This document contains model answers for questions within biology topic 1 (lifestyle, health and risk), topic 2 (Genes and health), topic 3 (the voice of the genome), topic 4 (biodiversity and natural resources)
Suggest why multicellular organisms have a circulatory system (3 marks)
To pump oxygen and glucose around the body and overcome the limitations of diffusion as
multicellular organisms have a small surface area to volume ratio
Suggest how double circulation enables mammals to carry out effective gas exchange
The left side of the heart pumps blood to the body and the right side pumps blood to the
lungs. The two sides are separated by the septum which prevents oxygenated and
deoxygenated blood from mixing, allowing a high concentration gradient for diffusion to be
maintained.
Explain why many animals need a heart and circulatory system (4 marks)
The heart is needed to pump blood containing oxygen and glucose around the body. Many
animals have a small surface area to volume ratio, therefore they cannot depend on diffusion
alone which is why the circulatory system and heart is needed to overcome the limitations of
diffusion. The circulatory system is also needed to meet the high demand for oxygen as
many animals have a high metabolic rate.
Describe how atherosclerosis develops (6 marks)
High blood pressure causes damage to the endothelium of the coronary arteries which then
initiates an inflammatory response. Macrophages will then migrate to the damaged area,
engulf LDL cholesterol and become foam cells. The foam cells burst and release LDL
cholesterol into the damaged endothelium. Cholesterol builds up in the damaged
endothelium and the cholesterol as well as calcium salts and fibrous tissue form an
atheroma . This results in the narrowing of the lumen of the artery and loss of elasticity in the
walls of the artery. This will increase the blood pressure and cause further damage to the
endothelium which is the reason as to why atherosclerosis is said to be self perpetuating.
Explain why a stent is used in the treatment of atherosclerosis in a coronary artery
To widen the lumen of the coronary artery and restore blood flow so that there is more
oxygen and glucose getting to the cells for aerobic respiration to take place as the atheroma
had blocked and narrowed the coronary artery, reducing the blood flow.
Describe the blood clotting process (6 marks)
The blood clotting process can be described as a cascade of events. Thromboplastin, an
enzyme, is released from platelets and damaged cells. Thromboplastic catalyses the
conversion of prothrombin into the enzyme thrombin. Thrombin then catalyses the
conversion of soluble fibrinogen into insoluble fibrin. These form a mesh of fibres which
trapm blood cells and platelets. Calcium ions and vitamin K atre also required for the clotting
process.
, Explain how a blockage in the coronary arteries could result in a myocardial infarction (heart
attack) (6 marks)
A blockage in the coronary artery restricts blood flow to the heart cells. This results in less
oxygen and glucose reaching cells of the heart, therefore there will be less aerobic
respiration. Anaerobic respiration begins which results in a buildup of lactic acid in the heart
cells. This reduces the pH and the enzymes denature. There is also insufficient ATP
produced to enable contraction of heart muscle and the cells begin to die.
Explain how a blockage in the arteries leading to the brain could result in an individual
suffering a stroke (6 marks)
A blockage in an artery leading to the brain restricts blood flow to the brain cells. This results
in less oxygen and glucose reaching the brain cells, therefore there will be less aerobic
respiration. Anaerobic respiration begins. This results in a buildup of lactic acid in the brain
cells which reduces the pH and the enzymes denature. There’s also insufficient ATP
produced to enable brain cells to function and the cells begin to die.
Describe an investigation that could be carried out to find out the effect of caffeine on
Daphnia
Using a pipette remove a Daphnia and place onto a microscope slide with a few strands of
cotton wool to immobilise it. Ensure that all Daphnia used are the same size, species and
have the same level of motility. Add three drops of pond water (this acts as a control at 0%
caffeine). Allow Daphnia to acclimatise for 3 minutes before counting the heart rate (this can
be any number, I just chose 3 but if you change the number make sure it’s not too long,
maybe maxxxx 10 minutes and make sure to say you are keeping it the same for each
daphnia). Using a microscope, identify the heart, count the heart rate for 15 seconds and
multiply by 4 to convert to beat per minute. Repeat 3 times to calculate the average heart
rate (discard anomalies). Repeat the procedure for 0.1%, 0.2%, 0.3%, 0.4% and 0.5%
caffeine.
Give two reasons why Daphnia is a suitable organism for investigating the effect of caffeine
on heart rate (2 marks)
Daphnia are ideal as they are transparent, therefore you can see their heart. There are fewer
ethical concerns as they are invertebrates and simple organisms with a less developed
nervous system, therefore they aren’t likely to feel pain. Extra point if you forget others -
Daphnia can also absorb caffeine from the surrounding solutions very quickly
State 2 variables that you would need to control for a valid investigation into the effect of
caffeine on the heart rate of Daphnia
The volume of caffeine solution should be controlled and can be controlled by using a pipette
to deliver 2cm3 of each concentration of caffeine. The time for the Daphnia to acclimatise
should be controlled and can be controlled by leaving the Daphnia to acclimatise for 3
minutes at each concentration of caffeine and use a stopwatch to time 3 minutes. Extra point
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