipase
is an enzyme that helps break down lipids (fats), and lactase is an enzyme that
helps break down lactose
...
while lowering activation energy
Enzymes work by reducing the amount of activation energy needed to start a
reaction so reactions can occur more easily
...
But

Chapter 4: The Living Cell
they wouldn’t do it nearly often enough to keep up with the fast pace of life
in a cell
...
That’s where the
enzyme urease comes into play
...

Because reactions can occur more easily with enzymes, they occur more
often
...
One way to
understand how enzymes speed up reactions is to think about reactions in
terms of energy
...
In the urea and water example,
the reactants would need to collide with each other in just the right way for
them to exchange partners and form into carbon dioxide and ammonia
...
They don’t
...
In other words, enzymes don’t add energy; they just
make it so the reactants have enough energy on their own
...
Inorganic partners, such as iron, potassium, magnesium, and zinc
ions, are called cofactors
...
Examples of coenzymes
include many derivatives of vitamins
...


Controlling enzymes through
feedback inhibition
Cells manage their activity by controlling their enzymes via feedback inhibition, a process in which a reaction pathway proceeds normally until the final
product is produced at too high of a level
...

(An allosteric site is literally an “other shape” site
...
) By controlling enzymes,

63

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Part I: Biology Basics
cells regulate their chemical reactions and, ultimately, the physiology of the
entire organism
...
The quantity of the final product provides feedback to the beginning of the pathway
...

By inhibiting the activity of an initial enzyme, the entire pathway is stopped
...
It’s like keeping yourself from spending money on
a huge quantity of food that you won’t eat and would just end up storing until
it rots
...
In fact, the final product is constantly binding,
letting go, and then binding again
...


Chapter 5

Acquiring Energy to Run the Motor
In This Chapter
▶ Recognizing the important role energy plays in organisms
▶ Making food with photosynthesis
▶ Metabolizing food for energy through cellular respiration
▶ Counting calories

J

ust like you need to put gas in your car’s engine so your car can move,
you need to put food in your body so it can function
...
Every person, as well as every other living thing, needs to “fill its tank”
with matter and energy in the form of food
...
Animals obtain their food by
eating plants and other animals, whereas plants make their own food
...
We also demonstrate why cells need energy and take a
look at how cells obtain and then store energy and matter
...
Chances are, however, if
you were asked to state what energy is, you might have some trouble
...
The funny thing is that physicists, who
spend a lot of time studying energy, define energy in exactly the way most
people think about it: Energy is something that allows work to be done
...
Although they may seem very different,
the kinds of energy you can think of represent the two main types of energy:
✓ Potential energy: This is the energy that’s stored in something because
of the way it’s arranged or structured
...
Food and gasoline also contain potential
energy called chemical potential energy (energy that’s stored in the
bonds of molecules)
...
Light, heat, and moving
objects all contain kinetic energy
...

They also explain how the cells of living things use and transfer energy, as
well as how they obtain it (here’s a hint: it’s all about food)
...
The electricity that people get
from hydroelectric power (or coal-burning power plants, wind turbines,
or solar panels) isn’t created from nothing
...
And when people use, say, electricity, that
energy doesn’t disappear
...

The idea that energy can’t be created or destroyed is known as the First
Law of Thermodynamics
...
To
understand this rule, picture a flowing river that’s used as a source of
hydroelectric power
...

✓ Energy is transformed when it changes from one form to another
...
The potential energy
of the water behind the plant’s dam is transformed first into the kinetic
energy of moving water, then the kinetic energy of a spinning turbine,
and finally the kinetic energy of moving electrons
...
The First Law of Thermodynamics (explained in the preceding section) applies to your metabolism, which is all the chemical reactions
occurring in your cells at one time
...
Specifically,
small molecules are combined into large molecules for repair, growth,
or storage
...

During chemical reactions, atoms receive new bonding partners, and energy
may be transferred
...
)
Each type of food molecule you’re familiar with — carbohydrates, proteins,
and fats — are large molecules that can be broken down into smaller subunits
...
After cells break large food
molecules down into their subunits, they can more easily reconnect the subunits and reform them into the specific molecules that they need
...
Energy from
catabolic reactions is transferred to ATP, which then provides energy for
anabolic reactions
...
When ATP supplies energy to a process, one of
its phosphates gets transferred to another molecule, turning ATP into adenosine diphosphate (ADP)
...
Cells constantly build and
break down ATP, creating the ATP/ADP cycle shown in Figure 5-1
...


Complex molecules, such
as starch, proteins, and lipids

Heat
released

Cells have large molecules that contain stored energy, but when they’re busy
doing work, they need a handy source of energy
...

Cells keep ATP on hand to supply energy for all the work that they do
...
You may have money deposited in the
bank, but that money isn’t always easy to get, which is why you keep some
cash in your pocket to quickly buy what you need
...
For living
things, the energy stored in large molecules is like money in the bank
...
Then, when cells need more
ATP, they have to go back to the bank of large molecules and break some
more down
...

✓ Organisms need matter to build their cells so they can grow, repair
themselves, and reproduce
...
Your body repairs the damage
by building new skin cells to cover the scraped area
...

✓ Organisms need energy so they can move, build new materials, and
transport materials around their cells
...
When
you walk up stairs, the muscle cells in your legs contract, and each
contraction uses some energy
...
Your individual cells also
need energy to do their work
...


Finding food versus producing your own
All organisms need food, but there’s one major difference in how they
approach this problem: Some organisms, such as plants, can make their own
food; other organisms, like you, have to eat other organisms to obtain their
food
...
Auto means “self,” and troph
means “feed,” so autotrophs are self-feeders
...

✓ Heterotrophs have to eat other organisms to get their food
...
Animals,
fungi, and most bacteria are examples of heterotrophs
...

More specifically, food is made through one process and broken down
through another
...
(The carbon dioxide provides the matter plants need for
food building
...

✓ Cellular respiration: Both autotrophs and heterotrophs do cellular respiration, a process that uses oxygen to help break down food molecules
such as sugars
...
As the energy is transferred to the cells, the matter
from the food molecules is released as carbon dioxide and water
...
Photosynthesis consumes carbon dioxide and water,
producing food and oxygen
...
Scientists write the big picture view of
both processes as the following equations:
Photosynthesis:
6 CO2 + 6 H2O + Light Energy → C6H12O6 + 6 O2
Cellular respiration:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Usable Energy
Don’t fall for the idea that only heterotrophs such as animals engage in cellular respiration
...
Think of it like this:
Photosynthesis is a food-making pathway that autotrophs use to store matter
and energy for later
...
There wouldn’t be much point in packing the lunch if you
weren’t going to eat it later, right? The same is true for a plant
...
When it needs that matter and energy, it
uses cellular respiration to “unpack” its food
...
With those sugars, plus some nitrogen and minerals from
the soil, autotrophs can make all the types of molecules they need to build
their cells
...
To build glucose, autotrophs need carbon, hydrogen, and oxygen atoms, plus energy to combine them into sugar
...

✓ The hydrogen for the sugars comes from water found in the soil
...

A common misconception is that plants get the matter they need to grow from
the soil
...
However, some very careful scientific observations

Chapter 5: Acquiring Energy to Run the Motor
by a Belgian scientist named Jean Baptiste van Helmont showed that a tree
that gained 169 pounds in mass as it grew took only 2 ounces of dry material
from the soil (not counting water)
...
Instead, they get most of the matter they
need to grow from the carbon dioxide in the air
...
Plants collect a lot of
carbon dioxide molecules (CO2) and combine them with water molecules (H2O)
to build sugars such as glucose (C6H12O6)
...

Photosynthesis occurs in two main steps (Figure 5-2 depicts both in action):
✓ The light reactions of photosynthesis transform light energy into
chemical energy
...

✓ The light-independent reactions of photosynthesis produce food
...

The next sections delve deeper into the process of photosynthesis
...


ATP
+

Light
Reactions

P
Light-Independent
Reactions

ATP
Ele

02

ctro
ns

NADPH

Sugar

71

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Part I: Biology Basics

Transforming energy from the
ultimate energy source
The Sun is a perfect energy source — a nuclear reactor positioned at a safe
distance from planet Earth
...
if
only you could capture it
...
5 billion years ago, showing that photosynthetic autotrophs were
way ahead of humans on this one
...
You’re probably most familiar with the pigment chlorophyll, which
colors the leaves of plants green
...

During the light reactions of photosynthesis, chloroplasts absorb light energy
from the Sun and then transform it into the chemical energy stored in ATP
...
The electrons
from the water molecules help with the energy transformation from light
energy to chemical energy in ATP
...


Putting matter and energy together
Plants use the energy in ATP (which is a product of the light reactions) to combine carbon dioxide molecules and water molecules to create glucose during the
light-independent reactions
...
They then use the energy from the ATP
and the electrons that came from water to convert the carbon dioxide to sugar
...

As their name indicates, the light-independent reactions of photosynthesis don’t
need direct sunlight to occur
...

When plants have made more glucose than they need, they store their excess
matter and energy by combining glucose molecules into larger carbohydrate molecules, such as starch
...


Chapter 5: Acquiring Energy to Run the Motor

Cellular Respiration: Using Oxygen
to Break Down Food for Energy
Autotrophs and heterotrophs do cellular respiration to break down food to
transfer the energy from food to ATP
...

Three separate pathways combine to form the process of cellular respiration
(you can see them all in action in Figure 5-3)
...
The third pathway, oxidative phosphorylation, transfers the energy from the food molecules to ATP
...
After glycolysis,
pyruvate is broken down into a two-carbon molecule called acetyl-coA
...

✓ During oxidative phosphorylation, which occurs in the inner membrane
or cristae of the mitochondrion), cells transfer energy from the breakdown of food to ATP
...


Electron
Transport
Chain

6 H2O

O2

6 CO2
ATP

ATP
ATP

For a more in-depth look at cellular respiration, check out the following sections
...
Respiration, which
is more commonly referred to as breathing, is the physical act of inhaling
and exhaling
...


Breaking down food
After the large molecules in food are broken down into their smaller subunits,
the small molecules can be further broken down to transfer their energy to
ATP
...
Each rearrangement produces a new molecule in the pathway and
can also produce other useful molecules for the cell
...

✓ Oxidize food molecules and transfer electrons and energy to coenzymes: Oxidation is the process that removes electrons from molecules;
reduction is the process that gives electrons to molecules
...
NAD+ and
FAD receive the electrons as part of hydrogen (H) atoms, which change
them to their reduced forms, NADH and FADH2
...

NAD+ and FAD act like electron shuttle buses for the cell
...
When the electrons get on the bus, the driver puts up
the H sign to show that the bus is full
...
The buses are now empty again, so they drive back to another
oxidation reaction to collect new passengers
...

✓ Release carbon dioxide (CO2): Cells return CO2 to the environment as
waste, which is great for the autotrophs that require CO2 to produce the
food that heterotrophs eat
...
Cells break down simple sugars, such as glucose, in the first
pathway — glycolysis
...


Chapter 5: Acquiring Energy to Run the Motor
Following is a summary of how different molecules break down in the first
two pathways of cellular respiration:
✓ During glycolysis, glucose breaks down into two molecules of pyruvate
...
During glycolysis, energy transfers
result in a net gain of two ATP and two molecules of the reduced form of
the coenzyme NADH
...
One carbon atom from pyruvate is released from the cell
as CO2
...
(The conversion
of pyruvate to acetyl-coA produces two molecules of carbon dioxide,
and the Krebs cycle produces four
...

The conversion of pyruvate to acetyl-coA produces two molecules of
NADH
...


Transferring energy to ATP
In the inner membranes of the mitochondria in your cells, hundreds of little
cellular machines are busily working to transfer energy from food molecules
to ATP
...

The coenzymes NADH and FADH2 carry energy and electrons from glycolysis
and the Krebs cycle to the electron transport chain
...
Oxygen collects the electrons at the end of the
chain
...
) When oxygen accepts the electrons, it also picks up protons (H+) and becomes water (H2O)
...
The buckets are the proteins, or electron carriers, and the water
inside the buckets represents the electrons
...

While electrons are transferred along the electron transport chain, the proteins use energy to move protons (H+) across the inner membranes of the

75

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Part I: Biology Basics
mitochondria
...
These protons then flow back across the mitochondria’s
membranes through a protein called ATP synthase that transforms the kinetic
energy from the moving protons into chemical energy in ATP by capturing
the energy in chemical bonds as it adds phosphate molecules to ADP
...

At the end of the entire process of cellular respiration, the energy transferred
from glucose is stored in 36 to 38 molecules of ATP, which are available to be
used for cellular work
...


H+
H+

ATP
synthase

sp
on tran ort c
ha
Electr
in

H+

H+
ct r
Ele

ADP+Pi
H+

o

H+
ranspo
nt

rt
c

ha
in

ATP

Mitochondrial membrane
H+

Outer compartment
Cristae membrane
Matrix

H+

1⁄ O
2 2

H + + NADH
F ADH2

K
r
e
b
s

c
y
c
l
e

H2O
NAD +
F AD

Energy and Your Body
Your body takes in chemical potential energy when you eat food and then
transfers the energy from that food to your cells
...

Energy can be measured in many different ways, but the energy in food is
measured in calories
...
It takes 1 calorie to raise the temperature of 1 gram of water by 1
degree Celsius (not Fahrenheit)
...
(Kilo means “1,000,” so a kilocalorie is equal to 1,000 calories
...
From here on out, we use
the term Calorie (with a capital C) to represent the kilocalories you’re familiar with from nutrition facts labels
...

Here’s how to calculate BMR:
1
...

2
...
25
...
Add these two numbers together
...
Multiply your age by 5 and then subtract this number from the one
you got in Step 3
...
If you’re male, add 5 to the total you found in Step 4; if you’re female,
subtract 161 from the total you found in Step 4
...
Use the preceding
calculation and Table 5-1 to figure out how many Calories you need to consume to maintain your lifestyle
...


Multiply Your BMR by
...
2

Lightly active (light exercise or sports 1 to
3 days per week)

1
...
55

Very active (hard exercise or sports 6 to 7
days per week)

1
...
9

In the past, humans had to work hard to find their food and sometimes came
up empty-handed
...
It packs
energy-rich fat onto your hips, thighs, abdomen, and buttocks
...
Every 3,500 extra Calories equals 1 pound of fat
...


77

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Part I: Biology Basics

Part II

Cell Reproduction
and Genetics:
Let’s Talk about
Sex, Baby

L

In this part
...

They also tend to pass their traits on to their offspring
...
Scientists today know more about the mysteries of DNA than ever before
...

In this part, we explain the steps of cell division and how
DNA determines the characteristics of organisms
...
Asexual reproduction by mitosis creates cells that are genetically identical to the parent cell
...
Meiosis and sexual reproduction result in
greater genetic diversity in offspring and, consequently, in the populations
of living things
...
We also introduce you to the
ways sexual reproduction adds variety to species of all kinds
...
And, when you think about it, life is really
all about continuation — living things keep on keepin’ on from one generation to the next, passing on critical genetic information
...
After all,
have you ever seen a chair or table replicate itself? Only living things have
the ability to pass on genetic information and replicate themselves
...
If a cell makes an exact
copy of itself, it’s engaging in asexual reproduction
...
Some
single-celled eukaryotes and individual cells within a multicellular eukaryote

82

Part II: Cell Reproduction and Genetics: Let’s Talk about Sex, Baby
also reproduce asexually
...
If a cell produces a new cell that contains only half of
its genetic information, that cell has engaged in sexual reproduction
...

Cells divide for the following important reasons:
✓ To make copies of cells for growth: You started out as a single cell after
mom’s egg met dad’s sperm, but today you have about 10 trillion cells
in your body
...
When you watch plants grow taller or baby animals grow into adults, you’re seeing mitosis at work
...
For instance, you constantly shed skin cells
from your surface
...
And if an organism gets injured, its body uses mitosis to produce the cells necessary to repair the injury
...
During
sexual reproduction, gametes (cells, specifically eggs and sperm, containing half the genetic information of their parent cells) get together
to make new individuals
...


Welcome to DNA Replication 101
If one cell is going to divide to produce two new cells, the first cell must copy
all of its parts before it can split in half
...

Cells use a process called DNA replication to copy their genetic material
...
It’s particularly important that each new cell receives an accurate copy of the genetic information because this copy, whether it’s accurate
or faulty, directs the structure and function of the new cells
...
The entire DNA strand doesn’t unzip all at once, however
...
The partly
open/partly closed area where the replication is actively happening is
called the replication fork (this is the Y-shaped area in Figure 6-1)
...
To build complementary strands, DNA polymerase follows the base-pairing rules for the DNA nucleotides: A always pairs with
T, and C always pairs with G (see Chapter 3 for further details about
nucleotides)
...
When DNA polymerase is done creating complementary pairs, each parental strand has a brand-new partner strand
...

Several enzymes help DNA polymerase with the process of DNA replication
(you can see them and DNA polymerase hard at work in Figure 6-1):
✓ Helicase separates the original parental strands to open the DNA
...
DNA polymerase needs these primers in
order to get started copying the DNA
...

✓ DNA ligase forms covalent bonds in the backbone of the new DNA molecules to seal up the small breaks created by the starting and stopping
of new strands
...
Note in Figure 6-1 the numbers 5' and 3' (read “5
prime” and “3 prime”)
...
You can see that the 5' end of one strand lines up with the 3'
end of the other strand
...
Because
the two strands have opposite polarity, they’re antiparallel strands
...


Overall direction of
DNA polymerase
activity and
DNA replication

3'

5'

Parental DNA
(DNA template)

DNA
ligase

Chapter 6: Dividing to Conquer: Cell Division
The antiparallel strands of the parent DNA create some problems for DNA polymerase
...
But DNA
polymerase needs to use the parent DNA strands as a pattern, and they’re going
in opposite directions
...
Refer to Figure 6-1
...

✓ One new strand of DNA, called the lagging strand, grows in fragments
...
Notice how the right side of the replication fork
looks a little messier? That’s because the replication process doesn’t
occur smoothly over here
...
DNA polymerase starts making a piece of this new strand
but has to move away from the fork to do so (because it can only work
in one direction)
...
As a result, the lagging strand is
made in lots of little pieces called Okazaki fragments
...


Cell Division: Out with the Old,
In with the New
Cell division is the process by which new cells are formed to replace dead
ones, repair damaged tissue, or allow organisms to grow and reproduce
...
This alternation between not dividing and dividing is known as
the cell cycle, and it has specific parts:
✓ The nondividing part of the cell cycle is called interphase
...
If the cell is a singlecelled organism, it’s probably busy finding food and growing
...

Maybe it’s a skin cell protecting you from bacteria or a fat cell storing
energy for later
...

• Cells that reproduce asexually, like a skin cell that needs to replace
some of your lost skin, divide by mitosis, a process that produces
cells that are identical to the parent cell
...
In you, the only cells that reproduce
by meiosis are cells in your gonads
...
Cells in testes produce gametes called sperm, and cells in ovaries produce gametes called eggs
...

We cover both processes (as well as the interphase) in the sections that follow,
but Table 6-1 can help you sort out the important differences at a glance
...


Two separate divisions are necessary
to complete the process
...


Homologous chromosomes must synapse to complete the process, which
occurs in prophase I
...


Crossing-over is an important part of
meiosis and one that leads to genetic
variation
...


Sister chromatids separate only in anaphase II, not anaphase I
...
)

Daughter cells have the same number
of chromosomes as their parent cells,
meaning they’re diploid
...


Daughter cells have genetic information that’s identical to that of their
parent cells
...


Chapter 6: Dividing to Conquer: Cell Division
Mitosis

Meiosis

The function of mitosis is asexual
reproduction in some organisms
...


Meiosis creates gametes or spores, the
first step in the reproductive process
for sexually reproducing organisms,
including plants and animals
...
For instance, nerve cells send signals, glandular cells secrete hormones, and muscle cells contract
...

The nuclear membrane is intact throughout interphase, as you can see in
Figure 6-2
...
Cells that are going to divide copy their DNA during interphase
...
Each
chromosome is made up of just a single double-stranded piece of DNA
(double-stranded is just another way of saying that the DNA is a double
helix)
...
They never divide; instead,
they just hang out and do their cellular thing
...

✓ S phase: This phase is when the cell gets ready to divide and puts the
pedal to the metal for DNA replication
...

You can see replicated chromosomes in Figure 6-2, in the cell labeled
Prophase
...

✓ G2 phase: During this phase, the cell is packing its bags and getting
ready to hit the road for cell division by making the cytoskeletal

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Part II: Cell Reproduction and Genetics: Let’s Talk about Sex, Baby
proteins it needs to move the chromosomes around
...
A network of spindle fibers spreads
throughout the cell during mitosis to form the mitotic spindle, which is
represented by the thin curving lines drawn in the cells in Figure 6-2
...


Late Interphase
Nuclear pore
Nucleus
Nucleolus
Centriole

Chromatin

Prophase
Fragments of
nuclear envelope
Centromere
Chromatids

Mitosis
Spindles

Metaphase

Chromosomes are
aligned at equator
Telophase

Anaphase

Early Interphase
Daughter cells
Figure 6-2:
Interphase
and mitosis
...
During mitosis,
the cell makes final preparations for its impending split
...


Chapter 6: Dividing to Conquer: Cell Division
The process of mitosis occurs in four phases, with the fourth phase initiating
a final process called cytokinesis
...


Examining the four phases of mitosis
Although the cell cycle is a continuous process, with one stage flowing into
another, scientists divide the events of mitosis into four phases based on the
major events in each stage
...
(During interphase,
the DNA is spread throughout the nucleus of the cell in long thin strands
that would be pretty hard to sort out
...
During prophase:
• The chromosomes coil up and become visible
...

• The mitotic spindle forms and attaches to the chromosomes
...

✓ Metaphase: The chromosomes are tugged by the mitotic spindle until
they’re all lined up in the middle of the cell
...
)
✓ Anaphase: The replicated chromosomes separate so that the two sister
chromatids (identical halves) from each replicated chromosome go to
opposite sides (see the cell labeled Anaphase in Figure 6-2)
...

✓ Telophase: The cell gets ready to divide into two by forming new
nuclear membranes around the separated sets of chromosomes
...

The events of telophase are essentially the reverse of prophase
...

• The chromosomes uncoil and spread throughout the nucleus
...

• The nucleoli reform and become visible again
...
(Cyto- means “cell,” and kinesis
means “movement,” so cytokinesis literally means “moving cells
...
Cytoskeletal proteins act like a belt around
the cell, contracting down and squeezing the cell in two (imagine squeezing a ball of dough at the center until it becomes two balls of dough)
...
Because a
rigid cell wall is involved, the cell can’t be squeezed in two
...
The vesicles are basically little bags made of membrane that carry the wall material, so when they fuse together, their membranes form the plasma membranes of the new cells
...

After cytokinesis is complete, the new cells move immediately into the G1
stage of interphase
...


Cleavage
furrow

Contracting ring
of microfilaments

Daughter cells
Cell wall

Figure 6-3:
Cytokinesis
...
Human body cells have 46
chromosomes, 2 each of 23 different kinds
...
The two matched chromosomes
in each pair are called homologous chromosomes (homo- means “same,” so
these are chromosomes that have the same kind of genetic information)
...
For every gene that your mom gave you, your
dad also gave you a copy, so you have two copies of every gene (with the
exception of genes on the X and Y chromosomes if you’re male)
...
If one of the two has a gene that affects eye color, for example, the
other chromosome has the same gene in the same location
...


1

2

3

6

7

8

13

14

15

19
Figure 6-4:
A human
karyotype
...

Through sexual reproduction (see Figure 6-5), a sperm and an egg join
together to create a new individual, returning the chromosome number to
46
...
And when gametes are produced, they can’t just get
any 23 chromosomes — they have to get one of each pair of chromosomes
...
The resulting person wouldn’t have the correct genetic
information and probably wouldn’t survive
...


Diploid
zygote
(2n=46)

2n

Mitosis and
development

Meiosis is the type of cell division that separates chromosomes so gametes
receive one of each type of chromosome
...

Consequently, gametes have what’s known as a haploid number of chromosomes, or a single set
...


Chapter 6: Dividing to Conquer: Cell Division
Two cell divisions occur in meiosis, and the two halves of meiosis are called
meiosis I and meiosis II
...
Each daughter cell receives one of each
chromosome pair, but the chromosomes are still replicated
...
These two copies, called sister chromatids, are held
together, forming replicated chromosomes
...
)
✓ During meiosis II, the replicated chromosomes send one sister chromatid from each replicated chromosome to new daughter cells
...
(Notice how the four
daughter cells in Figure 6-6b don’t have sister chromatids?)

Crossing-Over
A A a a

A

Normal Meiosis
a

A

a

and
Meiosis I
A A

B

Bb b
a a

B

b b
A a a

B
A

Meiosis II

b
a

B b

B b

B

b B b

Abnormal Meiosis

Figure 6-6:
Crossingover,
meiosis, and
nondisjunction
...
In females, the process begins
a lot earlier — in the fetal stage
...
With the onset of
puberty, the cells take turns entering meiosis II
...
you get the idea
...

When a human sperm cell and a human egg cell — each with 23 chromosomes —
unite in the process of fertilization, the diploid condition of the cell is restored
...

The phases of meiosis are very similar to the phases of mitosis; they even
have the same names, which can make distinguishing between the two rather
tough
...

The next sections delve into the details of each phase of meiosis I and meiosis II
...
The phases are as follows:
✓ Prophase I: During this phase, the cell’s nuclear membrane breaks
down, the chromatids coil to form visible chromosomes, the nucleoli
break down and disappear, and the spindles form and attach to the
chromosomes
...
Prophase I is when something that’s
absolutely critical to the successful separation of homologous chromosomes occurs: synapsis
...
The synapsis process begins when the homologous chromosomes move and lie next to each other
...
This swapping of materials
results in four completely unique chromatids
...

Crossing-over between homologous chromosomes during prophase I
increases the genetic variability among gametes produced by the same
organism
...
This is one
of the reasons that siblings can be so different from each other
...
The difference between metaphase I of meiosis and metaphase of mitosis is that the homologous pairs line up in the
former, whereas individual chromosomes line up in the latter
...

✓ Telophase I: This is when the cell takes a step back (or forward, depending on your perspective) to an interphase-like condition by reversing the
events of prophase I
...


Meiosis II
During meiosis II, both daughter cells produced by meiosis I continue their
dance of division so that — in most cases — four gametes are the end result
...

Meiosis II separates the sister chromatids of each replicated chromosome and
sends them to opposite sides of the cell
...

✓ Prophase II: As in mitosis’s prophase and meiosis’s prophase I, the
nuclear membrane disintegrates, the nucleoli disappear, and the spindles form and attach to the chromosomes
...
Just as in any old metaphase, the chromosomes line up at the equatorial plane
...

✓ Anaphase II: The sister chromatids of each replicated chromosome
move away from each other to opposite sides of the cell
...

After meiosis II, it’s time for cytokinesis, which creates four haploid cells
(which is impressive considering you had just one diploid cell at the beginning of meiosis)
...
You can see the effects of this
genetic variability if you look at the children in a large family and note how
each person is unique
...

The sections that follow familiarize you with some of the specific causes of
genetic variation courtesy of meiosis and sexual reproduction
...
These mistakes are called spontaneous mutations, and they introduce changes into the genetic code
...
When changes occur in a cell that produces gametes, future
generations are affected
...
)

Crossing-over
When homologous chromosomes come together during prophase I of meiosis,
they exchange bits of DNA with each other
...

Crossing-over is one way of explaining how a person can have red hair from his
mother’s father and a prominent chin from his mother’s mother
...


Independent assortment
Independent assortment occurs when homologous chromosomes separate
during anaphase I of meiosis
...

So, the way the pairs are oriented during meiosis in one cell is different from
the way they’re oriented in another cell
...
How many different combinations of homologous chromosomes are possible in a human cell undergoing meiosis? Oh, just 223 — that’s 8,388,608 to be exact
...


Fertilization
Fertilization presents yet another opportunity for genetic diversity
...
Fertilization
is random, so the sperm that wins the race in one fertilization event is going
to be different than the sperm that wins the next race
...
So, fertilization produces random combinations of genetically diverse sperm and eggs, creating virtually unlimited
possibilities for variation
...
Well, almost
...


Nondisjunction
Nothing’s perfect, even in the cellular world, which is why sometimes meiosis doesn’t occur quite right
...
The point of meiosis is to
reduce the number of chromosomes from diploid to haploid, something that
normally happens when homologous chromosomes separate from each other
during anaphase I
...

What happens next isn’t pretty
...
This condition usually means the cells are doomed to die
...
Well, that should be great for these cells, shouldn’t it?
It should mean they’ll have an increased chance for genetic variation, and
that’s a good thing, right?
Wrong! An extra chromosome is like an extra letter from the IRS
...
Many times these overendowed cells simply die, and

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that’s the end of the story
...
The real tragedy, then, is when an abnormal cell goes on
to unite with a normal cell
...

The term scientists use for this occurrence is trisomy
...
One possible abnormality occurring from an extra chromosome is Down syndrome, a condition that often results in some mental and
developmental impairment and premature aging
...
If an egg with two number 21 chromosomes is fertilized
with a normal sperm cell with just one number 21, the resulting offspring has
47 chromosomes (24 + 23 = 47), and Down syndrome occurs
...
If a cell has been waiting its
turn for 40 or 45 years, it’s pretty darned old — in cellular terms at least
...
Meiosis is a continuous process for
them, producing new cells all the time
...
Like all other genetic
characteristics, gender is determined at a chromosomal level
...
The 23 pairs of human chromosomes can be
divided into 22 pairs of autosomes, chromosomes that aren’t involved in the
determination of gender, and one pair of sex chromosomes
...
But only guys get a special gene, located on the Y chromosome, that
jump-starts the formation of testes in boy fetuses when they’re about 6 weeks
old
...
The Y chromosome is smaller than all the other chromosomes, but it packs one powerful little gene!

Chapter 6: Dividing to Conquer: Cell Division

Monocultures, a threat to genetic diversity
Up until about the 1960s, most American farms
were smaller operations that planted diverse
crops and relied fairly heavily upon human labor
to get the crops in
...
After all, machines work best at specialized, repetitive tasks
...
This practice worries many scientists because they recognize
the power and value of genetic diversity
...

In addition, large industrial farms increasingly
rely upon artificial fertilizers and pesticides to
support their specialized monocultures, which
can upset the balance between the farm and
the natural ecology
...
Small farms
are trying to make a comeback by producing
diverse, organic crops, and companies are
starting to collect older varieties of crop plants,
called heirloom varieties, and reintroduce them
into the human food supply
...
It all started more than 150 years ago when a monk
named Gregor Mendel conducted breeding experiments with pea plants that
led him to discover the fundamental rules of inheritance
...

In this chapter, we show you one of Mendel’s experiments and present some
of the most important rules of inheritance
...
What do all
three sets of parents have in common? They all passed their traits on to their
offspring
...

When living things reproduce, they make copies of their DNA and pass some
of that DNA on to the next generation
...

Of course, in sexually reproducing species, offspring aren’t exactly like their
parents for several reasons:
✓ Offspring receive half of their genetic information from their father
and half from their mother
...
So each
offspring brings together a potentially new combination of its parents’
traits
...
The
result is that there really is only one you — even if you have siblings,
you’re all a little bit different
...
DNA changes
slightly every time it’s copied due to mutation (see Chapters 6 and 8 for
the full scoop on mutation)
...
For instance, Queen Victoria
of England had children and grandchildren who suffered from hemophilia, a deadly disease in which your blood doesn’t clot properly, but
none of her ancestors had the disease
...
Queen Victoria didn’t have the disease, but she passed
the mutation on to several of her children
...

✓ Some traits are acquired rather than inherited
...
Even if your parents can do
these things, you still have to figure out how to do them on your own
...

✓ Some inherited traits are affected by the environment
...
Even something like height can be affected
by your environment — your DNA controls your basic height, but nutrition plays a big role in whether you reach your full potential
...
After all, as soon as a new baby is born, people start trying to decide
who the baby looks like
...

Mendel lived in the mid-19th century
...
So a tall father and a short mother
were expected to have average-size kids
...
)
Mendel, who was very interested in science and math, tested these ideas
about inheritance by breeding pea plants in the abbey garden
...
Although other people had bred plants and animals
for desirable characteristics before, Mendel was extremely careful in his
experiments and used math to look at inheritance in a new way, revealing
patterns that no one else had noticed
...


Pure breeding the parentals
Mendel used pure-breeding plants (plants that always reproduce the same
characteristics in their offspring) to ensure that he knew exactly what genetic
message he was starting with when he chose a particular plant for his experiments
...

To make pure-breeding plants for his experiments, Mendel self-pollinated
plants that had the characteristic he wanted to study, weeding out any
offspring that were different until all the offspring always had his chosen
characteristic
...
) For example, Mendel self-pollinated
tall pea plants, pulling out any short offspring until he had plants that would
produce only tall offspring
...


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Pure-breeding organisms that are used as the parents in a genetic cross are
called parentals, or the P1 generation
...

According to the idea of blending inheritance, all the offspring should have
been average in height
...
It almost
seemed like the short characteristic had disappeared, but when Mendel
mated tall pea plants from this new F1 generation and grew their offspring,
he saw both tall and short pea plants, indicating that the short characteristic
had merely been hidden
...

The F1 and F2 generations get their names from the word filial, which means
“something that relates to a son or daughter
...


Reviewing Mendel’s results
The results of Mendel’s pea plant experiments were very exciting because
they didn’t follow what was expected
...

From his results, Mendel proposed several ideas that laid the foundation for
the science of genetics:
✓ Traits are determined by factors that are passed from parents to offspring
...

✓ Each organism has two copies of the genes that control every trait
...
The offspring
winds up with two copies of each gene because it gets one copy from
mom and one copy from dad
...

Variations that are hidden are recessive, whereas variations that hide
other variations are dominant
...

✓ The genes that control traits don’t blend with each other, nor do they
change from one generation to the next
...


Chapter 7: Making Mendel Proud: Understanding Genetics
Sexually reproducing organisms have two copies of every gene, but they give
only one copy of each gene to their offspring
...
Scientists now call this idea Mendel’s Law of Segregation
...
As the science of genetics grew and developed, so did the language used by geneticists
...
Some genes are thousands of nucleotides long; others are less than a hundred
...
Each gene is the
blueprint for a worker molecule in your cells, usually a protein
...

For example, the darkness of your skin, hair, and eyes is determined by
how much of the brown pigment melanin is deposited there
...
If your genes contain the code for proteins that do these jobs well, your coloring is darker
...

✓ Alleles: Different forms of a gene are called alleles; they explain why
Mendel saw both tall and short pea plants
...
Plants with two alleles for tallness are tall; plants
with two alleles for shortness are short
...
In other words, the allele for tall is
dominant to the allele for short in pea plants
...
So, for a gene that controls skin color, alleles for dark
color are dominant to alleles for light color
...


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✓ Loci: These are the locations on a chromosome where genes are found
...

In organisms of the same species, the same gene is found at the same
locus in every organism
...
The gene for blood type A, B, or O
is always found on the same locus on Chromosome 9, and the gene for
cystic fibrosis is always found on the same locus on Chromosome 7
...
Traits such as your
height, weight, and the color of your skin, hair, and eyes result from the interaction of several genes
...
Polygenic traits usually show a wide range
of variety in the population
...
This difference is because human height is polygenic and pea height
is controlled by just one gene
...
They use a letter to stand for each gene, capitalizing
the letter for dominant alleles (for a definition of alleles, see the preceding
section)
...

For the cross Mendel did between tall and short pea plants, see the earlier
“‘Monk’ing Around with Peas: Mendel’s Laws of Inheritance” section for more
on this experiment, the letter T can be used to represent the gene for plant
height
...


Figure 7-1:
Mendel’s
cross T
between tall
and short T
pea plants
...
Here they are:
✓ Genotype: The combination of alleles that an organism has is its genotype
...

✓ Phenotype: The appearance of an organism’s traits is its phenotype
...

A tool called a Punnett square helps geneticists predict what kinds of offspring might result from a particular genetic cross
...
The alleles
that each parent can contribute to the offspring are written along the sides of
the square where it says Sperm and Eggs
...

If Mendel had used modern genetic notation and terminology, he might have
analyzed his experiment like this (look to Figure 7-1 for reference if you need it):
1
...
The tall
parent’s alleles are shown as TT, and the short parent’s alleles are
shown as tt
...

2
...
Because the
parentals are purebred, they can give only one type of allele
...
Copies of these
alleles are packaged into gametes (sperm and egg cells) as the pea
plants reproduce
...
The sperm and egg of the parents combine, giving their F1 offspring two
alleles for the height gene
...
Because their alleles are different, the F1 pea plants are heterozygous for the plant height trait (heteromeans “other”)
...
This is
exactly what Mendel saw — the short trait from his parentals seemed to
disappear in the F1 generation
...
When F1 plants are crossed, they can each make two kinds of gametes —
those that carry a dominant allele and those that carry a recessive allele
...

5
...
For every one
TT offspring, there should be two Tt offspring and one tt offspring
...

6
...
So, the Punnett
square predicts that for every three tall plants, there’ll be just one
short plant
...
This is precisely what Mendel saw — for every one short plant
he saw in his F2 generation, he saw about three tall ones
...
(Mono- means “one,” and
hybrid means “something from two different sources,” so a monohybrid is an
organism that has two different alleles for one trait
...


Studying Genetic Traits in Humans
One of the reasons plants make good subjects for genetic studies is because
you can control their mating
...
Also, humans don’t produce as many offspring as
plants do, and human children take a very long time to grow up so you can
evaluate the appearance of traits
...


Chapter 7: Making Mendel Proud: Understanding Genetics
The sections that follow show you how geneticists go about studying family
trees and how they test for different inheritance scenarios
...


Creating pedigree charts
The first steps in understanding the inheritance of a human trait are to gather
information on which people in a family have the trait and record that information in a geneticist’s version of a family tree, which is called a pedigree
chart
...

✓ Squares indicate males; circles indicate females
...

✓ A line drawn down from a marriage indicates that the marriage produced a child
...

✓ A filled-in symbol indicates people whose traits are being studied; an
open symbol is used for people who don’t have those traits
...

✓ Roman numerals shown to the left of each row represent the different
generations
...
The deceased
person in Figure 7-2c, for example, is identified as Individual VI-1
...
The trait shown in Figure 7-2c, for
example, must be caused by a recessive allele
...
However, neither of this person’s parents shows the trait
...
When an allele is present but not seen in a person’s phenotype, the trait must be recessive
...

Grandfather is from
generation I and
referred to as I-1;
proband, from
generation III,
is referred
to as III-1
...


V
1

2

VI

c

1

2

3

4

6

I
1
Heart attack
51 yo

2

II
1
III P

2
1

3

4

Chapter 7: Making Mendel Proud: Understanding Genetics

Testing different inheritance scenarios
One pedigree chart alone doesn’t always provide enough information to
determine the inheritance pattern of a trait
...
Decide which type of inheritance you want to test
...

2
...

If you’re testing to see whether the trait is dominant, then you can propose that A should represent the dominant allele and a should represent
the recessive allele
...
Assign genotypes to people whose genotype is certain
...
(If they
had even just one copy of the dominant allele, then you’d see the trait,
and their symbols would be shaded
...
Write their
genotypes under their symbols
...
Work from the individuals whose genotypes are certain to figure out
the genotypes of the other individuals
...
For
example, Individual I-2 has the trait, which means she must have at least
one copy of the dominant allele
...
To figure out her
second allele, look at her children
...
Because you’re testing whether this trait could be dominant, then
any kid who has even just one A is going to show the trait
...
Consequently, she must be able to
give the little a allele too, which makes her genotype Aa
...

5
...

For example, if you proposed that the trait in Figure 7-2c was caused by
a dominant allele, then Individual VI-1 would have to have had at least

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one dominant allele
...
Because the proposed
genotypes are impossible, you must reject the hypothesis that this trait
could be carried by a dominant allele
...
In other words, the trait
never hides like a recessive trait does
...
If you set up a hypothesis that the trait is
recessive and test your idea using the preceding steps, you can give everyone a genotype without encountering an impossible conflict
...

In fact, sometimes they have to study many pedigrees before they can prove
the inheritance of a particular trait
...
For example,
a red-headed child may have a red-headed grandparent but blondehaired parents
...

✓ Traits carried by dominant alleles often show up in every generation
...
However, people showing the dominant
brown-eyed trait may have only one copy of the dominant allele, so they
could potentially pass on recessive alleles to their children
...
In
fact, whenever two parents who show a particular trait have kids who
don’t show the trait, then you know for sure that the trait is dominant
...

That’s because DNA controls the structure and function of organisms, largely
because it’s essential to the production of the proteins that determine your
traits
...

We show you just how important DNA and proteins are to your everyday life
in this chapter
...


Proteins Make Traits Happen,
and DNA Makes the Proteins
You probably know that DNA is your genetic blueprint and that it carries the
instructions for your traits
...
DNA contains the instructions for the construction of the molecules that carry out the functions of
your cells
...


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Think of your cells as little factories that have to carry out certain functions
...
DNA is the instructions for the construction of each type of robot
...
Based on how the robots work, the factory accomplishes specific tasks
...
If one
of these molecules isn’t working correctly, your cells will work differently
than they’re supposed to, which could affect your traits
...
Because many of
the functional molecules in your cells are proteins, genes often contain the
instructions for building the polypeptide chains that make up proteins (for
more on protein structure, head to Chapter 3)
...

Sometimes it’s hard to imagine how one little protein can affect you in an
important way
...
How can just one faulty protein make a difference?
Well, if your skin cells couldn’t make the protein collagen, your skin would
fall off at the slightest touch
...
So you see, all the functions of your
body that you probably take for granted — the way it’s built, the way it looks,
and the way it functions — are controlled by the actions of proteins
...
Every time a cell reproduces, it must make a copy of these instructions for the new cell
...
Here’s an outline of
the process:
✓ Cells use transcription to copy the information in DNA into RNA
molecules
...

✓ Cells use translation to build proteins from the information carried in
mRNA molecules
...

Transcription and translation are two pretty similar sounding words for two
very different processes in cells
...
When you transcribe something, you copy it
...
DNA and RNA are similar molecules, so it’s not
like you’re really changing anything — you’re just copying the information
down
...
Translation in cells takes the information in mRNA
and uses it to build a protein, which is a different type of molecule
...

The sections that follow give you an in-depth look at transcription, RNA processing, and translation
...
These chemical units are
joined together in different combinations that form the instructions for cells’
functional molecules, which are mostly proteins
...
(RNA
polymerase is shown in Step 2 of Figure 8-1
...
RNA polymerase slides along the gene, matching RNA
nucleotides to the DNA nucleotides in the gene
...
The exception is
that RNA contains nucleotides with uracil (U) rather than thymine (T)
...
(Figure 8-1 gives you the visual of this
...
)

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---

A -A -A -A
A -A -A -A - 3'
-ANucleus
A- A
DNA
poly-A tail
5' 3'
exon
te m p la te
D NA
-

A -A
A-

in t

on
n tr

i

ro

n

in tr
on

6

P
G

5'

G

5
5'

P

4

P

(Steps 1, 2, 3, 4)

P
5'cap

P

5'

Transcription

n

P

Figure 8-1:
Transcribing
DNA and
processing mRNA
within the
nucleus of a
eukaryotic
cell
...
Your
genes are extremely important and need to be protected, so they’re kept safe
in the nucleus at all times
...

You can think of your chromosomes like drawers in a file cabinet
...
The original blueprint (the DNA) is kept
safely locked away in the file cabinet
...
The following sections introduce you to the other players and walk
you through the process of transcription step by step
...
These proteins look for certain sequences in the
DNA that mark the beginnings of genes; these sequences are called promoters
...

Many promoters contain a particular sequence called the TATA box because
it contains alternating T and A nucleotides
...
(Step 1 in Figure 8-1 depicts a
gene’s promoter, along with its TATA box
...
Transcription terminators can work in different ways, but they all
stop transcription
...
)

Walking through the process
As you can see from the following, the process of transcription is pretty
straightforward:
1
...

By binding to the promoter, RNA polymerase gets set up on the DNA so
it’s pointed in the right direction to copy the gene
...
RNA polymerase separates the two strands of the DNA double helix in
a small area
...
(The strand of DNA that’s
being used as a pattern in Figure 8-1 is labeled as the DNA template
...
)
As RNA polymerase slides along the DNA, it opens a new area, and the
DNA behind it closes back up
...
RNA polymerase uses base-pairing rules to build an RNA strand that’s
complementary to the DNA in the template strand
...


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Part II: Cell Reproduction and Genetics: Let’s Talk about Sex, Baby
4
...

Some terminators have a sequence that causes the new RNA to fold up
on itself at the end, making a little bump that causes RNA polymerase to
get knocked off of the DNA
...
Some of
these RNA molecules are worker molecules for the cell, others are part of cellular structures, and one type — mRNA — carries the code for proteins to the
cytoplasm
...
In
fact, when the mRNA is hot off the presses, it’s called a pre-mRNA or primary
transcript because it’s not quite finished
...

The 5' cap (shown in Step 5 of Figure 8-1) tells the cell it should translate
this piece of RNA
...
Like its name suggests, the poly-A tail (see Step 5 of Figure 8-1) is
a chain of repeating nucleotides that contain adenine (A)
...

✓ The pre-mRNA is spliced to remove introns (noncoding sequences)
...
Your cells
remove the introns before shipping the mRNA out to the cytoplasm (see
Step 6 in Figure 8-1)
...
When your cells cut the introns out of premRNA, the exons all come together to form the blueprint for the protein
...


Chapter 8: Reading the Book of Life: DNA and Proteins

Converting the code to the
right language: Translation
After a mature mRNA leaves the nucleus of a cell, it heads for a ribosome in
the cell’s cytoplasm where the code it contains can be translated to produce
a protein (for more on ribosomes, see Chapter 4)
...

A group of three nucleotides in mRNA is called a codon
...

Each codon specifies one amino acid in the polypeptide chain of a protein
...
So to find out what the codon CGU
represents:
1
...

The letter C is the second letter down, so the amino acid represented by
the C portion of the codon CGU is found in the second row of the table
...
Then look to the top of the table and find the column marked by the
second letter in the codon
...

3
...

The letter U is listed first, so the amino acid represented by the U portion of the codon CGU is the first one listed in the intersection of the
second row and the last column under the Second Letter heading
...

To translate a molecule of mRNA, begin at the start codon closest to the 5’ cap
of the mRNA, divide the message up into codons, and look the codons up in a
table of the genetic code that shows the names of the 20 different amino acids
found in the proteins of living things
...


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First
Letter

Third
Letter

Second Letter
U

A

C

G

phenylalanine

serine

STOP

STOP

A

serine

STOP

tryptophan

G

proline

histidine

arginine

U

proline

histidine

arginine

C

leucine

proline

glutamine

arginine

A

proline

glutamine

arginine

G

isoleucine

threonine

asparagine

serine

U

isoleucine

threonine

asparagine

serine

C

isoleucine
methionine
& START

threonine

lysine

arginine

A

threonine

lysine

arginine

G

valine

alanine

aspartate

glycine

U

valine
G

C

leucine

leucine

Figure 8-2:
The genetic
code
...
They also
help you understand the overall process of translation
...
coli
...
AUG is called the start codon
because translation begins here
...
AUG also represents the amino acid
methionine, so methionine is the first amino acid added to the polypeptide chain
...
Translation
ends when a stop codon is read in the mRNA
...

When stop codons are read in the mRNA, translation stops without
adding any new amino acids to the polypeptide chain
...
For
instance, arginine is represented by more than one codon; CGU, CGC,
CGA, and CGG all represent arginine
...

In order for your cells to decode mRNA, they need the help of an important
worker: transfer RNA (tRNA)
...
Like all RNA molecules, tRNA is made of nucleotides that can pair up
with other nucleotides according to base-pairing rules
...
Each tRNA has a
special group of three nucleotides, called an anticodon, that pairs up with the
codons in mRNA
...
So, the tRNA
that has the right anticodon to pair with a specific codon adds its amino acid
to the growing polypeptide chain
...
The specific relationship between tRNA anticodons and
mRNA codons ensures that each codon always specifies a particular amino
acid
...
Follow along in
Figure 8-3 as we present these three steps:
1
...

The small subunit of the ribosome binds to the mRNA
...
The start codon is AUG, so the first tRNA has the anticodon UAC
(see #2 in Figure 8-3)
...

2
...


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Each tRNA enters a pocket in the ribosome called the A site (see #3 in
Figure 8-3)
...
When a tRNA is parked
in the A site and the P site, the ribosome catalyzes the formation of a peptide bond between the growing polypeptide chain and the new amino acid
...

After the new amino acid is added to the growing chain, the ribosome
slides down the mRNA, moving a new codon into the A site
...

3
...

The ribosome slides down the mRNA until a stop codon enters the A
site
...
Translation
stops, and the ribosome and mRNA separate from each other
...
Often, more than one polypeptide
chain combines with another chain to form the complete protein
...

Why? Because throughout your life, tiny genetic
changes may occur that you don’t even realize
are happening — a tiny mutation caused by an
X-ray here or another tiny mutation caused by
breathing in polluted air there
...
Each individual mutation may be harmless, but after genetic changes
accumulate over time, the chance that some
mutation will occur to change the proteins that
control cell division grows greater
...
As even greater numbers
of mutations accumulate in the cells over time,
their characteristics change, and the tumor may
become malignant (more likely to spread and
cause death)
...

People living in the United States have a 1 in 3
chance of developing cancer during their lifetimes
...


Chapter 8: Reading the Book of Life: DNA and Proteins

Nucleus
5'

3'

transcription
G C

3'
5'

tRNA
3' 5'

RNA
polymerase

U A

U A G

C G
small
and
large
ribosome
subunits

A

T

DNA

G A G

ala
mRNA
his

ite

A
A A

Ps

5'

A U G

it
As

G

U

U

A C

C

4

C A C

U

cys

pro

3
G

sn

n
U

A

tio

A

-a

U

U

m

et

3'

Asite

A

Psite

G

A

C

A C A G G U
U G U C C A

small rRNA
subunit
Figure 8-3:
Translating
mRNA into
protein
...
A mutation is a change from the original DNA strand —
in other words, the nucleotides aren’t in the order that they should be
...
When proteins change, the functions of cells, and the traits of organisms, can also change
...
Two main types of mutations occur:
✓ Spontaneous mutations: These result from uncorrected mistakes by
DNA polymerase, the enzyme that copies DNA
...
In general, DNA polymerase makes
one mistake for every billion base pairs of DNA it copies
...
unless you’re talking about your DNA
...
Cancer, for example, usually occurs as
people age because they’ve lived long enough to accumulate mutations
in certain genes that control cell division
...
Anything that increases the
error rate of DNA polymerase is a mutagen
...

When mutations occur during DNA replication, some daughter cells formed
by mitosis or meiosis inherit the genetic change (we explain how cells divide
in Chapter 6)
...
If the parent DNA molecule
has a nucleotide containing thymine (T), then DNA polymerase should
bring in a nucleotide containing adenine (A) for the new strand of DNA
...
Because just one
nucleotide was changed, the mutation is called a point mutation
...


Chapter 8: Reading the Book of Life: DNA and Proteins
• Silent mutations have no effect on the protein or organism
...

• Missense mutations change the amino acids in the protein
...
The severity of missense mutations depends on how different the original amino acid
is from the new amino acid and where in the protein the change
occurs
...
If the DNA changes so that a
codon in the mRNA becomes a stop codon, then the polypeptide
chain gets cut short
...

✓ Deletions: When DNA polymerase fails to copy all the DNA in the parent
strand, that’s a deletion
...
If one or two nucleotides are deleted, then the codons
in the mRNA will be skewed from their proper threes, and the resulting
polypeptide chain will be very altered
...
Deletions of
three nucleotides result in the deletion of one amino acid
...

✓ Insertions: When DNA polymerase slips and copies nucleotides in the
parent DNA more than once, an insertion occurs
...
Huntington’s disease, an illness
that causes the nervous system to degenerate starting when a person
is in his 30s or 40s, is caused by insertions of the sequence CAG into
a normal gene up to 100 times
...


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Fighting for breath
Cystic fibrosis (CF), a disease that clogs the
lungs and smaller passageways of the body
with mucus, is the most common genetic disease found among people of northern European
ancestry (about 30,000 people are living with CF
in the United States alone)
...
People with CF don’t usually live
past young adulthood because their lungs ultimately fail from all the damaging infections
...

All of this difficulty and pain is caused by a
mutation in one protein: the CFTR protein
...
The
movement of chloride affects the movement
of water, which is why the mucus gets so thick
on the outside of cells in people who have the

disease
...
That doesn’t seem like a
very big change, but the loss of that one amino
acid alters the polypeptide chain so it doesn’t
fold up properly
...
So, in people with the most common form
of CF, the CFTR protein never even makes it to
the plasma membrane
...
One new and very exciting development is the discovery of a drug
that helps mutant CFTR proteins make it to the
plasma membrane
...
The researchers who discovered this
effect are taking their discovery to the next level
by working on appropriate doses of the drug
and testing it on people who suffer from CF
...
Because each one of your cells has a complete set of your
chromosomes, your cells are able to practice gene regulation, meaning they
can choose which genes to use (or not use) and when
...
Gene regulation is the process cells use to choose which genes to
express at any one time
...
”)

Chapter 8: Reading the Book of Life: DNA and Proteins
Genes are regulated by the action of proteins that bind to DNA and either
help or block RNA polymerase from accessing the genes
...
They bind to special sequences on the DNA near genes’ promoters
and make it possible for RNA polymerase to bind the promoter
...

Gene regulation allows your cells to do two things: adapt to environmental
changes and make it so that each cell type has a distinct role in the body
...


Adapting to environmental changes
The world around you is always changing, which means you need to be able
to respond to environmental signals in order to maintain your physiological
balance
...
When your cells need to
respond to environmental changes, they turn genes on or off to make the proteins needed for the response
...
To protect your skin, the cells on
the tip of your nose need to darken a bit by making more of the skin pigment
melanin
...
RNA polymerase reads the genes, making mRNA that contains the
blueprints for the necessary proteins
...
The proteins do their jobs, and the skin on your nose turns a
darker color
...


Becoming an expert through
differentiation
You have more than 200 different types of cells in your body, including skin
cells, muscle cells, and kidney cells
...
To a cell, the right tool for the job is usually a specific protein
...

Cell differentiation is the process that makes cells specialized for certain tasks
...


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Cells differentiate from one another due to gene regulation
...
As that cell and its descendents divided, however, signals
caused different groups of cells to change their gene expression
...
As you grew and developed in your mother’s uterus, your cells
became more and more distinct from each other
...
Each of
these changes occurred as cells transcribed and translated the genes for the
proteins that they needed to do their particular job
...
It’s specialized
for a certain task and can’t access the genes for proteins that aren’t in its job
description
...
When they
divide, their descendants can either remain
stem cells or become differentiated into a specialized cell type
...
They’re therefore
extremely important to the body because they
can help replace cells and repair damage in
almost every kind of tissue
...

For many years the best source of stem cells for
research was human embryos made by in vitro
fertilization but no longer wanted by the people
who donated the sperm and egg
...
Human embryonic stem
cells are special because they’re pluripotent,
meaning they have the potential to become
every type of human cell
...
For example, hematopoietic stem cells from the bone marrow have
the ability to divide and produce many different
types of blood cells, but they typically can’t produce nerve cells
...
However, some people feel that
destroying human embryos is morally wrong,
no matter how early in development they are
(embryos frozen after in vitro fertilization typically have about five to eight cells)
...
Those who support stem
cell research argue that the potential benefits
of stem cells for treating disease and saving
lives make it imperative that scientists continue
their research with embryonic stem cells
...
A
group of scientists has figured out a way to
make this happen, but additional research is
needed to determine whether these induced
pluripotent stem cells are truly equivalent to
embryonic stem cells
...
After Mendel showed that traits were
controlled by hereditary factors that pass from one generation to the next,
scientists were determined to figure out the nature of these factors and
how they were transmitted
...

Almost 100 years after Mendel, James Watson and Francis Crick figured out
that DNA was a double helix and proposed how it might be copied
...

During the last 40 years, scientists have developed an amazing array of tools
to read DNA, copy it, cut it, sort it, and put it together in new combinations
...
A new world of human heredity is now open
for exploration as scientists seek to understand the meanings hidden within
human DNA — what they find out will likely change the way we see ourselves
and our place in the world
...


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Understanding Just What’s
Involved in DNA Technology
For years the very structure of DNA made studying it rather challenging
...
Fortunately, the advent of
DNA technology, the tools and techniques used for reading and manipulating
the DNA code, has made working with DNA much easier
...
They can also
compare different versions of the same gene to see exactly where diseasecausing variations occur
...


Cutting DNA with restriction enzymes
Scientists use restriction enzymes, essentially little molecular scissors, in
the lab to cut DNA into smaller pieces so they can analyze and manipulate it
more easily
...
The enzymes slide along the DNA,
and wherever they find their restriction site, they cut the DNA helix
...


Restriction
enzyme
Figure 9-1:
Restriction
enzymes
...
For example, they can put genes into crop plants to
make them resistant to pesticides or to increase their nutritional value
...

Because the DNA from all cells is essentially the same, scientists can even
combine DNA from very different sources
...

When a DNA molecule contains DNA from more than one source, it’s called
recombinant DNA
...
Table 9-1 lists a few useful proteins that are made through
genetic engineering
...
First, they choose a restriction enzyme that forms sticky ends when it
cuts DNA
...
Because they’re complementary,
the pieces of single-stranded DNA can stick to each other by forming
hydrogen bonds (see Chapter 3 for more on bonds and DNA)
...
A and T are complementary base pairs, so these ends can
form hydrogen bonds and stick to each other
...
Next, they cut the human DNA and bacterial DNA with the same
restriction enzyme
...

3
...

Because the two types of DNA have the same sticky ends, some of the
pieces stick together
...
Finally, they use the enzyme DNA ligase to seal the sugar-phosphate
backbone between the bacterial and human DNA
...


Using gel electrophoresis to
separate molecules
Scientists separate molecules from cells such as DNA and proteins in order
to study them
...
When scientists want to separate DNA molecules from cells in order to look for relationships between DNA from two different sources, they use gel electrophoresis,
which separates molecules based on their size and electrical charge
...
They then place the gel in a box, called an electrophoresis chamber, that’s filled with a salty, electricity-conducting buffer
solution
...
When the scientists run an electrical current
through the gel (see Figure 9-2c), the gel becomes like a racetrack for the
DNA molecules, only instead of trying to cross the finish line, the DNA is
trying to get to the positively charged end of the box
...
The stain sticks to the DNA, creating stripes
called bands (see Figure 9-2d)
...


Chapter 9: Engineering the Code: DNA Technology
DNA
sample

b The pieces of DNA
are put into small
pockets, called wells, in
the slab of gel
...


Restriction
enzymes

a Restriction enzymes cut DNA into small
pieces of various sizes
...
gel, the smaller fragments move quicker
and farther than the larger DNA fragments
...
The negatively
charged DNA fragments move
towards the positively charged
cathode
...
It gives medical
researchers the ability to make many copies of a gene whenever they want to
genetically engineer something (see the earlier “Combining DNA from different sources” section for more on genetic engineering)
...

To begin PCR, the DNA sample that contains the gene to be copied is combined with thousands of copies of primers that frame the gene on both sides
(see Figure 9-3)
...

The basic steps of PCR are repeated over and over until you have billions of
copies of the DNA sequence between the two primers
...


2 copies

4 copies
8 copies

16 copies

32 copies

PCR works a little like chain e-mails
...
In PCR, first a DNA molecule is copied,
then the copies are copied, and so on, until you have 30 billion copies in just a
few hours
...
It also allows them to make comparisons between normal versions of a gene and disease-causing versions of a gene
...

As you can see in Figure 9-4, DNA sequencing uses a special kind of nucleotide, called ddNTP (short for dideoxyribonucleotide triphosphate)
...
When a ddNTP is added to a
growing chain of DNA, DNA polymerase can’t add any more nucleotides
...

Most DNA sequencing done today is cycle sequencing, a process that creates
partial copies of a DNA sequence, all of which are stopped at different points
...
As the partial
sequences pass through the machine, a laser reads a fluorescent tag on each
ddNTP, noting the DNA sequence
...
Cycle sequencing uses both normal DNA nucleotides and
ddNTPs and makes only partial copies of DNA that are all slightly different
...


Mapping the Genes of Humanity
The Human Genome Project (HGP) was a hugely ambitious task to determine
the nucleotide sequence of all the DNA in a human cell
...
Fortunately, scientists cooperated and technology
improved during the project, allowing the majority of the human genome to be
sequenced by 2003
...
)

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5’
3’

5’

5’

GCCTAC TGGGACTCAGTCC
CGGATGACCC T GAGTCAGG

GCCTAC TGGGACTCAGTCC

GCCTAC TGGGACTCAGTCC
GAGTCAGG

3’
5’

3’

1
...
Primer finds complement
Taq polymerase adds dNTPs
5’
Primer

5’

GCCTAC TGGGACTCAGTCC
TGAGTCAGG

3’
3
...


G
C

And so on
...
If you were
a researcher and you wanted to study a specific human gene, first you’d have
to know what chromosome it “lived” on
...
Armed with a roadmap of where every gene is located, researchers can turn their attention toward making good use of that information, like
seeking out the genes that cause disease
...
The
questions people are pondering include the
following:
✓ If a person’s genome can be read, should
insurance companies or employers be
allowed to know about increased risks for
disease?
✓ Should people be allowed to screen their
embryos to prevent diseased children from
being born or to select only the ones with
desired characteristics?
✓ Should only people with “good” genetic
stock be allowed to have children?
These questions may seem far-fetched, but
history shows that they aren’t
...
People who joined the eugenics

movement believed that certain human characteristics were more desirable than others; they
wanted to control human breeding to “better”
the human race
...

Many people are afraid that greater knowledge
about the human genome will again be used
to harm
...
Scientists seek knowledge, but they can’t
always control how that knowledge is used
...
In fact, one of the primary goals
of the Human Genome Project was to “address
the ethical, legal, and social issues that may
arise from the project
...


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Genetically Modifying Organisms
Genetically modified organisms (abbreviated as GMOs and sometimes called
genetically engineered organisms or transgenic organisms) contain genes from
other species that were introduced using recombinant DNA technology (see
the earlier “Combining DNA from different sources” section for more on this
type of DNA technology)
...
The
sections that follow take a look at both sides of the “Are GMOs good or bad?”
debate
...
It not only makes growing crops easier
but it can also boost the profitability of those crops
...
Here are some specific scenarios that illustrate how
GMOs can be beneficial:
✓ If crop plants are given genes to resist herbicides and pesticides, then
a farmer can spray the fields with those chemicals, killing only the
weeds and pests, not the crop plant
...
It can also increase crop yields
and profits for the farmer
...

Improved nutrition in crop plants could be a huge benefit in poor
countries where malnutrition stunts the growth and development of
children, making them more susceptible to disease
...
According to the World Health Organization, vitamin A deficiencies
cause 250,000 to 500,000 children to go blind each year
...

✓ If farm animals raised for human consumption are given genes to
increase their yield of meat, eggs, and milk, then more food may be
available for the growing human population, and these greater yields
may also increase profits for farmers
...
BGH is a normal growth hormone found in cows; rBGH
is a slightly altered version that’s produced by genetically engineered
bacteria
...


Why GMOs cause concern
What make GMOs so controversial are the ethical concerns
...
The concerns expressed include the following:
✓ The use of GMOs in agriculture unfairly benefits big agricultural companies and pushes out smaller farmers
...
The
prices on these seeds can be much higher than for traditional crops,
giving large agricultural companies an advantage in the marketplace
...

✓ The use of GMOs in agriculture encourages unsound environmental
practices and discourages best farming practices
...
Not only do these
pesticides and herbicides affect the health of plants and animals living
in the area around farms but they can also get into the drinking water
and possibly affect human health
...

✓ Animals that are engineered to produce more milk, eggs, or meat
may be at greater risk for health problems
...
Overuse of antibiotics is
a human health concern because it reduces the effectiveness of antibiotics on bacteria that cause human infections
...
Farmers can put up
fences, but wind blows all over the place
...


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✓ Increased levels of bovine hormones in dairy products may have
effects on humans who drink the milk
...
Human bodies also make
IGF-1, and increased levels of this hormone have been found in patients
with some types of cancer
...

✓ Genetic modification of foods may introduce allergens into foods, and
labeling may not be sufficient to protect the consumer
...

However, if foods contain products from GMOs, it’s possible that the
introduced genes produced a product that’s not indicated on the food
label
...
Some
people see humans as becoming out of balance with the rest of nature
and think we need to slow down and try to leave less of a footprint on
the world
...


DNA fingerprinting
Although the genomes of human beings are
extremely similar — 99
...
In
fact, all people have a DNA fingerprint, which is
their personal genetic profile
...
By looking at all 13 areas, not just 1 or
2 of them, scientists decrease the chances of
getting a random match between two samples
...
However, solving
crimes isn’t the only use for DNA fingerprinting
...


ife on Earth comes in all forms, shapes, and sizes
...
All the wonderfully diverse
organisms of this planet are connected to each other in
fundamental cycles of energy and matter transfer
...

Organisms that are successful in obtaining what they need
reproduce, creating offspring in their own image
...
In
this part, we also explain the connections between living
things in space and time
...

Yet as we transform the world in order to meet our needs, we’re changing it in ways that make it less hospitable to other species
...
It’s your chance to get
acquainted with the diversity of life around you and discover how biologists
organize all of those diverse life-forms into a specific classification system
...
Almost
everywhere biologists have looked on this planet — from the deepest, darkest caves to the lush Amazonian rain forests to the depths of the oceans —
they’ve found life
...
In the Amazonian rain
forest, plants grow attached to the tops of trees, collecting water and forming little ponds in the sky that become home to insects and tree frogs
...
Each of these environments
presents a unique set of resources and challenges, and life on Earth is incredibly diverse due to the ways in which organisms have responded to these
challenges over time
...


Valuing biodiversity
Most people choose to live with species that are a lot like them — other
people, dogs, cats, and farm animals, for example
...
On the other hand, some people are fascinated by the diversity of
life on Earth and make a habit of watching nature shows on television; visiting zoos, aquariums, and botanical preserves; or traveling to different places
on Earth to see unique organisms in their natural habitats
...
Scientists who
study the interconnections between different types of living things and
their environments (see Chapter 11) believe that biodiversity is important for maintaining balance in natural systems
...

✓ Many economies rely upon natural environments
...

✓ Human medicines come from other living things
...

✓ Biodiversity adds to the beauty of nature
...


Chapter 10: Biodiversity and Classification

Surveying the threats posed
by human actions
As the human population grows and uses more and more of the Earth’s
resources (head to Chapter 11 for the scoop on human population growth),
the populations of other species are declining as a direct result
...
People
need places to live and farms to raise food
...
Whenever people convert land for their
own use, they destroy the habitats of other species, causing habitat loss
...
This habitat fragmentation has the biggest impact on large
animals, such as mountain gorillas and tigers, that need big habitats in
which to roam
...

Automobiles and factories burn gasoline and coal, releasing pollution
into the air
...
After pollution enters the air and water,
it travels around the globe and can hurt multiple species, including
humans
...

Because they can reproduce, living things such as trees and fish are
considered renewable resources
...
If too few members of a species remain,
then survival of that species becomes very unlikely
...

✓ Human movements around the globe sometimes carry species into
new environments
...
Introduced species that are very
aggressive and take over habitats are called invasive species
...
One example of an invasive species is water hyacinth, a plant that was introduced
into the American South during the 1884 exposition in New Orleans
...
Maintenance crews in modern-day Florida
work constantly to try and weed out water hyacinth in order to keep the
state’s rivers and lakes usable for recreation and other species
...
In fact, the rate of extinctions is
increasing along with the size of the human population
...

Many scientists believe Earth is experiencing its sixth mass extinction, a certain time period in geologic history that shows dramatic losses of many species
...
) Scientists
theorize that most of the past mass extinctions were caused by major
changes in Earth’s climate and that the current extinctions (most recently
including black rhinos, Zanzibar leopards, and golden toads) began as a
result of human land use but may increase as a result of global warming
...
Living things are connected
to each other and their environment in how they obtain food and other
resources necessary for survival
...

The sections that follow introduce you to two classifications of species that
biologists are keeping an eye on when it comes to questions of extinction
...

Species that have such great effects on the balance of other species in their
environment are called keystone species
...
If biodiversity gets too low, then the future of life itself becomes
threatened
...
Purple seastars prey on mussels
in the intertidal zone
...
If the seastars are removed from the intertidal zone,
however, the mussels take over, and many species of marine animals disappear from the environment
...

In the Pacific Northwest region of the United States, the health of old-growth
forests is measured by the success of the northern spotted owl, a creature
that can only make its home and find food in mature forests that are hundreds of years old
...
Of course, old-growth forests aren’t just
home to spotted owls — they shelter a rich diversity of living things including plants, such as sitka spruce and Western hemlock, and animals, such as
elk, bald eagles, and flying squirrels
...
If
old-growth forests become extinct in the Pacific Northwest, the effects will be
far reaching and have many negative impacts on the people and other species in the area
...
So what can people do to protect biodiversity and the health of the
environment in the face of the increasing demands of the human population?
No one has all the answers, but here are a few ideas worth trying:
✓ Keep wild habitats as large as possible and connect smaller ones with
wildlife corridors (stretches of land or water that wild animals travel as
they migrate or search for food) so organisms that need a big habitat to
thrive can move between smaller ones
...
Technologies that have minimal
effects on the environment are called clean or green technologies
...

✓ Strive for sustainability in human practices including manufacturing,
fishing, logging, and agriculture
...

The Great Law of the Iroquois says that “people must consider the
impact of their actions not just on the current generation, but on future
generations that aren’t yet born
...
” A generation spans roughly 25 years, so
if people follow the rule of the Iroquois, they must consider the effects
their actions will have 175 years from now
...
This includes being careful about
the transport of not-so-obvious species
...


Meet Your Neighbors: Looking
at Life on Earth
Life on Earth is incredibly diverse, beautiful, and complex
...
The deeper you
delve into the living world around you, the more you can appreciate the similarities between all life on Earth — and be fascinated by the differences
...


Unsung heroes: Bacteria
Most people are familiar with disease-causing bacteria such as Streptococcus
pyogenes, Mycobacterium tuberculosis, and Staphylococcus aureus
...
Instead, they
play important roles in the environment and health of living things, including

Chapter 10: Biodiversity and Classification
humans
...
coli living in your intestines make vitamins that you need to stay healthy
...

Generally speaking, bacteria range in size from 1 to 10 micrometers in length
and are invisible to the naked eye
...
They reproduce asexually by a process
called binary fission
...

Others have flagella (little whiplike appendages made of protein) that they
swish around to swim through their watery homes
...
Their great metabolic
diversity has allowed them to colonize just about every environment on
Earth
...
In fact, you can’t tell the difference between the two just by looking, even if you look very closely using an
electron microscope, because they’re about the same size and shape, have
similar cell structures, and divide by binary fission
...
Then, in the 1970s, a scientist
named Carl Woese started doing genetic comparisons between prokaryotes
...

The first archaeans were discovered in extreme environments (think salt
lakes and hot springs), so they have a reputation for being extremophiles
(-phile means “love,” so extremophiles means “extreme-loving”)
...
They’re happily living in the dirt outside your home
right now, and they’re abundant in the ocean
...


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A taste of the familiar: Eukaryotes
Unless you’re a closet biologist, you’re probably most familiar with life in
eukaryotic form because you encounter it every day
...

On the most fundamental level, all eukaryotes are quite similar
...

Despite these similarities, we bet you still feel that you’re pretty different
from a carrot
...
The differences between you and
a carrot are what separate you into two different kingdoms
...
If you’re wondering when the
fur, scales, and claws come into play, these familiar animal characteristics get factored in much later, at the point when animals get divided up
into phyla, families, and orders (see the “Organizing life into smaller and
smaller groups” section later in this chapter for more on these groupings)
...

✓ Plantae: Plants are photosynthetic organisms that start life as embryos
supported by maternal tissue
...
All plants have cells with cell walls
made of cellulose
...
(Flip to Chapter 20 for
more on plant structures and life cycles
...
Algae and plants are so closely related that many people

Chapter 10: Biodiversity and Classification
include algae in the plant kingdom, but many biologists draw the line at
including algae in the plant kingdom
...

They get their nutrition by breaking down and digesting dead matter
...
Kingdom Fungi includes mushrooms, molds that you see on
your bread and cheese, and many rusts that attack plants
...

✓ Protista: Kingdom Protista is defined as everything else that’s eukaryotic
...
Biologists have studied animals, plants, and fungi for
a long time and defined them as distinct groups long ago
...
A whole world of
microscopic protists exists in a drop of pond water
...
But so far no one has pushed to make
that happen, which is certainly good news for you because we bet you
don’t want to memorize the names of 15 kingdoms of eukaryotes
...

But, in the strictest sense of the word, viruses
aren’t really alive because they can’t reproduce
outside of a host cell
...

They’re just very tiny pieces of DNA or RNA
covered with protein as protection
...

No one really knows how viruses evolved
...
Others think
viruses are cellular escapees, genes that ran
away from home but can’t replicate until they
return to a specific kind of host cell
...
For
the details on how viruses attack cells and reproduce, head to Chapter 17
...
This “tree of
life” allows them to categorize all the diverse organisms that call planet Earth
home and organize them into manageable classifications
...
The types of clues they use to figure out these relationships
include
✓ Physical structures: The structures that biologists use for comparison
may be large, like feathers, or very small, like a cell wall (flip to Chapter
4 for more on this and other parts of a cell’s structure)
...

Biologists consider reproductive structures to be especially important
for determining relationships
...

Bacteria, for example, are the only cells that make a hybrid sugarprotein molecule called peptidoglycan
...

✓ Genetic information: An organism’s genetic code determines its traits,
so by reading the genetic code in DNA, biologists can go right to the
source of differences between species
...
coli, have some traits in
common
...
coli’s ribosomal proteins
...
Characteristics that organisms have in common
are called shared characteristics
...
That history indicates that all life on Earth began from one

Chapter 10: Biodiversity and Classification
original universal ancestor after the Earth formed 4
...
All the
diversity of life that exists today is related because it’s descended from that
original ancestor
...


Mastering the domains
You can interpret the degree of relationship between two organisms by looking at their positions on a phylogenetic tree
...

One branch represents all the animals, and another branch represents
all the plants
...
The distance between animals and plants is a great
deal less than the distance between animals and any of the bacteria, so
animals are much more closely related to plants than they are to bacteria
...
Groups with
a common point that’s far away separated further back in time than
groups with a common point that’s near
...
The
three domains of life are
✓ Bacteria: Consisting mostly of single-celled organisms, bacteria are
prokaryotic, meaning they lack a nuclear membrane around their DNA
(refer to Chapter 4 for the details on prokaryotic cells)
...

✓ Archaea: These are single-celled, prokaryotic organisms
...

✓ Eukarya: Organisms in the Eukarya domain may be single-celled or
multicellular; either way, their cells are eukaryotic, meaning they have a
nuclear membrane around their DNA (see Chapter 4 for more on eukaryotic cells)
...


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Organizing life into smaller
and smaller groups
Being able to categorize the three largest, and most distantly related, groups
of living things on Earth into domains (as explained in the preceding section)
is great, but biologists need smaller groups to work with in order to determine how similar different types of organisms are
...
Within this hierarchy, living things are organized into
the largest, most-inclusive group down to the smallest, least-inclusive group
...
(Note that
organisms are placed into each category based on similarities within that
particular group of organisms
...
)
✓ Domain: Domains group organisms by fundamental characteristics
such as cell structure and chemistry
...

✓ Kingdom: Kingdoms group organisms based on developmental characteristics and nutritional strategy
...
(Kingdoms are most useful in
domain Eukarya because they’re not well defined for the prokaryotic
domains
...
For example, within kingdom Plantae, flowering plants (Angiophyta) are in a different phylum
than cone-bearing plants (Coniferophyta)
...
For example, within
phylum Angiophyta, plants that have two seed leaves (dicots, class
Magnoliopsida) are in a separate class than plants with one seed leaf
(monocots, class Liliopsida)
...
For example, within class

Chapter 10: Biodiversity and Classification
Magnoliopsida, nutmeg plants (Magnoliales) are put in a different order
than black pepper plants (Piperales) due to differences in their flower
and pollen structure
...
For example, within order
Magnoliales, buttercups (Ranunculaceae) are in a different family than
roses (Rosaceae) due to differences in their flower structure
...
For example, within family
Rosaceae, roses (Rosa) are in a different genus than cherries (Prunus)
thanks to differences in their flower structure
...
You can walk through a
rose garden and see many different colors of China roses (Rosa chinensis) that are all considered one species because they can reproduce with
each other
...
In your first round of organizing, you might make groups of
pants, shirts, socks, and shoes
...
Then perhaps you’d organize them by type of fabric, then
color, and so on
...
All of your clothing would be organized in a hierarchy, from the big category of clothing all the way down to the small category
of short-sleeved, button-down, blue shirts
...
Our favorite, because it’s so hard to forget, is Dumb Kids Playing Chase
On Freeways Get Squished
...
If you don’t like
this particular saying, just search the Internet for “taxonomic hierarchy mnemonic,” and you’ll find many more
...
For instance, you and
a carrot are both in domain Eukarya, so you definitely have some things in
common, but you have more characteristics in common with organisms that
are part of the animal kingdom
...
coli
...
coli

Domain

Eukarya

Eukarya

Eukarya

Bacteria

Kingdom

Animalia

Animalia

Plantae

Eubacteria

Phylum

Chordata

Chordata

Angiophyta

Proteobacteria

Class

Mammalia

Mammalia

Magnoliopsida

Gammaproteobacteria

Order

Primates

Carnivora

Apiales

Enterobacteriales

Family

Hominidae

Canidae

Apiaceae
(Umbelliferae)

Enterobacteriaceae

Genus

Homo

Canus

Daucus

Escherichia

Species

H
...
familiaris

D
...
coli

Of the organisms listed in Table 10-1, you have the most in common with
a dog
...
However, you also have
many differences, including the tooth structure that separates you into the
order Primates and a dog into the order Carnivora
...

Two organisms that belong to the same species are the most similar of all
...

Bacteria and archaea don’t reproduce sexually, so their species are defined by
chemical and genetic similarities
...

They’ve been doing this for hundreds of years according to a system developed by Swedish naturalist Carl Linnaeus in the 1750s
...
Linnaeus also
proposed the system of binomial nomenclature that modern biologists use to
give every type of living thing a unique name that has two parts
...
The rules for
using binomial nomenclature are as follows:
✓ The genus is always capitalized
...

✓ Both the genus and species should be italicized or underlined to indicate that the name is the official scientific name
...
sapiens
...
This chapter explores Earth’s various ecosystems and
details how the interactions between organisms work to keep life on Earth in
balance
...


Ecosystems Bring It All Together
Life thrives in every environment on Earth, and each of those environments
is its own ecosystem, a group of living and nonliving things that interact with
each other in a particular environment
...
The living parts, called biotic
factors, are all the organisms that live in the area
...

Ecosystems exist in the world’s oceans, rivers, forests — they even exist in
your backyard and local park
...
The catch is that the larger an ecosystem is, the
greater the number of smaller ecosystems existing within it
...


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Part III: It’s a Small, Interconnected World
A particular branch of science called ecology is devoted to the study of ecosystems, specifically how organisms interact with each other and their environment
...

The sections that follow explain how ecologists classify Earth’s various ecosystems and how they describe the interactions between the planet’s many
species
...


Ecosystem level
Community level
Forest
All organisms in forest

Population level
Group of salamanders

Organism level
Salamander

Brain
Organ system level
Nervous system

Organ level
Brain

Molecular level
Molecule of DNA

Figure 11-1:
The organization of
living things
...
For example,
a forest community may contain trees, shrubs, wildflowers, squirrels, birds,
bats, insects, mushrooms, bacteria, and much more
...
Six major types of biomes
exist:

Chapter 11: Observing How Organisms Get Along
✓ Freshwater biomes include ponds, rivers, streams, lakes, and wetlands
...
Wetlands, in particular, have the greatest
amount of diversity of any of the biomes
...
They cover 75 percent of the Earth’s surface and are very
important to the planet’s oxygen and food supply — more than half the
photosynthesis that occurs on Earth occurs in the ocean (we describe
the process of photosynthesis in Chapter 5)
...

Estuaries are areas where saltwater mingles with freshwater
...
Estuaries are an important habitat for many different species, including birds, fish, and shellfish
...

Unfortunately, estuaries are typically found on the coast, which is also
prime real estate for people
...

✓ Desert biomes receive minimal amounts of rainfall and cover approximately 20 percent of the Earth’s surface
...
Some familiar desert inhabitants are cacti, reptiles, birds,
camels, rabbits, and dingoes
...
They’re important for global carbon balance because they pull carbon dioxide out of the atmosphere through
the process of photosynthesis
...

Rain forests are evergreen forests that receive lots of rainfall and are
incredibly rich in species diversity
...

✓ Grassland biomes are dominated by grasses, but they’re also home to
many other species, such as birds, zebras, giraffes, lions, buffaloes, termites, and hyenas
...
Because
of these features, people converted many natural grasslands for agricultural purposes
...
Tundras
cover about 15 percent of the planet’s surface and are found at the poles
of the Earth as well as at high elevations
...
In both types of
tundra, nutrients are typically scarce, and the growing seasons are quite
short
...
In fact, they’re
often members of different species (meaning they can’t sexually reproduce
together)
...
Of course,
just like relationships between people, relationships between other species
can be good, bad, or just so-so
...
Case
in point: You give the bacteria in your small intestines a nice place to
live complete with lots of food, and they make vitamins for you
...
The
fungi, called mycorrhizae, grow on the plant roots and help the roots
absorb water and minerals from a wider area within the soil
...

✓ Competition: Both organisms suffer in a competitive relationship
...
Just think of a vegetable garden that’s overrun with weeds
...
As a result, all the plants grow smaller and
weaker in the crowded space than they would if they were growing by
themselves
...
When a lion eats a
gazelle, the benefits are purely the lion’s
...
The only real difference between these two
situations is the speed of the interaction
...


Chapter 11: Observing How Organisms Get Along

Studying Populations Is
Popular in Ecology
Each group of organisms of the same species living in the same area forms
a population
...
Because Doug firs and Western
red cedars are two different kinds of trees, ecologists consider two groups of
these trees in the same forest to be two different populations
...
(Population biology is a very similar field that
also includes the study of the genetics of populations
...
They also help you understand the ways in which populations
grow and change, as well as how scientists measure and study their growth,
and give you some insight into the massive growth of the human population
...
The unique thing
about population ecologists, though, is that they study these relationships by
examining the properties of populations rather than individuals
...


Population density
One way of looking at the structure of a population is in terms of its population
density (how many organisms occupy a specific area)
...
About 19
...
If you divide the number of people by the area,
you get a population density of about 413 people per square mile
...
In order to really
understand how the human population is distributed in the state of New
York, you need to compare the population density of the state to the population density of New York City
...

If all the people in New York City were evenly distributed, each person would
have 11⁄2 acres of space all to herself (there are 640 acres in 1 square mile)
...

All of these numbers just go to show that the human population in New York
is heavily concentrated in New York City and much less concentrated in
other areas of the state
...
Populations disperse in three main
ways:
✓ Clumped dispersion: In this type of dispersion, most organisms are
clustered together with few organisms in between
...

✓ Uniform dispersion: Uniformly dispersed organisms are spread evenly
throughout an area
...

✓ Random dispersion: In this type of dispersion, one place in the area is
as good as any other for finding the organism
...
) Examples of random dispersion include barnacles scattered on the surfaces of rocks and plants with wind-blown seeds settling
down on bare ground
...
Population ecologists typically use age-structure diagrams to
study these changes and note trends
...
The shape
of an age-structure diagram can tell you how fast a population is growing
...
Take a look at Figure 11-2a
...
The newest generations are larger than the generations before them, so the population size
is increasing
...
According to Figure 11-2b, the number of people above
and below reproductive age in Iceland is about equal, with a decrease
in the population as the older group ages
...

✓ An age-structure diagram that has a smaller base than middle portion
indicates the population is decreasing in size
...
The newest generations are smaller than the older generations, so the population is decreasing
...

The scientists followed groups of organisms that were all born at the same
time and looked at their survivorship, which is the number of organisms in
the group that are still alive at different times after birth
...

Three types of survivorship exist:
✓ Type I survivorship: Most offspring survive, and organisms live out
most of their life span, dying in old age
...

✓ Type II survivorship: Death occurs randomly throughout the life span,
usually due to predation or disease
...

✓ Type III survivorship: Most organisms die young, and few members of
the population survive to reproductive age
...
In other words, Type III organisms die young
...
Other animals eat many of the larvae before
they reach the adult stage (which is when they can reproduce)
...


6
c

5

4

3

2

1

0

0

1

Population (in millions)

2

3

4

5

6

Chapter 11: Observing How Organisms Get Along
1000
Type I
Example: Humans

Number of survivors (log scale)

100

Figure 11-3:
A survivorship curve
...
Why? Because those offspring have offspring, and
the population gets even bigger
...
Say each of the 3 original offspring has 3 offspring, adding 9 and
bringing the total population to 13 organisms
...
Although the rate of reproduction per individual, called the per capita
reproduction rate, remains the same, the population grows larger and larger
...


Understanding biotic potential
The maximum growth rate of a population under ideal conditions is referred
to as biotic potential
...
Other factors involved in determining
biotic potential include

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✓ The age of the organisms when they’re able to reproduce
✓ The number of offspring typically produced from one successful mating
✓ How often the organisms reproduce
✓ How long a period of time they’re capable of reproducing
✓ The number of offspring that survive to adulthood
Bacteria, for example, have a very high biotic potential
...
If one cell of E
...
For example, large populations may not have enough
food, water, or nest sites, causing fewer organisms to survive and reproduce
...

✓ Density-independent factors limit growth but aren’t affected by population density
...

Some populations can remain very steady in the face of these factors,
whereas others fluctuate quite a bit
...
If a population depends heavily on one type of food, for example, and that food becomes unavailable,
the death rate will increase rapidly
...
Organisms with high reproductive
rates may have sudden booms in population as conditions change
...

✓ Populations may rise and fall because of interactions between predators and prey
...
When that happens, the prey population crashes, followed by the predator population
as the predators starve
...


Chapter 11: Observing How Organisms Get Along
Reaching carrying capacity
When a population hits carrying capacity, it has reached the maximum amount
of organisms of a single population that can survive in one habitat (the scientific name for a home)
...
If carrying capacity is exceeded even temporarily, the habitat
may be damaged, further reducing the amount of resources available and
leading to increased deaths
...
However, if the habitat is damaged, the carrying capacity may be lowered even further, necessitating even
more deaths to restore balance
...
J-shaped
growth curves, like the one in Figure 11-4a, depict exponential growth
...
In nature, populations may show exponential
growth for short periods of time, but then environmental factors act to limit
their growth rate
...
In logistic
growth, the growth rate is high when population density is low and then
slows as population density increases
...
The natural growth
rate of a population (r) is equal to the per capita
birth rate (b) minus the per capita death rate (d)
...

If migration is occurring, meaning organisms
are moving from one place to another, immigration is added to the birth rate, and emigration is
added to the death rate
...
Different species have characteristic

values for rmax
...
coli
...
In other words:
ΔN÷Δt = Nrmax
...


0

Time

a Exponential (unrestricted) growth

Population size

Carrying capacity
of environment
Population size

170

The growth rate
slows down
The
growth rate
accelerates

0

Point of
maximum
growth (rmax)
Time

b Logistic (restricted) growth

Taking a closer look at the
human population
There’s no doubt about it: Humans are the dominant population on Earth,
and our numbers keep on rising
...
The following sections provide some
insight into this and introduce you to the special tool population ecologists
have derived to study human population growth
...
Food wasn’t as readily available as it is now
...
People
didn’t shower or wash their hands as often, so they spread diseases more
easily
...

Yet in the last 100 to 200 years, the food supply has increased and hygiene
and medicines have reduced deaths due to common illnesses and diseases
...
As you can see in Figure 11-5, the human population has
grown exponentially in relatively recent history
...


7

Old Stone
Age

New Stone
Age

Bronze
Age

Iron
Ages

Middle
Ages

6
Metal Working

5
Hunter-gatherers
4
3
2

Irrigation
Ploughing

Cave Art
Agricultural
Revolution

Industrial
Era

Christian
Era

1
0
500,000 10,000

8,000

6,000

4,000

YEARS BEFORE PRESENT

2,000

0

BC AD

If Figure 11-5 doesn’t impress you, here are a few statistics that might:
✓ The human population doubled in the 40 years between 1950 and 1990
...

✓ The global human population passed the 6 billion mark at the end of the
20th century
...
Imagine that for a minute
...
you get the idea
...
The exact carrying capacity of the Earth for humans isn’t
known because, unlike other species, humans can use technology to increase
the Earth’s carrying capacity for the species
...
Humans also use
about half of the world’s freshwater
...
(This pressure on other species from human
impacts is already being seen, endangering species such as gorillas, cheetahs, lions, tigers, sharks, and killer whales
...
Technology, education, and other
factors affect how different human populations grow
...
On the other hand, poorer, less industrialized
nations (such as many countries in Africa) have very high birth rates relative
to their death rates and have rapidly growing populations
...
In less industrialized nations, families that have more children gain an economic benefit
because the children are needed for labor-intensive tasks
...

Population ecologists have developed a special demographic transition model
to note the stages of development the human population goes through in any
given country on its way to stabilization
...
Basic sanitation and
modern medicine aren’t yet available to lower the death rate and extend
the life span
...

✓ Stage 2: Sanitation and medicine lower the death rate, but the economy
still encourages a high birth rate
...

✓ Stage 3: Increased urbanization reduces the need for large families, and
the cost of raising and educating children encourages fewer births
...
The population still grows, however, as earlier generations reach reproductive
age
...

✓ Stage 4: The population becomes stable, and birth rates equal death
rates
...


Chapter 11: Observing How Organisms Get Along
The Demographic Transition Model
Birth rate
Total
population

Death
rate

Time
Figure 11-6:
The demographic
transition
model
...
The interactions between organisms
influence behavior and help the organisms establish complex relationships
...
In fact, all the various organisms in an ecosystem can be
divided into four categories called trophic levels based on how they get their
food:
✓ Producers make their own food
...
Producers can also
be called autotrophs (see Chapter 5 for more on autotrophs and the process of photosynthesis)
...
Because producers are mainly
plants, primary consumers are also called herbivores (plant-eating
animals)
...
Because primary consumers are animals, secondary consumers are also called carnivores
(meat-eating animals)
...

Organisms in the different trophic levels are linked together in a food chain,
a sequence of organisms in a community in which each organism feeds on
the one below it in the chain
...


Sun
Atmosphere

Energy
Heat
Plants
Primary
Energy consumer

Heat

Secondary
consumer

Figure 11-7:
Energy flow
in ecosystems shown
through a
food chain
...
You, for example,
may eat a slice of pizza with pepperoni
...
The pepperoni, however, came from an animal, so when you
eat the pepperoni, you’re acting as a secondary consumer
...
When you eat pepperoni pizza, you’re eating food from both plants and animals
...

Also, organisms that eat more than one type of food belong to more than
one food chain
...

✓ Some organisms get their food by breaking down dead things
...

Detritivores, such as worms, small insects, crabs, and vultures, also eat
the dead
...


Going with the (energy) flow
The energy living things need to grow flows from one organism to another
through food
...
”
In the sections that follow, we reveal the principles that govern energy as
well as the way in which scientists measure the flow of energy from organisms at different levels of the food chain
...
This statement represents a
fundamental law of the universe called the First Law of Thermodynamics
...
No living thing can make the energy it needs
all by itself
...


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✓ When energy is moved from one place to another, it’s transferred
...

When describing energy transfers, be sure to say where the energy is
coming from and where it’s going to
...

When plants do photosynthesis, they absorb light energy from the Sun
and convert it into the chemical energy stored in carbohydrates
...

When describing energy transformations, be sure to state the form of
energy both before and after the transformation
...
This statement is one way of representing another law of the universe, called the Second Law of
Thermodynamics
...
After energy is transferred to heat, it’s
no longer useful as a source of energy to living things
...

The Second Law of Thermodynamics has many impacts on energy and
can be stated in several different ways
...
” What this means
is that any process that makes things more random — like breaking
down molecules or spreading molecules randomly over an area — can
occur without the input of energy
...
Food
molecules represent a very concentrated form of energy — that’s why
living things like them so much
...
So, according to the Second Law
of Thermodynamics, if energy from food molecules is involved in an
energy transfer, some of that energy is going to become more randomly
dispersed, meaning it transforms into heat energy
...
” These statements can be confusing because they make it
sound like energy disappears somehow
...
The correct interpretation of statements like these is that useful energy is lost from
the system as it’s transformed into heat
...


Chapter 11: Observing How Organisms Get Along
Never use the words lost, disappear, destroyed, or created when you’re talking
about energy
...


The energy pyramid
Scientists use an energy pyramid (also called a trophic pyramid; see Figure
11-8) to illustrate the flow of energy from one trophic level to the next
...
To estimate ecological efficiency, ecologists use a rule of thumb called
the 10-percent rule, which says that only about 10 percent of the energy available to one trophic level gets transferred to the next trophic level
...
5

195
1,950
10,950

Tertiary
Consumers

10%

Secondary Consumers
Primary Consumers
Producers

heat
10%

heat
10%
1%

Figure 11-8:
The energy
pyramid
...
About 1 percent of the energy available to producers is captured
and stored in food
...
As producers transfer energy for growth, some energy
is also transformed into heat that’s transferred to the environment
...
Just like

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producers, the primary consumers grow, transferring energy from food into
ATP for cellular work and into the molecules that make up their bodies
...
This process repeats
itself when secondary consumers eat primary consumers and when tertiary
consumers eat secondary consumers
...

But the energy pyramid doesn’t end there
...
Decomposers and detritivores use
this dead matter as their source of food, transferring energy from food into
ATP and molecules and giving off some energy as heat
...
Past the tertiary consumer level, too much energy
has been depleted from the system
...
For example, you eat food that contains proteins, carbohydrates, and fats, and your body is made of proteins, carbohydrates, and fats (see Chapter 3 for more on these molecules)
...
Your cells then have two
options:
✓ They can use the food for energy by breaking it down into carbon dioxide and water through cellular respiration (see Chapter 5)
...

Yes, that second option means you are what you eat — well, almost
...
In other words, your cells are
made of human molecules that are rebuilt from the parts of molecules taken
from the plants and animals you’ve eaten
...
(Likewise, the living things your food used
to be got their molecules by recycling them from somewhere else
...
The crust came from
the grains of plants, and the pepperoni (for the sake of argument) came from a
pig
...
Pigs get their molecules by eating whatever food the
farmer gives them, which is likely some type of plant
...

One of the most fascinating facts about the Earth is that almost all the matter
on this planet today has been here since the Earth first formed
...

Consequently, ecologists say that matter cycles through ecosystems
...

Four biogeochemical cycles that are particularly important to living things
are the hydrologic cycle, the carbon cycle, the phosphorous cycle, and the
nitrogen cycle
...
Water returns to
the environment when plants transpire (as explained in Chapter 21) and animals perspire
...
As moist air rises and cools, water condenses again and returns to
the Earth’s surface as precipitation (think rain, snow, sleet, and hail)
...


The carbon cycle
The carbon cycle (depicted in Figure 11-9) may be the most important biogeochemical cycle to living things because the proteins, carbohydrates, and
fats that make up their bodies all have a carbon backbone (see Chapter 3 for
more on these molecules)
...
Animals consume plants or other animals, incorporating the carbon that was in their food molecules into the molecules that make
up their own bodies
...


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CO2 cycle

Auto and factory
emissions release CO2
Plant respiration
releases CO2
Photosynthesis absorbs CO2

Organic
compound

Organic
carbon

Grass
Decaying organisms
photosynthesis Animal respiration
release CO2
absorbs CO2
releases CO2
Organic
carbon
(grass)

Figure 11-9:
The carbon
cycle
...
Cellular respiration releases the carbon atoms back into the
environment as carbon dioxide, where it’s again available to producers for
photosynthesis
...
Carbon can actually be stored in the environment
for longer periods of time
...

✓ Fossil fuels contain carbon that was stored in the bodies of living things
long ago and then trapped in a way that the proteins, carbohydrates, and
fats were converted to coal, oil, and natural gas deposits
...

✓ Carbon is also stored in the world’s oceans, in the form of dissolved
carbon dioxide
...


Chapter 11: Observing How Organisms Get Along
The phosphorus cycle
Phosphorous is an important component of the molecules that make up
living things
...
The phosphorous cycle involves plants obtaining phosphorous when they absorb inorganic phosphate and water from the soil
and animals obtaining phosphorous when they eat plants or other animals
...
When phosphorus gets returned to the soil, it’s either absorbed
again by plants or it becomes part of the sediment layers that eventually
form rocks
...


The nitrogen cycle
Not only is nitrogen part of the amino acids that make up proteins but it’s
also found in DNA and RNA (see Chapter 3 for more on these molecules)
...

Because nitrogen exists in so many forms, the nitrogen cycle (shown in
Figure 11-10) is pretty complex
...
Nitrogen gas in the atmosphere
can’t be incorporated into the molecules of living things, so all the
organisms on Earth depend upon the activity of bacteria that live in the
soil and in the roots of plants
...
Plants obtain nitrogen by absorbing
ammonia and nitrate along with water from the soil; animals get their
nitrogen by eating plants or other animals
...
However, the nitrogen fixation that occurs from lightning strikes isn’t enough to supply
ecosystems with all the nitrogen they need, and industrial nitrogen fixation requires a lot of energy
...
As decomposers break
down the proteins in dead things, they may not need all the nitrogen
from those proteins for themselves
...
In the
soil, ammonia converts into ammonium ion (NH4+)
...


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✓ Nitrification converts ammonia to nitrite and nitrate
...
Other
bacteria get their energy by converting the NO2– into nitrate (NO3–)
...
Some
bacteria in the soil use nitrate (NO3–) rather than oxygen for cellular
respiration (see Chapter 5 for more on cellular respiration)
...


NO3–
N2
Rain
Lightning

–NO2

Atmospheric N2O

NH3

Volcanoes
Industrial
fixation

Fossil
fuels

Ion uptake

Dead plants, animals, manure

Ammonification
NH4+
Nitrification
Cyclic salts
NH4+ = Ammonium ion
NO2 = Nitrite

Figure 11-10:
The nitrogen
cycle
...
These objects are evidence of
how humans have changed and expanded their knowledge over the millenia
...
But what was the starting point of evolution, and from what did the
earliest humans evolve?
This chapter tells you about the beliefs people had regarding evolution; how
Charles Darwin came up with his theory of biological evolution; and what
the current thoughts are on the origin of species, how humans have evolved,
and how life on Earth began
...


What People Used to Believe
From the time when ancient Greece was the world’s cultural hotspot until
the early 1800s, philosophers, scientists, and the general public believed that
plants and animals were specially created at one time and that new species

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Part III: It’s a Small, Interconnected World
hadn’t been introduced since then
...
) In this view, every living thing was created in its ideal form by
the hand of God for a special purpose
...

People also thought the Earth and the universe it occupied were unchanging, or static, throughout time
...
These ideas held through much of human history,
extending virtually unquestioned through the Middle Ages, when people even
accepted that their place in society was unchanging and predestined by their
birth
...

✓ Various explorers fell upon the New World (the Western Hemisphere
of the Earth)
...

The New World and the people that lived there weren’t mentioned in
the Bible, causing Europeans to debate whether the New World was
created at the same time as the Old World and whether the people who
lived there were descendants of Adam
...

✓ William Smith, a British surveyor, classified the types of ground material
in Britain in preparation for the excavation of a canal system across the
island
...

He also found that the deeper he went into the layers, the more different
the fossils appeared from the plants and animals that lived in Britain at
the time
...

✓ Georges Cuvier, a French anatomist, demonstrated that fossil bones
found in Europe, such as those of wooly mammoths, could be recognized as very similar to existing species, such as elephants, but were
clearly not from anything currently living
...
His idea,
called uniformitarianism, was that the processes he observed on the
Earth in the 1700s were the same processes that had occurred on the
Earth since its creation
...
He
was no less religious than others of his day, but he had a very active, curious
mind and was acquainted with much of the scientific thinking of the time
...
These observations led to the
creation of two of the most important biology-related theories of all time: biological evolution and natural selection
...


Owing it all to the birds
While traveling on the HMS Beagle, Darwin visited the Galapagos Islands,
which lie nearly 600 miles off the western coast of South America
...

Characteristics of organisms that make them suited to their environment are
called adaptations
...
Each island had its own unique species of finch that was distinct from the other species and from the finches on the mainland
...
On the islands, some finches ate seeds,
others ate insects, and some even ate cactuses
...

Darwin thought that all the finches had a common ancestor from mainland South America that either flew or floated to the newly formed islands,
perhaps during occasional storms
...
Geographic isolation means they also can’t mate with each other and combine their genes
(sequences in DNA that control the traits of living things; see Chapter 8)
...
Birds whose traits
made them more successful at obtaining food were more likely to survive

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and reproduce, passing their genes and traits on to their offspring
...

Eventually, the island birds became so different from their ancestors, and
from each other, that they were unique species
...
Adaptive radiation happens when members of one species get into environmental niches and
have very little competition for resources at the outset
...
As the population increases, competition for resources begins,
and the original species breaks off into several new species that adapt to different environmental conditions
...
Darwin introduced the
world to this concept in his 1854 work, On the Origin of Species
...
In other words, Darwin believed in descent with
modification
...
Species that accumulate enough changes may become so different from related organisms that
they become a new species because they can no longer successfully mate with
related populations; this process is referred to as speciation
...
org
...


The idea of natural selection
Darwin concluded that biological evolution occurred as a result of natural
selection, which is the theory that in any given generation, some individuals
are more likely to survive and reproduce than others
...
Natural selection therefore acts against
unfavorable traits
...
”
In biological terms, fitness doesn’t have anything to do with your BMI or how
often you work out
...
So, survival of the fittest really refers to the passing on of those traits
that enable individuals to survive and successfully reproduce
...


Comparing natural selection with artificial selection
Darwin compared his theory of natural selection with the artificial selection
that results from selective breeding in agriculture
...
Farmers in Darwin’s day
bred the cows that gave the most milk, the chickens that laid the most
eggs, and the pigs that got the biggest, creating many different breeds of
each species
...

✓ Natural selection occurs when environmental factors “choose” which
plants or animals will survive and reproduce
...
If the eagle’s prey is mice, which can be
white or dark colored (see Figure 12-1a), and the mice live in the forest
against dark-colored soil, then the eagle is going to be able to see the
white mice more easily
...
Dark mice have genes that specify dark-colored
fur, so their offspring will also have dark fur
...

In this example, the eagle is the selection pressure — an environmental
factor that causes some organisms to survive (the dark-colored mice)
and others not to survive (the white-colored mice)
...


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a

b

c

Figure 12-1:
Natural
selection in
action
...
Human beings are somewhat unique among living things in that
we can make conscious choices about how many offspring we have
...

✓ Those individuals must have different characteristics
...
Now scientists
know that differences in organisms arise due to mutations in DNA combined with the mixing of genetic information during sexual reproduction
(for more information on genetic variation due to sexual reproduction,
see Chapter 6)
...
During
Darwin’s time, the laws of inheritance were just beginning to be figured
out, so Darwin didn’t know exactly how parents passed on their traits
...

✓ Organisms with the best-suited characteristics for their environment
are more likely to survive and reproduce
...
If there’s competition for survival and not all the organisms
are the same, then the ones with the advantageous traits are more likely

Chapter 12: Evolving Species in an Ever-Changing World
to survive
...

If these four conditions are met, then the new generation of individuals will
be different from the original generation in the frequency and distribution of
traits, which is pretty much the definition of biological evolution
...
How the population changes depends upon the particular selection
pressure the population is under and which traits are favored in that circumstance
...

The four types of natural selection are as follows:
✓ Stabilizing selection: This type eliminates extreme or unusual traits
...
Over
time, nature selects against extreme variations of the trait
...
Extremely small or extremely large babies are less likely to
survive, so alleles that cause these extremes don’t last in the population
...
Over generations, the selected traits become
common, and the other traits become more and more extreme until
they’re eventually phased out
...
Ancestral horse species were
built for moving through wooded areas and were much smaller than
modern day horses
...

✓ Disruptive selection: In this type, the environment favors extreme or
unusual traits and selects against the common traits
...
In the wild,
natural state, tall weeds compete for the resource of light better than
short weeds
...

✓ Sexual selection: Females increase the fitness of their offspring by choosing males with superior fitness; females are therefore concerned with
quality
...
Because males are concerned
with quantity, competition between males for opportunities to mate

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exists in contests of strength
...
Because females choose their
mates, males have also developed traits to attract females, such as certain
mating behaviors and bright coloring
...
Individuals live
or die and reproduce or don’t reproduce depending on their circumstances
...

Imagine a giraffe whose neck isn’t quite long enough to reach the tastiest
leaves at the top of the tree
...
However, if another giraffe in the herd has
a longer neck, gets more leaves, grows better, and makes more calves that
inherit his long neck, then future generations of giraffes in that area may have
longer necks
...

Because a great amount of data supports the idea of biological evolution
through natural selection, and because no scientific evidence has yet been
found to prove this idea false, this idea is considered a scientific theory
...
)
The following sections describe some of the evidence, both old and new,
that supports Darwin’s theory and the tools modern scientists have used to
obtain it
...

Case in point: All living things store their genetic material in DNA and build
proteins out of the same 20 amino acids
...
That stored
energy is then used to power cellular processes such as the production of
proteins, which is directed by the genes on strands of DNA
...
Just like you have structural characteristics that are similar to those of your family members (think small ears,
a large nose, and so on), structural similarities also exist between more distantly related groups
...
From the outside, the arm
of a human, the front leg of a cat, the flipper of a whale, and the wing of a
bat seem very different, but when you look at the bones within them, you
see that they all contain the same ones — an upper “arm,” an elbow, a lower
“arm,” and five “fingers
...
Scientists call similar structures such as these homologous structures (homo- means “same”)
...

The homologous structures of mammals are particularly interesting in the
case of whales because they reveal whales’ close relationship to land-dwelling
animals
...


Geographic distribution of species
How populations of species are distributed around the globe helps solidify
Darwin’s theory of biological evolution
...
Basically, if biological evolution is
real, then you’d expect groups of organisms that are related to each other to
be clustered near each other because related organisms come from the same
common ancestor
...
) On the other hand, if biological evolution
isn’t real, then there’s no reason for related groups of organisms to be found

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near each other
...
When biogeographers
compare the distribution of organisms living today, they find that species are
distributed around the Earth in a pattern that reflects their genetic relationships to one another
...
This hypothesis was later supported when modern scientists performed a genetic analysis of the Galapagos Islands’ finches and were
able to demonstrate their relationship to each other and to their mainland
ancestors
...


Human

Cat
Whale

Bat

Since Darwin’s time, many other examples have been found that illustrate
how geographic distribution has influenced the biological evolution of organisms
...
Hawaii has types of living
things that exist only on those islands but are related to living things found

Chapter 12: Evolving Species in an Ever-Changing World
on the North and South American continents
...

Similarly, North and South America were separate continents before the
Isthmus of Panama formed
...

Armadillos, porcupines, and opossums called South America home, whereas
mountain lions, raccoons, and sloths lived in North America
...


Molecular biology
Molecular biology is the branch of biology that focuses on the structure and
function of the molecules that make up cells
...

With the development of DNA technology that allows for reading of the
actual gene sequence in DNA (see Chapter 8 for more on DNA), modern
scientists have also been able to compare gene sequences among species
...

One of these highly conserved sequences produces a protein called cytochrome c, which is part of the electron transport chain that occurs in
mitochondria
...
The cytochrome c protein in rhesus monkeys differs from
humans and chimpanzees by just 1 amino acid (out of a total of 104), indicating that rhesus monkeys are slightly more distantly related to humans
...

During Darwin’s day, the science of paleontology, which studies prehistoric

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life through fossil evidence, was just being born
...

Hundreds of thousands of fossils have been found, showing the changing
forms of organisms
...

Based on the fossil record, paleontologists have established a solid timeline of
the appearance of different types of living things, beginning with the appearance of prokaryotic cells (see Chapter 4) and continuing through modern
humans
...
In fact, you need only look in the newspaper or
hop online to see evidence of biological evolution in action in the form of
antibiotic-resistant bacteria
...
aureus) could be
killed by penicillin
...
aureus bacteria
...
aureus
bacteria were those that could best withstand the penicillin
...
Today, most populations of S
...

Another strain of S
...
For most
strains of MRSA, vancomycin is the last effective treatment, but for some
new, highly dangerous strains, vancomycin is beginning to fail
...
aureus — were
reported
...

Using antibiotics is a double-edged sword
...

The potentially good news is that because doctors and scientists understand
biological evolution, they’re able to recognize what’s happening and can take
action to counteract these trends (such as prescribing fewer antibiotics)
...
5 billion years old — that’s
plenty old enough to allow for the many changes in Earth’s species due to
biological evolution
...
Some isotopes, called
radioactive isotopes, discard particles over time and change into other elements
...
Using the known
rates of radioactive decay and the types of elements that were originally
present in the rocks, scientists can calculate how long the elements in a particular rock have been discarding particles — in other words, they can figure
out the age of the rock (including rocks with fossils)
...
They prefer to take the Bible’s creation story literally
...
Most creationists
believe the creation story that’s told in the Bible’s book of Genesis
...
According to the ancient Greek
philosopher Aristotle, no accidents occur in nature; therefore, everything in
nature is created for a purpose
...

At the root of the controversy about biological evolution, then, seems to be
this question: If living things developed in all their wonderful complexity due
to natural processes and without the direct involvement of God, what does
that do to man’s place in the world? Is mankind not “special” to God?
If you have strong religious beliefs and you think that accepting biological evolution as a fact would somehow make you less special to God, then it’s easy to
see how belief in biological evolution creates conflict
...
In fact, many scientists have strong religious beliefs,

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and many religious leaders have come forward to say that they believe in biological evolution
...
But scientists stress the difference between beliefs, or faith, and science
...
Scientific ideas, or hypotheses, must be
testable — able to be proven false — by observation and experimentation (see Chapter 2 for more on the nature of science)
...
God is widely
believed to be a supernatural being, outside the workings of the natural
world
...

✓ Because intelligent design and creationism invoke the existence of a
supernatural designer or creator, they’re neither scientific ideas nor
scientific theories and can’t be tested or observed by scientific means
...

Creationism and intelligent design don’t follow the fundamental rules of science and can’t be considered scientific ideas
...


Table 12-1

Faith-Based versus Scientific Views on Evolution

What Creationists &
Believers in Intelligent
Design Say
Nature is beautiful and complex
...
These wonderful
designs couldn’t have arisen
by random chance; an intelligent designer must exist
...
Change is
random, but biological evolution is based on
change and natural selection
...
If particular organisms and
structures seem perfectly suited to their environment, that’s because natural selection has made
them that way
...


Complex processes and structures aren’t suddenly
created out of nothing
...
By accumulating
several changes that remake existing structures,
new processes and structures are created
...
Also, the missing link
between humans and apes
has never been found
...
Two
particularly important fossils that show transitions
between species are those of Archaeopteryx, a
feathered reptile that appears to mark the transition between dinosaurs and birds, and Tiktaalik, an
animal that appears intermediate between fish and
four-legged animals
...


Biological evolution is controversial even among scientists,
and some scientists have
proven it wrong
...
Scientists often argue and conduct experiments about the details of how biological evolution
occurs — after all, this behavior is at the heart of
scientific inquiry — but scientists don’t question
whether biological evolution is a fact
...


How Humans Evolved
You’re a member of the Homo sapiens species
...


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The closest living relatives to humans are other primates, such as apes and
chimpanzees
...
They have large brains, grasping hands, and three-dimensional
vision
...
)
In the sections that follow, we tell you all about the tools scientists use to fill
in the blanks about how humans evolved as well as the discoveries and connections they’ve made over the years
...
Scientists use fossils to piece
together clues about where humans came from and what our relationship is
to other primates
...

Scientific theories that are supported by lots of evidence from many lines of
research, like the theory of biological evolution, don’t usually change substantially in response to new evidence
...

Scientists’ ideas about the biological evolution of humans have developed
over time
...
Calling his
discovery Java Man, Dubois thought he’d found the link between ape
and man
...
Dubois had actually found a member of the
species Homo erectus, one of the earliest walking hominids
...

✓ During the 1930s, a researcher named Raymond Dart examined a small
skull that was found in Taung, a town in South Africa
...
The
remnants were called Taung Child
...
Dart was ridiculed for

Chapter 12: Evolving Species in an Ever-Changing World
suggesting that a human ancestor was “out of Africa,” when the thinking
at that time was that the first human species came from Asia (due to the
hullabaloo surrounding Java Man)
...
He classified his skull as Homo habilis,
meaning handyman, because crude stone tools were found near the
bones
...
Three decades later, their son Richard noticed
the jaw of a saber-toothed tiger sticking out of the archaeological site
...
The skeletons were also classified as those of Homo
habilis and were dated at about 2 million years old
...
6 million years old
...
2-million-year-old
hominid ancestor
...
However, the shape of the jaw
was like that of a chimpanzee
...
Meave named her find
Australopithecus anamensis
...
” In particular, a 3
...

✓ Bones from a 4
...
The skeleton is called Ardipithecus ramidus, and
because it’s the oldest known ancestral fossil, scientists are using it to
try and determine whether this organism was in fact a direct ancestor to
humans
...
Table 12-2 gives you an overview of the physical
changes that occurred as apes evolved into humans
...
Consequently, apes don’t have elbows, which
allow the arm to straighten, but humans do
...
The size and
shape of the skull has changed as the size and shape of the
brain has changed
...
And the bony ridge
above the eyebrows of humans has shrunk significantly in
comparison with human predecessors
...


Hands

The hand of a human and a chimpanzee are amazingly similar
...
Humans and other primates have
prehensile (grasping) thumbs, which allow the gripping of
objects
...


Jaws

The human jaw and teeth have shrunk
...
Instead, humans have developed
chins to help support the thinner jawbone
...


Knees

Knees allow humans to walk upright
...

Waddling slows a human down, and humans occasionally
need to run
...
This anatomic feature disappeared about 25 million
years ago
...


Chapter 12: Evolving Species in an Ever-Changing World

Digging into DNA
The development of DNA technology has played a huge role in helping scientists read some of the human history encoded in DNA (we cover the complexities of DNA in Chapter 8)
...
Humans are most closely related to
chimpanzees; our DNA sequences are about 97 percent identical
...
That species then branched off into two lines about 5 to 6
million years ago
...

✓ How hominids migrated: By comparing the genetic relationships
between hominids, the age of certain fossils, and the geographic locations of these fossils, scientists can figure out where species originated
and where they traveled
...
Typically, two organisms that
can successfully produce offspring are considered to be in the same species, whereas organisms that can’t produce offspring together are considered to be unique species
...
However, scientists can
look at the DNA sequences from fossils to see who was mingling DNA
...


Check out the big brain
on the Homo sapien
It’s one thing to know how Homo sapiens evolved into today’s modern
humans
...
For example, why did the human brain become so much larger than
that of other hominids? The clues about why things happened the way they
did are pretty scarce, but they do exist in the form of tools found with a skeleton, evidence of burial of human remains, and evidence of the use of fire
...
Some of these hypotheses are
as follows:
✓ As human ancestors began to walk upright, they soon began to hunt
...
One factor
that led to this development was climate change
...

In an open savanna, it’s much easier to see prey (especially if you’re
standing)
...

✓ Eating plenty of meat, with all the fats and proteins meat contains, made
hominid brains bigger, and bigger brains were selected for over time
...
)
✓ As the shape and size of brains changed and enlarged, ancestral females
had to give birth earlier so the offspring’s head could fit through the
pelvic bones
...
This change
meant that the mother couldn’t contribute to hunting, but she still
needed adequate nutrition to make milk to breastfeed her baby
...
The fact that the mother had to rely on others for
her survival and that of her baby led to the formation of close ties with
other members of the clan
...


Table 12-3

The Evolution of Hominid Brains

Genus and Species
Name

Brain Development

Australopithecines
anamensis,
Australopithecines
afarensis

Brains were about 400 cubic centimeters (cc) in size,
comparable to that of chimpanzees or gorillas
...


Homo habilis

Brains were about 650 cc
...


Homo erectus

Brains were 850 to 900 cc
...


Homo neanderthalensis

Brains were 1,300 cc
...


Homo sapiens

Brains are between 1,200 and 1,600 cc
...


Part IV

Systems Galore!
Animal Structure
and Function

H

In this part
...
The body plans of animals are very
diverse, but they all have certain things in common,
including the need for oxygen and food
...

In this part, we introduce the fundamentals of the many
organ systems in the human body
...


Chapter 13

Pondering the Principles of
Physiology
In This Chapter
▶ Connecting structure with function
▶ Understanding important physiological concepts such as evolution and homeostasis

P

hysiology is the study of the function of all living things in their normal
state
...
In order to survive, living things must be able
to regulate their functions and respond to changes in the environment
...


Studying Function at All Levels of Life
To truly be able to understand a living being, you need to have a good mental
picture of its structure and the function of its body and cells
...
Anatomy is the study of the structure of living things, and
physiology is the study of how these structures function
...

For example, the function of the heart is to pump blood around the body
...
In order for the heart to function properly,
flaps of tissue within the heart, called valves, must close off chambers within
the heart so that the blood doesn’t flow back into it
...
In these people, the heart pumps the blood inefficiently because

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Part IV: Systems Galore! Animal Structure and Function
some blood flows back into the heart instead of going out into the arteries
...
Heart valve defects are just one example of how differences in the
structure of an organism can affect its function
...
Some scientists even study ecological physiology by looking at how the physiology of
organisms is interrelated with their environment
...
The foundation of physiology rests upon the function of cells, but to understand the
function of cells, or the details of a physiological process, you need to
be able to follow the interactions of molecules within the cell
...
)
✓ Organisms are made of organ systems, which are made of organs,
which are made of tissues
...
And the functions of the organs
depend upon the function of their tissues, which are groups of similar
cells
...
An organism’s interaction with the living
and nonliving things in its environment can influence its physiology
...
Likewise, interactions with pathogens can
cause disease, which has a negative impact on an organism’s physiology
...
)
To understand the function of a structure at any level in the organization
of living things, you often need to know something about one of the lower
levels
...
Sometimes the sum of all the parts
is greater than what you expect
...

The properties of an entire system that are greater than the functions of the
individual parts have a special name — emergent properties
...
Each system has its own parts and processes and makes unique
contributions to the whole
...
With these big ideas
in mind, you can more easily see the similarities in the different systems and
understand some of the fundamental processes that regulate their functions
...
Scientists can look at the structures and functions of different kinds
of organisms and compare them to reveal how biological evolution creates
variations on a theme to improve the functioning of a part of an animal (be it
tissue, organ, or an entire organ system) so that the animal can better cope
in its environment
...
Within the kidney, a special tube called the loop of Henle helps set up
conditions that allow mammals to reabsorb water from the fluid that enters
the kidney, concentrating the urine and conserving water for the organism
...
Many desert mammals have an extralong loop of Henle in their
kidneys that allows them to reabsorb most of their water
...
By comparing these desert mammals to
their non-desert-dwelling relatives, scientists can discover evidence of the
evolution of the loop of Henle’s function
...
It experiences fairly
large changes, such as temperature changes as the Sun rises and sets
...
It’s mainly affected by the
diet of the animal and the amount of water that the animal drinks
...
Animals therefore use control systems to respond
to and counteract changes in their external environment in order to keep their
internal environment within a certain range that allows them to survive
...

Many different homeostatic processes maintain the balance of variables such
as pH level, glucose level, and body temperature in an animal’s body
...
In negative feedback, a change triggers a response that reverses the change
...
The body
responds by releasing insulin into the bloodstream, which signals the body
to transfer glucose from the blood into the cells and lowers the level of glucose in the bloodstream
...
If changes occur in the internal
environment, the changes are measured and compared to the set point
...
For example, blood glucose must stay within
a certain range or else a person will develop the disease diabetes
...


Chapter 13: Pondering the Principles of Physiology
To help you understand how homeostasis works, think of the body like a heating and cooling system
...
If the
temperature of the room is higher than the desired set point, the thermostat
sends signals to turn on the cooling system
...
Just like your body, the heating system has a mechanism for measuring the change in the variable (in this case, temperature) and then
responding to that change (by turning on the heating and cooling systems)
...
Although the
details of each control system are different, they all have the same three
components:
✓ A receptor: The receptor measures changes in the variable, such as
blood pressure, body temperature, or heart rate, and sends information
to the control center
...

✓ An effector: Often a muscle or a gland, an effector carries out the body’s
response
...
The set point for a variable can change depending on the situation the
organism is in
...
It may drop low while you sleep, or it may be high when you exercise
...


Getting the message across
plasma membranes
Cells communicate with other cells, with tissues, and with organs
...
The plasma
membranes of cells separate them from their environment, maintaining a
delicate balance between the outside and the inside of the cell (for more
on plasma membranes, see Chapter 4)
...
The function of the entire organism
depends upon the coordinated functioning of all the cells within the body
...
During signal transduction:
1
...

Signaling molecules that bind to receptors are called ligands
...

2
...

For example, the receptor may change shape
...
The receptor interacts with a messenger molecule inside the cell that
receives the signal and changes in response
...
The intracellular messenger interacts with a target protein that causes
a change in the behavior of the cell
...


Recognizing that what comes
in, must go out
Organisms must take in matter and energy from their environment in order
to survive, but they can’t create (or destroy) either one
...
The reactions that
make this possible are the metabolism of an organism (see Chapter 5 for
more on metabolism)
...
Simply
stated, ins must equal outs
...


Chapter 14

Moving and Shaking: Skeletal and
Muscular Systems
In This Chapter
▶ Seeing how animals move from one place to another
▶ Surveying the various skeletal systems
▶ Understanding what makes muscles so valuable

T

he coordinated efforts of muscles and skeletons are what make animal
movements possible
...
Prepare to find out all about how
animals move from place to place as you discover the different types of skeletons and the fundamentals of muscle function in this chapter
...
Each of these
types of locomotion, movement from one place to another, requires animals
to use energy to overcome the forces of friction and gravity that would otherwise hold them to the Earth
...

✓ Swimming animals, such as fish and whales, have bodies that are shaped
to minimize resistance as they move through the water
...

✓ Birds have hollow bones and wings that are shaped like those of an airplane to create added lift during flight
...


212

Part IV: Systems Galore! Animal Structure and Function
✓ Rabbits, kangaroos, and other animals that jump or hop have extralarge
leg muscles and strong tendons to help put some spring in their hop
...


The Types of Skeletal Systems
Skeletons support animals, give their bodies shape, and protect their internal
organs, but not all animals have the same type of skeleton
...
Animals with this
skeleton type move and change their shape by squeezing their water-filled
chambers — just like what happens when you squeeze a water balloon
...
You’re probably quite familiar with these hard
exterior coverings because they’re found on crabs, lobsters, and many
insects
...
After an animal
molts, its new exoskeleton is soft — as in a soft-shelled crab
...
After all, it’s the kind of skeleton you have
...
The human endoskeleton is hard because
it’s partially constructed of the mineral calcium
...

Animals with hydrostatic skeletons and exoskeletons are considered invertebrates, meaning they don’t have a backbone
...

The following sections not only break down the parts of a vertebrate animal’s
skeleton but they also get you more familiar with the important components
of your skeleton — bones and joints
...
Today, these animals show their relationship to each other in part
due to homologous structures — structures that are equivalent to each other
in their origin (see Chapter 12 for more on homologous structures and their
importance to the study of evolution)
...
The axial skeleton includes the skull, the backbone (also
called the vertebral column), and the rib cage
...

✓ The appendicular skeleton: This part extends from the axial skeleton
out into the arms and legs (which are also known as appendages)
...

In some vertebrates, such as snakes, the appendicular skeleton has
become extremely reduced or nonexistent
...
The
dry white bones of these images are very different from the living bones that
are in your body right now
...

✓ Fibrous connective tissue covers the exterior of bones and helps heal
breaks in an injured bone by forming new bone
...
The cells actually make the matrix, which consists of collagen that
has been hardened by the attachment of calcium and phosphate crystals
...

The tissues found within living bone fall into two categories:
✓ Spongy bone tissues are filled with little holes, similar to those you see
in volcanic rocks
...


213

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✓ Compact bone tissues are hard and dense
...
If the
body suddenly loses a large amount of blood, it converts the yellow
bone marrow to red bone marrow so that blood cell production can be
increased
...


Metatarsal bones
Phalanges (toes)

From LifeART®, Super Anatomy 1, © 2002, Lippincott Williams & Wilkins

Chapter 14: Moving and Shaking: Skeletal and Muscular Systems

Got broken bones?
The number of broken bones in American
children is on the rise, and doctors think this
increase may be due to kids exercising less
and drinking less milk
...
Milk is important because the calcium
and vitamin D found within it are vital for the

development of healthy, strong bones
...
To get your daily dose, drink four 8-ounce
glasses per day, or take a calcium supplement
(with your doctor’s permission, of course)
...
Bones are held together at joints by ligaments, which
are strong, fibrous, connective tissues
...
Your
arms and legs fit into your skeleton with ball and socket joints, which is
why you’re able to rotate your arms and legs in all directions
...
When you rotate your arm so
that your palm faces up, then down, then up again, you’re using a pivot
joint
...
Your elbows and
knees have pivot joints that allow you to extend and contract your arms
and legs
...
Without muscles, you
couldn’t walk, run, or play sports
...


215

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Part IV: Systems Galore! Animal Structure and Function
Following is a rundown of all the things muscles do for you:
✓ Muscles allow you to stand upright
...
Your muscles contract so you can push against the surface of the Earth and stand upright
and assume different positions
...
Every little movement that
your body performs, including blinking and smiling (or frowning), is controlled by your muscles
...
Muscles all along your digestive tract keep
food moving downward and outward
...
If they didn’t contract to squeeze food
throughout your digestive system, you’d never be able to obtain the
nutrients you need to survive
...
Blood vessels contain muscle
tissue that allows them to dilate so blood can flow faster or to contract
so blood flow slows down
...
(Not to mention that your
heart is actually a muscle; without it, your blood wouldn’t be flowing
anywhere, period!)
✓ Muscles help you maintain a normal body temperature
...
This fact explains why you shiver when you’re cold; shivering
is your body’s way of trying to generate heat
...
The ligaments and tendons at the
ends of your muscles wrap around joints, holding together the joints —
and therefore the bones of your skeleton
...
To
find out about the specific types of muscle tissue in your body and how your
muscles contract, check out the next sections
...
Myofibrils are
perfectly aligned, which makes muscles look striped, or striated
...


Chapter 14: Moving and Shaking: Skeletal and Muscular Systems

Figure 14-2:
The human
muscular
system
...
The fibers of cardiac muscle have
one nucleus (so they’re uninucleated), are striated (so they have light
and dark bands), and are cylindrical in shape and branched
...
Between
contractions, cardiac fibers relax completely so the muscle doesn’t get
fatigued
...

✓ Smooth muscle is found in the walls of internal organs that are hollow,
such as the stomach, bladder, intestines, or lungs
...
Smooth muscle contraction occurs involuntarily and more slowly than skeletal muscle contraction, which means smooth muscle can stay contracted longer than
skeletal muscle and not fatigue as easily
...
The fibers of skeletal muscle have many nuclei (so they’re multinucleated) and are both striated and cylindrical; they run the length of
the muscle
...
The movement and contraction of skeletal
muscle can be stimulated consciously, which means you consciously
decide that you’re going to stand up and walk across the room, an
action that requires the use of muscle
...


Muscle contraction
Muscle contractions rely on the movements of the filaments that make up
myofibrils
...

The two filament types found in myofibrils are
✓ Actin (thin) filaments: An actin, or thin, filament is made up of two
strands of actin, which is a protein that’s wound in a double helix (just
like DNA)
...

✓ Myosin (thick) filaments: A myosin, or thick, filament contains groups of
myosin, a type of protein with a bulbous end
...


Chapter 14: Moving and Shaking: Skeletal and Muscular Systems
The actin filaments are attached to something called a Z-line, and the myosin
filaments lie between the actin filaments, unattached to Z-lines
...
You can see all of these
parts and more in Figure 14-3, which shows you how skeletal muscle is connected to the nervous system and how it contracts
...


Muscle fiber nucleus

1 sarcomere

Sarcoplasmic reticulum
T-tubule

Z-line

The other element necessary for muscle contractions is adenosine triphosphate, or ATP for short (we cover this energy-storing molecule in greater
detail in Chapter 5)
...
After muscle cells use up their available
ATP, they get more by
✓ Using energy from stored phosphocreatine molecules: Phosphocreatine,
which is made up of ATP and creatine, forms during periods of no
contraction
...

✓ Increasing the rate of cellular respiration: Muscle cells are loaded
with mitochondria, organelles that perform cellular respiration
...
As
your muscle cells use up their ATP, you breathe harder to supply them
with more oxygen so they can do more cellular respiration
...
Human muscle cells take every two molecules of
ADP produced during contraction and recombine them to make a new
ATP molecule plus a molecule of adenosine monophosphate, or AMP
...
Cells make a lot more
ATP for each glucose molecule they break down by cellular respiration
than they do by lactic acid fermentation
...

According to the sliding-filament theory, muscle contraction occurs via the following process:
1
...

The ADP and Pi stay attached to the myosin
...
Calcium binds to the troponin in the actin filament, which causes the
tropomyosin in the actin filament to move out of the way so the binding sites on the actin filament can open
...
After the actin filament’s binding sites are exposed, myosin binds to
the actin, which causes myosin to release the ADP and Pi
...
When myosin releases the ADP and Pi so it can link to actin, the shape
of the bulbous end of the myosin filament changes and the actin filament slides toward the middle of the sarcomere, pulling the Z-lines at
the end of the sarcomere closer together
...

5
...


Chapter 15

Going with the Flow: Respiratory
and Circulatory Systems
In This Chapter
▶ Discovering the four ways animals exchange gases
▶ Understanding how circulatory systems feed cells and take out their trash
▶ Examining the heart and circulatory systems of not-so-complex animals
▶ Tracing the path of blood through your heart and blood vessels
▶ Surveying the details of your body’s most important fluid — blood

E

very living thing needs to be able to exchange materials (think food,
oxygen, and waste products) with the environment and circulate these
materials around their bodies
...

In this chapter, we present some of the different processes used by animals
to exchange and move important materials
...


Passing Gas: How Animals “Breathe”
All animals, from worms and fish to insects and humans, must exchange
gases between themselves and their environment on a continual basis
throughout every moment of their lives
...
This latter
group relies on breathing to simultaneously move oxygen gas from the air
into the body and remove carbon dioxide from the body and return it to
the air
...


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Part IV: Systems Galore! Animal Structure and Function
Respiration is the entire process of taking air in, exchanging needed gases for
unnecessary gases, using the needed gases, and releasing the waste form of
gases
...

Worms and amphibians employ this system
...

✓ Tracheal exchange systems rely on a network of tubes that end in holes
to move oxygen and carbon dioxide throughout the bodies of certain
types of insects
...
Land animals, including humans, and marine mammals, such as dolphins and whales, have lungs
...
The integument is the outer covering of an animal
...

Small animals that constantly stay moist may “breathe” right through their
skin
...

(Refer to Chapter 4 for a full explanation of diffusion
...

Earthworms are a perfect example of integumentary exchange in action
...
” As an
earthworm moves through the soil, it loosens the soil, creating air pockets
...

You know how worms get flooded out of the ground when it rains and end up
all over your driveway and sidewalk? Well, they head right back into the soil
as soon as they can (and not just because they’re potential bird food)
...
When this

Chapter 15: Going with the Flow: Respiratory and Circulatory Systems
happens, they die
...
The salt dehydrates its outer surface, which prevents it
from exchanging gases
...
The membranes in gills are
very thin (usually just one cell thick), which allows for easy gas exchange
...
Also, gaseous waste can diffuse from the capillaries into the cells of the gills and pass
out into the watery environment
...
In fish, the
gills are membranous filaments covered by a flap called an operculum, which
is the flap you can see opening and closing on the head of a fish
...
After water enters the
mouth, it’s forced over the gills and then out the back of the operculum
...
Oxygen from the water diffuses into the
capillaries in the gills, and carbon dioxide diffuses out of the capillaries in the
gills
...

Because the water outside the gill and blood inside the gill are moving in
opposite directions, the exchange of gases in a fish gill is referred to as countercurrent exchange
...


Tracheal exchange systems
Tracheal exchange systems are made possible by a network of tubes called
a trachea
...
You can find this system in insects
...

In insects, the trachea is the network of tubes that runs through the entire
body and opens to the air; in humans, the trachea is a tube that carries air
down into the lungs
...
The cells of the body exchange
air directly with the tracheal system, and the oxygen and carbon dioxide
don’t need to be carried through a circulatory system because the tracheal
system runs through all parts of the insect’s body
...
They contract muscles to pump air in and
out of their tracheal systems
...
The bags “pump” like fireplace bellows after
pressure from muscles is applied
...

Gills extend out off of an organism, and lungs are internal growths of the
surface of the body
...
They basically work by providing lots of moist surface
area for the diffusion of oxygen and carbon dioxide
...
We use humans as the model for the mechanics
of the lungs in order to give you a better understanding of how your body
works
...
Inside the
lungs, the trachea branches off into bronchi (small passageways that move air
into the lungs), which then branch and rebranch off into smaller bronchioles
(smaller versions of bronchi)
...
Each alveolus (that’s the singular word for
alveoli) is wrapped with capillaries so that gas exchange can occur between
the lungs and the blood
...
A pair of ribs surrounds the chest cavity to protect
the lungs (and heart) and to assist in the motions of breathing
...


Chapter 15: Going with the Flow: Respiratory and Circulatory Systems

Nasal cavities
Nose
Mouth
Thyroid cartilage
Larynx
Laryngopharynx

Nasopharynx
Oropharynx
Epiglottis
Esophagus
Trachea
Left bronchus

Figure 15-1:
Anatomic
structures
of the
human
respiratory
system
...
Because the lungs have more room
when your chest is expanded, they open up, similar to how a balloon blows
up when it’s filled with air
...
When your diaphragm
relaxes, your rib cage moves back downward and inward, increasing air pressure inside your lungs and forcing air out
...

Following is a breakdown of how oxygen passes through all the branches of
your respiratory system when your lungs fill up:
1
...

Inside your nasal cavity, hair, cilia, and mucus trap dust and dirt particles, purifying the air that enters your lungs
...
(Don’t worry about swallowing dirt; it enters your stomach
where it’s digested and excreted
...
Oxygen then moves into the middle part of your throat and through
the space around your vocal cords
...
When you breathe, air passes through your pharynx
on its way to the lungs
...
The place where your mouth connects is called the oropharynx; the place where your nose connects is called the nasopharynx
...
Next, oxygen enters your trachea, flows through the bronchi and
bronchioles, and then flows into the alveoli
...
Oxygen and carbon dioxide diffuse
across the membranes of the alveoli, and the capillaries move the
freshly oxygenated blood into your circulatory system
...


Plasma
Carbon dioxide
molecules move
out of blood cell
and into lung cell

CO2 (carbon dioxide)
Red blood cell

Figure 15-2:
Oxygenation
of blood
at the
respiratory
membrane
...
Gas exchange in
the lungs is an example of diffusion
...
Your capillaries in
turn have a higher concentration of carbon dioxide than oxygen
...
Meanwhile, the carbon dioxide diffuses
across the capillaries’ membranes and the alveoli’s membranes into the
lungs for expulsion from your body
...
While this
happens, your diaphragm relaxes, and the carbon dioxide waste leaves your
body as you exhale
...
This system makes sure
that all the animal’s cells obtain the nutrients they need to function and that
all the cells dispose of waste so it doesn’t build up within the animal’s body
and cause illness (or, yikes, death)
...
We fill you in on
both types in the next sections
...
When the hemolymph flows into the hemocoel, it
directly bathes the tissues of the organism with nutrients — no blood vessels are involved
...
Insects
and some mollusks (specifically snails and clams) possess an open circulatory system
...
Oxygen is
circulated via the tracheal exchange system (which we describe earlier in this
chapter)
...
It has a network of vessels (think of them as highways that
connect one organ to another) that perform the transportation and keep
your blood from seeping out
...

The three types of blood vessels are
✓ Arteries
✓ Veins
✓ Capillaries
Animals with backbones, called vertebrates, possess a closed circulatory
system
...

Closed circulatory systems, which are said to be closed because they have
vessels that contain the fluid, are more efficient than open circulatory systems
because they need to meet the dual demand of delivering both oxygen and
nutrients to cells
...
That fluid is either hemolymph or blood, depending on the type
of circulatory system an animal has, and it transports either nutrients or a
combination of nutrients and oxygen to the animal’s cells
...
However, in animals with a closed circulatory system, the process happens differently depending on how the system is set up
...


Chapter 15: Going with the Flow: Respiratory and Circulatory Systems

A worm’s heart and circulatory system
Although you may think earthworms are insects that possess an open circulatory system, they’re not (technically they’re annelids)
...

Earthworms have just one dorsal (top side) blood vessel and one ventral
(bottom side) blood vessel, plus a network of capillaries
...
It
pumps blood away from the heart through the ventral blood vessel
...


A fish’s heart and circulatory system
A fish’s heart has two separate chambers, one that receives blood from the
body and another that pumps the blood out over the gills
...
Overall, the
process of how blood passes through a fish is rather simple
...
When a fish’s heart pumps, blood leaves the heart through the ventral
aorta that runs along the underside of the fish
...
The ventral aorta carries the blood to the gills, and the blood then
passes through the capillaries along the gills to pick up oxygen
...

3
...

4
...

This part of the loop is referred to as systemic circulation
...
After the blood has reached all the cells within the fish, it returns to
the heart
...
(Blood pressure is the force that sends blood through
an animal’s circulatory system
...
Because these animals are larger, they need to have a
higher blood pressure to push the blood throughout their entire bodies
...

✓ The other circuit is for systemic circulation, which carries oxygenated
blood from the heart to the rest of the body
...

Mesenteric a
...


Digestive tract
Hepatic
portal v
...


Iliac vein

Renal a
...
The heart is divided into left and right halves, so there’s a left
atrium and a left ventricle, as well as a right atrium and a right ventricle
...

Note: If Figure 15-4 seems confusing to you because it looks as if the right
atrium is on the left side of the heart, pretend you’re looking at someone’s
heart through her chest
...

Left pulmonary artery
Right pulmonary artery
Aortic arch
Pulmonary trunk
Superior
vena cava

Aorta
Left pulmonary
veins
Right pulmonary
veins

Right atrium
Right AV valve

Left atrium
Left AV valve

Pulmonary
Figure 15-4: Semilunar valve
The structures of the
Right ventricle
human heart
and the flow Inferior vena cava
of blood
through
them
...
The right side of your heart pumps blood to your lungs, while the left
side of your heart pumps blood to the rest of your body
...

Valves separate one chamber of the heart from another
...
When your
heart is working properly, the valves open and close fully so blood can flow
through it in only one direction
...
This valve is also referred to as the tricuspid valve
because it has three flaps in its structure
...
Semilunar means “half-moon” and refers to the shape of the
valve
...
This valve is also called the bicuspid valve because it has only
two flaps in its structure
...

Like the pulmonary semilunar valve, this valve has a half-moon shape
...
You find out just how blood moves through your heart and the
rest of your body, and you discover what gets your heart beating in the first
place
...
Deaths from heart disease are
usually attributed to heart attacks, but heart
attacks can be caused by many factors, including the following:
✓ Atherosclerosis: Blockages in the arteries
occur when fats, especially cholesterol,
accumulate in the lining of the arteries
...
These fatty deposits are
called plaques
...

✓ Hypertension: More commonly referred
to as “high blood pressure,” hypertension
puts added stress on the arteries of the

heart, increasing the risk of damage and
fatty deposits along artery walls
...
People with this condition have
difficulty breathing during exercise or times
of stress because the blocked arteries slow
the flow of blood, preventing enough oxygen
from being delivered to the heart muscle’s
tissues
...

✓ Thromboembolism: If an artery is blocked
by a plaque, blood cells can stick to the
plaque, eventually forming a blood clot that
can travel through the bloodstream and
block blood vessels
...
If a
thrombus breaks free and moves around
the bloodstream, it’s called an embolism
...
Even though it’s only as big as a
clenched adult fist, it pumps 5 liters of blood (the equivalent to 21⁄2 big bottles
of soda) throughout your body 70 times a minute
...
It doesn’t even get an entire second to rest
...
8 seconds of your life; this is known as the cardiac cycle
...
Here’s exactly what happens:
✓ The left and right atria contract
...

✓ The atria and ventricles rest (for just 0
...

When the atria and ventricles are resting, the muscle fibers within them
aren’t contracting
...
With most of the blood from the
atria now in the ventricles, the atria contract to squeeze any remaining blood
down into the ventricles
...

The period of relaxation in the heart muscle is referred to as diastole, and the
period of contraction in the heart muscle is called systole
...

In a blood pressure reading, such as the normal value of 120/80 mmHg, 120
is the systolic blood pressure, the pressure at which blood is forced from
the ventricles into the arteries when the ventricles contract, and 80 is the
diastolic blood pressure, the pressure in the blood vessels when the muscle
fibers are relaxed
...

If your blood pressure is 140/90 mmHg, which is the borderline value between
normal and high blood pressure, that means your heart is working harder to
pump blood through your body and not relaxing as well between pumps
...
The culprit could be a hormonal imbalance, a dietary problem
(too much sodium or caffeine), a mechanical problem in the heart, a side
effect of medication, or blockages in your blood vessels
...
As each atrium and ventricle contracts, blood is
pumped into certain major blood vessels that connect to your heart and then
continues flowing throughout your circulatory system
...

The following sections describe the process of pulmonary and systemic circulation, as well as the process of capillary exchange (which gets nutrients
into and wastes out of your cells)
...
Following is a rundown
of how blood moves during pulmonary circulation (trace the path in Figure
15-4 as you read):
1
...

Superior means “higher,” and inferior means “lower,” so the superior
vena cava is at the top of the right atrium, and the inferior vena cava is
at the bottom of the right atrium
...
From the right atrium, the deoxygenated blood drains into the right
ventricle through the right AV valve
...

3
...

The pulmonary semilunar valve keeps blood from flowing back into the
right ventricle after it’s in the pulmonary artery
...
The pulmonary artery carries the blood that’s very low in oxygen to
the lungs, where it becomes oxygenated
...
Here’s
how blood moves through this pathway (you can follow along by tracing the
path in Figure 15-4):
1
...

Note that your pulmonary veins are the only veins in your body that
contain oxygenated blood; all of your other veins contain deoxygenated
blood
...
The pulmonary veins push the oxygenated blood into the left atrium,
which then relaxes, allowing the blood to drain into the left ventricle
through the left AV valve
...
As the left ventricle contracts, the oxygenated blood is pumped into
the main artery of the body — the aorta
...

4
...

Throughout your body, arterioles meet up with capillaries where oxygen
is exchanged for carbon dioxide
...

Your capillaries are only as thick as one cell, so the contents within them can
easily exit by diffusing through the capillaries’ membranes (see Chapter 4 for
more on diffusion)
...


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Through capillary exchange, oxygen leaves red blood cells in the bloodstream
and enters all the other cells of the body
...
At the same time,
the other cells expel waste products, including carbon dioxide, that then enter
the capillaries
...
The venules branch into bigger vessels
called veins, which then carry the deoxygenated blood toward the main vein —
the vena cava
...

The pressure created when the ventricles contract is what forces blood
through the arteries
...
Blood pressure doesn’t
force blood through the veins as it does through the arteries
...

As your limbs and trunk move, deoxygenated blood is pushed farther along
the venules and veins, eventually returning to the heart
...


Seeing what makes your ticker tick
Electrical impulses from your heart muscle cause your heart to beat
...
The nodes send out signals that stimulate contraction of the heart muscle cells, causing your heart to beat
...
Each beat of your heart is started by an electrical signal from the sinoatrial (SA) node in your right atrium
...
(Yes, your heart already contains a pacemaker
...
)
2
...

3
...

The AV node is located in the lower part of the right atrium
...

4
...


Chapter 15: Going with the Flow: Respiratory and Circulatory Systems
The bundle of His lies between the right and left ventricles and connects
with specialized fibers called Purkinje fibers
...
When the impulse reaches the Purkinje fibers, it causes the ventricles
to contract, completing the heartbeat
...
The first heart sound, the lub, is caused by
AV valves closing to prevent backflow from the ventricles into the atria
...


A Bloody-Important Fluid
Blood is the fluid that sustains life in animals with a closed circulatory
system — including you
...
The following sections introduce you to the elements that make up
your blood and the special process that keeps you from losing too much
blood when you cut yourself
...
These solid parts are your red blood cells, white blood
cells, and platelets
...

Note: We use the word solid simply to differentiate platelets and blood cells
from the liquid portion of blood
...
If they were, they wouldn’t be able to squeeze through your
capillaries
...
Hemoglobin, the
iron-containing molecule that harnesses oxygen, exists in the red blood
cells
...
By transporting oxygen and hemoglobin, your red blood cells are an
extremely important part of homeostasis — how your body tries to constantly
achieve and maintain balance
...
Anemia can be
caused by dietary deficiencies, metabolic disorders, hereditary conditions, or
damaged bone marrow
...
They live about 120
days shuttling oxygen and carbon dioxide, and then certain white blood cells
destroy them in the liver and spleen
...
The rest of the material in the old red blood cells is degraded and transported to the digestive system, where much of it ends up in fecal matter
...
If a person
has a low white blood cell count, her immune system isn’t functioning properly
...

Following are the five important types of white blood cells you should know:
✓ Basophils release histamines, those annoying little chemical molecules
that cause you to swell up with hives, itch like crazy, sneeze, wheeze,
and get teary-eyed when you’re around something you’re allergic to
...

✓ Eosinophils help defend the body against invading organisms, particularly parasitic worms
...

Two of their important functions are to destroy virally infected cells and
to make defensive proteins called antibodies
...
Macrophages digest bacteria
and viruses (macro- means “big,” and phago means “to eat,” so a macrophage is literally a big eater)
...
These
cells eat bacteria; in doing so, they keep your system from being overrun by every germ with which it comes in contact
...

Platelets form when pieces are torn off of cells called megakaryocytes
...
They survive in the blood for about ten days
...
Low numbers of platelets can indicate certain cancers and
chronic bleeding disorders
...


The plasma “stream” in your bloodstream
The liquid portion of your blood is plasma
...
In fact, when you think
about it, plasma literally puts the “stream” in bloodstream
...
Two
major proteins found in plasma are
✓ Gamma globulin: Also called immunoglobulin, gamma globulin is a broad
term for a class of defensive proteins that make up the different types of
antibodies
...

✓ Fibrinogen: This protein is involved in blood clotting
...
First, the injured blood vessel constricts, reducing blood flow to the
injured blood vessel, which helps limit blood loss
...
) With the injured blood vessel constricted, the platelets present in the
blood that’s passing through that vessel start to stick to the collagen fibers
that are part of the blood vessel wall
...


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After the platelet plug is formed, enzymes called clotting factors (your body
has 12 of them) initiate a chain of reactions to create a clot
...
(Calcium is required for this reaction
to occur
...

✓ Fibrin threads entwine the platelet plug, forming a meshlike framework
...
(Note: Because red blood cells are tangled in the meshwork, clots
appear to be red
...
)

Chapter 16

Checking Out the Plumbing:
Animal Digestive and
Excretory Systems
In This Chapter
▶ Looking at how different types of animals consume and remove food
▶ Taking an in-depth look at the human digestive system
▶ Playing with the building blocks of healthy food choices
▶ Discovering how waste products leave the human body

A

fter an animal ingests or absorbs food, its digestive system immediately
starts breaking down the food to release the nutrients within it
...

Want to know more about the ins and outs of digestive and excretory systems?
Then you’re in the right place
...
We then present
the workings of the human digestive system and the fate of food and wastes in
your body
...


Obtaining Food and Breaking It Down
All animals need food as a source of energy and materials for growth (as
explained in Chapter 5), but the various types of animals have different strategies for obtaining the food they need
...
They use teeth, claws, tentacles,
or pinchers to tear off pieces of food and ingest them
...


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Part IV: Systems Galore! Animal Structure and Function
✓ Filter feeders strain liquids to capture tiny particles suspended in
the fluid
...
Clams, for example, pull seawater
through their bodies and pass it over their mucus-covered gills, trapping the small organisms and organic matter that were suspended in the
water
...

✓ Fluid feeders suck nutrient-rich fluids from other organisms
...
Aphids and mosquitoes, for example, puncture other
organisms and draw fluid from them — aphids draw the sugary sap out
of plants, and mosquitoes draw blood out of animals
...

✓ Substrate feeders live right in or on their food and eat as they move
through it
...
Just think of earthworms and maggots
...

Similarly, when flies lay their eggs in bodies, the maggots that hatch out
of the eggs eat their way through the food (the decomposing organism)
until they reach the outside
...

✓ Digestion occurs when the animal’s body gets busy breaking down the
food
...
It begins when an animal consumes the food
and continues until the food enters its stomach
...
It also begins
as soon as food is consumed and the enzymes in the mouth go to
work
...

✓ Absorption occurs when cells within the animal move small food molecules from the digestive system to the insides of the cells
...


Chapter 16: Checking Out the Plumbing: Animal Digestive & Excretory Systems

The Ins and Outs of Digestive Systems
The basic way an animal’s digestive system works has a great deal to do with
whether it can spend a few hours between meals or whether it has to keep
consuming food constantly just to stay alive
...


Incomplete versus complete
digestive tracts
Of the animals that you can see without a microscope, the ones with the
most primitive digestive system are animals with incomplete digestive tracts,
meaning they have a gut with just one opening that serves as both mouth and
anus
...
) Jellyfish are a classic example of an animal with an
incomplete digestive tract
...
Although simple, this type of system is considered a complete
digestive tract
...

The benefit of a complete digestive tract is that it allows thorough digestion before excretion occurs
...
An organism with a complete
digestive tract doesn’t have to take in food constantly to replace food that’s
excreted before the nutrients could be acquired from it
...
Most of these animals
are either permanently attached to something (think clams or mussels) or
incredibly slow movers
...
These animals
are generally more active and somewhat nomadic
...
If an animal such
as a lion were a continuous feeder that had to hunt and eat constantly, it’d be
exhausted and spend much more time out in the open savanna, increasing the
chance that it could become prey for another predator
...
You can consume food rapidly, but
you digest it gradually so you don’t have to eat again for several hours
...
In humans, this organ is the stomach
...
The act of chewing (the
technical term for it is mastication) is the first step in food digestion for humans
...
From your stomach, it passes into the small intestine
...
In the sections that follow, we fill you in
on the role that each of these parts of the digestive system plays in digestion
...


Rectum

From LifeART®, Super Anatomy 1, © 2002, Lippincott Williams & Wilkins

Chapter 16: Checking Out the Plumbing: Animal Digestive & Excretory Systems

The busiest stop of all — your mouth
Your mouth does more than let you shout at the television during sporting
events or talk to that cute guy or gal sitting next to you in biology class
...
And don’t think your teeth are
the only participants in this process just because they mash your food into
smaller and smaller bits
...
In addition to what your teeth do, your
✓ Taste buds detect the nutrients that make up the food you’re eating —
such as carbohydrates, proteins, and fats — so the cells of your digestive
system can release the right enzymes to chemically digest your food
...

You know how you salivate just before you’re about to eat something?
That’s the effect of your eyes or nose sensing something delicious and
sending a message to your brain that you’re about to open your mouth
and take a bite
...

After your teeth have chewed, your taste buds have sent along the information about what you’re eating, and the enzymes in your saliva have started
breaking apart starches, you’re ready to swallow
...
(The esophagus is the
tube that connects your mouth to your stomach
...

When the swallowed food drops into your stomach, it’s referred to as a bolus
...

If you eat too much, your stomach produces more acid, and the contents of
your overly full stomach can be forced back up into your esophagus, which
runs in front of the heart
...


The inner workings of your stomach
When food particles reach your stomach, the organ churns them up, and the
enzyme pepsin starts breaking down the food’s proteins into smaller chains

245

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Part IV: Systems Galore! Animal Structure and Function
of amino acids (see Chapter 4 for more on enzymes)
...
Your
pyloric sphincter muscle occasionally opens the valve, allowing your stomach’s contents into your small intestine a little bit at a time
...
Well, when pepsin is secreted, it’s in its
inactive form, called pepsinogen
...
When it’s in the cavity of the stomach, pepsinogen gets converted to its active form, pepsin, by losing a few dozen of its
amino acids
...


The long and winding road
of your small intestine
When food molecules hit your small intestine, they get broken down into
even smaller units (so your cells can absorb them) with a little help from
your liver and pancreas
...
For
years the medical community thought stomach
ulcers were largely caused by stress, worry, frustration, and other negative emotions
...
pylori)
in the stomachs of people with ulcers
...
pylori in fact caused the ulcers, but
no one believed them
...

Marshall, who didn’t have any stomach ulcers,
did the unthinkable — he drank a culture of live
H
...
Marshall

developed ulcers, proving that infection with the
bacterium could indeed cause stomach ulcers
...
pylori inflames the lining of the stomach,
causing the organ’s protective mucus to disappear and allowing the enzymes and stomach
acids secreted during digestion to eat away at
the proteins in the tissue of the stomach wall
...
Fortunately, antibiotic therapy can
often successfully treat the condition by removing the H
...


Chapter 16: Checking Out the Plumbing: Animal Digestive & Excretory Systems
The liver secretes bile (a yellow-brown or greenish fluid) into the small intestine
...
Meanwhile, the
pancreas releases pancreatic juice into the mixture that contains the following enzymes to help chemically digest fats and carbohydrates:
✓ Lipase breaks apart fat molecules into fatty acids and glycerol
...
The disaccharidases then break apart
into monosaccharides that can be absorbed by the cells lining your
small intestine
...
After they break the peptides down into small chains, aminopeptidases finish them off by breaking apart the peptides into individual,
absorbable amino acids
...
To
protect the cells of your digestive system, the enzymes aren’t activated
until they reach the cavity of your small intestine
...
The small intestine is much longer than the
large intestine (10 feet long versus 5 feet long)
...

After several hours in your digestive system, the carbohydrates, fats, and
proteins from your food are all in their smallest components: monosaccharides (such as glucose), fatty acids and glycerol, and amino acids (see
Chapter 3 for details on these molecules)
...


Absorbing the Stuff Your Body Needs
During the digestion process, the nutrients your body can use are absorbed
into the cells lining your small intestine
...
The next sections
outline how nutrients move throughout your system and how your liver constantly works to make sure you have the right amount of blood glucose (blood
sugar) necessary to keep you going
...
In other words, energy obtained from adenosine triphosphate (ATP)
molecules is expended to move sugars (which came from consumed carbohydrates) and amino acids (which came from consumed proteins) into the
intestinal cells (see Chapter 4 for the full scoop on active transport)
...

Capillary exchange relies on two things: capillaries, teeny-tiny blood vessels
with extremely thin walls, and interstitial fluid, the fluid that fills every space
between every cell in your body, cushioning and hydrating the cells
...

This extracellular fluid is made up mostly of interstitial fluid (16 percent) and
plasma (4 percent; we fill you in on plasma in Chapter 15)
...

The nutrients gained from digested food diffuse through the walls of your
small intestine, through the capillaries’ walls, across the interstitial fluid, and
into your cells
...
(To discover how your kidneys remove wastes from your body, head to the later
related section in this chapter
...

They get coated with proteins and acquire a new name: chylomicrons
...


Glucose regulation
Perhaps the most important stop digested sugars make as they travel through
your bloodstream is your liver
...


Chapter 16: Checking Out the Plumbing: Animal Digestive & Excretory Systems
✓ If the level of glucose is too high (a condition called hyperglycemia), the
liver removes some of the glucose from the blood and turns it into the
storage polysaccharide glycogen
...
The fat molecules are
then carried away by your bloodstream and deposited around your
body in your adipose tissue (fat)
...
If all the glycogen stores are used up,
the liver starts to break down stored fats to obtain glucose for your cells
...
Glucose is so important,
in fact, that your body will literally digest itself in order to get glucose to your
brain
...
Proteins in the muscles are broken down into amino acids, which can
be converted into glucose
...
When your body starts breaking down proteins in your
heart, death is a serious possibility
...
If you didn’t have such
an evolved sense of taste, maybe you’d be like other animals and just eat
what’s part of your natural diet only when you’re truly hungry
...
Would you do that to your car on a regular basis? Or would you
rather use the premium stuff to make sure your car’s engine doesn’t knock
and ping?
If you want to keep your bodily systems from knocking and pinging, we
strongly encourage you to follow the nutrition recommendations made
by the United States Department of Agriculture (USDA)
...
More detailed information, such as the difference between whole
grains and refined carbohydrates in the bread, cereal, and pasta group, are
available on the USDA’s MyPyramid Web site at www
...
gov
...


Carbohydrates: The culprits
of your food cravings
Carbohydrates are compounds of carbon, hydrogen, and oxygen that supply
your body with short-term energy (we cover the chemical structure of carbs
in greater detail in Chapter 3)
...
You’ve witnessed this yourself if you’ve ever held a
marshmallow over a campfire too long
...
You can acquire it
directly from foods containing carbohydrates (such as breads, pastas, sweets,
and fruits)
...

When it comes to your diet, all carbohydrates are not created equal
...
They help
prevent heart disease and constipation
...

Lots of products advertise that they’re “made with whole grains,” but
that assertion doesn’t tell you what the proportion of whole grains in
the food actually is
...

Foods that are high in fiber are made with lots of whole grains
...
They break
down very quickly and cause a rapid rise in blood glucose
...
It’s best to avoid these types of carbs as much as you can
...
So, to create more muscle fibers, new cells, and other elements that
help your body run, you need to take in protein (to get an idea of a protein’s
chemical structure, see Chapter 3)
...
Your body requires nine amino acids
in particular to construct proteins, which is why those nine amino acids
are referred to as essential amino acids (we list them for you in Table 16-1)
...
Because these
amino acids are made in the body, they’re considered nonessential amino
acids; it’s not essential that you consume foods containing them because you
can get them another way
...


Table 16-1

The Amino Acids Humans Can Consume

Essential Amino Acids

Nonessential Amino Acids

Histidine

Alanine

Isoleucine

Arginine

Leucine

Asparagine

Lysine

Aspartate

Methionine

Cysteine

Phenylalanine

Glutamate

Threonine

Glutamine

Tryptophan

Glycine

Valine

Proline
Serine
Tyrosine

When you think of protein sources, you probably think of meat
...
Both your muscles and the muscles of other animals
are made from protein
...

Beans, nuts, and soy are additional sources of protein, but the protein they
contain is plant protein, not animal protein
...
Because animals acquire essential amino acids plus make their
own nonessential amino acids, animal protein is considered complete — it
has all the amino acids humans need
...


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Fats: You need some, but don’t overdo it
Your body needs fats to make tissues and hormones and insulate your nerves
(just like a rubber coating often insulates wires)
...
It gives your body shape, reduces heat loss by insulating your organs
and muscles, and cushions your body and organs (much like shock absorbers)
...
First, your body quickly burns off
the glucose that’s readily available in your cells
...


Lipoproteins and your risk for heart disease
Lipoproteins are compounds made from a fat
and a protein
...

You’re capable of producing four types of lipoproteins:
✓ High-density lipoproteins (HDLs)
✓ Low-density lipoproteins (LDLs)
✓ Very low-density lipoproteins (VLDLs)
✓ Chylomicrons
Sometimes in the news you read or hear about
HDL being “good” cholesterol and LDL being
“bad” cholesterol
...
They
just attach to and transport cholesterol
...

Chylomicrons are very small, newly created
lipoproteins that fall into the VLDL category
...

As VLDLs travel through your bloodstream,
they lose some lipids, pick up cholesterol, and
become LDLs
...
While doing that, the cholesterol can get stuck to the wall of the blood
vessel, causing deposits called plaque to form
...
If that happens, a heart attack or
stroke may occur
...

HDLs, on the other hand, are the lipoproteins
that contain more protein than lipid, which
makes them denser and gives them their name
...
Instead, they
shuttle cholesterol right out of the body
...
Remember: You always want
to have more of these dense little guys floating
in your blood than LDLs or VLDLs
...

✓ Unsaturated fats are good for you
...

✓ Saturated fats are unhealthy
...

Contrary to popular belief, fat doesn’t make people fat
...


Minerals and vitamins: The fuel
for your enzymes
In addition to carbohydrates, proteins, and fats, your body needs certain
minerals and vitamins to help your enzymes function (see Chapter 4 for more
on enzymes)
...
Your body doesn’t need a ton of minerals to stay healthy, but
some are essential for its proper functioning
...
Table 16-2 lists all the major minerals and
trace elements your body needs
...
They’re
made up of the same carbon, hydrogen, oxygen, and nitrogen atoms as carbohydrates, proteins, and fats are
...
The phospholipids carry the “dissolved” vitamins through the
bloodstream and into your cells
...


Exploring the Human Excretory System
When the human body breaks down food, it uses as many of the nutrients
as possible to fuel cellular processes
...
What’s left is waste that your body removes
via your excretory system, which consists of your large intestine and kidneys
...


Getting to know your large intestine and
how it eliminates solid wastes
After the usable nutrients from food are absorbed into the bloodstream from
the small intestine, the leftover material continues on to the large intestine
(also called the colon)
...
Feces
pass out of your large intestine and into the rectum, which acts like a holding tank
...
This feat, signaling the end of the digestive process, is performed
through the anus
...
If too much water is absorbed, constipation
occurs; if too little water is absorbed, diarrhea occurs
...
One of the bacteria
that lives in your colon is Escherichia coli (or
E
...
Any strain of E
...
coli
contamination can also contribute to sepsis
(bacteria in the bloodstream, traveling around
your body causing infections elsewhere), which
can lead to coma and death
...
coli gets into food
is from dirty hands
...
If you don’t wash your hands
to remove any potential bacteria lingering there
and then you pick up food with your hands and
eat it, you may ingest the bacteria and make
yourself sick
...
Sodium ions are necessary for many cellular processes,
such as the active transport of materials across cell membranes (a process
described in Chapter 4)
...
If the amount of ions in your body isn’t in the normal range, serious
effects occur
...


Flowing through how your kidneys
remove nitrogenous wastes
Nitrogenous wastes — unnecessary, excess materials containing nitrogen and
resulting from the breakdown of proteins and nucleic acids — are released
from the body in urine
...

You have two kidneys, one on each side of your back, just below your ribs
...
As you can see, each kidney
has three distinct areas:
✓ The renal cortex, which is the outer layer
✓ The renal medulla, which is the middle layer
✓ The renal pelvis, which becomes a ureter
Each kidney contains more than 1 million nephrons, microscopic tubules that
make urine
...
From there, the urine flows down the ureter, which
is the tube that connects the kidney to the bladder
...
The
bladder holds a maximum of about one pint of urine, but you begin to feel the
need to urinate when your bladder is only one-third full
...


Capsule
Renal cortex

Anatomy of the Kidneys

Renal medulla
Left kidney

Renal pelvis
Calyx
Renal pyramid

Blood Supply of the Nephron
Glomerulus Proximal convoluted tubule
Arteriole
Distal convoluted
Ureter Renal Renal
artery
vein
tubule

Cortex
Collecting duct

Medulla
Figure 16-2:
Structure of
the kidneys
and the
nephrons
inside the
kidneys
...
Basically,
the need to urinate becomes more urgent and
frequent, and sometimes urine leaks out of the
bladder uncontrolled
...
Men, however, have an additional
urinary issue: enlargement of the prostate gland
...
Its function is to add

fluid to semen as the semen passes through the
urethra in the penis
...
If the condition progresses far
enough, urine can back up into the kidneys,
which can lead to kidney disease
...


Urine leaves the body through the urethra (see Figure 16-3), a tube at the
bottom of the bladder that opens to the outside of the body
...
When you want to start urinating, the sphincter
muscle relaxes, opening the urethra and letting the urine out
...


Urinary bladder
Urethra

From LifeART®, Super Anatomy 1, © 2002, Lippincott Williams & Wilkins

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Chapter 17

Fighting Back: Human Defenses
In This Chapter
▶ Distinguishing the good microbes from the bad
▶ Checking out the components of your innate and adaptive immune systems
▶ Helping your immune system out when it needs it
▶ Seeing how age affects your internal defense system

Y

ou encounter bacteria and viruses all the time, some of which have
the potential to make you very sick
...
) Whether these potential
pathogens cause you harm depends on a complicated give and take between
their invasion tools and your defenses
...

In this chapter, we present the structures and cells that keep you safe from
microbes and review the options available to you when your body’s defenses
need a helping hand
...


Microbial Encounters of the
Best and Worst Kinds
Microbes (bacteria and viruses) exist on every surface
...
So how can you tell a good microbe from a
bad one? The next sections solve the puzzle
...

Your normal microbiota are beneficial to you because they
✓ Aid the digestive process and assist with blood clotting by releasing
vitamin K
...
So consider vitamin K the rent the
bacteria pay for using your intestines as their home
...

✓ Make chemicals called bacteriocins that inhibit the growth of other
bacteria
...
These bad bacteria are pathogens, the microbes that cause infectious
disease
...
They can also enter through a
wound or be passed along through sexual contact
...
This bacterium
normally lives and reproduces inside rodents, but if infected rodents
and humans are living near each other, the plague bacterium can be
transferred to humans by fleas that bite the rodents and then bite the
humans
...
Other bacteria take
advantage of you when you’re down
...
Most of the time, the bacteria are well-behaved, just hanging
about in warm, dark crevices of the throat
...
The bacteria get a little power hungry

Chapter 17: Fighting Back: Human Defenses
and begin reproducing rapidly, which can lead to a sinus or ear infection, or even pneumonia
...
If, for example, food is improperly processed, bacterial
toxins may become the secret ingredient in your meals
...
This illness is usually caused by improper canning, which allows the bacteria Clostridium botulinum to grow in the
food and release their toxins
...


Viruses: All bad, all the time
Viruses are the pirate raiders of the microbial world
...
Although, viruses are very different in structure than bacteria,
they can also make you sick
...
The virus attaches its proteins to a receptor on a cell
...
If your key doesn’t fit, you can’t get in
...

2
...

The viral nucleic acid reprograms the cell, turning it into a viral production factory
...
The cell even uses its own molecules and
energy reserves (ATP) to produce the viral parts
...

3
...

Eventually, this viral replication creates too much of a crowd for the
cell to handle and the cell explodes, releasing viral particles to go wreak
havoc in other cells in the host’s body
...
In #8 in Figure 17-1, you can see completed viral
particles exiting the human cell
...
Free Virus
...
Binding and Fusion: Virus binds to CD4
and coreceptor on host cell and then
fuses with the cell
...
Penetration: The viral capsid enters the
cell and releases its contents into the
cytoplasm
...
Reverse Transcription: The enzyme
reverse transcriptase converts the
single-stranded viral RNA molecules into
double-stranded DNA
...
Recombination: The enzyme integrase
combines the viral DNA into the host cell
DNA
...
Transcription: Viral DNA is transcribed to
produce long chains of viral protein
...
Assembly: Sets of viral proteins come
together
...
Budding: Release of immature virus
occurs as viral proteins push out of the
host cell, wrapping themselves in a new
envelope
...


7

8

9
...


Figure 17-1:
How viruses
attack cells
...
Maturation: The viral enzyme protease
finishes cutting the viral proteins, and
the proteins combine to complete the
formation of the virus
...


Built to Protect You: Innate
Human Defenses
Usually you’re not aware of all the microbes roaming the world because a)
you can’t see them and b) your innate immunity keeps most of them from
bothering you
...
Like the walls of a fortress, your
innate defenses can repel all attackers (meaning they’re not specifically targeted for one particular pathogen)
...

When that happens, you need your adaptive immunity to come to your
rescue
...
)
Your innate defenses have several ways of fending off the potential pathogens
you encounter:
✓ Physical barriers: Your skin and mucous membranes are the barriers
that physically block access to your tissues and organs
...

✓ Chemical barriers: The pH of your stomach acid is a chemical barrier
that prevents microbial growth
...

✓ Dendritic cells: These cells patrol your body in search of microbes and
alert your immune system of impending invasions
...

✓ Phagocytes: These are certain white blood cells that seek and destroy
microbes that have successfully entered your body
...
Think of phagocytes as
your body’s hand-to-hand combat specialists
...

✓ Filters: The mucus in your nose and throat and the hairs in your nose
act as filters that trap microbes and prevent them from getting deeper
into your body
...
Your lymphatic system screens your body fluids for the presence
of microbes and destroys any it finds
...

We cover each of these innate defense mechanisms in greater detail in the
sections that follow
...
Both the skin

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and mucous membranes are epithelia, tissues composed of multiple cell
layers that are packed tightly together in order to prevent microbes from
sneaking in
...
Your skin is good at keeping microbes out for these reasons as well:
✓ It’s dry
...

✓ It’s flaky
...

✓ It’s tough
...

✓ It’s acidic
...

Just like your skin guards the exterior of your body, your mucous membranes protect your wet interior surfaces
...
Although
your mucous membranes aren’t quite as tough as your skin, they have some
unique defenses of their own:
✓ They’re sticky
...

✓ They move stuff out
...
For example, tears wash the
eyes, urine flushes out the urethra, and peristalsis moves material
through the intestines
...
The mucus moves to a location where you can
cough it out, protecting your lower respiratory tract from infection (see
Chapter 4 for more on cilia)
...
These tiny, invisible defenders bind to microbes, breaking

Chapter 17: Fighting Back: Human Defenses
them down and just generally making it difficult for them to get a foothold in
your body
...
Here are the names of a few of ’em:
✓ Lysozyme is a protein that breaks down one of the chemicals found in
bacterial cell walls (lyse- is to break, and zyme means “enzyme,” so a
lysozyme is an enzyme that breaks down bacteria)
...

✓ Transferrin in your blood binds iron so microbes don’t have enough
iron for their growth
...

✓ Interferons are proteins that are released by cells infected with viruses
...
Cells that receive a warning from interferon produce proteins to
help protect themselves against viral attack
...
Because of these special receptors, called toll-like receptors, dendritic cells are very good at recognizing
foreign microbes
...

Dendritic cells do two things that are key to your ability to fight infections:
✓ They release communicating molecules called cytokines
...
The cytokines tell your
immune system that microbes have been detected and help activate the
cells you need to fight back
...
Helper T cells are very important to
your pathogen-fighting ability because they recognize foreign antigens
and send signals directing other cells of your immune system to fight
...

When they find them, they grab them and eat them alive (phago- means “eat,”
and -cyte means “cell,” so phagocytes are “eater-cells”)
...

The two types of phagocytes are
✓ Neutrophils: These phagocytes multiply early during an infection and
are the first ones to arrive on the scene during inflammation
...
(Macromeans “big,” and phage means “eat,” so macrophages are literally “big
eaters
...
The microbes and your own damaged cells trigger a
cascade of events that leads to inflammation, a local defensive response to
cellular damage that’s characterized by redness, pain, heat, and swelling
...

Molecules such as histamine that are released during inflammation lead to
vasodilation and increased blood vessel permeability
...
The blood flowing to the infected area delivers clotting elements that trigger blood clots and help confine the infection to one location
...
As a result of the increased blood
flow, the infected area becomes warm and red
...
This allows cells and materials to leave the blood and
enter the tissues where the infection is happening
...
Fluid leaks from the blood vessels into the tissues and swelling occurs
...
After
fluid leaves the blood and enters the tissues, it needs to be cleaned before
it’s returned to the blood
...


Lymph node
Thoracic duct

Lymphatic vessel

Figure 17-2:
The lymphatic
system
...
(Note: Lymphatic vessels form a circulatory

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system that’s similar to, but separate from, your blood vessels
...
As lymph passes through the
lymph nodes, defensive proteins and white blood cells clean it of any
foreign material, including microbes
...

✓ Lymphatic organs: Lymph nodes, the spleen, the tonsils, and the
thymus are all lymphatic organs
...
Patches of lymphatic
tissue are also scattered around in different organs of your body
...
It’s considered a lymphatic organ, though, because
it contains so many white blood cells and because its job is to clean up
foreign material
...
But every now and
then, a microbe comes along that gets around your innate defenses and into
your body
...

Your adaptive immunity gets its name because it adapts and changes as you
go through life and are exposed to specific microbes
...
coli, only those white blood cells that recognize particular
molecules on E
...
If you face a different infection, say the
bacteria Staphylococcus aureus, only the set of white blood cells that recognizes specific molecules on S
...
In other words, when
your adaptive defenses come to your rescue, exactly the right team of white
blood cells is activated to fight each pathogen
...

One of the awesome features of your adaptive immunity is that it can remember a pathogen it has encountered before
...

Certain cells of your immune system, called memory cells, remain in a semiactivated state after your first encounter with a microbe
...
When the same pathogen shows up again, these cells multiply

Chapter 17: Fighting Back: Human Defenses
quickly and efficiently destroy the pathogen before you even realize it came
back
...

We describe the other components of your adaptive immune system in the
following sections
...
(They’re called T cells because they mature in the thymus,
which is one of your lymphatic organs
...

Helper T cells are also called CD4 cells because they have a protein on their
surface called CD4
...
Here’s how the process works:
1
...

By putting antigens on their surfaces, the antigen-presenting cells can
show the antigen to the helper T cells
...
Antigen-presenting cells also release cytokines, signaling that they’ve
detected a foreign antigen
...
Helper T cells bind to the displayed antigen using a receptor called a
T cell receptor
...
So, only the T cells that are the right T cells to fight this
antigen will be activated
...
Receptors
on the helper T cells bind the signals, acting like ears so the T cells can
“hear” the alarm call of the antigen-presenting cells
...


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Soldiers on the march:
B cells and antibodies
B cells are white blood cells that become activated when they detect foreign
antigens with their B cell receptors or receive signals from helper T cells
...

Plasma cells produce antibodies, defensive proteins that bind specifically
to antigens
...
Anything in the body
that’s tagged with antibodies — such as invading pathogens — is marked for
destruction by the immune system
...

✓ Antibodies stick to pathogens and drag them into clumps
...

✓ Antibodies stick to the surfaces of viruses, preventing them from binding to new host cells
...
Each archer
is trained to hit just one type of target
...

Each adaptive immune response is tailored specifically to fight the invading
pathogen
...
So, out of the thousands of different B (and T) cells your body can produce, only a small subset
reacts to each pathogen
...
Cytotoxic T cells are white blood
cells that are experts at detecting infected host cells
...

Cytotoxic T cells are also called CD8 cells because they have a protein on their
surface called CD8
...
This is where science and medicine come
in
...
Doctors study how the body
works and how to recognize the signs of different illnesses so they know which
tools to use to help you fight off disease
...

The next sections introduce you to these immune system helpers
...
The first and
most famous antibiotic, penicillin, is produced by a mold that looks a lot like
the green stuff you see on old bread in your kitchen
...

The structures and enzymes that antibiotics target are unique to bacterial
cells, so they have little effect on human cells (see Chapter 4 for more on the
differences between bacterial and human cells)
...
Funding for research on new
antibiotics decreased because people thought they had enough weapons in
their arsenal
...
Today, humans are faced with a new microbial problem:
antibiotic-resistant bacteria
...

The conundrum modern doctors now face is that using antibiotics increases
the chances that antibiotic-resistant strains of bacteria will develop
...
In other words,
when antibiotics are used, the most susceptible bacteria die first, leaving the
more resistant bacteria to survive
...

Repeat this cycle a few times, and the antibiotic no longer works at all
...
And
that’s just part of the problem
...

Scientists and doctors are teaming up again to fight the threat of antibioticresistant bacteria
...
By saving antibiotics for when they’re really needed,
doctors can slow down natural selection and help keep antibiotics working
for as long as possible
...

Bacteria-blasting viruses were first discovered in the early years of the
last century at the Pasteur Institute in Paris
...
He saw phages take on and completely destroy
a whole colony of much larger bacteria
...

Until about 1940, these tiny microbes (they’re only about a fortieth of the size
of bacteria) were the miracle cure for many bacterial infections
...
Because you have to find just the right bacteria to appeal to
the palate of a specific phage or else the deal is off, antibiotics — which have
a much broader spectrum — seemed like a better solution to the problem of
infection
...
Here are the prominent ones:
✓ Phages are among the most abundant creatures on Earth
...
They blissfully swim around in piles of sewage and hide in
cozy little corners in your body
...
After phages invade a bacterial cell, as many
as 200 new phages are produced per hour
...
Then it’s bye-bye bacterium
...
The
infant phages move on to nearby bacteria, making short work of every
cell in their path
...

Scientists are currently working to solve the problems that remain with
phage therapy, which include the time it takes to identify which phages like
to knock off which bacteria
...


Fighting viruses with antiviral drugs
Controlling viruses is even more difficult than controlling bacteria
...

They’re difficult to see and isolate, and they’re equally difficult to classify
...
So, in many cases, all doctors can do is treat the symptoms of viral illnesses rather than the illnesses themselves
...
These human proteins can now be made
in a lab by scientists who genetically engineer bacteria (flip to Chapter 9
for more on genetic engineering)
...

The term antibiotic specifically applies to drugs that fight bacterial cells
...


Getting ahead of the game with vaccines
Vaccines, solutions containing pieces of microbes that are introduced into the
body, prevent diseases by generating immunologic memory
...
The antigen-presenting cells pick up the pieces and
show them to the helper T cells
...
In all the excitement of the adaptive immune response,
the memory B and T cells are developed
...
If it does, your
immune system kicks into gear so fast and hard that the pathogen is blown
away before you even realize it was ever there
...
Because of these fears or mistrust of
vaccines, some people are choosing not to vaccinate their children, a decision that ultimately puts
the children at greater risk for infectious disease
...
All vaccines have
risks and can cause side effects
...
S
...

✓ Many diseases that are perceived as mere
nuisances can actually have extremely
serious complications
...
Measles infection can result in
complications such as encephalitis (swelling of the brain) and pneumonia
...
This statistic is especially tragic when you consider that measles is a vaccine-preventable disease
...
Most younger people
who live in rich nations such as the United
States or countries in Europe have grown
up in a time when vaccinations were easily
available
...
Because of a lack of knowledge,
the fear of infectious diseases has declined
in these countries, leading people to question the need for vaccinations
...

The Internet brings a world of information
right into your home
...
Books
are checked by editors, and scientific and
medical articles are carefully reviewed by
groups of scientists and doctors before
they’re published
...

An official-looking Web site can fool people
about the reliability of its information, so
always check the source of your information
...

cdc
...
chop
...


Chapter 17: Fighting Back: Human Defenses
Vaccines are the only tool people have to control the spread of some viral
diseases
...
The parts of the pathogen are included, but the pathogen can’t reproduce
...
The pathogens
have been altered in the lab so they have most of their original form,
except for the parts that let them make you sick
...

Smallpox has been virtually wiped off the face of the Earth by vaccination
...
Eradication of smallpox, polio, and measles is possible because humans are the only host species for these viruses, which means the viruses can’t multiply and mutate in
animal hosts
...

Flu viruses are a bit different
...
When a virus mutates, it can continually adapt to new
intracellular environments and escape from the host’s immune response
...
Case in point:
The swine flu pandemic of 2009 was caused by a strain of H1N1 influenza
that had a unique mixture of genes from three different strains of flu, some
of which hadn’t infected humans before
...
This lack of immunity allowed
the virus to spread far and wide, causing the pandemic
...

During the busy, trying time of puberty, the thymus starts to get smaller and
smaller until it’s virtually nonexistent later in adulthood
...
Production of B cells starts
to wane as well
...


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Weakening of the immune system may explain why people toward the high
end of the average life span (78 years for people living in the United States)
become more prone to infection
...
One example of an autoimmune disease that’s much more common in older people than younger folk
is arthritis
...


Chapter 18

The Nervous and Endocrine
Systems, Messengers
Extraordinaire
In This Chapter
▶ Diving into the ins and outs of nervous systems
▶ Figuring out how the brain and senses work
▶ Seeing how a nerve impulse travels through your nervous system
▶ Discovering how the endocrine system uses hormones to regulate your inner workings

W

ith all the metabolic processes and reactions going on in living
things, organisms need to be able to exert some control in order to
avoid chaos
...
The nervous system,
which consists of a brain and nerves, is responsible for picking up information from the organism’s sense organs, interpreting that information, and
coordinating a response
...
In this chapter, we fill you in on the structure and function of both systems and explore
how the human body responds to their signals
...
The complexity of
an animal’s nervous system depends on its lifestyle and body plan
...
A starfish is a good example of an animal with a nerve net
...
It’s housed in the head
...

The tendency in animals to have neurons concentrated in the head end of
the body is called cephalization
...

In the following sections, we give you more detail about the CNS and PNS so
you can tell the two apart aside from where they’re located
...


Distinguishing between the CNS and PNS
In all animals with a backbone, including you, the CNS (pictured in Figure 18-1)
consists of a brain and a spinal cord
...
The spinal cord controls the flow of information to and from the
brain; it sits within a liquid called cerebrospinal fluid that guards the CNS against
shocks caused by movement and helps supply nutrients and remove wastes
...
One layer of protection is
the blood-brain barrier, which is created by the capillaries surrounding the brain
...
The second layer of protection is the meninges, two layers of
connective tissue that surround the brain and spinal cord
...
It controls many of an animal’s voluntary
responses to signals in its environment
...

✓ Autonomic nervous system: This part of the PNS controls the (mostly involuntary) internal processes in the body, such as heartbeat and digestion
...
This is the part of the nervous system

Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire
responsible for the fight-or-flight response, which stimulates a
surge of adrenaline to give the body quick energy so it can escape
danger
...

• The parasympathetic nervous system stimulates more routine functions, such as the secretion of digestive enzymes or saliva
...


Musculocutaneous
nerve

Cervical nerves
(8 pairs)

Phrenic nerve
Thoracic nerves
(12 pairs)
Radial nerve
Median nerve
Ulnar nerve

Lumbar nerves
(5 pairs)
Femoral nerve

Sacral nerves
(5 pairs)

Sciatic nerve

Internal saphenous nerve
Anterior tibial nerve
Musculocutaneous nerve

Figure 18-1:
The human
nervous
system
...

Neurons are the cells that receive and transmit signals; neuroglial cells are the
support systems for the neurons (in other words, they protect and nourish
the neurons)
...

✓ Each neuron contains a nerve cell body with a nucleus and organelles
such as mitochondria, endoplasmic reticulum, and a Golgi apparatus
(see Chapter 4 for more on cells and organelles)
...
The dendrites act like tiny antennae that
pick up signals from other cells
...
The axon is insulated by a myelin sheath made up
of segments called Schwann cells
...


CNS

Axon
Nucleus of Schwann cell

Impulse from

280

Synaptic bouton

Axon

Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire
Nerve impulses enter a neuron through the dendrites
...
When the impulses reach the branches at the end of the axon,
they’re transmitted to the next neuron
...


Processing signals with the
three types of neurons
The three major functions of a nervous system are to collect, interpret, and
respond to signals
...

✓ Sensory neurons collect sensory information and bring it to the CNS
...
However, they’re also responsible for receiving internally generated impulses regarding adjustments that are necessary for the maintenance of homeostasis
...

✓ Interneurons within the CNS integrate the sensory information and
send out responding signals
...
When an interneuron receives an impulse from a sensory neuron,
the interneuron determines what (if any) response to generate
...
To continue with the example from the preceding bullet, the
interneurons in the cerebral cortex of your brain will process the incoming sensory information and send out responding signals
...
Also called efferent neurons, motor
neurons stimulate effector cells that generate reactions
...


Acting without thinking
Sometimes the nervous system can work without the brain, as in a reflex arc
...


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When you touch a hot stovetop, your sensory nerves detect the excessive
heat and instantly fire off a message to your motor nerves that says, “Pull
your hand away!” The motor nerves call the proper muscles into action to
move your hand away before you can even “think” about it
...


What a Sensation! The Brain
and the Five Senses
The brain is the master organ of the body in animals with a central nervous
system because it takes in all the information received by the animals’ sense
organs and produces the appropriate responses
...
These three parts are further organized into
four major regions that we present in the following list:
✓ Cerebrum: Also called the telencephalon, the cerebrum is the largest
part of the brain and is responsible for consciousness
...
Each cerebral hemisphere has four lobes
named for the bones of the skull that cover them: frontal, parietal, temporal, and occipital
...

✓ Diencephalon: Found at the center of the brain, the diencephalon is a
structure that consists of the thalamus and hypothalamus
...
At the base of the
hypothalamus is the pituitary gland, which helps maintain homeostasis
in the body by secreting many important hormones
...

✓ Brain stem: Located below the cerebellum, the brain stem is made up
of three structures: the midbrain, the pons, and the medulla oblongata
...

Bet you didn’t know that the spinal cord is actually a continuation of
the brain stem
...


Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire
The human sense organs — eyes, ears, tongue, skin, and nose — help to protect the body
...
Each
sense organ contains different receptors
...
They’re present in
skin, visceral organs (visceral meaning in the abdominal cavity), muscles, and joints
...

Table 18-1 compares the various types of receptors found in an animal’s nervous system
...


Oooh, that smell: Olfaction
If you walk in the door of your home and smell an apple pie baking and peppers and onions sautéing, how do you know that the apple pie is apple pie and
that the pepper and onions are in fact peppers and onions and not eggplant

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and zucchini? The key lies in your olfactory cells (you can remember the
name of these cells by thinking that they “smell like an old factory”); they’re
responsible for your sense of smell
...
They have cilia on one end
that project into the nasal cavity (see Chapter 4 for more on cilia)
...

As you breathe, anything that’s in the air you take in enters your nasal cavity
...
The olfactory cells are chemoreceptors, which means they have protein receptors that
can detect subtle differences in chemicals
...
There, the chemicals
bind to the cilia, generating a nerve impulse that’s carried through the olfactory cells, into the olfactory nerve fiber, up to the olfactory bulb, and directly
to your brain
...
If the scent
is something you’ve smelled before and are familiar with, your brain recalls
the information that has been stored in your memory
...


Mmm, mmm, good: Taste
The senses of smell and taste work closely together
...
That’s because taste buds and olfactory cells
(described in the preceding section) are chemoreceptors designed to detect
chemicals
...
The taste receptor cells within your taste buds
allow you to detect five different types of taste: sweet, sour, bitter, salty, and
umami (savory)
...
Those little bumps are actually papillae; the taste buds exist in
the grooves between each papilla
...
Each taste bud has a pore at one end that allows the chemicals in
the food to enter the taste bud and reach the taste receptor cells
...


Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire
The sense of taste allows you to enjoy food, which you must ingest to live, but
it also serves a higher function
...
This function allows your digestive system to work optimally to
retrieve as many nutrients as possible from food
...
When a sound
wave hits your eardrum, the eardrum moves tiny bones (specifically the malleus, incus, and stapes)
...
When the cilia
move, they create an impulse that’s sent through the cochlea to the eighth
cranial nerve, which carries the impulse to the brain so it can interpret the
information as a specific sound
...
In other words,
they keep you from falling over because they contain fluid within the semicircular canals of the inner ear
...
The cilia transmit impulses to your brain about
angular and rotational movement, as well as movement through vertical and
horizontal planes, all of which helps your body keep its balance
...


Seeing is believing: Sight
Vision is perhaps the most complex of all the senses because it depends
upon the correct structure and function of all the parts of your eye
...
The pupil is the “black hole”
at the very center of your iris; it dilates to allow more light into the eye
and contracts to allow less light into the eye
...

✓ The lens of the eye is located just behind the pupil
...
Specifically,
the lens flattens so you can see farther away, and it becomes rounded
so you can see things that are near to you
...
(People lose the ability of
accommodation as they grow older, prompting the need for glasses
...
This substance gives shape to the
eyeball and also transmits light to the very back of the eyeball, where
the retina lies
...

• Cones detect fine detail and color and work best in bright light
...
(Color blindness occurs when one type of cone is lacking
...
)
Light strikes the rods and cones, generating nerve impulses that travel to
two types of neurons: first to the bipolar cells and then to the ganglionic
cells
...

Approximately 150 million rods are in a retina, but only 1 million ganglionic
cells and nerve fibers are there, which means many more rods can be stimulated than there are cells and nerve fibers to carry the impulses
...


A touchy-feely subject: Touch
Your eyes, ears, nose, and tongue all contain special receptors
...

✓ Mechanoreceptors allow you to feel pressure or fine touches, like a hug,
a handshake, or a gentle stroke
...


Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire
These three types of general receptors are interspersed throughout your
skin’s surface, but they’re not distributed evenly
...
For another thing, some
parts of your skin have more receptors than other parts
...

When your general receptors are activated, they generate an impulse that’s
carried to your spinal cord and then up to your brain
...


Traveling from one end to the other
Before a nerve impulse can enter the brain, it must first pass from one side
of a neuron to the other
...
In this state, the neuron is polarized with
sodium on the outside of its membrane and potassium on the inside
...
)
The outside of a polarized neuron contains excess sodium ions (Na+); the
inside of it contains excess potassium ions (K+)
...
So, the cell becomes
more positive outside and less positive — or negative — inside
...
Sodium ions move inside the neuron’s membrane, causing an action
potential
...
When a stimulus reaches a resting neuron, the gated ion

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channels on the resting neuron’s membrane open suddenly, allowing
the Na+ that was on the outside of the membrane to rush into the cell
...

Each neuron has a threshold level
...
After the stimulus goes above the threshold level,
more gated ion channels open, allowing more Na+ inside the cell
...
In this state, the neuron continues to open Na+ channels all along the
membrane, creating an all-or-none phenomenon
...

When an impulse travels down an axon covered by a myelin sheath, the
impulse must move between the uninsulated gaps that exist between
each Schwann cell
...
During
the action potential, the impulse undergoes saltatory conduction (think
salt, as in the sodium ions that allow this to happen) and jumps from
one node of Ranvier to the next node of Ranvier, increasing the speed at
which the impulse can travel
...
Potassium ions move outside the membrane, and sodium ions stay
inside the membrane, repolarizing the cell
...
With K+ moving to the outside, the cell’s balance
is restored by repolarizing the membrane
...
) Just after the K+ gates open, the Na+ gates close; otherwise, the membrane wouldn’t be able to repolarize
...
The neuron becomes hyperpolarized when there are more potassium
ions on the outside than there are sodium ions on the inside
...
This causes the cell’s potential to
drop slightly lower than the resting potential, and the membrane is said
to be hyperpolarized
...
After the
impulse has traveled through the neuron, the action potential is over,
and the cell membrane returns to normal
...
The neuron enters a refractory period, which returns potassium to the
inside of the cell and sodium to the outside of the cell
...
A protein
called the sodium-potassium pump returns the ions to their rightful sides of
the neuron’s cell membrane
...


Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire
Action Refractory
potential period

Membrane Potential (mV)

50

Figure 18-3:
The transmission
of a nerve
impulse
...
Gaps exist between the
axon of one neuron and the dendrites of the next neuron
...

The gap between two neurons is called a synaptic cleft or synapse
...
However, outside of the brain,
such as when a neuron sends a signal to a muscle cell, nerve impulses are conducted across synapses by a series of chemical changes, which occur as follows:
1
...

At the end of the axon from which the impulse is coming (called the
presynaptic cell because the axon precedes the synapse), the membrane
depolarizes, allowing the gated ion channels to open so they can let in
calcium ions (Ca2+)
...
Synaptic vesicles release a neurotransmitter
...
The synaptic vesicles then
release a chemical called a neurotransmitter into the synapse
...
The neurotransmitter binds with receptors on the postsynaptic neuron
...
The proteins serve as the receptors, and
different proteins serve as receptors for different neurotransmitters —
that is, neurotransmitters have specific receptors
...
Excitation or inhibition of the postsynaptic membrane occurs
...
For example, if the neurotransmitter causes the Na+ channels to open, the membrane of the postsynaptic neuron becomes depolarized, and the impulse is carried through
that neuron
...

If you’re wondering what happens to the neurotransmitter after it binds
to the receptor, here’s the story: After the neurotransmitter produces
its effect, whether that effect is excitation or inhibition, it’s released by
the receptor and goes back into the synapse
...
Then the
presynaptic cell “recycles” the degraded neurotransmitter, sending the
chemicals back into the presynaptic membrane so that during the next
impulse, when the synaptic vesicles bind to the presynaptic membrane,
the complete neurotransmitter can again be released
...


Table 18-2

Characteristics of Common Neurotransmitters

Neurotransmitter

Source

Function

Acetylcholine

Secreted at gaps
between the neurons
and muscle cells

Stimulates or inhibits contraction of muscles, depending on
receptor

Dopamine

Created from amino
acids

Affects movement, emotion,
and feelings of pleasure, and
plays an important role in drug
addiction

Epinephrine

Created from amino
acids

Responsible for fight-or-flight
response

Norepinephrine

Released by postganglionic axons

Increases blood pressure

Serotonin

Produced through
enzymatic reaction
involving tryptophan

Regulates sleep, calms anxiety,
and affects sexual behavior

Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire

The Endocrine System: All Hormones
Are Not Raging
The endocrine system (shown in Figure 18-4) is the system that handles hormone production and secretion within an organism
...


Brain
Hypothalamus
Pituitary gland
Pineal gland
Parathyroid gland
Thyroid gland
Thymus

Adrenal gland
Pancreas

Ovaries
in female

Testes in male
Figure 18-4:
The
endocrine
system
...
Hormones are carried in the bloodstream to
a target tissue elsewhere in the body, where they must be absorbed into the
tissue before they can have an effect
...
Endocrine
glands secrete their products into the bloodstream, which remains within the
body
...
Examples of exocrine gland secretions are sweat and saliva
...


Seeing how hormones work
Hormones are long-distance messengers, carrying their message through the
bloodstream to target cells, the cells that respond to the hormone, throughout the body
...
(Cells that don’t
have receptors for a particular hormone don’t respond to that hormone
...

Hormones in vertebrates can be divided into two groups:
✓ Peptide hormones, such as insulin, are short chains of amino acids; you
can think of them as very small proteins
...

The receptors for peptide hormones are embedded in the plasma membranes of target cells
...
The internal part of
the receptor interacts with molecules inside the cell to cause a change
in behavior
...

✓ Steroid hormones, such as testosterone and estrogen, are lipids, so
they’re hydrophobic (water fearing) and can pass easily through the
hydrophobic layer of the plasma membrane and enter cells
...

Once inside the cell, steroid hormones pass through the cytoplasm of the
cell and diffuse into the nucleus
...
The activated
hormone-receptor complex directly causes a change in the behavior of
the cell, often by acting as transcription factors that turn on the transcription of certain genes
...


Surveying the general
functions of hormones
Hormones play several important roles, whether they come from a plant, an
invertebrate animal, or a vertebrate animal
...
The extremes of having too many or too few growth hormones are obvious — giants or midgets, respectively
...
Hormones also regulate
growth in plants, and you can find out more about that in Chapter 21
...
(Metamorphosis is the process that changes a larva
or caterpillar into a pupa and then into a moth or a butterfly
...
Plant hormones regulate developmental events such as seed germination and flowering
...

But for other animals and plants, reproduction needs to occur during
certain seasons of the year when climate and food supplies are optimal
...

So many different hormones are found in animals, that we can’t possibly tell
you about them all
...


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Table 18-3

Several Important Mammalian Hormones

Hormone

Gland

Function

Adrenaline
(epinephrine)

Adrenal gland

Increases metabolism and glucose
in the blood; constricts some blood
vessels

Aldosterone
(mineralocorticoids)

Adrenal gland

Regulates the balance of salt
and water in the body by causing
kidneys to reabsorb sodium and
release potassium

Antidiuretic
hormone

Pituitary gland

Signals kidneys to retain water

Estrogen

Ovaries

Stimulates growth of the uterine
lining; triggers and maintains
secondary sex characteristics in
females

Follicle-stimulating
hormone (FSH)

Pituitary gland

Stimulates production of eggs and
sperm

Glucagon

Pancreas

Raises glucose (sugar) in the blood

Growth hormone

Pituitary gland

Stimulates growth of bones; promotes metabolic functions

Insulin

Pancreas

Lowers glucose (sugar) in the blood

Luteinizing
hormone (LH)

Pituitary gland

Stimulates ovaries and testes

Melatonin

Pineal gland

Regulates sleep and wake cycles

Oxytocin

Pituitary gland

Triggers contraction of the uterus
and mammary glands (to release
milk)

Progesterone

Ovaries

Supports growth of the uterine lining

Prolactin

Pituitary gland

Stimulates milk production

Testosterone

Testes

Stimulates sperm formation; triggers
and maintains secondary sex characteristics in males

Thyroid-stimulating
hormone

Pituitary gland

Stimulates the thyroid gland

Thyroxine (T 4)

Thyroid

Stimulates and maintains
metabolism

Chapter 19

Reproduction 101:
Making More Animals
In This Chapter
▶ Becoming aware of how asexual reproduction occurs in animals
▶ Getting an up-close-and-personal look at sexual reproduction
▶ Seeing how the birds and bees (and other animals) do it
▶ Figuring out how a cell “knows” where to go and what to do
▶ Exploring the complexities of development and aging

T

his chapter is your chance to find out all about how babies are made
...
Get ready to discover what happens inside
a female’s body to prepare for reproduction, how different types of animals
(including humans) actually mate, how offspring develop prior to birth, and
how gender is determined in humans
...
Also, asexual organisms don’t really die;
instead, they just bud off into new versions of themselves and continue on
...


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Part IV: Systems Galore! Animal Structure and Function
Asexual reproduction occurs by several different methods in a variety of
animals:
✓ Budding happens when a small outgrowth begins on the original organism
...
Several species of invertebrates, including
the hydra, produce offspring by budding
...
Sea anemones are an example of an invertebrate that reproduces
asexually by fission
...
Starfish are among
the animals that use fragmentation to reproduce
...
Yet what makes asexual reproduction an asset
for some species — the fact that it doesn’t allow for change — also makes it
a disadvantage
...
If the disease can easily
kill the organisms, for example, they’ll all die
...

Species ultimately have a better chance of surviving changes if their members
have some differences from one another
...
The new organisms that result
from sexual reproduction develop and grow over time
...
Mating combines the two single cells to produce an
entirely new organism that contains either eggs or sperm
...

The following sections delve into the details of sexual reproduction, from the
cells and mating rituals that make it possible to how humans go about creating new life
...
)

Chapter 19: Reproduction 101: Making More Animals

Getting to know gametes
Gametes are the sex cells of sexually reproducing organisms
...
Each sperm and each egg contain half the
number of chromosomes that are normally present in the whole organism
...

Gametogenesis is the process that produces gametes
...
Human cells, for example,
have 46 chromosomes, so human gametes have only 23
...
We explain exactly how gametogenesis works in
the sections that follow
...
The differences lie in how the animals mate and transfer their gametes
...
Beginning at puberty, human males start producing millions of sperm each day
...

The process of spermatogenesis begins in spermatogonia, cells containing 46
chromosomes
...
When
a human male’s hormones pull the trigger to initiate spermatogenesis, the
spermatogonia go through mitosis to produce cells called primary spermatocytes that also contain 46 chromosomes
...
Each primary spermatocyte undergoes meiosis to produce two secondary spermatocytes
...

2
...

3
...

Spermatozoa is just the technical name for what you know as a sperm
...
The tail is a flagellum that
moves the sperm through body fluids — in other words, it’s what allows
the sperm to swim
...


Oh, oh, oogenesis: Making eggs
Oogenesis is how human females produce eggs, the female gamete
...
These eggs lie dormant from
birth until puberty, at which time the female’s hormones kick-start the eggs
into the menstrual cycle, which continues monthly from puberty until the
woman begins menopause
...
These cells grow in size and mature
into primary oocytes
...
Primary oocytes begin going through meiosis but pause early in the
first half of the process
...

2
...

Ovulation, the release of an egg from an ovary, occurs at the midpoint of
the menstrual cycle
...
Both the secondary oocyte and the polar body
contain 23 replicated chromosomes
...
The secondary oocyte and first polar body complete the second division of meiosis
...
The first
polar body divides equally into two polar bodies
...

The splitting of the cytoplasm, called cytokinesis, is unequal so that the
egg ends up full of cytoplasm
...
Meiosis in one original oogonium produces just one functional egg
...


Chapter 19: Reproduction 101: Making More Animals
In human females, the meiotic division that pauses in the oocyte can remain
paused for 40 years or more! From before a woman is born until her ovulation
ends during menopause, oocytes are in “hang time,” just waiting to develop
into an egg and get fertilized
...


Mating rituals and other preparations
for the big event
Mating in humans can take place whenever a man and a woman are in the
mood to do so
...

Pretend for a moment that you’re a female oyster living in the ocean
...
With that many eggs, your mating process is really left to chance
...
Leaving the continuation of the oyster species to chance is one reason why oysters release such huge numbers of eggs
in the first place
...
Right; if
they did, the ocean would be overflowing with oysters, and pearls wouldn’t
be so expensive
...
Animals have reproductive cycles and specific mating seasons to
ensure this type of scenario doesn’t happen
...
We also fill you in on the
details of human reproductive cycles because they play a huge part in the
continuation of mankind
...
In other words, they need to be attempting to mate at the same
time
...
Often that’s the time
of year when the offspring has the best chance for survival
...
The best time for a fawn
(a baby deer) to be born is in the spring because food is plentiful, temperatures are a bit warmer, leaves are on the trees, and shrubs can provide cover
...
So, backing up six months from
spring puts the mating season for deer around October or November
...
The strongest
buck, which is supposedly the one with the strongest genes, gets to mate and
pass on its genetic material to continue the species
...

For instance, aquatic (water-living) animals that live in the desert reproduce
only when the scarce desert rainfall produces a temporary pond
...
In diapause, the metabolism of the animal is very low, and extreme heat and dry
weather don’t affect it
...
Then, the new generation gets to
sit in the desert in diapause waiting for the next thunderclouds to appear in
the sky
...
Nor
do they suffer angst over whether the other bee will remain committed or
worry about whether their partner will be faithful
...

Although love may not be a requirement for sexual reproduction, attraction
most certainly is
...
During mating rituals, animals (usually males) “show off” their
best features in the hope of proving they’d be good partners
...
Consider doves
...

But before they mate, they build a home (sound familiar?)
...
During the period of time that they’re building the nest,
they take a break and copulate (that’s the formal way of saying they
had sex)
...
When the chicks are old
enough to start feeding themselves (in about two to three weeks), the
adults repeat the reproductive cycle and start courting all over again
...
Secondary sex characteristics
in humans include hair growth and distribution (beards in males), deepening of the voice (in males), increase in muscle mass (males), increase
in amount and distribution of fat (in females), and development of
breasts (in females)
...


Human reproductive cycles
Even though humans are capable of reproducing year-round, reproductive
cycles are still involved
...
Human sexual
reproduction is therefore controlled by the monthly ovarian cycle (the development of the egg in the ovary) and menstrual cycle (the periodic series of
changes associated with menstruation), both of which are controlled by hormones (for more on hormones, see Chapter 18)
...
Believe it or not, the brain runs this process
...
When the levels decline, the hypothalamus
secretes a hormone called gonadotropin-releasing hormone (GnRH) that heads
straight for the pituitary gland (which is also found in the center of the brain)
and stimulates part of the pituitary to secrete follicle-stimulating hormone
(FSH) and luteinizing hormone (LH)
...
As the follicles grow, they release the hormone estrogen
...
LH stimulates the
release of the egg from the follicle in the ovary — in other words, LH triggers
ovulation
...
These hormones
prepare the body for a possible pregnancy by spurring the tissues lining the
uterus to develop thicker blood vessels, which brings more nutrients into the
uterus
...
If fertilization
✓ Has occurred: The fertilized egg implants in the lining of the uterus
and an embryo begins developing
...
The presence
of hCG ensures that estrogen and progesterone production continue so
the lining of the uterus remains nourished by larger blood vessels
...
Therefore, the production of hCG by the embryo
declines after the placenta is up and running
...
Because hCG is produced
solely by fertilized eggs, only women with a fertilized egg in their bodies
should have detectable levels of hCG
...
The lack of FSH and LH
stops the production of estrogen and progesterone, which causes the
lining of the uterus, sometimes referred to as the endometrium, to stop
receiving all that extra nourishment
...
The first day of menstrual flow is the first day of the
menstrual cycle (pictured in Figure 19-1)
...

The ovarian cycle and the menstrual cycle occur simultaneously and are synchronized to each other by hormones, but each cycle consists of different events
...
It occurs in the ovary, takes about 28 days to go from beginning
to end, and is controlled by GnRH, FSH, LH, and estrogen
...
It occurs in the uterus, takes about 28
days, and is controlled by the levels of progesterone and estrogen
...

Not every fertilized egg results in a bouncing baby boy or girl
...
If an
embryo doesn’t produce a sufficient amount of hCG, the pregnancy fails to
continue, and the embryo aborts itself (a spontaneous abortion is another term
for a miscarriage)
...


Shrinking corpus luteum

Full corpus luteum

Ovulation

Mature follicle

Developing follicle

Immature follicle

Developing follicle

Chapter 19: Reproduction 101: Making More Animals

Progesterone

Menstruation

Estrogen

Follicular
phase
Figure 19-1:
The menstrual cycle
...
” If the egg becomes
fertilized and implants in the uterus, the corpus
luteum hangs around to help out with the beginning stages of pregnancy
...
(The progesterone helps keep the lining
of the uterus rich with blood and nutrients for
the developing embryo
...


Notice how we said “in most cases”? About
10 percent of the time, the corpus luteum
hangs out in the ovary far longer than it should
...
When that happens, the corpus
luteum can turn into a cyst, which is aptly called
a corpus luteum cyst
...
Only then does it need
to be removed surgically
...
After all,
the whole point of sexual reproduction is to create a new generation that
contains the genetic information from the previous generations
...

For instance, humans carry 46 chromosomes in each cell, whereas chimpanzees have 48 per cell
...

Eggs are actually surrounded by a layer of proteins on top of the plasma membrane that contains receptor molecules made solely for receiving sperm of the
same species
...
Only human sperm can crack the code to
get into the egg
...
(If your
parents have yet to have this conversation with you, you can let them know
they’re off the hook
...
As you can see in Figure
19-2, the male reproductive system is made up of the penis, the testes, and
the seminiferous tubules
...

The female reproductive system consists of the vagina, the uterus, the ovaries, and the fallopian tubes (see Figure 19-3)
...


Sexual intercourse
In order to prepare the body for sexual intercourse (the insertion of the man’s
penis into the woman’s vagina), men and women engage in activities that
increase arousal (responsiveness to sensory stimulation)
...
This erection allows the penis to stiffen so it can

Chapter 19: Reproduction 101: Making More Animals
remain inside a woman’s vagina during intercourse
...
It has erectile tissue and a glans tip, just like
a penis does
...
This lubrication prepares the vagina for
sexual intercourse so the erect penis can be inserted into it easily
...
The cervix is the bottom end of the uterus,
which extends down into the vagina
...
During sexual intercourse, sperm travel from the man’s
epididymides (tubules in the scrotum that store produced sperm) to his vas
deferens, tubes that carry sperm from the scrotum to the urethra so they can
be ejaculated
...


Urinary bladder
Pubic bone

Vertebrae
Rectum
Seminal vesicle

Prostate gland

Urethra

Bulbourethral
(Cowper's) gland
Anus
Vas deferens
Epididymis

Glans penis

Figure 19-2:
The male
reproductive system
...

From LifeART®, Super Anatomy 1, © 2002, Lippincott Williams & Wilkins

Orgasm
Believe it or not, orgasm, the highly pleasurable climax of sexual intercourse,
serves a physiological purpose
...
The
semen contains the following “ingredients” that help promote fertilization:
✓ Fructose: This sugar gives the sperm energy to swim upstream
...

✓ A pH of 7
...

Orgasm occurs at the height of sexual stimulation and is signaled by muscular contractions and a pleasurable feeling of release
...

The average amount of semen expelled during one ejaculation is less than 1
teaspoon, but it contains more than 400 million sperm
...
Shutting out urine allows the urethra
to be used solely for ejaculation at that time
...
)
In females, the height of sexual stimulation also causes intense muscular contractions and a pleasurable feeling of release
...
The muscular
contractions of the uterus slightly open the cervix, which allows sperm to get
inside the uterus and also helps “pull” sperm upward toward the fallopian tubes
...
They have to travel from wherever they’re deposited in the vagina,
through the muscular cervix, up through the entire uterus, and finally into
the fallopian tubes, which is where fertilization (the joining of sperm and egg)
actually occurs
...

If the sperm does find its way to the egg, it must penetrate the egg in order to
supply it with its 23 chromosomes
...
To get through all that, the
sperm produces enzymes in a structure near its nucleus called the acrosome
...
But the sperm isn’t alone in its efforts
...
After the sperm has successfully joined with the egg, the two
gametes create a cell that contains the full human chromosome count of 46
...
All kinds of animals reproduce sexually
...
Note: We
highlight these animals’ mating styles and zygote formation because they
give an overview of the different strategies for sexual reproduction that occur
in the animal kingdom
...
” (Partheno- is Greek for “virgin” [as in the
Parthenon], and genesis means “production
...
The queen never mates with the drones again because she
doesn’t have to — she has stored their sperm cells inside her body, leaving her in total control of when fertilization occurs
...
Those fertilized eggs develop into females, many of which are
worker bees (these bees are born diploid but never produce gametes,
which means they can’t reproduce)
...
When the queen lays eggs but withholds sperm and
prevents fertilization, the unfertilized eggs develop into male drones
...
(If you’re confused
by what haploid and diploid mean, see Chapter 6
...
The egg becomes fertilized and is deposited outside the
female bird’s body to continue developing until it’s time to hatch
...

Just after fertilization, one spot on the yolk of an egg goes through a
series of divisions called cleavage
...
The blastoderm is the initial cell tissue that begins to develop into
a baby bird; it separates into an epiblast, which is the top layer, and a
hypoblast, which is the bottom layer
...

✓ Earthworms: Earthworms are hermaphrodites, meaning they have both
female and male reproductive parts (specifically ovaries, testes, seminal vesicles, vas deferens, and seminal receptacles)
...

Citella are the external, smooth, nonsegmented parts of an earthworm;
their job is to secrete mucus and help the sperm get from the vas deferens of one worm to the seminal receptacle of the other worm
...
The
sperm and eggs are fertilized inside the cocoon, and the zygotes stay
enclosed in it until they hatch in the soil
...
All planarian worms are hermaphrodites
...
Then they use
their female organs to create zygotes
...

✓ Sea urchins: Male and female sea urchins look exactly the same on the
outside — they both have a ring of genital pores at the center of their
bodies
...
Fertilization
is left to chance, but it’s helped by the fact that sea urchins live in close
contact, their eggs have a sticky coat to which sperm adhere, and ejaculation by any one sea urchin signals the other males to ejaculate too
...
After fertilization
takes place, the term development describes how the fertilized egg becomes
another new organism that possesses a mix of its parents’ DNA
...
Note: We focus on the development of human offspring because that’s most relevant to your life
...


From single cells to blastocyst
After the nucleus of a sperm and the nucleus of an egg fuse, fertilization is
complete, and the new, diploid cell is referred to as a zygote
...
As it travels, the zygote undergoes
cleavage, a rapid series of mitotic divisions that result in a multicellular
embryo (see Step 3 in Figure 19-4)
...
At this
point, the zygote is a solid ball of cells called a morula
...
Zygote divides
Fallopian tube
2
...
Conception
(Implantation)

14 days
after fertilization

Fimbria

Corpus luteum

Figure 19-4:
Fertilization,
conception,
and early
embryonic
and fetal
development of
humans
...
Ovulation
Oocyte is released into fallopian tube

Embryo
(25 days)

Fetus (12 weeks)
Umbilical cord
Placenta

Head
Heart
Tail

Body stalk
(future umbilical cord)

Cell division continues, but the morula becomes filled with liquid, which
pushes the increasing number of cells out toward the periphery of the
embryo’s membrane, forming a hollow ball of cells called a blastula
...
Different layers of cells
become specialized within the blastocyst, taking the first step toward forming specialized tissues:
✓ The flattened cells along the edge of the blastocyst form the trophoblast
...

✓ The sphere of larger, rounded cells that’s destined to become the
embryo is called the embryoblast
...
After the blastocyst “eats” its way into the wall of the uterus, it sinks
into the wall and implants itself
...
If conception occurs, the trophoblast cells of the blastocyst go on
to form the chorion, which becomes part of the placenta
...
Each layer of cells in the gastrula eventually becomes a different type of tissue:
✓ The outer layer of the gastrula is the ectoderm, which develops into the
skin and nervous systems
...

✓ The innermost layer is the endoderm, which gives rise to the linings of
your digestive and respiratory tracts, as well as organs such as the liver
and pancreas
...
An egg can be fertilized, but a
woman isn’t pregnant until the blastocyst is rooted in her uterine wall where it
can develop further
...
That’s because every organ in your body forms during
the embryonic period — essentially the first trimester of pregnancy
...
This cellular migration is referred to as morphogenesis
because it gives the embryo a shape (morph- is Greek for form or structure)
...
The chorion combines
with tissues created by the mother to become the placenta, an organ that’s
filled with blood vessels and provides a large surface area for the exchange of
gases, nutrients, and wastes
...
In humans, the allantois eventually becomes the body stalk and

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then the umbilical cord, which connects the fetus to the placenta (both of
which are shown in Figure 19-4)
...
Amniotic fluid cushions movements created
by the mother and protects the developing organism from bumps
...

The genetic material in the cells of amniotic fluid matches that of the developing embryo, so doctors can use amniocentesis (a procedure that uses a needle
to remove a small amount of amniotic fluid for genetic testing) to see whether
the embryo will have a genetic defect
...
Cells that split off the neural tube and form the neural
crest become the teeth, bones, skin pigments, and muscles of the skull, for
example
...


Fetal development and birth
In humans, the fetal period encompasses the last six months of pregnancy,
or the second and third trimesters
...
All fetuses do
in the uterus is continue to grow and develop features such as hair and nails
...

Prostaglandins and the hormone oxytocin cause the uterus to contract, but
the initial production of these hormones is thought to be triggered by an
as-yet-unknown chemical produced by the fetus
...
If labor doesn’t
begin naturally, medical personnel give the mother prostaglandin suppositories and/or synthetic oxytocin — called pitocin — to induce labor
...
A life begins, and development continues
...


Chapter 19: Reproduction 101: Making More Animals

Differentiation, Development,
and Determination
We bet you never realized that a large part of who you are is controlled by
three D’s: differentiation, development, and determination
...
Development is
the overall process of an organism going through stages of differentiation;
over time, the changes occurring at the cellular level during development
become visible
...

Think about this: You started out as one tiny cell
...
As that first cell divided, some of its descendants became determined to be heart cells, skin cells, brain cells, and liver cells
...
What makes each cell type
different from the other isn’t what kind of genetic information it has but how
it uses that genetic information
...

If you think of the different types of cells in your body as workers that each
have a different job to do, then it makes sense to think about each worker
needing a different set of tools
...

And to get proteins, cells access the genes in the DNA that contain the blueprints for those proteins
...

In the next few sections, we look at the signals that direct cells to become
specialized for certain tasks in the body
...


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The ability to become any type of cell
Initially, each and every cell in your body (and the bodies of many other animals) has totipotency — the ability to develop into any kind of cell or even a
whole organism
...

Differentiation, then, occurs as a result of signals that cause cells to use only
some of the genetic information they contain
...
Following are just a couple
of the experiments scientists have conducted to try and figure out how to
reset the programming of a cell:
✓ Two researchers, Robert Briggs and T
...
King, tested tadpole cells to
see whether they lost the ability to be reprogrammed and, if so, when
they did
...
In other words, one
cell from a blastula could develop into a whole new tadpole
...

✓ Another researcher, J
...
Gurdon, had success in “growing” normal frog
embryos from adult frog skin cells
...
When the nucleus from the differentiated skin cell was placed into the environment of the egg cell cytoplasm,
the nucleus directed the growth and development of a frog tadpole that
was genetically identical to the frog that had donated the nucleus from
its skin cell
...

Gurdon’s experiment was the first successful attempt to clone an
organism — produce an organism that’s genetically identical to the
organism that donates the transplanted nucleus
...

Animal cloning experiments demonstrate that the nuclei of differentiated cells
retain all the genetic information necessary to become other cell types
...
You know how you can grow a whole plant from a cutting of another
plant? The cutting doesn’t contain roots, but it’s able to grow them because
it can still access the genes necessary for the function of root cells
...


The factors that affect differentiation
and development
When embryonic development begins, all the cells in the embryo are totipotent until signals around the cells make the cells turn into nervous system
cells, muscle tissue cells, heart cells, lung cells
...
Most
developmental changes depend upon signals in the environment of embryonic cells that tell them exactly what to do and when to do it
...
Cells that wield
this power are called organizers, and they exert their influence by secreting certain chemicals or by interacting directly with target cells through
cell-to-cell contact
...
The eyes start out as bulging outgrowths (or optic
vesicles) on the sides of the early brain
...

✓ Cell migration: When cells move to new locations during development,
that’s considered cell migration
...
Once there, they attach to similar cells and differentiate to become a particular kind of tissue
...

✓ Homeotic genes: Special genes that turn other genes on or off are
homeotic genes
...
The proteins
produced from homeotic genes interact with DNA, affecting the expression of other genes
...
When certain genes are
turned off, the protein normally created is withheld so it can’t affect
development
...
The powerful effect of homeotic genes can be seen
in genetic studies of fruit flies
...

Several years ago, a stretch of DNA about 180 nucleotides long (that’s
not very big in the DNA world) was found in most of the homeotic genes
in many species
...
A homeobox is the sequence in
the homeotic gene that remains unchanged generation after generation
...

✓ Programmed cell death: Also called apoptosis, programmed cell death
causes cells to commit suicide at particular times during development
in order to remove cells from the developing organism
...

✓ Cytoplasmic factors: These can create different local environments in
the cytoplasm of a cell, leading to different developmental fates for the
descendents of the cell
...
So,
some cells may get more of certain cytoplasmic factors than other cells
...
For instance, differences in the cytoplasm of cells
early in development establish the anterior-posterior axis in the embryo,
which ultimately leads to the differentiation of the head from the rest of
the body
...
Then they take control of the actual
appearance of the body
...


Gender differentiation in humans
Humans are no strangers to the effects of hormones during development
...

In the very early stages of development, human fetuses have two sets of
ducts: one for the female reproductive system, and one for the male reproductive system
...
Humans remain in this stage until about seven weeks after
fertilization (about the end of the second month of pregnancy), which is why

Chapter 19: Reproduction 101: Making More Animals
an ultrasound done any earlier than this time can’t tell the sex of the developing embryo
...
)
The two sets of ducts are the Wolffian ducts, which eventually become the
male vas deferens, epididymis (on the testes), and seminal vesicles, and the
Müllerian ducts, which eventually become the oviducts, uterus, and vagina
...
Of the 46 human chromosomes, the last pair — the two
Chromosomes 23 — are either two X chromosomes or an X and a Y chromosome
...
If two
X chromosomes are inside the cells of the developing reproductive system, the
female ducts develop, and the male ducts disintegrate
...

The following sections provide the specifics on how primary sex characteristics develop and list some of the ways that can happen incorrectly
...
SRY contains the blueprint for a protein
called testes determining factor (TDF), which is a transcription factor that
interacts with DNA to turn on the transcription of the genes necessary for
testes development
...
)
After the testes are formed, they begin to secrete the hormone testosterone (in
the form dihydrotestosterone, or DHT)
...

The tubules necessary for ejaculation of semen are complete at about 14 weeks
of gestation (which is the beginning of the second trimester of pregnancy)
...
The urogenital tubercle
becomes the glans penis in the male, the urogenital folds become the shaft of
the penis, and the urogenital swellings become the scrotum
...


How girls become girls
The absence of DHT in a fetus is what spurs the development of female
external genitalia
...


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A female’s external genitalia develop even if the internal genitalia fail to
develop
...


Problems with sexual development
The complex process of sexual differentiation involving genes and hormones
isn’t without error
...
Embryos with an abnormal androgen
receptor can’t bind the DHT necessary to produce male genitalia
...

✓ Hermaphrodites: People with some male and some female characteristics are hermaphrodites
...
In embryos that oversecrete adrenal androgens (hormones that
are involved in the normal synthesis of DHT and testosterone), a genetic
female may have masculinized external genitalia complete with a penis
but have normal ovaries and other female internal reproductive structures
...

✓ Klinefelter’s syndrome: Males with Klinefelter’s syndrome have two X
chromosomes and one Y chromosome (XXY)
...
As a result, male secondary sex characteristics, such as facial hair, may not develop completely,
and the male is usually infertile
...
Treatment with hormone therapy can greatly reduce
these effects and allow males to develop more normally and have
normal sex lives
...
First, a genetically female (XX) individual
may be missing part or all of one of the X chromosomes, resulting in
an XO individual (a person with only one sex chromosome, an X) that’s
neither completely female nor male
...
This deletion prevents development of testes, so no DHT
is produced
...
Women with Turner syndrome are often shorter
than other women, may have extra folds of skin around the neck, and
may fail to enter puberty
...


Part V

It’s Not Easy Being
Green: Plant
Structure and
Function

P

In this part
...
Yet plants are also remarkable in their own right
...
You wouldn’t fare so well, but a plant would be just
fine because it can make its own food
...

Not too shabby for an organism that can’t make a sound,
huh?
In this part, you get to know all about the structure and
function of the green things that call planet Earth home
...
After all, it has flat leaves for gathering
sunlight, roots for drawing water up from the soil, and flowers and fruits
for reproduction
...

In this chapter, we present the fundamental structures of plants, how they
get the energy they need to grow, and their reproductive strategies
...
Plants have two basic organ systems: a root system (which exists
underground) and a shoot system (found aboveground)
...
The shoot system ensures the plant gets enough sunlight to
conduct photosynthesis; it also transports water upward from the roots and
moves sugars throughout the plant
...

Biologists look at the types of tissues a plant has to help them classify plants
into four different groups
...


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Part V: It’s Not Easy Being Green: Plant Structure and Function

Plant tissues
All plants have tissues, but not all plants possess all three of the following
types of tissues:
✓ Dermal tissue: Consisting primarily of epidermal cells, dermal tissue
covers the entire surface of a plant
...

✓ Ground tissue: This tissue type makes up most of a plant’s body and
contains three types of cells:
• Parenchyma cells are the most common ground tissue cells
...

• Collenchyma cells have thick cell walls in order to help support
the plant
...

✓ Vascular tissue: The system of tubules inside a plant that carries nutrients around is made up of vascular tissue
...
Vascular tissue also contains the vascular cambium, a tissue
of cells that can divide to produce new cells for the xylem and phloem
...
You can see
the basic cells and structures of a vascular plant in Figure 20-1
...

✓ Ferns have vascular tissue, but they don’t produce seeds
...


Chapter 20: Living the Life of a Plant
✓ Angiosperms (or flowering plants) have vascular tissue and produce
both flowers and seeds
...

• Dicots, like beans, oak trees, and daisies, have seeds that contain
two cotyledons
...


Mesophyll

Phloem
transport
Vascular
bundle

H20

Stomate

Root hairs
Root
Root apex
Root cap

Table 20-1 presents several of the key structural differences between monocots and dicots
...
All plant cells have
primary cell walls made of cellulose, but the cells of woody plants have extra
reinforcement from a secondary cell wall that contains lots of a tough compound called lignin
...
Plants that live year after year, called
perennials, may become woody
...
You can see these differences most clearly if you look
at a cross section (a section cut at right angles to the long axis) of a stem
...

When you look at a cross section of the stem of an herbaceous dicot, you see
that
✓ The center of the stem consists of pith (a soft, spongy tissue), which has
many thin-walled cells called parenchymal cells
...

✓ The vascular tissue is organized in vascular bundles that contain both
xylem and phloem, as well as some vascular cambium (all of which are
described in the earlier “Plant tissues” section)
...


Chapter 20: Living the Life of a Plant
✓ Outside the vascular bundle ring is the stem’s cortex
...

✓ On the surface of the stem are the epidermis and the cuticle
...
As they grow, however, the bundles merge with each other to form
rings of vascular tissue that circle the stem
...

✓ The xylem tissue forms a ring around the pith
...
(You can count these rings in the stem of a tree to tell how
old it was when it was cut
...

The inner part of a woody stem is called heartwood
...
Outside the heartwood is the sapwood, newer
layers of xylem tissue that transport water and minerals up through the
stem
...
As the stem
grows, the vascular cambium divides to produce new xylem cells toward
the inside of the stem and new phloem cells toward the outside of the
stem
...
The phloem of
woody plants gets pushed farther and farther outward as the xylem
tissue increases in size year after year
...

The only phloem that serves to transport materials through the woody
plant is the phloem that’s newly formed during the most recent growing
season
...
Bark includes the outermost cells of the stem and a
layer of cork cells just beneath that outermost layer
...


Cambrium
Phloem

Obtaining Matter and Energy for Growth
The biggest difference between plants and animals is how they get the matter
and energy they need for growth
...
Plants absorb sunlight
and use that energy to make glucose from carbon dioxide and water during
the process of photosynthesis (we describe photosynthesis in detail in
Chapter 5); glucose is the food plants can use as a source of energy or matter
for growth
...
Shoots
grow upward, bringing leaves toward the Sun
...

✓ The root system absorbs water and minerals from the soil
...
Minerals perform
the same function for plants as they do for you — they improve general
metabolism by helping enzymes function properly
...


Chapter 20: Living the Life of a Plant
✓ Stomates in the leaves allow plants to take carbon dioxide from the
atmosphere and return oxygen to it
...
Also, photosynthesis produces oxygen when the hydrogen and oxygen atoms in
water are separated
...

Plants extract energy from food molecules the same way animals do — by
cellular respiration (see Chapter 5 for more on cellular respiration)
...
During the day, however, photosynthesis absorbs so
much carbon dioxide and releases so much oxygen that plant respiration
isn’t detectable
...


Going It Alone: Asexual Reproduction
Plants that reproduce asexually make copies of themselves in order to produce offspring that are genetically identical to them
...
The
disadvantage is that all the offspring are genetically identical, which decreases
the ability of the population to survive changes in the environment
...
Other ways a plant can reproduce asexually include
fragmentation, a form of asexual reproduction that involves pieces of an individual growing into new individuals
...
Likewise, if you cut a potato into pieces, each piece that has an “eye”
can produce a new potato plant
...

Other plants, such as strawberry plants, produce special structures that
help them spread asexually
...
Wherever that stolon starts to put roots down is where a new strawberry plant grows
...


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Part V: It’s Not Easy Being Green: Plant Structure and Function

Mixing Sperm and Eggs:
Sexual Reproduction
Plants do have sex, believe it or not
...
Then a sperm and an egg meet, creating offspring that have different
combinations of genetic material than the parent plants
...


The life of a plant
The life cycles of plants are a bit more complicated than those of animals
...
In
plants, however, gametes can almost have a life of their own
...
Here’s a breakdown
of the cycle:
1
...

2
...

The gametophyte step of the plant life cycle is a fundamental difference
between plants and animals
...
In plants, there’s
a little break between meiosis and the production of sperm and eggs
...

3
...

In animals, sperm and egg are produced by meiosis, but in plants, meiosis occurs to produce the gametophyte
...
The gametes merge, producing cells called zygotes that contain the
same number of chromosomes as the parent plant (so the zygotes are
diploid)
...
Zygotes divide by mitosis and develop into sporophytes so the life
cycle can begin again
...


MITOSIS
MITOSIS
Gametophyte
(n)

Gametes
(n)

The plants you see when you go for a walk in the woods may be sporophytes
or gametophytes; it all depends on the type of plant you’re looking at
...
If you see little structures like flagpoles sticking off the moss,
then you’re looking at a sporophyte
...
Inside the little flags, called capsules, meiosis is occurring to produce spores
...
If you look on the back of a fern’s
leaves, you can find little brown structures that seem dusty to the touch
...
Fern gametophytes are teeny — about as big
as the fingernail on your pinky — making them very tough to find in the
wild
...
The gametophyte generation in conifers is very small and contained within their cones
...
In flowering plants, the gametophyte generation is very small and contained
within the flowers
...
Flowers form on specialized shoots of
the plant, and they have specific parts
...

✓ Sepals are the lowest layer of leaves on the flower
...

✓ Petals are modified leaves that are often brightly colored to attract pollinators (see the next section for more on pollinators)
...
Each stamen consists of a
threadlike filament and a little sac called the anther
...

✓ Pistils are the female parts of a flower
...
Inside the ovary, meiosis and mitosis produce the
female gametophyte and the egg, which are housed inside an ovule
...
Pollen lands on the
stigma and then travels down through the style to deliver sperm to the
eggs inside the ovary
...

Some flowering plants, like grasses, are wind pollinated, which means they
make lots and lots of pollen and trust the wind to blow it to the right place
...

Here’s how different plants attract their animal pollinators:
✓ Bird- and bee-pollinated plants are usually brightly colored to attract
the animals; they may also provide nectar to encourage visits
...
These runways are invisible to human eyes but visible to the bees, who can see ultraviolet light
...
In this case,
the wasps attempt reproduction with the flowers and get covered with
pollen before moving on to the next flower to try again
...

✓ Bat- and moth-pollinated flowers are usually white so they’ll be more visible at night, which is when they open
...
The pollen tube grows down through the flower’s
style so the sperm cells inside the pollen can be delivered right to the ovules
inside the flower’s ovary
...


Embryo

Endosperm (3n)

Fertilized egg (2n)

FERTILIZATION
Antipodals
Polar nuclei
Synergids
Egg
Tube nucleus
Sperm nuclei
Pollen tube

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After pollination has occurred, two sperm nuclei enter the ovule (the part of
the ovary that contains the egg and develops into the seed after fertilization),
and one fuses with an egg to form the zygote
...
In flowering plants, the
fusion of two sperm cells, one with an egg and one with the polar nuclei, is
called double fertilization
...
The
first cell division produces two cells: one large, one small
...

Additional cell divisions form the embryo in such a way that the cells at
the bottom grow downward to become roots, and the cells at the top grow
upward to become shoots
...
The cotyledons, or
seed leaves, develop at the top end of the embryo; they’re temporary structures that serve as nutrient storage sites for the developing plant
...


A little protection for the embryo: Seeds
Seeds are protective structures that contain plant embryos and nutritive
tissue to support the embryo until it can survive on its own
...
After a seed develops, it usually dries out, and its water content drops
very low
...
So the seeds that you
buy in a little packet at the local nursery are very much alive, but they’re in a
state similar to that of a hibernating bear
...
As water becomes available, the embryo’s metabolism
speeds up, and it begins to grow by using the stored food inside the seed
...


Chapter 21

Probing into Plant Physiology
In This Chapter
▶ Moving water and other nutrients through plants
▶ Getting sugars where they need to go
▶ Triggering plant responses with hormones

P

hotosynthesis (described in Chapter 5) isn’t the only life-sustaining
process carried out by plants
...
Their hormones,
meanwhile, are sending messages to promote growth toward sunlight and
blossoming, among other things
...
Here, you
discover the processes plants use to transport nutrients, fluids, and sugars
throughout their bodies
...


How Nutrients, Fluids, and
Sugars Move through Plants
Just like you have a circulatory system that moves food and oxygen throughout your body, plants have a system to move nutrients, fluids, and sugars
throughout their bodies
...
) The following sections fill you in on the different nutrients plants
must absorb to stay healthy as well as how they move sugars from their
leaves and water from their roots (without losing too much of it)
...
They also need mineral elements to build their molecules
and make sure their enzymes are working properly
...

Plants get carbon, hydrogen, and oxygen by taking carbon dioxide from the
atmosphere and water from the soil
...

Plants obtain their necessary mineral elements from the soil as well
...
Macronutrients help with molecule construction, and micronutrients act
as partners for enzymes and other proteins to help them function
...
Table 21-1 lists the specific macro- and micronutrients plants
absorb from soil
...

Hopkins Café, Mighty Good
...
All of these elements are macronutrients
for plants, with the exception of iron, which is considered a micronutrient
...
Without carbon, hydrogen, and oxygen (from carbon dioxide
and water), plants can’t grow at all
...

We list these problems and the mineral deficiencies they’re associated with
in Table 21-2
...
To understand how these processes work, you first need to know one
key feature of water: Water molecules tend to stick together, literally
...
The stickiness of water helps keep the water molecules
together when you drink water through a straw — a process that’s very similar to one of the methods plants use to move water through their bodies
...
Root cells have a higher concentration of minerals than the soil they’re in, so during osmosis, water
flows toward the higher concentration of dissolved substances found in
the root cells
...

✓ Capillary action: This causes liquids to rise up through the tubes in
the xylem of plants
...
The adhesion forces water to be
pulled up the column of vessel elements in the xylem and in the tubules
in the cell wall
...
As water evaporates through the
stomates in the leaves (or any part of the plant exposed to air), it creates a negative pressure (also called tension or suction) in the leaves
and tissues of the xylem
...
When water molecules stick to each other through cohesion (where like — as opposed to different — substances stick together),
they fill the column in the xylem and act as a huge single molecule of
water
...

The back and forth of transpiration and cohesion is known as the
cohesion-tension theory
...
The suction you apply to the straw is like the evaporation
from the leaves of the plant
...


Chapter 21: Probing into Plant Physiology

Water plus sap equals
...
They’re
a mixture of water and sap, a sugar solution
from the phloem (Chapter 20 describes this and
other elements of a plant’s structure)
...
(We describe
how this occurs in the nearby “Transporting
water and other nutrients from the ground up”
section
...
Unlike xylem, which can only
carry water upward, phloem carries sap upward and downward from sugar
sources to sugar sinks
...

✓ Sugar sinks are plant organs, such as roots, tubers, or bulbs, that consume or store sugars
...
First, sugars are loaded into phloem cells called sieve tube elements
within sugar sources, creating a high concentration of sugar at the
source
...

2
...

During osmosis, water moves into the areas with the highest concentration of solutes (in this case, sugars)
...
The inflow of water increases pressure at the source, causing the
movement of water and carbohydrates toward the sieve tube elements
at a sugar sink
...
As water flows from the tank into the hose, it pushes the
water in front of it down the hose
...
Sugars are removed from cells at the sugar sink, keeping the concentration of sugars low
...
But
before the sugar sink can turn into a sugar source, carbohydrates in a
sink are actively transported out of the sink and into needy plant cells
...

Sugar sinks that store carbohydrates can become sugar sources for plants
when sugars are needed
...
Whenever a plant needs
sugar, like at night or in the winter when photosynthesis doesn’t occur as well,
the plant can break down its starches into simple sugars, allowing a tissue
that would normally be a sugar sink to become a sugar source
...
As long as
a plant has a continuous incoming source of minerals, water, carbon dioxide,
and light, it can fend for itself
...

The cuticle is a layer of cells found on the top surfaces of a plant’s leaves (see
Figure 21-1)
...
Many plants have cuticles that contain waxes that resist the movement of water into and out of a leaf, much like wax on your car keeps water
off the paint
...
(An individual opening is
called a stomate, or stoma; several openings are called stomates, or stomata
...
However, if
the stomates are open too long or on a really hot day, the plant can lose too
much water
...

Guard cells can swell and contract in order to open and close the stomates
...
At night, when photosynthesis isn’t occurring, the guard cells release
some water and collapse together, closing the stomates
...
They have long, pointy structures called
stylets that let them suck sap right out of the
plant phloem
...
An aphid can stay attached to a plant
for hours, sucking out the sap all the while
...
The aphids fill up, leaving the
plant starved of its sugar mixture
...
They allow aphids to attach to plants
and insert their stylets, and then they cut the
aphids away but leave the stylets embedded
in the plants
...


Epidermis

Mesophyll
Water-filled cells
Water-filled xylem
Figure 21-1:
A plant’s
cuticle and
guard cells
keep it from
losing too
much water
...
Then,
during the day when it’s hot and dry, they keep their stomates closed to conserve water, performing photosynthesis with the carbon dioxide they stored
during the night
...
Plant hormones control many of the plant behaviors you’re used to seeing, such as the ripening of fruit, the growth of shoots
upward and roots downward, the growth of plants toward the light, the dropping of leaves in the fall, and the growth and flowering of plants at particular
times of the year
...
If a plant receives equal light
on all sides, its stem grows straight
...
This may seem backward, but when
the shady side of the stem grows, the stem, in its crookedness, actually
bends toward the light
...

✓ Gibberellins promote both cell division and cell elongation, causing
shoots to elongate so plants can grow taller and leaves can grow bigger
...

✓ Cytokinins stimulate cell division, promote leaf expansion, and slow
down the aging of leaves
...

✓ Abscisic acid inhibits cell growth and can help prevent water loss by
triggering stomates to close
...

✓ Ethylene stimulates the ripening of fruit and signals deciduous trees to
drop their leaves in the fall
...

Some of the flavor-making processes that occur in fruits happen while
the fruits are still on the plant
...

That’s why you can buy a big, beautiful tomato at the grocery store and
take it home only to discover that it doesn’t have much flavor — it was
probably picked unripe and then treated with ethylene
...


For Dummies Part of Tens chapter is meant to contain some fun facts or useful information
...
In Chapter 22, you can read about
ten fascinating biology discoveries
...
) In Chapter 23, we provide a list of ten
pretty interesting ways that biology affects your life
...
We list them in no particular order because they’ve all made a
significant impact on the advancement of biology as a science and increased
what people know and understand about the living world
...
That year, a Dutch cloth merchant named Antony van
Leeuwenhoek discovered the microbial world by peering through a homemade microscope
...
His discovery of a previously unseen universe not only turned
people’s worldviews inside out but also laid the foundation for the understanding that microbes cause disease
...
Fleming
was studying a strain of staphylococcus bacteria when some of his petri
dishes became contaminated with Penicillium mold
...


344

Part VI: The Part of Tens
The compound penicillin was purified from the mold and first used to treat
infections in soldiers during World War II
...


Protecting People from Smallpox
Would you believe that the idea of vaccinating people against diseases such
as smallpox, measles, and mumps originated in ancient China? Healers there
ground up scabs taken from a smallpox survivor into a powder and blew this
dust into the nostrils of their patients
...


Defining DNA Structure
James Watson and Francis Crick figured out how a code could be captured
in the structure of DNA molecules, opening the door to an understanding
of how DNA carries the blueprints for proteins
...
Using metal
plates to represent the bases, they built a giant model of DNA that was
accepted as correct almost immediately
...

This identification of a genetic defect, and the realization that this defect
causes a disease, opened the floodgates of genetic research
...
Genetic
tests for these diseases are available to detect whether an unborn baby has
a defective gene or whether two potential parents would likely produce an
affected baby
...


Chapter 22: Ten Great Biology Discoveries

Discovering Modern Genetic Principles
Gregor Mendel, a mid-19th century Austrian monk, used pea plants to perform the fundamental studies of heredity that serve as the basis for genetic
concepts to this day
...

Through his experiments, Mendel was able to establish that genetic factors
are passed from parents to offspring and remain unchanged in the offspring
so that they can be passed on again to the next generation
...


Evolving the Theory of Natural Selection
Charles Darwin’s study of giant tortoises and finches on the Galapagos
Islands led to his famous theory of natural selection (also known as “survival of the fittest”), which he published in his 1859 book titled On the Origin
of Species
...
These
better-suited variations tend to thrive in the given area, whereas less-suited
variations of the same species either don’t do as well or just die off
...
The significance of Darwin’s theory of natural selection can be seen
today in the evolution of antibiotic-resistant strains of bacteria
...
As Schleiden described the
plant cells he’d been studying, Schwann was struck by their similarity to
animal cells
...

✓ The cell is the smallest unit of living things
...


345

346

Part VI: The Part of Tens

Moving Energy through the Krebs Cycle
The Krebs cycle, named for German-born British biochemist Sir Hans Adolf
Krebs, is the major metabolic process that occurs in all living organisms
...
Defining how organisms use energy at the
cellular level opened the door for further research on metabolic disorders
and diseases
...
Today, PCR is used for
✓ Making lots of DNA for sequencing
✓ Finding and analyzing DNA from very small samples for use in forensics
✓ Detecting the presence of disease-causing microbes in human samples
✓ Producing numerous copies of genes for genetic engineering

Chapter 23

Ten Ways Biology
Affects Your Life
In This Chapter
▶ Seeing how biology provides you with the essentials (food, clean water, and life)
▶ Discovering how humans manipulate organisms to create designer genes, medicines,

and more

S

ometimes science seems like something that happens in a lab somewhere far removed from everyday life
...
Following is a rundown of
ten important ways that biology affects your life
...
Either way, you just may be surprised by a couple of them
...
So you can thank the process of photosynthesis (covered
in Chapter 5) the next time you sit down to a luscious-looking salad or steak
dish
...
People do too
...


Putting Microbial Enzymes to Work
Microbes aren’t just for making foods; they have a wide variety of industrial
applications too
...
If you take vitamin C, chances are that vitamin was produced
by a fungus
...
So you see, not all microbes are to
be feared
...


Designing Genes
The food you eat could very likely contain genetically modified organisms
(GMOs) — living things whose genes have been altered by scientists in order
to give them useful traits
...


Obtaining Fossil Fuels for Energy
The fossil fuels that power modern society are the remnants of photosynthesis from long ago
...
When these living things died, they were deposited in such a way that
their remains converted into coal, natural gas, and oil
...
But maybe one solution to the problem lies in mimicking the green organisms that stockpiled this energy in the first place —
people could act like plants and go solar!

Causing and Treating Infectious Disease
Whenever you get sick from an infectious disease, such as a cold or strep
throat, you’re dealing with the reproduction of an alien invader
...
Also, whenever you take an antibiotic, you’re taking a medicine made
by an organism such as a fungus or a bacterium
...
If your cells weren’t functioning, your tissues, organs, and
organ systems wouldn’t be either
...
Wetlands are areas
that are saturated by water most of the time
...
As
water slowly filters through wetlands, plants and microorganisms have time
to absorb human wastes such as fertilizers and sewage, cleaning the water
and making it safer for humans and other animals to consume
...
Unfortunately, wetlands are under
incredible pressure from development and oil exploration, and they’re disappearing at a rapid rate
...

Bacteria break down the organic matter in sewage, helping to clean the water
before it’s released back into the environment
...
Case in point: You meet someone you’re attracted to, signals cause hormones to be released, and suddenly your conscious mind isn’t
making all the decisions
...
During that time, your body went
through an incredible transformation based solely on the signals from these
potent chemical messengers
...
These super-resistant cells multiply and take
over the available space
...
This fact explains why
sometimes doctors don’t have the drugs to help people who are infected with
an antibiotic-resistant bacteria, such as MRSA (which stands for methicillinresistant Staphylococcus aureus)
...
If you need an example, consider the case of polar bears
...
Not quite so noticeable, but also endangered, are 1,900
other species of plants and animals
...
Each species needs certain conditions and resources to thrive, and the sheer number of humans on
Earth is threatening to overwhelm many ecosystems
...
For example, as humans develop coastal regions, we’re drastically
reducing the area of our estuaries, which are important breeding grounds for
many species of fish
...
(Up to 80 percent of
fish species that are harvested commercially spend some part of their lives in
estuaries
...
See eukaryotic cells
alleles, gene, 105
alveoli, lung, 56
amino acids
essential versus nonessential, 251
highly conserved sequences, 193
mRNA codons, 119–123
nitrogen cycle, 181–182
protein building blocks, 39–41
ammonification, 181-182
amoebas
...
See also human beings;
vertebrates
carbon cycle, 179–180
cloning, 314
differences from plants, 12, 52–53
food consumption strategies, 241–242
GMO benefits/concerns, 138–140
hormone functions in, 293–294
introduced species, 148
population growth effects on, 145–146
species extinction, 146–147
annual plants, 324–325
antibiotics
bacterial resistance, 194, 271–272, 350
biology and, 348
penicillin, 343–344
antiviral drugs, 273
apoptosis, 316
appendicular skeleton, 212–213
Archaea, domain, 153
archaens, 149
Archaeopteryx (bird fossil), 15
Ardipithecus ramidus, 199
arteries, 228
arthritis, 276
artificial selection, 187–188
asexual reproduction
cell division, 81–82
methods, 295–296
plants, 327
atherosclerosis
...
See Krebs cycle
Australopithecus afarensis, 199, 202
Australopithecus anamensis, 199, 202
autoimmune diseases, 276
autonomic nervous system, 278–279
autosomes, 98–99
autotrophs, 69, 173–175
auxins, 340
axial skeleton, 212–213

•B•
bacteria
...
See life, chemistry of
biodiversity
importance of, 143–144
population growth impact on, 145–146
preserving, 144
protecting, 147–148
species extinction, 146–147
biogeochemical cycles
...
See also circulatory systems
bone marrow production, 213–214
capillary exchange, 235–236
clotting factors, 239–240
immune defenses, 265
oxygen diffusion, 226–227
platelets and plasma, 239
pulmonary/systemic circulation, 234–235
red blood cells, 237–238
white blood cells, 238
blood pressure, systolic/diastolic, 233
blue-green algae
...
See skeletal systems
bovine growth hormone (BGH), 138–139
brain
major parts/regions, 282
as the master organ, 278
reflex actions, 281–282
role in reproductive cycle, 301
Briggs, Robert (scientist), 314
bryophytes, 322
buffering agents, 35

•C•
Calories, 76–77
cancer and aging, 122, 344
capillaries, 228
carbohydrates
basis for life, 36–39
carbon cycle, 179–180
making wise food choices, 250
plasma membrane role, 54
carbon cycle, 179–180

Index
carbon dating, 195
carbon fixation, 72
carbon-based molecules
as basis for life, 36
carbohydrates, 36–39
lipids, 43–45
nucleic acids, 41–43
proteins, 39–41
cardiac cycle
...
See helper T cells
CD8 cells (cytotoxic T cells), 270–271
cell differentiation
basics of, 127–128
embryonic, 315–316
gene regulation, 313–316
sexual development, 316–318
totipotency, 314–315
cell division
aging and, 275–276
cancer and uncontrolled, 122
cell cycle, 85–87
DNA mutations, 124–125
DNA replication, 82–85
genetic variability, 96–99
interphase, 87–88
meiosis, 10, 91–95
mitosis, 88–90
reproduction, 81–82
stem cells and, 128
cell membrane
...
See also eukaryotic cells; prokaryotic
cells
basic structures and functions, 47–48
communication across membranes,
209–210
DNA in, 41–43
elements/electrolytes found in, 31
origins of cell theory, 345
origins and properties of life, 10, 13–15
cellular respiration
...
See also cell division;
meiosis; mitosis
characteristics and functions, 57
gender determination, 98–99
gender differentiation, 316–318
Human Genome Project, 17–18, 135–137
meiosis, 91–95
chylomicrons, 252
cilia, 52, 57, 264
circulatory systems
basic functions, 12, 227
closed systems, 228, 237–240
countercurrent exchange systems,
223, 229
heart function in humans, 230–237
open systems, 227–229
oxygen diffusion, 226–227
red blood cell production, 213–214

353

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Biology For Dummies, 2nd Edition
class, organism organization, 153–156
classification systems, eukaryote, 152–153
clean technology, environmental, 147–148
cloning, 314
Clostridium botulinum, 261
codons, 119–123
coenzymes/cofactors, enzyme, 63
collagen, 40–41
communities (biomes), types, 160–162
comparative anatomy, 191
competition
adaptive radiation, 186
population growth and, 171–172
species interaction, 162
conception, 310–311
connective tissues, 40–41
controlled variables, 18
countercurrent exchange (fish), 223, 229
covalent bonds, 32–33
creationism, 183–184, 195–197
Crick, Francis (biologist), 129, 344
crossing-over, genetic, 96
Cuvier, Georges (anatomist), 184
cycle sequencing, 135
cystic fibrosis (CF), 126, 344
cytokines, 265
cytokinesis, 90, 95
cytokinins, 340
cytoplasm, 48, 52–53
cytosine (C), 41–43
cytoskeleton, 51–52, 57
cytotoxic T cells (CD8 cells), 270–271

•D•
Dart, Raymond (anthropologist), 198–199
Darwin, Charles (scientist), 185–190, 345
data, quantitative/qualitative, 19
deductive reasoning, 18
dehydration synthesis, 38–39
demographics, population, 164–167, 172–173
dendritic cells, 265
denitrification, 182
density, population
growth factors, 167–168
growth rate, 169–170
habitat carrying capacity, 169
population ecology, 163–164

deoxyribonucleic acid (DNA)
...
See DNA technology;
genetically modified organisms
detritivores/decomposers, 175
d’Hérelle, Félix (microbiologist), 272
diabetes, 38
diastolic blood pressure, 233
dicot plants, 323–326
diffusion
capillary exchange, 235–236
membrane transport, 55–56
oxygen, 226–227
pulmonary circulation, 234
systemic circulation, 235
digestion
bacteria role, 260
food consumption strategies, 241–242
lysosomes and cellular, 59
types of, 242
digestive systems
basic functions, 12, 242
complete and incomplete tracts, 243
continuous and discontinuous, 243–244
healthy food choices, 249–254
human system components, 244–247
mucous membranes, 263–264
nutrient absorption, 247–249
waste elimination, 254–255
diploid zygotes, 91–94
disaccharides, 37
discovery science, 16–17
disease
...
See also
bacteria; medicines; microbes; viruses
antibiotic-resistant bacteria, 271–272
Clostridium botulinum, 261

Index
Escherichia coli, 9–10, 49–50, 149, 255, 268
Heliobacter pylori, 246
MRSA, 194, 350
nosocomial infections, 272
smallpox, 275, 344
Staphylococcus pyogenes, 148–149, 194,
268, 343–344
Streptococcus aureus, 49, 148–149, 260
VRSA, 194
Yersinia pestis, 260
dispersion, population, 164
distribution (biogeography), 191–193
diversity, genetic, 96–99, 152–153
DNA fingerprinting, 140
DNA technology
...
coli
adaptive immunity, 268
importance of hand-washing, 255
life functions of, 9–10
prokaryotic characteristics, 49–50
ears (sense of hearing), 285
ecological physiology, 206
ecology, defined, 160
ecosystems
...
See gametogenesis
electrolytes, 31
electron transport chains, 75–76
electrons, 29–31
elements, 30–32
elimination, food
...
See also cellular respiration;
photosynthesis
basal metabolic rate (BMR), 76–77
basic principles, 66
characteristics and function, 65–66
chloroplast role, 60–61
food consumption strategies, 241–242
food production, 68–70
fossil fuels, 348
Law of Mass Balance, 210
metabolic reactions, 67
mitochondrial role, 60
plant growth, 326–327
energy transfer
...
See also ecosystems
adaptation to, 185–186, 211–212
biodiversity, 143–148
biogeochemical cycles, 178–182
cell mutations from, 122
ecological physiology, 206
ecotourism, 144
gene regulation and, 127
GMO benefits/concerns, 138–140

355

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Biology For Dummies, 2nd Edition
environment (continued)
homeostasis, 208–209
mating season, 299–300
protecting Earth’s resources, 349–350
enzymes
beneficial uses, 347–348
cellular respiration, 73–75
characteristics and functions, 61–63
cofactors and coenzymes, 63
digestive system, 245–247
DNA replication, 83–85
feedback inhibition, 63–64
lysosomes, 59
mineral and vitamin requirement, 253–254
peroxisomes, 59–60
proteins as, 40–41
restriction enzymes, 130
role of immune defenses, 264–265
error, experimental, 21
essential amino acids, 251
estrogen, 44, 294, 301
ethylene, 340
eugenics, 137
Eukarya, domain, 153
eukaryotic cells
...
See biological evolution
excretory system
basic functions, 12
intestines, 254–255
kidneys, 255–257
mucous membranes, 263–264
exoskeletons, 212
experiment design, 18–22
extinction
...
See human
development
fibrinogen, 239
flagella, characteristics and functions, 57
flavin adenine dinucleotide (FAD/FADH2),
73–75
Fleming, Alexander (biologist), 343–344
flowering plants
...
See also deoxyribonucleic acid
(DNA); DNA technology
cancer and aging effects, 122
defined, 105
DNA in formation of, 41–43
homeotic genes, 315–316
mutations, 96, 103, 124–126
protein synthesis, 113–114
regulation, 126–128
RNA processing, 118
transcription factors, 115–118
translation, 119–123
genetic abnormalities, 96–98, 318
...
See also DNA
technology
genetic testing, for disease, 344
genetically modified organisms (GMOs),
10, 138–140, 348
genetics
...
See
also human development; physiology;
plant physiology
guanine (G), 41–43
Gurdon, J
...
(scinetist), 314
gymnosperms (conifers), 322

•H•
H1N1 influenza, 275
habitat carrying capacity, 169
haploid gametes, 91–94
HDL (high-density lipoproteins), 252
health/healthy lifestyle
antibiotic-resistance in, 194
bacterial role in, 148–149
biodiversity role in, 143–146
blood, 237–239
bone mass, 215
caloric needs for, 76–77
dietary sugars and, 36–38
DNA mutations and, 122, 126
gene mapping, 135–137
genetic engineering benefits, 131
GMO benefits/concerns, 138–140
hand-washing, 255
minerals and vitamins, 253–254
stomach ulcers, 246
wise food choices, 249–253
hearing, sense of, 285
heart disease
causes, 232
cholesterol, 44
discovery of cholesterol, 21
lipoproteins and, 252
trans fats, 23
heart function
capillary exchange, 235–236
cardiac cycle, 233

357

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Biology For Dummies, 2nd Edition
heart function (continued)
countercurrent exchange system, 229
humans and higher animals, 230–232
integumentary exchange system, 228–229
pulmonary circulation, 234
systemic circulation, 235
what causes it to beat, 236–237
heat, in energy transfer, 15
heirloom varieties, agricultural, 99
Heliobacter pylori, 246
helper T cells (CD4 cells), 265, 275
hemoglobin
...
See also
animals
brain development, 201–202
demographic transition stages, 172–173
evolutionary origins, 197–198

fossil records, 198–200
genetic records, 201
population growth rate, 170–172
study of genetic traits, 108–112
human development
blastocyst to embryo, 311–312
cell differentiation and development,
313–315
embryonic development, 315–316
from fertilization to blastocyst, 309–311
fetal development to birth, 312
gender determination, 316–317
genetic testing, 344
sexual development problems, 318
human digestive system, 244–247
Human Genome Project (HGP), 17–18,
129, 135–137
human growth hormone (HGH), 294
human pedigree charts, 109–110
human reproduction
...
See heart disease
hypertonic solutions, 56
hypothesis, 16
hypothesis-based science
applying the scientific method, 16–18
experiment design, 18–19
following an example of, 20–22
new ideas and old hypotheses, 22–23
hypotonic solutions, 56

Index

•I•
icons explained, 5
Ignatowski, A
...
(scientist), 21
immune system
adaptive defenses, 268–269
antibiotic use, 271–272
antiviral drug use, 273
B cells and antibodies, 270
bacteriophage use, 272–273
basic functions of, 12
cytotoxic T cells (CD8 cells), 270–271
dendritic cells, 265
good versus bad bacteria, 260–261
helper T cells (CD4 cells), 269
inflammation and vasodilation, 266
innate defenses, 262–263
lymphatic system, 267–268
phagocytes, 266
proteins and body fluids, 264–265
skin and mucous membranes, 263–264
vaccines, 273–275
virus attacks on, 261–262
weakened by aging and illness, 275–276
white blood cells, 239
impermeability, 55–56
independent assortment, genetic, 96–97
independent variables, 18
indicator species, 146–147
induced mutations, 124
inductive reasoning, 19
inflammation, 266
influenza, 275
ingestion, food, 242
inheritance, genetic
...
See also Web sites
for scientific information, 25–26
as source of rumors, 274
interphase, 85–88
intestines
...
See heart disease
isotonic solutions, 56
isotopes, 32

•J•
Johanson, Don (paleoanthropologist), 199
joints and ligaments, 215, 276

•K•
karotype (chromosome map), 91
keystone species, 146–147
kidneys, structure and function, 255–257
kinetic energy, 66
King, T
...
(scientist), 314
kingdoms, eukaryote, 150–151, 153–156
Klinefelter’s syndrome, 318
Krebs, Hans Adolf (biochemist), 346
Krebs cycle, 73–76, 346

•L•
lactic acid fermentation, 220
Law of Mass Balance, 210
Law of the Iroquois, 148
Laws of Thermodynamics, 14, 66, 175–177
LDL (low-density lipoproteins), 252
Leakey, Louis (archaeologist), 199
Leakey, Mary (archaeologist), 199
Leakey, Meave (paleontologist), 199
Leeuwenhoek, Antony van (scientist), 343
leptons, 29

359

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Biology For Dummies, 2nd Edition
life, chemistry of
acids and bases, 33–35
atoms/elements/isotopes, 28–32
biochemistry of living things, 190–191
buffering agents, 35
carbohydrates, 36–39
forms and measuring of matter, 27–28
fresh water requirements, 349
hormones and, 349
lipids in, 43–45
molecules/compounds/bonds, 32–33
nucleic acids in, 41–43
physiology and, 205–206
proteins in, 39–41, 113–114
life, interconnectedness of
...
See health/healthy
lifestyle
light energy
...
See photosynthesis
lipids, 43–45
lipoproteins, 252
liquids, as form of matter, 28
liver functions, 247–249
loci, gene, 105
locomotion, 211–212
lungs, human
...
See animals; human beings
Marshall, Barry (physician), 246
mass, 28, 70–72
Mass Balance, Law of, 210

matter
acids and bases, 33–35
atoms/elements/isotopes, 28–32
carbon-based molecules, 36–45
creation by photosynthesis, 70–72
ecosystem recycling, 178–182
forms and measurement of, 27–28
molecules/compounds/bonds, 32–33
media/popular press, 25
medicines
...
See also
ribonucleic acid
characteristics and functions, 58
creation of, 114–118
protein synthesis, 119–123
metabolism, 67, 76–77
metaphase, 89, 94–95
microbes
...
See vitamins and minerals
mitochondria
basic structure and function, 48
characteristics, 60
energy transfer, 75–76
eukaryotic cells, 51–52
highly conserved sequences, 193
lipid characteristics, 44
mitosis
asexual reproduction, 81–82
cytokinesis, 90
DNA mutations, 124–125
phases of, 88–89
plants, 328–329
mnemonics, taxonomic, 155
molecular biology, 114–123, 193
molecules
acids and bases, 33–34
carbohydrates, 36–39
components/structure, 32–33
lipids, 43–45
membrane transport, 55–56
nucleic acids, 41–43
proteins, 39–41
monocot plants, 323–325
monoculture, genetic diversity, 99
monohybrid cross, 108
monosaccharides, 36, 67
mouth, digestive processes in the, 245
MRSA (methicillin-resistant Staphylococcus
aureus), 194, 350
mucous membranes, 263–264
Mullis, Kary (biochemist), 346
muscular dystrophy, 344
muscular systems
ATP/ADP role, 219–220
basic functions, 11, 215–216
filaments and myofibrils, 218–219
types of, 216–218
mutations
...
See eukaryotic cells
organic chemistry, 36
organisms, shared characteristics, 13–15
orgasm, 306–307
On the Origin of Species (Darwin), 186
osmosis, 55–56
oxidation reactions, 74
oxidative phosphorylation, 73–76
oxygen diffusion, 226–227

•P•
paleontology, 193–194
Paley, William (philosopher), 195
pancreas functions, 247, 294
parasites
relationship with other species, 162
viruses as, 151, 262
parthenogenesis, 308
passive transport, membrane, 55–56
pathogens
...
See also energy
basic processes, 71
characteristics and function, 69–70
energy transfer, 15, 72
plant growth from, 326–327
phototropism, 14–15, 340
phylogenetic trees, 152–153, 193
phylum, organism organization, 153–156
physiology
...
See eukaryotic cells
plant hormones
...
See also physiology
differences from animals, 52
hormone functions, 340
mineral requirements, 335
nutrient requirements, 333–334
sugar transport (phloem), 337–338
transpiration (water loss), 338–340
water transport (xylem), 336–337
Plantae, kingdom, 150–151
plants
...
See also bacteria
asexual reproduction, 81–82
basic characteristics, 49–50
extremophiles, 149
phylogenetic tree, 153
properties of life, defined, 13–15
prophase, 89, 94–95
protein synthesis
...
See DNA technology
red blood cells
bone marrow production, 213–214
capillary exchange, 235–236
components/functions, 237–238
hemoglobin, 41
oxygen diffusion, 226–227
pulmonary circulation, 234
systemic circulation, 235
reduction reactions, 74
religion, intelligent design, 195–197
Remember icon explained, 5
replicates, experiment, 21
reproduction
...
See also messenger
RNA (mRNA)
nitrogen cycle, 181–182
phosphorus cycle, 181
structure and function, 43
ribosomes, 50–52, 58
RNA processing
...
See
endoplasmic reticulum (ER)

•S•
sample size, experiment, 21
saturated fats, 43–45, 253
...
See
endoplasmic reticulum (ER)
smooth muscle, 218
solar energy, 348
solids, as form of matter, 28
solutions, buffering agents, 35
somatic nervous system, 278–279
species
evidence of evolution, 191–195
hominid fossil records, 198–200
hominid genetic records, 201–202
interactions between, 162
organism organization, 153–156
species extinction
environmental change, 11
human activity and, 146–147
population growth and, 171–172
resource and habitat destruction, 350
sperm cells, human
...
See genetically
modified organisms (GMOs)
translocation, 336–338
transpiration, plant
water cycle, 179
water loss, 338–340
water movement, 336
transport proteins, 41
triglycerides, 43–45
trophic levels, ecosystem, 173–175
trophic pyramid, 177–178
Turner syndrome, 318

•T•

•V•

T cells
...
See heart disease
thymine (T), 41–43
thyroid, 294
Tip icon explained, 5
tooth decay, 38
totipotency, 314–315
touch, sense of, 286–287
tracheal exchange (insects), 223–224
trans fatty acids, 23
transcription, 115–118

vaccines, 273–275, 344
vacuoles, 48, 51–52
van Helmont, Jean Baptiste (chemist), 71
variables, experiment design, 18
variation, genetic, 96–99
vascular plants
angiosperms, 323–324
gymnosperms, 322
herbaceous and woody stems, 324–325
transpiration losses, 338–340
xylem-phloem transport, 322, 336–338
vasodilation, 266
vegetarianism, 251
veins, 228
vertebrates
circulatory system, 228
environmental adaptations, 211–212
muscular system, 215–220
skeletal system, 212–215
viruses
...
See also fats
and oils
urinary system
...
S
...
S
...
See digestive systems
water cycle (hydrologic cycle), 179
water resources, protection of, 349–350
water transport, plant
movement system, 333
phloem system, 337–338
tissues, 322
transpiration losses, 338–340
xylem system, 336–337
Watson, James (biologist), 129, 344
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