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Biology – Key Themes Unit 3
There are several processes or ideas in biology which you need to be able to explain
clearly. These questions frequently arise in exams and are often worth between 2-6
marks.
Here are some for you to learn:
1. What is osmosis? (2 marks)
 Osmosis is the movement of water from a dilute to a more concentrated
solution
 Across a partially permeable membrane
2. How does active transport differ from diffusion? (2 marks)
 Active transport moves substances from a low to a high concentration (Diffusion
moves substances from a high to a low concentration
 Active transport requires energy (diffusion does not)
3. How do isotonic drinks rehydrate body cells after intense exercise? (3 marks)
 Isotonic drinks are the same concentration as your body cells
 They contain lots of water so that it can move into the cells by osmosis
 They contain salt and sugar which move into your cells by diffusion and active
transport
4. Explain why the lungs are an effective gas exchange surface (3 marks)
 Lungs have a large surface area – provided by alveoli
 Alveoli and capillaries have thin walls – providing a short diffusion distance
 There is an efficient blood supply – lots of capillaries
 There is a high concentration gradient – lots of oxygen in the alveoli due to
frequent breathing and low concentration in blood due to constant circulation
5. How do we breathe in? (4 marks)
 Intercostal muscles and diaphragm contract (diaphragm flattens)
 Ribs move up and out
 Volume increases in thorax (chest)
 Pressure decreases in thorax (chest)
 Air moves from a higher pressure outside of the lungs into the lungs
*Remember breathing out is just the opposite of each of these statements*
6. Explain how a negative pressure breathing aid works (3 marks)
 Patient lies with their chest inside a sealed metal cylinder
 Air is pumped out of the chamber creating a vacuum
 This causes the chest wall to move up – increasing the volume – and decreasing
the pressure
 This allows the patient to breathe in (air moves from a higher pressure outside
of the lungs into the lungs)
7. Explain how a positive pressure breathing aid works (2 marks)
 Forces a measured ‘breath’ of air into the lungs (like blowing up a balloon)
 Once the lungs have been inflated the air pressure stops so that the lungs can
deflate back to their original size
8. Explain why the small intestine is an effective exchange surface (3 marks)
 Large surface area – provided by villi and microvilli
 Thin walls – providing a short diffusion distance
 There is an efficient blood supply – lots of capillaries
 There is usually a high concentration gradient – lots of nutrients in the small
intestines after a meal and low concentration in blood due to constant
circulation
9. Describe how a leaf is adapted for gas exchange (2 marks)
 Stomata and guard cells – on the underside of a leaf which allow gases to diffuse
in and out when required
 Concentration gradient maintained as plants are using carbon dioxide during
photosynthesis (there will be a low concentration in the cells and a higher
concentration in the air)
10. Explain the process of transpiration (3 marks)
 Water evaporates from the surface of the leaves
 Water is pulled through the xylem to take its place
 This is called a transpiration stream
 Water moves into the roots by osmosis to replace this water
11. Describe how a named factor can affect the rate of transpiration (2 marks)
 Increased wind/Increased light intensity/Increased temperature/ Decreased
humidity
 Increases the rate of evaporation
 Which creates a transpiration stream
12. Describe an experiment which can be used to test the rate of transpiration (2 marks)
 Use a potometer
 Has a bubble which moves closer to the plant when transpiration occurs
 The bubble will move quicker, the quicker that transpiration occurs
13. Describe the journey of blood through the right side of the heart (4 marks)
 Deoxygenated blood goes in through the vena cava
 Into the right atrium
 Through an atrioventricular/cuspid valve
 Into the right ventricle
 Out of the pulmonary artery (to the lungs)
14. Describe the journey of blood through the left side of the heart (4 marks)
 Oxygenated blood goes in through the pulmonary vein
 Into the left atrium
 Through an atrioventricular/cuspid valve
 Into the left ventricle
 Out of the aorta (to the body)
15. Compare and contrast the 3 main types of blood vessel (4 marks)
 Arteries carry blood away from the heart, veins carry blood towards the heart
 Arteries have thicker walls than veins containing muscle and elastic tissue
 Veins contain valves to stop blood flowing backwards, arteries do not
 Capillaries have very thin walls to allow substances to diffuse in and out
16. Explain what causes a heart attack (myocardial infarction) (3 marks)
 Coronary arteries become narrower due to fatty deposits
 Blood flow to the heart tissue is blocked
 Heart tissue doesn’t get oxygen for respiration
 Heart tissue dies – causing a heart attack
17. Describe how stents can be used to prevent heart attacks (2 marks)
 A stent is a metal mesh which is placed in to an artery to hold it open
 A balloon is inflated to help put the stent in place in the artery
18. Describe the role of the 4 main components of blood (4 marks)
 Reds blood cells – carry oxygen
 White blood cells – are part of the body’s defence against microbes (producing
antibodies)
 Platelets – are small fragments of cells that form a clot at the site of a wound
 Plasma – fluid which contains blood cells, carbon dioxide, urine and hormones
19. Explain how red blood cells are adapted to perform their job (3 marks)
 Biconcave discs - increasing surface area for carrying oxygen
 No nucleus – increasing space for carrying oxygen
 Contain haemoglobin which combines with oxygen to form oxyhaemoglobin
20. What are the advantages and disadvantages of using donor blood? (3 marks)
 Advantage - donor blood can do all the same functions as artificial blood
(carrying oxygen, clotting etc.)
 Disadvantage – donor blood is not always readily available
 Disadvantage – donor blood has to be the same blood type has the recipient
21. What are the advantages and disadvantages of using artificial blood? (3 marks)
 Advantage – artificial blood does not need to be refrigerated (donor blood does)
 Advantage – it does not contain cells do blood matching is not necessary
 Disadvantage – expensive
 Disadvantage – does not carry as much oxygen as normal blood
 Disadvantage – can cause unpleasant side effects
22. Use examples to explain what is meant by the term homeostasis (3 marks)
 Homeostasis = controlling internal conditions in the body
 Temperature must be kept around 37°C (monitored by brain – hypothalamus)
 Glucose levels must be kept constant (monitored by pancreas)
 Water levels must be kept constant (monitored by kidneys)
 Waste must be removed (by kidneys)
23. Describe the processes which lead to the production of urine by the kidneys (4 marks)
 The kidney filters the blood – all small molecules leave into the filtrate
 Large molecules – e.g. protein and blood cells stay in the blood
 Useful molecules are reabsorbed – e.g. glucose, dissolved ions and as much
water as the body needs
 Urea, excess ions and water stay in the filtrate and pass from the kidney to the
bladder as urine
24. Describe how a dialysis machine can be used to artificially filter blood (4 marks)
 Blood leaves the arm and passes through partially permeable membranes in the
dialysis machine
 The dialysis machine contains dialysis fluid which contains the same
concentration of useful substances as the patients’ blood
 This means that useful substances, e.g. glucose, do not leave the blood by
diffusion
 But urea diffuses out of the blood into the dialysis fluid
25. Explain the advantages and disadvantages of treating kidney failure with a transplant
(4 marks)
 Advantage – patient no longer needs dialysis
 Advantage – cheaper in the long-term, as regular hospital visits are no longer
needed
 Disadvantage –Kidney must be a good ‘match’ to prevent rejection
 Disadvantage – There aren’t enough donors – creating ‘waiting lists’
 Disadvantage – Recipient must take immunosuppressant drugs to prevent
rejection
26. Describe the role of the thermoregulatory centre in monitoring core body
temperature (4 marks)
 Body temperature is monitored by the brain (thermoregulatory
centre/hypothalamus)
 Receptors detect a change in blood temperature
 If core temperature rises, the following effectors are triggered: increased blood
flow to the surface of the skin (vasodilation), sweat glands produce sweat
 If core temperature falls, the following effectors are triggered: decreased blood
flow to the surface of the skin (vasoconstriction), shivering of muscles to release
heat energy
27. Explain what type 1 diabetes is and how it can be treated (3 marks)
 Type 1 diabetes is when no/too little insulin is produced
 It is controlled using insulin injections
 And careful attention to diet and levels of exercise
28. Describe the role of the pancreas in monitoring blood glucose levels (6 marks)
 Pancreas detects a change in blood glucose levels
 If blood glucose levels are too high – insulin is released
 Insulin causes cells/liver/muscle to take insulin in to cells from the blood
 Glucose is converted into glycogen
 If blood glucose levels are too low – glucagon is released
 Glucagon causes glycogen to be converted back into glucose
 Glucose is then released from cells/liver/muscle back in to the blood
29. Explain the cause of acid rain (3 marks)
 Sulfur dioxide is released in to the air by combustion of coal
 Sulfur dioxide dissolves in water in the air forming acid
 The solution falls as acid rain – this can be blown by the wind far away from
where the gases were produced
30. Describe the greenhouse effect (3 marks)
 Levels of greenhouse gases (e.g. carbon dioxide and methane) are released into
the atmosphere
 Greenhouse gases trap solar energy (infra-red radiation) and reflect it back to
earth
 This causes an increase in average Earth temperatures
31. Describe the impact of global warming on ecosystems (3 marks)
 Rises in sea levels due to melting of ice caps and glaciers  flooding
 Reduces biodiversity
 Can cause changes in migration patterns
 Can result in changes in distributions of species
32. Describe how bioethanol is produced and explain why it is carbon neutral (4 marks)
 Sugars are extracted from crops such as maize
 Sugars are fermented by yeast to produce ethanol
 The ethanol is extracted by distillation
 It is carbon neutral because it only replaces the carbon dioxide into the
atmosphere which was taken out by plants in the first place
33. Explain why intensive farming is more energy efficient than organic farming (4 marks)
 Animals in small enclosures – less movement = less energy lost due to
respiration
 Animals kept in warm sheds – less energy lost to maintain body temperature
 Antibiotics are put in food - to prevent the spread of infection
 Animals kept in sheds – to keep predators out
34. Explain what is meant by the term ‘sustainable fishing’ (3 marks)
 Sustainable – managing resources so that they don’t run out
 Fishermen have quotas – a strict allocation of fish per year
 Fishermen have certain sized nets to avoid catching young fish before they
reproduce
35. Explain how fusarium is produced sustainably on an industrial scale (4 marks)
 Fusarium is a protein-rich fungus, this is suitable for vegetarians
 The fungus is grown on a large scale in industrial fermenters
 The fermenters provide – oxygen for respiration
 The fermenters have a water-cooling jacket to prevent enzymes from
denaturing