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IGCSE BIOLOGY

Biology IGCSE
Revision Workbook
Edexcel Triple Award Specification
A little something to get you started……

IGCSE Revision Notes
Triple Award Specification
Key words are underlined in red
...


Section 1: The Nature and Variety of Living
Organisms
Characteristics of living organisms include:

M ovement
R espiration
S ensitivity
G rowth
R eproduction
E xcretion
N utrition
In addition, all living organisms contain nucleic acids (DNA) and
have the ability to control their internal conditions
...

Living organisms are classified into 5 groups, each of which has
certain characteristics you need to learn
...
Multicellular organisms
2
...
Cells have cellulose cell walls

carry out

4
...

Examples include flowering plants, such as a cereal (e
...
maize) and
a herbaceous legume (e
...
peas or beans)
...
Multicellular organisms
2
...
Cells have no cell walls
4
...
They often store carbohydrate as glycogen
Examples include mammals (e
...
humans) and insects (e
...
housefly)
...
They are saprophytic and feed by secreting digestive
enzymes onto food and absorbing the digested products
...
Cells do not contain chloroplasts and are not able to carry out
photosynthesis
...
Cells are joined together to form threads called hyphae
...

4
...

5
...

Examples include Mucor and Yeast (which is single-celled)
...
Made from single cells
2
...
Some bacteria can carry out rudimentary photosynthesis but
most are saprophytes
4
...


Protoctists
Basically, everything that doesn’t fit into the other kingdoms! Most
are single-celled organisms that have either:
1
...
g
...
plant-like characteristics (e
...
Chlorella)
...
g
...

2
...

4
...
They are not made from cells
...

They infect every type of living cell
...

The capsid is a protein coat and is used to protect the genetic
information and give the virus structure
...

Examples include the Tobacco Mosaic Virus and the Influenza virus
(that causes ‘flu)
...
You
need to know the following hierarchy of structures:
Organelles – intracellular structures that carry out specific
functions within a cell
Cells – the basic structural and functional unit from which all
biological organisms are made

Tissues – a group of specialised cells that are adapted to carry out
a specific function
...


Differences Between Plant and Animal Cells
Organelle
Chloroplast

Animal Cell
X

Plant Cell


Cell Wall

X



Sap Vacuole

X



Chlorophyll

X

Found in chloroplast

Size

Roughly 50чm long

Roughly 150чm long

Shape

No fixed shape

Rectangular

N
...
The cells are measured in чm (micrometres)
...

Functions of Organelles
Cytoplasm – the site of chemical reactions in the cell
Cell Membrane – controls what enters / leaves the cell (selectively
permeable)
Nucleus – contains nucleic acids that code for the synthesis of
specific proteins
...

Mitochondrion – site of respiration
Chloroplast – site of photosynthesis
Cell Wall – made from cellulose
...

Sap Vacuole – contains the cell sap
...


c) Biological Molecules
Food Tests
Lipids are tested for using the Emulsion test
Proteins are tested for using the Biuret test
Starch is tested for using Iodine solution
Glucose is tested for using the Benedict’s test

The Food Groups
Food Group
Lipids (fats & oils)
Carbohydrates
Proteins
Fibre
Water

Function
Used as a long-term energy store (much easier to
store than carbohydrates)
...

Made from single sugars or chains of sugars
...

Broken down into amino acids that our body absorbs
and assembles into new proteins
...

Regulates bowel movement
...

Essential as a solvent for chemical reactions (e
...

cytoplasm), heat loss (e
...
transpiration), transport
(e
...
blood), etc
...
g
...

Components of the Main Food Groups
The main food groups are carbohydrates, lipids and proteins
...

Carbohydrates are large molecules made from one or more sugars
(e
...
both starch and glycogen are both polymers (polysaccharides)
of glucose (a monosaccharide))
...

Lipids are made from one glycerol molecule and three fatty acid
molecules joined together
...
Initially, raising the temperature
increases the rate of reaction
...
Initially,
increasing
the
pH
increases the rate of reaction
...
However, after the optimum
temperature is reached the
enzyme begins to change shape
and the substrate stops being
able to bind to the active site
...
However, after the optimum pH is
reached the enzyme begins to
change shape and the substrate
stops being able to bind to the
active site
...
The enzyme becomes denatured
and stops working (the rate of
reaction is zero at this point)
...
The enzyme becomes denatured
and stops working (the rate of
reaction is zero at this point)
...
An example is the
enzyme catalase that breaks down hydrogen peroxide into water
and oxygen:
2H2O2



O2

+

2H2O

Catalase is found in potatoes
...
The rate of reaction is
proportional to the volume of O2 given off
...
e
...


d) Movement of Substances Into and Out of Cells
Diffusion – the movement of molecules from an area of high
concentration to an area of low concentration, down a concentration
gradient
...

Osmosis – the movement of water molecules from an area of high
concentration to an area of low concentration across a partially
permeable membrane
...

Active Transport – the movement of molecules from an area of low
concentration to an area of high concentration against the
concentration gradient
...

Diffusion and osmosis occur because molecules have kinetic energy
...
Eventually there will be an even mixture of
molecules that is called an equilibrium
...
This is
important because it provides support to plants
...
When plant cells start
to lose water they become flaccid
...
Eventually, flaccid cells become
plasmolysed as the cell membrane begins to peel away from the cell
wall
...

You need to give examples of diffusion and osmosis in living and nonliving situations
...
Diffusion of
gases in the lung or leaf are also good examples
...
e
...
) They do this through photosynthesis
...
Plants use glucose for the following:
-

Respiration
Stored as Starch
Turned into Cellulose (cellulose is a polymer of glucose)
Used to make fats and oils

At any point the rate of photosynthesis can be increased by adding
more CO2, more water, more light or heating towards optimum
temperature (photosynthesis is catalyzed by enzymes)
...
g
...
This is because a second factor
is limiting the rate of photosynthesis
...


Rate
of
p/s

Light is the rate-limiting factor
A second factor is limiting (e
...
CO2)

Light intensity

You need to know the parts of the leaf and their adaptations
...

Epidermis
Transparent protective layer
...

Palisade cells
Packed full of chloroplasts
...

Air Spaces
Increase the surface area inside the leaf to
maximise gas exchange across the surface of
the Spongy Mesophyll cells
...

Vein (containing Xylem) Steady supply of water to the leaf from roots
...
The best
example is using pond weed (Elodea) which produces bubbles of O2
as it photosynthesizes
...

Therefore, when you increase light intensity or give it more CO2,
the rate of bubble production increases
...
A good example is the
Geranium plant
...

However, if one leaf is put in aluminium foil and another is kept with
lime water both do not turn blue-black, implying both CO2 and light

are essential for starch production and, therefore, essential for
photosynthesis
...
This really means some of
every food group, but not too much or too little of a particular one
...
Per mass lipids have about 10x more energy in
them than carbohydrates
...
2 kJ)
...
e
...

- Males need to consume 2500 Calories a day
- Females need to consume 2000 Calories a day
However, this will change if:
-

you exercise
you are growing
you are ill
you are pregnant
you are old

You need to know an experiment that can show how much energy
there is in food
...
If you record the
change in temperature of the water you can use the equation below
to find out the energy the food gave to the water:
Energy = change in temp
...
2J/g/C
A potential problem is that not all the food will burn
...
To standardize this, you can divide
your calculated energy value by the change in mass to give you the

change in mass per gram of food (which will allow you to compare
values fairly between different food samples)
...
It forms an
essential part of the pigment in rods and cones
that detects light
...

Present in citrus fruit
...
Lack of Vitamin C causes
scurvy
...
It is essential
for regulating the growth of bones
...

Present in milk, cheese & dairy foods
...
Lack of
calcium can lead to osteoporosis
...
g
...
Part of haemoglobin
...


The purpose of digestion is to break large, insoluble pieces of food
into small, soluble molecules that can be absorbed through the gut
wall into the bloodstream
...
e
...
Carried out by:
- mouth and teeth chewing food
- stomach churning food
Chemical Digestion:

digestion using enzymes

You need to know the following enzymes:
Where it is
made

Where it works

Enzyme

Substrate

Products

Salivary Glands

Mouth

Amylase

Starch

Maltose

Stomach cells

Stomach

Protease

Protein

Amino Acids

Liver

Small Intestine

Bile Salts

Fat

Fat droplets

Amylase
Protease
Lipase

Starch
Protein
Fat

Maltase
Protease

Maltose
Protein

Maltose
Amino Acids
Glycerol & Fatty
acids
Glucose
Amino Acids

Pancreas

Small Intestine

Small Intestine

Small Intestine

Bile salts are not technically enzymes
...
They help by emulsifying lipid (i
...

turning large fat droplets into lots of tiny droplets)
...

Bile also has a second job
...
This is important for
neutralising stomach acid as soon as it leaves the stomach
...
Stomach acid does not play a significant role in
digestion
...


Absorption:

taking molecules into the bloodstream
...


Assimilation:

using food molecules to build new molecules in our
bodies, i
...
the food molecule physically becomes
part of our body
...
This is not excretion
because the unwanted food has never, technically,
been inside the body
...
This pushes
the bolus through the intestine
...
This increases the
rate of diffusion of molecules into the blood
...
This means there is always
a low concentration of food molecules in the
blood
...

Roughly 7m long
...

Villi and microvilli increase the surface area of
the small intestine by 1000x
...
The energy is essential for keeping the cell alive
as it powers processes like protein synthesis, growth, repair, cell
division, etc
...
This is
called anaerobic respiration
...
Anaerobic respiration allows the cell to carry on working
despite there being a shortage of oxygen (this is very useful in
muscle cells, particularly if you are running for your life!)
...

Lactic acid builds up inside muscle cells and quickly leads to muscle
fatigue and cramp
...

During recovery the lactic acid is transported to the liver via the
bloodstream
...

Oxygen is required for this which is called the Oxygen Debt
...
Instead, they make ethanol
...
It is used in the
baking and brewing processes
...
The best example is to suspend
some maggots or seeds near the top of a test tube sealed with a
bung (suspend the maggots / seeds in a wire mesh)
...


g) Gas Exchange
Gas Exchange in Flowering Plants
Remind yourself of the structure of the leaf
(Section 2e – Nutrition in Flowering Plants)
...
Remember that CO2 is used in photosynthesis and
produced by respiration, whereas O2 is used in respiration and
produced in photosynthesis!
Both processes run simultaneously
...
e
...
) is
governed by the formula:
Net Glucose

=

Total production

–

Amount used in respiration

The amount the plant uses in respiration is nearly constant
...
It is dependent on the ratelimiting factors (i
...
light intensity, CO2 level, water availability,
temperature, etc
...

Therefore, plants grow a lot during the summer and not much
during winter!

Leaf Structure
Air spaces

Stomata
Mesophyll cells
Leaf shape

Stomata distribution

Adaptation for Gas Exchange
Increase the surface area inside the leaf to
maximise gas exchange across the surface of
the Spongy Mesophyll cells
...

Leaves are thin and have a very large surface
area, both of which also increase the rate of
diffusion
...
This stops the build-up of excreted
products that would slow gas exchange
...
The best example is to seal
two leaves (still attached to the plant) in separate plastic bags with
some bicarbonate indicator solution
...
The leaf in the black bag produces CO2 via
respiration and the colour of the bicarbonate indicator changes
quickly to yellow
...

Bicarbonate Indicator Colours
Red in the presence of O2
Yellow in the presence of CO2

Gas Exchange in Humans
Larynx (voice box)
Trachea
Ribs
Bronchiole
Alveolus

Bronchus
Intercostal Muscle

Thoracic Cavity
contained within
pleural membranes

Diaphragm
How Breathing Works

1
...

3
...

5
...

Diaphragm contracts, moving
downwards
...

The pressure in the Thoracic
Cavity decreases
...


1
...

3
...

5
...

Diaphragm relaxes, moving
upwards
...

The pressure in the thoracic
cavity increases
...


Inhaling is an active process, i
...
it Exhaling is a passive process, i
...
no
requires
energy
for
muscle energy is required as there is no
contraction
...


Alveoli and their Adaptations
Adaptations for Gas Exchange
- Alveolus is one cell thick
- Capillary wall is one cell thick
- Many alveoli produce a huge
surface area
- Alveoli wall is moist
- Breathing maintains a steep
concentration gradient for O2
and CO2
- Blood movement maintains a
steep concentration gradient
for O2 and CO2
Smoking
Cigarette smoke contains tar, nicotine, carcinogens, CO and poisons
...
Also
destroys cilia (little hairs lining the airways that
‘waft’ and move mucus and trapped bacteria out of
the lungs)
...
This leads to
heart disease and vascular diseases
...

Damage the DNA of alveoli cells
...
The tumour is the start of cancer
...

The list is endless
...
g
...


You need to know an experiment that will show the effect of
exercise on humans
...
Do some
exercise, then take the same measurements again
...
The reason for this is that your rate of
respiration has increased (to supply the muscles with extra energy
for contraction)
...

Unfortunately, you also release more waste heat energy, so your
body heats up and you might have to increas sweating to cool it
down again
...
Therefore, all organisms need to exchange
gases with their environment
...
They can do this because their surface area is large
compared to their volume (large SA:Vol ratio)
...

Multicellular Organisms: cannot exchange gases directly through
their skin
...
g
...

Transport in Flowering Plants
Plants have two different networks of tubes inside them:
Phloem: transports sucrose and amino acids up and down the stem
Xylem: transports water and minerals up the stem

Phloem and Xylem are arranged in separate bundles (vascular
bundles) inside the stem
...
This arrangement is different in roots (but you
don’t need to know it)
...
It is not the same as transport in the xylem which occurs
by the process of transpiration
...

In the Roots
Water enters root hair cells by osmosis
...

This enables transpiration to happen even if the soil is very dry
...


Root hair cells increase
the root’s surface area

In the Stem
1
...

3
...


Water evaporates out of the top of the xylem
...

This pulls water molecules up the xylem
...


Extension (not on syllabus, but very interesting…)
Water molecules are slightly charged (polar)
...
This
means that water molecules tend to stick to each other
...
The water moves by osmosis into
leaf mesophyll cells where it evaporates into the air spaces and
finally diffuses out of the stomata into the air
...
This makes diffusion, osmosis and
evaporation happen faster
...
Humid air is less able to accept more water
molecules by evaporation (lower conc
...

Wind blows water vapour away from the stoma,
keeping the concentration gradient high / steep
...
Wider stomata can
allow faster diffusion of water vapour out of the leaf
...
The best experiment is
a potometer that measures how quickly a little bubble of air moves
up a glass tube attached to the bottom of a leafy stem
...
will all
change the speed the bubble moves up the tube
...
g
...
e
...


Red Blood Cells – adapted to carry O2 around the body
...
Other adaptations of RBCs include:
-

Smooth edges
Biconcave shape (increases surface area and allows folding)
Made in huge quantities
No nucleus (so more room for haemoglobin)

Platelets – help clot the blood
...


White Blood Cells – are part of the immune system
...


Macrophages (sometimes called Phagocytes)
Travel in the blood
...
e
...


Lymphoctyes
Stay in the lymph system (you don’t need
to know what this is)
...

Antibodies travel in the blood and
stick to foreign objects
...
foreign objects are stuck to
each other, stopping them
spreading; and

Engulfing and destroying is called
phagocytosis
...
macrophages can engulf many
foreign objects at the same
time, speeding up the killing
process
...
How?
CO2 +

H2O



HCO3-

+

H+

The CO2 reacts with water molecules to produce the Hydrogen
Carbonate ion
...
CO2 is, therefore, carried as an aqueous ion in the blood
plasma
...
the names of the 4 chambers of the heart;
2
...
the names of the two sets of valves in the heart
...
The left & right atria
contract at the same time
...
The
left & right ventricles contract at the same time
...
Blood enters the atria
...
Both atria start to contract, pushing the blood into the
ventricles through the open cuspid valves
...
When the ventricles are full, they begin to contract
...
The cuspid valves shut to stop backflow
...
Blood is forced out of the heart into the circulatory system
through the open semi-lunar valves
...
When the ventricles finish contracting, the semi-lunar valves
shut, stopping backflow
...
This is called a double
circulation
...

Adrenaline has two effects on the heart:
1
...
it makes each beat harder (stroke volume increases)
...

Extension
Cardiac Output

=

Heart Rate

x

Stroke Volume

CO = Volume of blood pumped per minute
HR = Number of beats per minute
SV = Volume of blood ejected per beat
Adrenaline increases both HR & SV, thereby greatly increasing CO
...
1-10m
m
Arteries carry high pressure blood away from the heart
...
Thick muscle layer to withstand high pressure blood
2
...
Protective collagen layer
4
...
Relatively small lumen

Vein
collagen&
connectivetissue
sm
oothm
uscle
&elastictissue
sem
ilunarvalve
lum
en(blood)
0
...

Key Points
1
...

3
...

5
...

Key Points
1
...
Lumen is the same width as one RBC (therefore more of RBC
is in contact with the wall, therefore shorter diffusion
distance)
3
...
Tiny (compare the scales and remind yourself what a чm is)
Something Extra You Need to Know
The vessel taking blood to the kidneys is the renal artery
...

The vessel taking blood to the liver is the hepatic artery
...

The Hepatic Portal Vein takes blood to the liver directly from the
gut, not from the heart, therefore, it’s not an artery but a portal
vein
...
Cunning, eh?

i) Excretion
Excretion: the removal of the waste products of metabolism
from living organisms
Excretion in Flowering Plants
CO2 and O2 are excreted by leaves via the stomata
...

Excretion in Humans
Humans have 3 main excretory organs:
1
...
Skin – excretes H2O
3
...

Extension - what’s urea?
We need to have a certain amount of protein in our diet to supply
the amino acids we need to make our own body proteins
...

Problem: when amino acids are broken down in the liver they make
ammonia which is very toxic
...

Therefore, urea is a product of the metabolism of amino acids
...
There are millions
of nephrons in a single kidney
...
Blood enters the kidney via the afferent arteriole (small
artery)
...
The arteriole splits into a ball of capillaries called the
glomerulus
...
The blood is under high pressure so all small substances are
forced out of the holes in the capillary walls = ultrafiltration
...

4
...

5
...
e
...

6
...

7
...

8
...

9
...

10
...

11
...

This is the first role of the nephron (role in excretion)
...


Blood water levels are sensed by the hypothalamus in the brain
...

When Blood Water Levels are Too Low
1
...

2
...

3
...

4
...

5
...

6
...

7
...

When water levels are too high exactly the opposite happens (i
...

the pituitary releases less ADH)
...
This
is called homeostasis
...

Humans have two systems that carry out homeostasis:
Nervous System – immediate responses to stimuli (sec - hours)
Endocrine System – long term responses to stimuli (hours - months)

Both systems respond to stimuli (i
...
events that change the internal
environment)
...
The message from detector to effector is
carried either via an electrical nerve impulse or as a hormone,
depending which homeostatic system is being used
...
Sense organs (e
...
pain receptors in the skin or
photoreceptors in the eye) are linked to the brain via nerve cells
called neurones
...
Nerve
impulses are very quick (~120m/s), allowing rapid responses to the
stimulus
...
This is a
defense mechanism allowing almost instant responses to threatening
or dangerous stimuli (e
...
pain)
...


A Reflex Arc

1
...

2
...

3
...

4
...

5
...

6
...

The entire process (stimulus to response) happens in less than a
second and does not involve the brain
...


Reflexes in the Eye

Structure

Function

Cornea

Refracts (bends) light entering the eye
...


Pupil

Hole which allows light into the eye
...


Ciliary muscle

Retina

Fovea
Optic nerve
Sclera

Changes the shape of the lens by
altering the tension on the suspensory
ligaments
...
e
...

Area where most light is focused; very
sensitive to colour (most cones here)
...

Outer protective layer of eye
...


Light is detected by photoreceptors in the eye
...
There are two types of
photoreceptor:
- rods that see only in black & white; and
- cones that see in either red, blue or green (3 types of cone)
...
responding to different light levels; and
2
...

Responding to Different Light Levels
In the dark
1
...
Reflex occurs
3
...
Pupil diameter increases
5
...
Photoreceptors detect
2
...
Muscles in the iris are the
effectors
- radial muscles in iris relax
- circular muscles in iris contract
4
...
Less light enters the eye

1
...

3
...

5
...

2
...

4
...


Near Object
Incoming light is divergent
Ciliary muscles contract
Suspensory ligaments are loose
Lens is fatter (more convex)
Light is refracted more

Light converges on the retina

Controlling Body Temperature
Too hot
Too cold
When you are hot, the following When you are cold, the following
happen (controlled by reflexes):
happen (controlled by reflexes):
1
...
Sweating increases
3
...
Hairs on skin stand up (more
insulating air is trapped)
2
...
Shivering starts so muscles
respire more, producing more
heat
4
...

Vasoconstriction – arteriole narrows
Vasodilation – arteriole widens

vasoconstriction

vasodilation
vasoconstriction

vasodilation

The net effect is to widen arterioles under the surface of the
skin when hot and narrow them when cold
...

Stimulates growth of uterus lining each
month and (indirectly) causes ovulation
...
As plants don’t have a nervous
system, their responses are limited to hormones only
...
Roots grow towards gravitational pull and stems grow
away
...

- Water
...
This is hydrotropism
...
Shoots grow towards light and roots grow away
...

Phototropism is controlled by hormones released by the growing tip
of the shoot
...
If you remove the
tip, the shoot stops growing
...

You need to know an experiment that demonstrates geotropism
...
Let the
root start to grow downwards then rotate the seed 90
...
A more
advanced (and less practical) experiment that shows geotropism is
that seeds germinating inside spacecraft have roots that grow
randomly!
You also need to know an experiment that demonstrates
phototropism
...

Two parents are involved
...
It involves
one parent only and produces offspring that are genetically
identical to the parent (clones)
...

Zygote: a cell that is the result of fertilisation
...

Reproduction in Flowering Plants

Part

Anther

Function
Colourful part of the flower
...
Makes pollen
...


Stigma

Female part of the plant
...


Ovary

Contains the ovules
...


Pollen

Male gamete
...

Protects the flower when it is in bud
...

When pollination occurs, the pollen grows a pollen tube down the
stigma of the flower
...

When fertilisation has happened, the flower will change in the
following ways:
1
...
Fertilised ovule turns into a seed
3
...
The seed contains a limited store of
carbohydrate and lipid that it uses as a fuel for respiration to
provide the energy for growth
...
The danger is
that the seed will run out of stored energy before it makes leaves
...

Plants can also reproduce asexually:
Natural methods
Runners – a root from one plant
grows a separate shoot that grows
into a new plant
...

See also rhizomes, corms, bulbs and
tubers (not mentioned on syllabus)

Artificial methods
Cuttings – a branch from one plant is
removed and planted in soil
...

See also grafting (not mentioned on
syllabus)

Reproduction in Humans
Male Reproductive System

Female Reproductive System

Pregnancy
When the egg and sperm fuse (fertilisation) the resulting zygote
begins to divide by mitosis (see next section) and becomes an
embryo
...
The
two blood streams never mix (otherwise the mother’s white blood
cells would attack the foetus!), but they are close enough for
diffusion to occur
...
This helps cushion the
embryo and protect it (lots of other roles…
...

Testosterone:
-

Causes testes to drop & penis to enlarge
Triggers spermatogenesis (sperm manufacture)
Causes growth of pubic and body hair
Causes larynx to enlarge (voice deepens)
Causes muscles to grow

Oestrogen:
-

Triggers menstruation to begin
Causes maturation of the vagina
Causes breasts to grow
Causes growth of pubic and body hair
Causes hips to widen
Oestrogen

Menstrual Cycle

Causes the endometrium
(uterus lining) to grow
...

Causes the ovum (egg) to
ripen inside a follicle in
the ovary
...


LH
Made by the pituitary
gland instead of FSH
...


Ovum starts to release
oestrogen as it ripens
...

Menstruation
Corpus
luteum
dies
...


You only need to know
about oestrogen and
progesterone

Endometrium is no longer
maintained and it falls
away
...


Ovulation
Egg is released into the
fallopian tube where it
stands the best chance
of being fertilised
...

Progesterone
Maintains endometrium
...


Corpus Luteum
The empty follicle turns
into a corpus luteum that
starts
to
make
progesterone
...
DNA is a genetic code
...
Each gene tells the cell
how to make a specific protein
...
g
...
Sometimes there are more than one version of a gene
...
g
...

DNA is a very long molecule
...
The coiled up DNA forms a chromosome
...
We have two
copies of each chromosome, so each cell contains 46 chromosomes
...
e
...
e
...

Key Word Summary
This topic, more than any other, confuses people
...
Produces 2 daughter cells

Meiosis
1
...
Daughter cells are diploid (i
...

have 23 pairs of chromosomes)

2
...
e
...
Daughter cells are genetically
identical to each other

3
...
Daughter cells are genetically
identical to the parent cell

4
...
Occurs in one stage

5
...
Happens
body

everywhere

Haploid Gamete

in

the

6
...


Each parent gives only one of each of the pairs of chromosomes to
their gametes
...

Alleles for the same gene can be:
- Dominant – always affect the phenotype (allele represented with
capital letter)
- Recessive – never affect the phenotype in the presence of a
dominant allele (allele represented with lower case letter)
- Co-dominant – affect the phenotype equally in the presence of
another co-dominant allele (both alleles have capital letters)
Inheritance
Inheritance patterns are always given using a genetic diagram
...
e
...
e
...
Boys
have an X and a Y, girls have two X chromosomes
...
the environment; and
2
...

New alleles arise in the population through mutation
...
The new protein might:
1
...
Work better than before (beneficial mutation)
3
...

Individuals with this kind of mutated allele are more likely to
survive, reproduce and pass their alleles on
...

Natural Selection
Darwin came up with this theory
...


Over time, this process leads to evolution
...
The frequency
that mutation occurs naturally can be increased by exposure to
radiation (e
...
gamma rays, X-rays and ultraviolet rays) and some
chemical mutagens (e
...
chemicals in tobacco)
...
This is because it is not
practical to count all of the species we’re interested in e
...
one
cannot count all of the grass plants in a field
...


Quadrats can be any size you like (e
...
5km by 5km sampling zebra
herds in Africa, or 5cm by 5cm sampling lichen on a tree), but there
are 3 different methods of using a quadrat
...


Quadrat

How it is used
A quadrat can be used to calculate the total
population of a species (e
...
snails)
...
This
technique only works for large organisms which can
be distinguished as individuals (not always easy for
plants, e
...
grass)
...
g
...
The
divided into 100 smaller squares
...


percentage
quadrat is
percentage
number of

A quadrat can be used to calculate the percentage
frequency of a species (e
...
daisies in a field)
...
You
simply count a 1 for each square the species is in
and a 0 for those where it is absent
...


b) Feeding Relationships
Food chains are used to show the relationships between species in a
habitat
...
g
...

Food chains can be built up into complex food webs
...

A Pyramid of Numbers
Foxes
Rabbits
Grass
This shows the populations (to scale) of the species in the chain
...
e
...
This occurs if there is a parasitic relationship in the food
chain e
...
one tree but many caterpillars eating the leaves!
To stop this, a pyramid of biomass is more frequently used
...

A Pyramid of Biomass
Bats
Caterpillars
Tree

Biomass – the mass of the organic material an organism is made
from (i
...
dry it out totally and weigh it; water doesn’t count!)
We can also represent the energy flow in a food chain using a
Pyramid of Energy Transfer
...
This is because at each level
energy is wasted on:
- Respiration (most of it as waste heat)
- Undigested / egested food
- Used in movement

c) Cycles within Ecosystems
The Water Cycle

Key ideas – Evaporation, Condensation, Precipitation
Transpiration (rather unhelpfully not shown on this diagram)

&

The Carbon Cycle

Key ideas
Combustion

–

Respiration,

Photosynthesis,

Decomposition

&

The Nitrogen Cycle
Nitrogen in air
(N2 gas)
Denitrifying Bacteria

Nitrogen in soil
(Ammonium – NH4+)

Nitrogen-Fixing Bacteria

Decomposition
(bacteria + fungi)

Nitrifying Bacteria
Nitrogen in soil
(Nitrate – NO3-)

Nitrogen in
animals (protein)
Assimilation

Active
Transport

Nitrogen in plants
(protein)

This is not particularly easy to understand
...
There are 4:
- Decomposers – turn nitrogen in protein into ammonium (NH4+)
- Denitrifying Bacteria – turn ammonium (NH4+) into N2
- Nitrifying bacteria – turn ammonium (NH4+) into nitrate (NO3-)
- Nitrogen-fixing bacteria – turn N2 into ammonium (NH4+)
Extension - leguminous plants
All of the above bacteria are naturally present in the soil
...
g
...
These plants are
called legumes (e
...
peas, clover etc)
...
e
...


d) Human Influence on the Environment
You need to know about the following environmental problems:
-

Acid rain
Greenhouse effect
Eutrophication
Deforestation

Acid Rain
SO2, CO2 and NOx (oxides of nitrogen) dissolve in rain to form
Sulphuric Acid, Carbonic Acid and Nitric Acid
...

Greenhouse Effect

Incoming radiation passes through the atmosphere and hits the
Earth where it is absorbed
...
This is the problem
...
This traps the heat in the atmosphere
...


Greenhouse Gas
Water Vapour
CO2
NOX
Methane

CFCs

Source
Humans haven’t had much effect on this – it’s a
naturally occurring greenhouse gas
Released during combustion of fossil fuels
Released during combustion of fossil fuels
Produced by cows (yes, cow farts) and rice paddy
fields
...

Used to be used as coolants in fridges and
propellants in aerosols
...


The theory goes that the greenhouse effect is causing global
warming which is bad
...
e
...
Nitrate enters a waterway (sewage or fertiliser run-off)
2
...
Algae block out light for plants living on the waterway bed
4
...
O2 levels fall
6
...
Dead fish and plants are decomposed by bacteria, using up
more O2 as they respire
8
...
Everything dies; waterway is incapable of supporting life

Deforestation
Cutting down trees and not replacing them is bad
...


Section 5: The Use of Biological Resources
a) Food Production
Food Production using Crop Plants
Greenhouses and polythene tunnels raise the temperature (by the
greenhouse effect), which increases the rate of photosynthesis,
which increases crop yield
...
This can be done
either using pesticides or biological control
...
g
...
Yeast are, therefore, used in the brewing industry
...
This is called malting
...
After a couple of days the barley seeds are boiled
(which kills them) and put into a fermenter with yeast and hops
...

You need to know an experiment that shows the production of CO2
by yeast, in different conditions
...
Any CO2 produced can be collected over
water or bubbled through lime water
...

It uses lactose sugar in the milk to produce lactic acid by anaerobic
respiration
...


A Fermenter

Important details
Cooling jacket – keeps the micro-organisms at the optimum
temperature
...
This stops waste products from
building up and keeps the ‘broth’ evenly mixed
...


Food Production using Fish Farming
Fish are farmed in fish farms because they are a good source of
protein
...
Precautions are taken to stop the fish fighting
with each other:
- Different fish species are kept in separate tanks
...

- Fish of different genders are kept separately (unless they are
being bred)
...
This stops
competition between fish of the same species (intraspecific
competition)
...
The fish are kept in sterile
water to limit disease which would spread very quickly in the
cramped ponds
...

Sometimes hormones are added to the water to speed growth
...
This is an example of selective breeding
...

Examples of this are increased yield and reduction of stem length in
wheat and increased yield of meat and milk in cattle
...
The strands coil up to form a
double helix
...

Thymine (T) pairs with Adenine (A)
Guanine (G) pairs with Cytosine (C)
The bases are a crucial part of DNA
...
coli
bacteria that make human insulin
...
Extract target gene (human insulin gene) from donor cell
...

2
...

3
...

4
...
This is done using a
vector
...

Now your transgenic bacterium is complete
...
e
...

Plants are good to genetically engineer because they are easier to
grow and there are fewer ethical issues
...
g
...
g
...
g
...
g
...
g
...
g
...
g
...
Usually
the individual has a very desirable phenotype and has often been
produced at the end of a selective breeding or GE programme
...
However, micropropagation (tissue culture) can be used in
large-scale cloning programmes
...
Samples of the culture can be taken
off and grown separately
...
This can be done
on a huge scale to produce 1000s of plantlets from a single culture
...
Take an embryonic cell
2
...
Replace with the nucleus from an adult cell from the animal
you want to clone
4
...

Cloning can be used beneficially in agriculture to increase the yield
of crop plants
...
g
...
coli bacterium that
makes human insulin has been cloned many times
...


THE END!



---