Biology Revision Essays

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What is the main job of the heart?
To pump blood, containing oxygen and nutrients, around the body.
Describe and explain red blood cells (2)
These are round, bi-concave shaped cells which carry oxygen around the body in a chemical called haemoglobin
Describe and explain platelets (2)
These make blood clot by binding together by acting on a protein called fibrinogen to provide a seal for wounds.
What are the differences between the three vessels (arteries, veins and capillaries)? (6)
Arteries carry oxygenated blood away from the heart at a high pressure. Therefore, they have thick elastic walls containing smooth muscle, and have narrow lumens and a pulse.
However, veins carry deoxygenated blood towards the heart at a low pressure. They often have valves to prevent the backflow of blood and do not have a pulse.
Capillaries are very narrow, with their walls consisting of a single flattened cells. They link branches of arterioles to branches of venules, and the exchange of substances takes place in them.
What is genetic engineering?
The deliberate modification of an organism's genes.
Give an advantage for GE
You can produce organisms with desirable features quickly
Give a disadvantage for GE
The inserted genes may have unexpected harmful effects, for example if the organism's genes mutated, it could become dangerous and unpredictable.
What are the stages of GE? (3/4)
The gene responsible for producing the desirable characteristic is selected, then cut from the DNA using enzymes, and isolated. The gene is inserted into the DNA of another organism, which then replicates, so there are multiple genetically modified organisms.
What are the stages of cloning Dolly?
First, the nucleus of a sheep's egg cell was removed to make it an empty foster egg. Then another nucleus, containing the useful genetic information, was inserted into the egg. The cell was then stimulated with an electric shock so it started dividing by mitosis, like a normal fertilised egg. The now embryo is implanted into a surrogate mother, to develop until its birth. This is called nuclear transfer.
What are the
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