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ADDITIONAL BIOLOGY
NOTES
B2
...
Microscopes are used to learn about the structure and functions of cells
...
Controls movement of substances in
and out of the cell
 Cytoplasm – contains organelles, and is where many chemical reactions take place
 Nucleus – organelle containing DNA, controlling cell
 Mitochondria – tiny organelles where respiration occurs
Plant cells only have:
 Cell wall – made of cellulose to support to cell
 Vacuole – space inside the cell filled with sap to keep cells rigid
 Chloroplasts – organelles containing chlorophyll for photosynthesis

B2
...
Bacterial cells have a cell wall made of a different
substance to cell walls of plants
...
Some bacteria also have flagella on
the outside of the cell, to help them move
...
In the 1930s the electron microscope was
invented, which produces very clear images and has helped us to
discover more about cells
...
3 DNA
DNA is the chemical which makes up your chromosomes that carry genetic information
...
Each gene
contains instructions for a specific protein, and often many genes work together to produce what is
needed for a single feature
...

The two strands are linked by bases
...

 Adenine (A) pairs with Thymine (T)
 Cytosine (C) pairs with Guanine (G)
The matching bases are known as complementary base pairs, joined together by weak hydrogen
bonds
...

We are all slightly different because we all have a slightly different sequence of bases
...
5 DNA Discovery
In 1950s London, Maurice Wilkins and Rosalind Franklin studied the structure of DNA using x-ray
beams
...
From this she could work out how the groups of atoms were arranged
...
When they published
their work, Franklin and Wilkins were only a footnote, but eventually their contribution became
clear and all scientists won a Nobel prize (apart from Franklin, who died 4 years earlier)
...
The project showed 99
...
Knowing this sequence has allowed us to develop:
 Improved testing for genetic disorders
 New ways of finding genes that increase the risk of certain diseases
 New treatments and cures e
...
gene therapy
 New ways of looking at how the genome has changed over time, helps with evolution
 Personalised medicines

B2
...
For example, the gene or human insulin can be inserted into bacterial plasmid
DNA
...
Organisms like these are known
as Genetically Modified Organisms (GMOs)
...

Plants and animals can also be genetically engineered, such as golden rice
...
Beta-carotene is needed
by humans to produce vitamin A, and without vitamin A the immune system does not work properly
or you go blind
...
This reduces the
amount of crop spraying needed, as the farmer just sprays one load instead of lots of little ones
...


B2
...
Human diploid cells contain 23 pairs of chromosomes
...


1
...
The copies of the chromosomes
separate and the cell divides
3
...
This produces two daughter
cells, which are genetically
identical to each other and the parent cell
This process is called asexual reproduction
...
Some plants do it
also
...

This requires two sex cells or gametes
...
The two gametes fuse during fertilisation to produce a diploid cell called a zygote,
which develops into an embryo
...
DNA replication
2
...
This produces 4 haploid daughter cells, each
containing one set of chromosomes
In a diploid cell, each chromosome in a pair contains
the same genes but may have different versions of
those genes, called alleles
...


B2
...
The nucleus of a body cell of the animal to be cloned is transferred into an enucleated egg
(one that has had its original nucleus removed)
2
...
This is implanted into the womb of a surrogate mother who is a different individual to the
parent
4
...
9 Stem Cells
In the UK scientists can produce clones, but they must be killed within 14 days
...

When a stem cell divides it can either produce more stem cells or produce other types of
differentiated (specialised cells), e
...
neurones, muscle cells, skin cells
...
However, embryonic cells can
develop into almost any type of human cell
...

One way of collecting embryonic stem cells is to use leftover embryos created for couples having
fertility treatment
...
This is why scientists want to use adult stem cells to make cloned embryos
...
Since the
embryo has a right to life this
is unethical
Once a stem cell has
differentiated it cannot turn
into another cell
...
10 Protein Manufacture
A cell uses the sequence of bases in DNA to build chains of amino acids
...
A specific order of bases in DNA produces a specific order of amino
acids, and therefore a particular protein
...

1
...
One strand of the gene is used as a template strand
3
...
mRNA has a base called uracil (U) instead of thymine (T)
5
...

1
...
The ribosome moves from one end to the other of the mRNA strand, decoding bases into
groups of three called base triplets, or codons
3
...
The two amino acids join together, and this
process continues until the ribosome
reaches the end of the mRNA
5
...
It is now a protein and will carry out its
specific function

B2
...
For example, insulin
has only a small chain of 51 amino acids, whereas haemoglobin is a large complex protein with four
linked chains of 145 amino acids on each
...
An
enzyme can only work in one type of reaction, specific to its shape and therefore specific to that
reaction
...

A mutation is a change in the sequence of bases in the genetic code
...
For example:
 Some mutations cause bacteria to become resistant to antibiotics, the bacteria survive when
they have the antibiotic and die when they don’t
 The sickle cell disease mutation causes cells to fold in a different way and have a different
shape

B2
...
Each reaction in the body is controlled by a particular group
of proteins, or enzymes
...
Enzymes either help large molecules break apart
(digestion) or help smaller chemicals join together (synthesis)
...
Complementary bases line
up along each half, and a different enzyme joins them together,
making two identical DNA molecules
...

Food molecules like carbs and fats are too large to pass across the
cell membranes of the gut wall and into the blood
...
Different enzymes are released into the mouth,
stomach and intestines to help digest food molecules into smaller ones to be absorbed by cells
...
After
the enzymes have digested the food, the smaller molecules are absorbed through the cell walls of
the microorganism
...


B2
...
There are 3 factors that affect
the rate of enzyme action:
 Temperature
 pH
 Substrate concentration
Enzymes don’t work as well above or
below optimum temperature or pH
...
Most enzymes work at a pH of 7, but
some digestive enzymes prefer more acidic conditions
...
Beyond that, there is no change
in rate because the enzyme cannot work any faster on the
substrate than that
...
For example:
 Carbohydrases catalyse the breakdown of carbohydrates
 Proteases catalyse the breakdown of proteins
The substrate fits neatly into the active site of an enzyme
...
This is called
the ‘lock-and-key’ hypothesis
...


B2
...
More active cells require more energy
...
Growing and dividing cells also require
lots of energy
...
Blood also carries waste carbon dioxide away from respiring cells
...
This
occurs when the particles of a substance are spread out, and move from
areas of high concentration to low concentration
...

Oxygen:

Carbon Dioxide:

 RBCs

Glucose:

 Mitochondria

 Blood Plasma

 Cytoplasm

 Small pores

 Small Pores

 Tissue fluid

 Tissue Fluid

 Tissue fluid

 Small pores

 Cytoplasm

 Cytoplasm

 Blood plasma

 Mitochondria

 Blood Plasma

 Mitochondria

Lung tissue is spongy and full of alveoli
...
Carbon dioxide also leaves
the blood by diffusion into air spaces
...


B2
...
During exercise muscles use up oxygen and glucose quickly so blood supply to the muscles
must also increase
...

This is the volume of blood pumped out of the heart on each beat
...
To ensure it does,
breathing rate increases to increase oxygen intake from the lungs
...

When this happens, anaerobic respiration takes place:
Glucose

Lactic Acid

This releases less energy than aerobic respiration
...
After exercise increased oxygen is required to break down the lactic and
release energy for other processes such as cell repair
...
Heart rate and breathing rate
remain high after exercise so the extra oxygen can be obtained and distributed quickly
...
18 Photosynthesis
Starch is several thousand joined together glucose
molecules
...
Plants manufacture their own glucose using
photosynthesis
...
Chlorophyll inside the chloroplasts
allows them to absorb light energy needed for photosynthesis
...

Leaves have several adaptations which make them suited for photosynthesis
...
This
allows CO2 in the atmosphere to diffuse into the leaf and be taken by photosynthesising
cells
...

Water vapour produced also evaporates from their surfaces and diffuses out of the leaf
 Air spaces inside the leaf give a large surface area to volume ratio for efficient gas exchange

B2
...
For photosynthesis to take place there must be:
 Carbon dioxide
 Water
 Suitable temperature
 Enough light
A plant grown in dim light with enough carbon dioxide will photosynthesis slowly
...
In any
process affected by several factors, the maximum rate the process can go is controlled by the factor
in the shortest supply, or the limiting factor
...
21 Water Transport
Plant roots anchor the plant in the ground and take up water and mineral salts from the soil
...
The root hairs provide a large surface area for substances to enter the root
...
Water moves across a partially permeable membrane
from a region where water is in higher concentration to where water is in lower concentration
(diffusion)
...
Absorbing
particles against a concentration gradient is called active transport
...

Once water and minerals have entered the root cells, they need to get to all the plant’s tissues
...
Xylem tissue consists of
long, dead, hollow tubes
...
Phloem tissue transport
converted glucose into sucrose to other parts of the plant
...
This maintains a concentration gradient so that more water can evaporate
and diffuse out of the leaf
...


B2
...
Organisms must be
adapted to their environment and be able to respond to any changes
...
Sampling means looking at a small portion of an area or population
...
This can also be used to estimate a population size, by scaling up
the mean number of a plant in a quadrat
...
This investigates changes caused by one environmental factor
...
Placed in random locations and you count number and types of plants
...


B2
...
The more evidence we have, the better the
conclusions we can draw, and we can now use computers to model
how organisms might have looked
...
This suggests all vertebrates
evolved from a common ancestor hundreds of millions of years ago
...


B2
...
For example,
children are regularly measured from growth and are compared in a chart to find out which
percentile of the population they fit into
...
Cells continuously divide in meristems (areas behind the tips of
the roots and shoots)
...
As the plant stem or
root grows, older meristem cells specialise, or differentiate
...

Growth in animals also involves cell division, but animals stop growing when they become adults
...
(See B2
...

Human cells do not elongate
...
27 Blood
Blood is made up of four main components:

 Plasma – yellow liquid that transports dissolved substances e
...
carbon dioxide, food
substances and hormones
 Red blood cells – these contain the red pigment haemoglobin which combines with oxygen
to form oxyhaemoglobin
...
Oxyhaemoglobin is transported in RBCs around the body to tissues, where
the oxygen is released so tissue cells can respire
...
There is
no nucleus to make as much room for haemoglobin as possible



White blood cells – these are the body’s defence system to

disease
...
Others surround and destroy any
foreign cells that get into the body
...




Platelets – tiny fragments of cells with no nuclei
...
The clot dries and
forms a scab to prevent microorganisms entering the body
...
28 The Heart
An organ contains several different tissues working
together to carry out a specific function
...

 Blood coming from the tissues is deoxygenated
...
The two
sides of the heart are completely separated by the
septum
...


 Vena cava (vein)– brings blood from the body into the right atrium
...
This carries deoxygenated blood to the
lungs where it picks up oxygen
 The oxygenated blood returns from the lungs to the left atrium in the pulmonary vein
...
29 The Circulatory System
Groups of specialised cells working together are called tissues, and tissues working together are
called organs
...
The heart and blood vessels from an organ
system called the circulatory system
...
There
are three types:
 Arteries – these carry blood away
from the heart
...
Therefore arteries have
strong thick walls
...
To help this
process capillaries have very thin
walls
...
They
are wide because the blood flows slowly at a low pressure
...
30 The Digestive System
The digestive system is an organ system where food is broken down through a process called
digestion
...
g
...


1
...
Teeth break up food which increases the surface
area for enzymes to work on
...
This gets coated with saliva which lubricates it and makes it easier to swallow
...
Oesophagus – muscular tube between the mouth and stomach
...
This is called peristalsis
3
...
It churns up food
by peristalsis to make a thick paste
4
...
Contains digestive enzymes made by the pancreas,
and also makes its own enzymes
...
Food is moved along by peristalsis
5
...
Large intestine – undigested food passes into this wide, thin-walled tube
...
Anus – where the undigested food is passed out of the body
8
...
It is
then taken to the liver where some molecules are broken down even more
...
The liver makes bile, which helps with the digestion of fats
9
...
31 Breaking down Food
Different types of digestive enzyme break down the three main types of food molecules –
carbohydrates, proteins and fats
...

The digestive enzymes that break down carbs are called carbohydrases
...
Amylase is present in saliva, and another amylase in made in
the pancreas and released into the small intestine
...

Pepsin is a protease made in the stomach, working best in acidic conditions
...
However the contents of the small intestine are alkaline and so the proteases released into
the small intestine work best at pH 8
...
Lipases chemically break down fat molecules into fatty acids
and glycerol
...
Large
globules have a small surface area to volume ratio and so lipases can only break them down very
slowly
...
Smaller droplets have a larger surface area, making it easier for lipases to
break them down rapidly
...
The bile from the gall bladder is alkaline
...
32 Villi
Good blood supply:
The products of digestion must be absorbed into the blood from the small intestine to be delivered
to the cells where they are needed
...

Large SA:
The lining of the small intestine has millions of finger like folds called villi that increase the SA of the
small intestine
...
Each villus has a network of blood
capillaries
...
This steep
concentration gradient between the two areas means diffusion takes place rapidly
...
Therefore there is only a short distance for soluble molecules to diffuse
...
People affected cannot absorb the products of digestion properly, and become very
thin
...
34 Probiotics and Prebiotics
Functional foods claim to make you healthier
...
Manufacturers of probiotics
claim they make you healthier by improving your digestive system, helping fight diseases and
reducing allergies
...


Plant stanol esters are oily substances found in plants
...
They are now used
in yogurt, drinks and spreads and are proven to have an effect
...
They act as food for the beneficial bacteria in
the gut and encourage their growth
...
The evidence is growing that these can help maintain good
health

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