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B2 Revision
Topics 1-4
DNA Genes are made of a chemical called DNA. In DNA
there 4 bases called Adenine, Cytosine, Thymine and
DNA contains instructions for making the cell and
telling it what to do.
DNA gives order of amino acids, only one side acts as
a code for making proteins (Coding Strand)
Plants and animals have a similar structure. They
have a nucleus which holds DNA as a set of
chromosomes. Each gene contains information to
make one protein.
Fermentation •A micro-organism is a living thing that is so tiny it can only be seen through a
microscope. Scientists cultivate, or grow, microorganisms in a liquid that contains
nutrients - called culture medium.
•Scientists have to control the growth carefully otherwise they will produce very quickly. As
they grow the microorganisms use up the nutrients in the culture medium and produce
waste products and other substances. – this process is called FERMENTATION
•We use fermentation for making wine and bear by using yeast. The yeasts uses sugar as
a nutrient and as energy. The sugar is broken down to leave two waste products, carbon
dioxide and alcohol (ethanol). When making beer or wine, alcohol is the product wanted,
however, fermentation by microorganisms can be used to produce many other useful
products. To do this, the microorganisms are cultivated in tanks called FERMENTERS.
•Microorganisms are grown in fermenters to produce products. Such as yoghurt, cheese,
vinegar and soy sauce. They are also used to make a range of different enzymes needed
in industrial processes. Moulds and bacteria are used to make antibiotics such as
penicillin. These are all examples of fermentation.
•Bacteria and other microorganisms contain DNA. They use the same genetic code as
humans. Scientists can make the bacteria produce new products by changing their DNA.
First they have to identify the protein that is needed as a medicine, such as insulin, which
is needed to control diabetes. Then the cut out the section of the human DNA that is used
for making insulin. They then add that that DNA to the bacteria. The bacteria now contain
the gene for making insulin. If they are cultivated in a fermenter, this will grow
massive numbers of bacteria and will produce lots of insulin.
Protein synthesis -
To make proteins two things must happen:
1. The instructions from the code must be carried from the DNA
in the nucleus top the ribosomes. TRANSCRIPTION.
2. Amino acids must be bought to the ribosomes to be build up
into a protein. TRANSLATION.
It takes place in the nucleus. The DNA unzips and the mRNA
enters and copies from the coding strand of the DNA. (But U
replaces T). After coping the code the mRNA leaves the nucleus
through the 'nucleur pore'.
The mRNA goes to the ribosomes in the cytoplasm and the
tRNAs bring appropriate amino acids to translate the mRNA.
The amino acids join together to form a polypethide and many
polypethides make up a protein.
Protein synthesis Transcription
Protein synthesis Translation
Respiration Respiration is the process of breaking down glucose to release
energy which takes place in every cell in your body. All living
things respire.
Aerobic Respiration
This is using oxygen- remember 'air'obic. It's the most
efficient way to release energy from glucose.
Glucose + Oxygen -> Carbon Dioxoide + Water (+ Energy)
Anaerobic Respiration
This is without oxygen when there is not enough available. It's
not the most efficient way.
Glucose -> Lactic Acid (+Energy)
Growth Cell division results in growth
Growth is a permanent increase in the size or mass of an organism. All growth
results from the production of new calls by Mitosis the bigger the organism, the
more cells it contains.
Plants have a special way of growing, when new cells are formed around root and
stem tips, their cell walls are still soft. The cells absorb water into their vacuoles
and get longer. This process is called elongation as the cells get longer the roots
or shoots get longer. The cell wall hardens and the cell keeps its new shape.
There are different ways of measuring growth. One way is to simply weigh the
organism. Body cells contain a large amount of water so most of this weight will
be water; this is called the wet weight. The amount of water can vary so the
results may be inaccurate.
Another, more accurate method is to dry out the body first. This is called the dry
weight. This method kills the organism, so it if often only used to compare
growth in plants.
Another way is to look at size and length. Plants can be measured from the shoot
tip to ground level to give their height. Measuring across the widest part of the
plant is called it’s spread. Height and spread are used by garden centers and
plant catalogues so customers know big a plant will grow.
Cell Division -
Stem Cell Stem cells are found in all multi-cellular organisms. They are
characterized by the ability to be able to renew themselves
through mitotic cell division and differentiating in a large range
of specialized cell types. In a developing embryo, stem cells can
differentiate into all of the specialized embryonic tissues. In
adult organisms, stem cells and progenitor cells act as a repair
system for the body, replenishing specialized cells, but also
maintain the normal turnover of regenerative organs, such as
blood, skin, or intestinal tissues.
Self-renewal - the ability to go through numerous cycles of
cell division while maintaining the undifferentiated state.
Potency - the capacity to differentiate into specialized cell
Tough Decisions •Termination – The legal limit for abortion is 23 weeks. This is
because after 23 weeks the child is developed enough to be born
alive and survive independent of its mothers womb.
•There are many people who disagree with the legalization of
abortions and believe it’s against human rights. However, as
you can see from below, more people support it than not.
A 2009 poll by MORI surveyed women's attitudes to abortion.
Asking if all women should have the right of access abortion
37% Strongly agree
20% Tend to agree
12% Neither agree nor disagree
7% Tend to disagree
12% Strongly disagree
3% Don't know
9% preferred not to answer
Performance enhancing drugs –
•Lean mass builders - used to amplify the growth of muscle and lean
body mass, and sometimes to reduce body fat. E.g. anabolic steroids,
beta-2 agonists and various human hormones.
•Stimulants - used by athletes to stimulate their bodies and perform at
optimum level, usually to increase alertness, decrease fatigue, and/or
increase aggressiveness. E.g. caffeine and amphetamines.
•Painkillers - mask athletes' pain so they can continue to compete and
perform beyond their usual pain thresholds. Blood pressure is increased
causing the cells in the muscles to be better supplied with oxygen.
•Sedatives - used by athletes in sports like archery which require steady
hands and precise aim, and also by athletes attempting to overcome
nervousness. Alcohol and marijuana are examples.
•Diuretics - remove water from athletes' bodies. They are often used by
athletes who need to meet weight restrictions.
•Masking drugs - used to stop detection of other drugs. An example is the
use of epitestosterone, it restores the testosterone to normal levels after
anabolic steroid supplementation.
Plant hormones Auxin - needed for plant growth. It controls the growth of roots
and shoots. Auxin is stored in the tips of new shoots and roots,
and causes growth by diffusion.
If you cut the tip off a shoot, the shoot will stop growing. If
the tip is replaced, it starts to grow again. However, auxin stops
sideward growth, so if the tip is removed, the shoot will grow
There is a different effect of auxin in roots. It prevents growth
vertically. This means the root will grow toward moisture, not
downward with gravity. This causes a build-up of auxin on the
bottom edge of the root.
If there is a build up of auxin on one part of a root or shoot, it
causes only the top side to grow, making the shoot/root bend
upward/downward respectively.
Plant hormones Gibberellin - promotes cell division and elongation. It also
helps seeds to sprout.
Cytokinin - also promotes cell division. High levels of this
hormone are found in areas of the plant that require the most
growth, such as roots, young leaves and developing fruits and
Abscisic acid - slows down the plant's metabolism so that it
doesn't grow during the winter. This leaves the plant more time
for phothesis and can help the plant survive harsh winter
Ethylene - after auxin/gibberellin initiates fruit growth,
ethylene helps the fruit to ripen.
Artificial selection Cut an earthworm in half and its head end will grow a tail. This
is called regeneration.
Only a few animals have this ability. No mammals have this
When an animal loses a part of its body, the cells around the
structure change their structure and become less
specialized. The cells then differentiate again to produce all
the different types of cell needed to grow the new limb.
Stem cell research is looking at these animals to try to find a
way to regenerate human body parts.
Selective breeding
Selective breeding means breeding from
individuals that have the characteristics you
most want. This increases the chance that
more offspring will also have these
Selective breeding can improve resistance to
disease, increase yield and make foods more
attractive to consumers.
Selective breeding can be used
in animals and plants.
Cloning Cloning is using an organisms DNA to create a genetically
identical new organism.
1. A sheep's egg cell is taken and the nucleus is removed.
(Haploid-it was a gamete)
2. Another nucleus was inserted into the egg cell, it was a
diploid nucleus from the cell of a parent sheep. It had the full
number of chromosomes. This is nucleus transfer.
3. The cell was stimulated, divided by mitosis and forms an
4. The embryo was implanted into the uterus of a female sheep,
which gives birth to it. The new sheep is genetically identical to
the parent sheep which the nucleus was taken from
Gene therapy Gene Therapy Could be Used to Treat Genetic Disorders
• Gene therapy is a new, experimental treatment for genetic
• It can involve inserting a new, functional version of a faulty
gene into a patient’s cells. These cells would then be able to
make the correct protein and the symptoms would disappear.
• Gene therapy would be targeted at areas that were badly
affected by the disease.
• In the long term, scientists hope to make these changes to the
patient’s DNA permanent, but so far, trails testing gene therapy
have only shown very temporary improvements.
• Gene therapy still needs a lot of researching and testing.
Potential dangers of gene therapy have already been found, e.g.
the introduced genetic material could insert into the middle of
another gene, causing a whole new set of medical problems, or
‘suicide genes’ could be taken up by health cells.
Cells Animal cells usually have an irregular shape, and plant cells usually have a regular shape
Cells are made up of different parts. It is easier to explain what these parts are by using
diagrams like the ones below.
Cells are very small. They are the basic
building blocks of all animals and plants.
Cell part
controls what goes in and out of
the cell
Animal cells and plant cells both contain:
cell membrane, cytoplasm, nucleus
controls the cell, contains DNA
Plant cells also contain these parts, not found in animal cells:
where chemical
chloroplasts, vacuole, cell wall
The table summarises the functions of these parts.
contains chlorophyll for
Photosynthesis -
Photosynthesis is when plants turn
energy from the sun into food
(Glucose) by using carbon dioxide. A
waste product (Oxygen) is formed.
Carbon + Water --> Glucose +
Limiting factors to photosynthesis -
•CO2 levels
If any of these increases, the rate of photosynthesis will increase up to a
point when one of the others has become the limiting factor.
If the temperature exceeds 45 degrees then the enzymes will denature
and the rate of photosynthesis will rapidly decrease.
Carbon cycle -
Nitrogen cycle Nitrogen is an important element in living things. It is found in
proteins and DNA. Plants get nitrogen in the form of nitrates
which they get from soil. The nitrogen can then pass into
animals as they eat the plants . Nitrogen is naturally recycled in
a similar way to the carbon cycle.
Nitrogen is mainly recycled by microorganisms in the soil.
Decomposers break down dead organisms and animal waste
(manure and urea) into ammonia, which contains nitrogen.
Nitrifying bacteria then use a series of reactions to convert the
ammonia into nitrates that plants can absorb.
Modern agriculture is extremely intensive. The natural nitrogen
cycle cannot replace nitrates as quickly as they are removed, so
farmers add industrially made nitrate fertilizers. However this
can cause problems in the local rivers.
Deforestation & global warming -
Extreme environments Organisms need to adapt to survive.
They need; a source of energy/food, water, a suitable temperature and a
source of oxygen to survive.
Black smokers are hydrothermal vents and the environment around
them is ‘extreme’. Magma heats up water and it is released as steam
through a vent into the sea. This makes the sea hot and acidic.
High altitudes (3000m+) are also ‘extreme’. Animals like snow leopards
adapt to have thick fur and can cope with low oxygen levels and high
levels of UV light.
The Antarctic is also ‘extreme’. The temperature can be as low as -70
Degrees Center grade, so animals like penguins have thick fur and fat
layers and group together in order to share warmth.
Adaptation Every organism in a habitat is adapted to living in that habitat.
This means they have evolved adaptations to survive in particular
conditions or environmental factors.
These factors include water, oxygen, light, temperature and the
other living organisms in the habitat.
If one of these factors change it will effect some of the organisms. Eg: if
less light reaches the bottom of a lake, some plants will no longer be
able to survive and die out. This causes less food for other organisms
living in that habitat.
Any organism that can’t adapt to the changes in the environment are
likely to have a smaller population. This may cause them to die out
altogether and become extinct.
Predation -
Competition -
Air pollution There are many causes of air pollution, but most of it is made from humans.
Nitrous oxide and carbon dioxide are the 2 main pollutants of the air carbon
dioxide comes burning our waste and such so we should recycle more. Volcanoes
also can be a big cause of air pollution from the gases that are giving off, but when
a volcanoes erupts it gives off many dangerous gases that we will end up breathing
into our lungs that will damage us but they also damage the environment by
emitting some harmful gases. A good example of a harmful gas was the great
London smog. This was harming the ozone layer and making it difficult for people
to breath outside of their homes. This is affecting many things such as habitats of
animals because the gases in the air are causing a lot of acid rain is being
produced destroying our environment at the same time as destroying our ozone.
The gas that is causing this is sulpher dioxide which we can decrease by taking
better care of our environment. We need to act now to make a change for the
better soon
As you can see by this graph
the rise in the pollution in the air has
increased dramatically in in the last
2000 years and it is making it more
difficult to sort out the problem.
Water pollution Two main types of water pollution – ACID RAIN and FERTILISERS
The main causes of acid rain are the burning of fuels and vehicle exhausts. These produce
the air pollutants of sulphur dioxide (SO2) and Nitrogen oxide (NO2).
These pollutants dissolve in water to form acids (ACID RAIN)
1. The fertiliser runs of into a river or pond.
2. The fertiliser makes the algae grow fast. The increased algae growth cuts out sunlight
and uses up oxygen.
3.The plants do not get enough sunlight and they die. Dead plants and algae build up on
the river/ pond bed.
4. The dead plants and algae rot, using up oxygen in the water. There are fewer animals in
the water.
Recycling -
-Recycling has many benefits. If all the glass, metals, plastic and paper in our
dustbins were recycled that would be nearly half the contents of the average bin.
- This could reduce the problem of waste disposal and landfill sites that are
getting full.
- Recycling uses less energy and produces less damaging carbon dioxide than
manufacturing new materials.
- For Example, recycled steel uses 75% less energy and produces only 15% of the
carbon dioxide produced when steel is made from iron ore.
- Not everything can be recycled and some materials are more difficult to recycle
than others.
- Plastics have to be sorted by hand and many types are not suitable for re-use
- Paper can only be recycled about five times before the fibres become too short
and weak.
- Refrigerators are a particular problem because of the harmful gases they
- Although recycling uses less energy and resources it is still an industrial
- Some materials need a lot of cleaning and reprocessing. Where materials are
difficult to recycle it can be easier and cheaper to make new products.
Environment, the human effect Human activity can have negative effects on
the environment. Manufactured gases called
CFCs have damaged the ozone layer in the
upper atmosphere. Ozone filters out much of
the ultraviolet light from the Sun, which can
damage the skin possibly leading to skin
cancer. Cases of skin cancer have almost
doubled in UK in the last 20 years therefore
the ozone layer is not protecting us as well as
it used to.
Lichens are good indicators of our impact
on the environment as they are very
sensitive to air pollution, especially sulphur
Mayfly larvae are found only in very clean
water with lots of oxygen. They are used as
living indicators to monitor water quality in
streams. Lots of mayfly larvae means that a
stream has high quality water.
Species in peril Species in peril means animals that are rare because they are in
danger or cannot adapt to climate change. Every time a species
becomes extinct biodiversity is reduced.
Careful management of the environment is called conservation.
The causes of this are: deforestation, hunting, co2 levels rising,
building and economy development, landfill sites.
All of these species are forced out of habitats because of these
causes and if we cut down on co2 levels and recycle more we could
improve the lives of us and animals.
More and more plants and animals are become extinct or rare
because of the changing climate due to our actions.
Two of every five species on the planet that have been assessed by
scientist face extinction.
Conservation managment Conservation measures protect species by maintaining their habitats and protecting them
from poachers and overhunting/havesting
There are several reasons why it’s important to conserve species and natural habitats:
Protecting endangered species – Many species are becoming endangered, often due
to hunting and the destruction of their habitats. They need to be protected to stop them
becoming extinct.
Protecting the human food supply – Overfishing has greatly reduced fish stocks in the
sea. Conservation measures (e.g. quotas on how many fish can be caught) encourage the
survival and growth of fish stocks. This protects the food supply for future generations.
Maintaining biodiversity – Biodiversity is the variety of different species in a habitat –
the more species there are, the greater the biodiversity. If one species in a habitat is
destroyed it affects the other species living there – the food web will be affected. It’s
important to protect biodiversity.
You can…
Coppicing – this involves cutting down trees down to just above ground level. The stumps
sprout straight, new stems which can be regularly harvested.
Reforestation – you can replant to recreate the habitat that has been lost.
Replacement planting – This is when new trees are planted at the same rate that others
are cutting down. So the total of trees remains the same.
Effects of exercise When you exercise, your muscles get energy from respiration. Glucose
and oxygen must be supplied while carbon dioxide is removed.
glucose + oxygen
carbon dioxide + water (+ energy)
If you exercise more vigorously, your muscle cells need more energy to
do the extra work. They need to respire faster, this means:
More oxygen must be absorbed by your lungs.
More carbon dioxide must be removed by your lungs.
More oxygen and glucose must be delivered to your muscles by your
More carbon dioxide must be removed from your muscles by your
Your breathing system and heart have to work harder. You breathe
faster and more deeply. This increases the rate of gas exchange in your
lungs: more oxygen is absorbed into your blood and more carbon
dioxide is removed. Your heart rate also increases, pumping more
blood to your muscles.
Improving measurements -