Biology

1. 1.

   Explain two ways in which a red blood cell is adapted to transport oxygen efficiently.

   [4 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: Its biconcave shape gives a large surface area. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: The large surface area increases the rate of oxygen diffusion. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: It has no nucleus, leaving more space for haemoglobin. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Develop this part of the answer: Haemoglobin binds oxygen for transport. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: For each feature, state how it improves oxygen transport.

   Marking points

   • Its biconcave shape gives a large surface area.
   • The large surface area increases the rate of oxygen diffusion.
   • It has no nucleus, leaving more space for haemoglobin.
   • Haemoglobin binds oxygen for transport.

   Examiner tip: For each feature, state how it improves oxygen transport.

2. 2.

   Grass stores 18 000 kJ of energy. Rabbits feeding on the grass store 1800 kJ. Calculate the percentage energy transfer and explain why not all energy is transferred.

   [4 marks]

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
   2. Work through this mathematical step: Uses percentage transfer = 1800 ÷ 18 000 × 100. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
   3. Develop this part of the answer: Obtains 10%. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: Some energy is released as heat during respiration. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Develop this part of the answer: Some material is not eaten or is lost in waste products. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Give biological reasons for loss, not only that energy is 'used'.

   Marking points

   • Uses percentage transfer = 1800 ÷ 18 000 × 100.
   • Obtains 10%.
   • Some energy is released as heat during respiration.
   • Some material is not eaten or is lost in waste products.

   Examiner tip: Give biological reasons for loss, not only that energy is 'used'.

3. 3.

   Describe the path taken by blood as it flows through the heart from the vena cava to the aorta, naming the chambers and valves in order.

   [4 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that deoxygenated blood enters the right atrium from the vena cava. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that blood passes through the tricuspid valve into the right ventricle, then to the lungs via the pulmonary artery. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that oxygenated blood returns from the lungs via the pulmonary vein into the left atrium. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Develop this part of the answer: States that blood passes through the bicuspid (mitral) valve into the left ventricle, then out through the aorta to the body. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The right side of the heart always deals with deoxygenated blood (to the lungs) and the left side always deals with oxygenated blood (to the body) — never confuse the two sides.

   Marking points

   • States that deoxygenated blood enters the right atrium from the vena cava.
   • States that blood passes through the tricuspid valve into the right ventricle, then to the lungs via the pulmonary artery.
   • States that oxygenated blood returns from the lungs via the pulmonary vein into the left atrium.
   • States that blood passes through the bicuspid (mitral) valve into the left ventricle, then out through the aorta to the body.

   Examiner tip: The right side of the heart always deals with deoxygenated blood (to the lungs) and the left side always deals with oxygenated blood (to the body) — never confuse the two sides.

4. 4.

   Explain why the left ventricle of the heart has a much thicker muscular wall than the right ventricle.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that the left ventricle must pump blood at high pressure to reach the entire body, a much longer and higher-resistance circuit. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that the right ventricle only needs to pump blood at lower pressure to the nearby lungs, a much shorter, lower-resistance circuit. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that a thicker muscular wall allows the left ventricle to contract with greater force, generating the higher pressure needed for the body's systemic circulation. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Wall thickness in the heart's chambers always correlates with the pressure that chamber needs to generate — the same principle applies to comparing atria (thin) with ventricles (thick).

   Marking points

   • States that the left ventricle must pump blood at high pressure to reach the entire body, a much longer and higher-resistance circuit.
   • States that the right ventricle only needs to pump blood at lower pressure to the nearby lungs, a much shorter, lower-resistance circuit.
   • States that a thicker muscular wall allows the left ventricle to contract with greater force, generating the higher pressure needed for the body's systemic circulation.

   Examiner tip: Wall thickness in the heart's chambers always correlates with the pressure that chamber needs to generate — the same principle applies to comparing atria (thin) with ventricles (thick).

5. 5.

   Outline the roles of insulin and the liver in maintaining a stable blood glucose concentration after a meal.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that after a meal, blood glucose concentration rises, and the pancreas responds by secreting insulin. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that insulin causes the liver (and muscle cells) to take up excess glucose from the blood. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that the liver converts this glucose into glycogen for storage, lowering blood glucose concentration back towards normal. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The liver's storage of glucose as glycogen is the key mechanism linking hormonal control (insulin) to an actual change in blood glucose concentration.

   Marking points

   • States that after a meal, blood glucose concentration rises, and the pancreas responds by secreting insulin.
   • States that insulin causes the liver (and muscle cells) to take up excess glucose from the blood.
   • States that the liver converts this glucose into glycogen for storage, lowering blood glucose concentration back towards normal.

   Examiner tip: The liver's storage of glucose as glycogen is the key mechanism linking hormonal control (insulin) to an actual change in blood glucose concentration.

6. 6.

   Describe the process of gas exchange occurring in the alveoli of the lungs.

   [4 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that oxygen concentration is higher in the alveolar air than in the blood in the surrounding capillaries. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that oxygen diffuses from the alveolar air into the blood, down its concentration gradient. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that carbon dioxide concentration is higher in the blood than in the alveolar air, so carbon dioxide diffuses from the blood into the alveolar air. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Develop this part of the answer: States that the thin walls of the alveoli and capillaries, and the large surface area of the alveoli, allow rapid diffusion of these gases. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Always state the direction of diffusion for each gas explicitly, based on comparing its concentration in the air and the blood.

   Marking points

   • States that oxygen concentration is higher in the alveolar air than in the blood in the surrounding capillaries.
   • States that oxygen diffuses from the alveolar air into the blood, down its concentration gradient.
   • States that carbon dioxide concentration is higher in the blood than in the alveolar air, so carbon dioxide diffuses from the blood into the alveolar air.
   • States that the thin walls of the alveoli and capillaries, and the large surface area of the alveoli, allow rapid diffusion of these gases.

   Examiner tip: Always state the direction of diffusion for each gas explicitly, based on comparing its concentration in the air and the blood.

7. 7.

   A predator-prey population graph shows fox and rabbit numbers oscillating, with fox numbers peaking shortly after rabbit numbers peak. Explain this pattern.

   [4 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that as rabbit (prey) numbers increase, there is more food available for foxes (predators). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that this leads to increased fox survival and reproduction, so fox numbers subsequently increase (with a time lag). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that increased fox numbers then leads to greater predation on rabbits, causing rabbit numbers to fall. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Develop this part of the answer: States that as rabbit numbers fall, food becomes scarcer for foxes, causing fox numbers to fall too, allowing rabbit numbers to eventually recover and the cycle to repeat. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The time lag between prey and predator population peaks is the key feature of predator-prey cycles — the predator population always responds after, not simultaneously with, the prey population.

   Marking points

   • States that as rabbit (prey) numbers increase, there is more food available for foxes (predators).
   • States that this leads to increased fox survival and reproduction, so fox numbers subsequently increase (with a time lag).
   • States that increased fox numbers then leads to greater predation on rabbits, causing rabbit numbers to fall.
   • States that as rabbit numbers fall, food becomes scarcer for foxes, causing fox numbers to fall too, allowing rabbit numbers to eventually recover and the cycle to repeat.

   Examiner tip: The time lag between prey and predator population peaks is the key feature of predator-prey cycles — the predator population always responds after, not simultaneously with, the prey population.

8. 8.

   Outline the function of the kidney in removing urea from the blood, and state why urea must be removed from the body.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that the kidney filters blood, removing urea (along with water and other substances) into the nephron tubules to form urine. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that urea is produced in the liver from the breakdown of excess amino acids (deamination). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that urea is toxic and must be removed from the body (excreted) to prevent it accumulating to harmful levels in the blood. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Urea is a waste product of amino acid breakdown in the liver, then removed from the blood by the kidney — do not confuse where it is produced with where it is removed.

   Marking points

   • States that the kidney filters blood, removing urea (along with water and other substances) into the nephron tubules to form urine.
   • States that urea is produced in the liver from the breakdown of excess amino acids (deamination).
   • States that urea is toxic and must be removed from the body (excreted) to prevent it accumulating to harmful levels in the blood.

   Examiner tip: Urea is a waste product of amino acid breakdown in the liver, then removed from the blood by the kidney — do not confuse where it is produced with where it is removed.

9. 9.

   Explain how deforestation of a tropical rainforest can lead to a reduction in local biodiversity.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that deforestation removes the habitat that many species of plants and animals depend on for food, shelter and breeding. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that species that cannot survive elsewhere, or cannot migrate quickly enough, may die out locally. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that the loss of these species (and disruption of the food webs they were part of) reduces the overall number of different species present, reducing biodiversity. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Biodiversity loss from deforestation is not just about the trees removed — it cascades through the entire food web that depended on that habitat.

   Marking points

   • States that deforestation removes the habitat that many species of plants and animals depend on for food, shelter and breeding.
   • States that species that cannot survive elsewhere, or cannot migrate quickly enough, may die out locally.
   • States that the loss of these species (and disruption of the food webs they were part of) reduces the overall number of different species present, reducing biodiversity.

   Examiner tip: Biodiversity loss from deforestation is not just about the trees removed — it cascades through the entire food web that depended on that habitat.

10. 10.

    Construct a simple food chain from the following organisms: fox, grass, rabbit. State which organism is the producer.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: Constructs the food chain in the correct order: grass → rabbit → fox. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: Uses arrows pointing in the correct direction, showing the direction of energy transfer (from eaten to eater). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that grass is the producer. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Food chain arrows always point in the direction of energy flow, from the organism being eaten to the organism eating it — not the other way around.

    Marking points

    • Constructs the food chain in the correct order: grass → rabbit → fox.
    • Uses arrows pointing in the correct direction, showing the direction of energy transfer (from eaten to eater).
    • States that grass is the producer.

    Examiner tip: Food chain arrows always point in the direction of energy flow, from the organism being eaten to the organism eating it — not the other way around.

11. 11.

    Describe how the volume of the thorax (chest cavity) changes during inhalation, and explain how this causes air to enter the lungs.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that the diaphragm contracts and flattens, and the external intercostal muscles contract, moving the ribcage up and out. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that these two actions increase the volume of the thorax. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that this increase in volume decreases the pressure inside the thorax (lungs) below atmospheric pressure. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: States that air then flows into the lungs from the higher-pressure atmosphere outside, down the pressure gradient, until the pressures are equal. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Air always moves from a region of higher pressure to a region of lower pressure — breathing works entirely by using muscles to create this pressure difference, not by 'sucking' air in directly.

    Marking points

    • States that the diaphragm contracts and flattens, and the external intercostal muscles contract, moving the ribcage up and out.
    • States that these two actions increase the volume of the thorax.
    • States that this increase in volume decreases the pressure inside the thorax (lungs) below atmospheric pressure.
    • States that air then flows into the lungs from the higher-pressure atmosphere outside, down the pressure gradient, until the pressures are equal.

    Examiner tip: Air always moves from a region of higher pressure to a region of lower pressure — breathing works entirely by using muscles to create this pressure difference, not by 'sucking' air in directly.

12. 12.

    State three features of the alveoli that adapt them for efficient gas exchange.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that there are millions of alveoli, giving a very large total surface area for gas exchange. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that alveoli have very thin walls (one cell thick), providing a short diffusion distance for gases. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that a dense network of capillaries surrounds each alveolus, maintaining a steep concentration gradient by constantly bringing fresh blood. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: These same three adaptations (large surface area, short diffusion distance, steep concentration gradient maintained by blood flow) apply to almost every efficient exchange surface in biology, not just the alveoli.

    Marking points

    • States that there are millions of alveoli, giving a very large total surface area for gas exchange.
    • States that alveoli have very thin walls (one cell thick), providing a short diffusion distance for gases.
    • States that a dense network of capillaries surrounds each alveolus, maintaining a steep concentration gradient by constantly bringing fresh blood.

    Examiner tip: These same three adaptations (large surface area, short diffusion distance, steep concentration gradient maintained by blood flow) apply to almost every efficient exchange surface in biology, not just the alveoli.

13. 13.

    Describe three features of the villi lining the small intestine that adapt them for the efficient absorption of digested food.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that villi have a large surface area, created by their finger-like projections (further increased by microvilli on their surface cells). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that villi have thin walls (a single layer of epithelial cells), providing a short diffusion distance. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that each villus contains a rich network of capillaries (blood supply), maintaining a steep concentration gradient for absorbed nutrients. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Villi and alveoli are adapted by exactly the same three principles (surface area, diffusion distance, concentration gradient) — recognising this pattern saves having to memorise each exchange surface separately.

    Marking points

    • States that villi have a large surface area, created by their finger-like projections (further increased by microvilli on their surface cells).
    • States that villi have thin walls (a single layer of epithelial cells), providing a short diffusion distance.
    • States that each villus contains a rich network of capillaries (blood supply), maintaining a steep concentration gradient for absorbed nutrients.

    Examiner tip: Villi and alveoli are adapted by exactly the same three principles (surface area, diffusion distance, concentration gradient) — recognising this pattern saves having to memorise each exchange surface separately.

14. 14.

    Compare the structure of arteries and veins, explaining how each structural difference relates to its function.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that arteries have thick, muscular walls containing elastic fibres, to withstand and maintain the high pressure of blood pumped from the heart. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that veins have thinner walls, since blood flows at lower pressure by the time it returns to the heart. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that veins contain valves, to prevent the backflow of blood, which flows against gravity in many parts of the body at low pressure. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: States that arteries have a narrower lumen relative to their wall thickness, while veins have a wider lumen, offering less resistance to the lower-pressure flow. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Every structural feature of a blood vessel exists because of the pressure and direction of the blood flowing through it — always link structure back to the pressure difference between arteries and veins.

    Marking points

    • States that arteries have thick, muscular walls containing elastic fibres, to withstand and maintain the high pressure of blood pumped from the heart.
    • States that veins have thinner walls, since blood flows at lower pressure by the time it returns to the heart.
    • States that veins contain valves, to prevent the backflow of blood, which flows against gravity in many parts of the body at low pressure.
    • States that arteries have a narrower lumen relative to their wall thickness, while veins have a wider lumen, offering less resistance to the lower-pressure flow.

    Examiner tip: Every structural feature of a blood vessel exists because of the pressure and direction of the blood flowing through it — always link structure back to the pressure difference between arteries and veins.

15. 15.

    Explain one advantage of a double circulatory system, in which blood passes through the heart twice on each complete circuit, compared with a single circulatory system.

    [2 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that blood returning from the lungs passes through the heart again before being sent to the rest of the body, allowing it to be re-pressurised. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that this maintains a higher blood pressure, and therefore a faster flow rate, to the body's organs than would be possible if blood went directly from the lungs to the body without repressurising. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Without a double circulation, blood pressure would drop significantly after passing through the low-pressure lung capillaries, leaving too little pressure to efficiently supply the rest of the body.

    Marking points

    • States that blood returning from the lungs passes through the heart again before being sent to the rest of the body, allowing it to be re-pressurised.
    • States that this maintains a higher blood pressure, and therefore a faster flow rate, to the body's organs than would be possible if blood went directly from the lungs to the body without repressurising.

    Examiner tip: Without a double circulation, blood pressure would drop significantly after passing through the low-pressure lung capillaries, leaving too little pressure to efficiently supply the rest of the body.

16. 16.

    Distinguish between excretion and egestion.

    [2 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that excretion is the removal of waste products made by the body's own metabolic (chemical) reactions, e.g. urea or carbon dioxide. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that egestion is the removal of undigested food (faeces) from the body, material that was never actually absorbed into the body's cells or blood. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The key distinction is where the waste material came from: excretion removes waste made inside body cells, while egestion removes material that was never inside the body's cells at all.

    Marking points

    • States that excretion is the removal of waste products made by the body's own metabolic (chemical) reactions, e.g. urea or carbon dioxide.
    • States that egestion is the removal of undigested food (faeces) from the body, material that was never actually absorbed into the body's cells or blood.

    Examiner tip: The key distinction is where the waste material came from: excretion removes waste made inside body cells, while egestion removes material that was never inside the body's cells at all.

17. 17.

    Describe two physiological responses of the human body to a rise in body temperature above normal, and explain how each response helps to cool the body.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that blood vessels near the skin surface dilate (vasodilation), increasing blood flow to the skin. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: Explains that this increases heat loss from the skin to the surroundings by radiation. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that sweat glands produce more sweat. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: Explains that the evaporation of sweat from the skin surface removes heat energy, cooling the body. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Vasodilation increases heat loss by radiation, while sweating increases heat loss by evaporation — both responses work together but through two genuinely different physical mechanisms.

    Marking points

    • States that blood vessels near the skin surface dilate (vasodilation), increasing blood flow to the skin.
    • Explains that this increases heat loss from the skin to the surroundings by radiation.
    • States that sweat glands produce more sweat.
    • Explains that the evaporation of sweat from the skin surface removes heat energy, cooling the body.

    Examiner tip: Vasodilation increases heat loss by radiation, while sweating increases heat loss by evaporation — both responses work together but through two genuinely different physical mechanisms.

18. 18.

    Describe the pathway of a simple reflex arc, such as withdrawing a hand from a hot object, naming the structures involved in order.

    [5 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that the stimulus (heat) is detected by a receptor in the skin. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that the impulse travels along a sensory neurone to the spinal cord. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that the impulse passes across a synapse to a relay neurone in the spinal cord. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: States that the impulse then passes across another synapse to a motor neurone. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Develop this part of the answer: States that the impulse travels along the motor neurone to an effector (muscle), which contracts to withdraw the hand. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    7. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: A reflex arc bypasses conscious decision-making in the brain (though the relay neurone in the spinal cord may still send a signal to the brain, causing the sensation to be noticed afterwards) — this is why the reflex response is so fast.

    Marking points

    • States that the stimulus (heat) is detected by a receptor in the skin.
    • States that the impulse travels along a sensory neurone to the spinal cord.
    • States that the impulse passes across a synapse to a relay neurone in the spinal cord.
    • States that the impulse then passes across another synapse to a motor neurone.
    • States that the impulse travels along the motor neurone to an effector (muscle), which contracts to withdraw the hand.

    Examiner tip: A reflex arc bypasses conscious decision-making in the brain (though the relay neurone in the spinal cord may still send a signal to the brain, causing the sensation to be noticed afterwards) — this is why the reflex response is so fast.

19. 19.

    State two differences between nervous control and hormonal (chemical) control of the body.

    [2 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that nervous impulses travel very fast as electrical impulses along neurones and have a short-lived, immediate effect, while hormones travel more slowly in the blood and have a longer-lasting effect. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that nervous responses act on precise, specific target locations via a direct neurone connection, while hormones are carried all over the body in the blood but only affect specific target organs/cells with matching receptors. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Nervous control is fast, short-lived and precisely targeted; hormonal control is slower, longer-lasting and reaches its targets by travelling throughout the entire bloodstream.

    Marking points

    • States that nervous impulses travel very fast as electrical impulses along neurones and have a short-lived, immediate effect, while hormones travel more slowly in the blood and have a longer-lasting effect.
    • States that nervous responses act on precise, specific target locations via a direct neurone connection, while hormones are carried all over the body in the blood but only affect specific target organs/cells with matching receptors.

    Examiner tip: Nervous control is fast, short-lived and precisely targeted; hormonal control is slower, longer-lasting and reaches its targets by travelling throughout the entire bloodstream.

20. 20.

    During a stressful or dangerous situation, adrenaline is released into the blood from the adrenal glands. State two effects of adrenaline on the body, and explain how each effect prepares the body for a 'fight or flight' response.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that adrenaline increases heart rate. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: Explains that this increases the rate of blood flow, delivering more oxygen and glucose to the muscles for respiration. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that adrenaline increases breathing rate (or depth). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: Explains that this increases the rate of oxygen uptake and carbon dioxide removal, supporting the increased rate of respiration needed for vigorous muscle activity. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Every effect of adrenaline serves the same underlying goal: rapidly increasing the supply of oxygen and glucose to the muscles to prepare the body for sudden physical action.

    Marking points

    • States that adrenaline increases heart rate.
    • Explains that this increases the rate of blood flow, delivering more oxygen and glucose to the muscles for respiration.
    • States that adrenaline increases breathing rate (or depth).
    • Explains that this increases the rate of oxygen uptake and carbon dioxide removal, supporting the increased rate of respiration needed for vigorous muscle activity.

    Examiner tip: Every effect of adrenaline serves the same underlying goal: rapidly increasing the supply of oxygen and glucose to the muscles to prepare the body for sudden physical action.

21. 21.

    Describe how carbon dioxide is removed from, and returned to, the atmosphere as part of the carbon cycle.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that carbon dioxide is removed from the atmosphere by photosynthesis in plants, which converts it into organic compounds. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that carbon dioxide is returned to the atmosphere by respiration in living organisms. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that carbon dioxide is also returned to the atmosphere by the combustion of fossil fuels and biomass, and by the decomposition of dead organic matter by microorganisms. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Photosynthesis and respiration are the two processes that balance the carbon cycle under natural conditions — human activities like burning fossil fuels add extra carbon dioxide on top of this natural balance.

    Marking points

    • States that carbon dioxide is removed from the atmosphere by photosynthesis in plants, which converts it into organic compounds.
    • States that carbon dioxide is returned to the atmosphere by respiration in living organisms.
    • States that carbon dioxide is also returned to the atmosphere by the combustion of fossil fuels and biomass, and by the decomposition of dead organic matter by microorganisms.

    Examiner tip: Photosynthesis and respiration are the two processes that balance the carbon cycle under natural conditions — human activities like burning fossil fuels add extra carbon dioxide on top of this natural balance.

22. 22.

    A pyramid of biomass for a food chain becomes narrower at each successive trophic level. Explain why biomass decreases at each higher trophic level.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that not all of the biomass present at one trophic level is eaten by organisms at the next level. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that of the biomass that is eaten, not all of it is absorbed (digested) — some is egested as faeces. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that much of the absorbed energy/biomass is used in respiration and lost as heat to the surroundings, so it is not converted into new biomass for growth. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: This is exactly the same underlying reason that percentage energy transfer between trophic levels is typically only around 10% — energy and biomass losses happen at every single step of a food chain.

    Marking points

    • States that not all of the biomass present at one trophic level is eaten by organisms at the next level.
    • States that of the biomass that is eaten, not all of it is absorbed (digested) — some is egested as faeces.
    • States that much of the absorbed energy/biomass is used in respiration and lost as heat to the surroundings, so it is not converted into new biomass for growth.

    Examiner tip: This is exactly the same underlying reason that percentage energy transfer between trophic levels is typically only around 10% — energy and biomass losses happen at every single step of a food chain.

23. 23.

    Describe the shape of a typical sigmoid (S-shaped) population growth curve, naming its three main phases.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States an initial lag phase, where population growth is slow, as few individuals are present to reproduce. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States an exponential (log) phase, where the population grows rapidly, since resources are plentiful and many individuals are reproducing. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States a stationary phase, where the population levels off as it reaches the carrying capacity of the environment, limited by factors such as food, space or predation, so growth rate falls to approximately zero. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The stationary phase is not population decline — birth rate and death rate become approximately equal at this point, keeping the population roughly constant around the environment's carrying capacity.

    Marking points

    • States an initial lag phase, where population growth is slow, as few individuals are present to reproduce.
    • States an exponential (log) phase, where the population grows rapidly, since resources are plentiful and many individuals are reproducing.
    • States a stationary phase, where the population levels off as it reaches the carrying capacity of the environment, limited by factors such as food, space or predation, so growth rate falls to approximately zero.

    Examiner tip: The stationary phase is not population decline — birth rate and death rate become approximately equal at this point, keeping the population roughly constant around the environment's carrying capacity.

24. 24.

    Excess fertiliser washes from farmland into a nearby river. Describe how this can lead to the death of fish in the river.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that the fertiliser increases the concentration of nutrients, e.g. nitrates or phosphates, in the water. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that this causes rapid growth (a bloom) of algae and other aquatic plants on the water's surface. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that this blocks light from reaching plants below the surface, which die; decomposing bacteria then multiply rapidly, feeding on the dead plant matter and algae. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: States that these decomposing bacteria use up (respire) the dissolved oxygen in the water, reducing oxygen levels so much that fish and other aquatic animals die from lack of oxygen. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: This process, called eutrophication, kills fish through oxygen depletion caused by decomposing bacteria — not through direct toxicity of the fertiliser itself.

    Marking points

    • States that the fertiliser increases the concentration of nutrients, e.g. nitrates or phosphates, in the water.
    • States that this causes rapid growth (a bloom) of algae and other aquatic plants on the water's surface.
    • States that this blocks light from reaching plants below the surface, which die; decomposing bacteria then multiply rapidly, feeding on the dead plant matter and algae.
    • States that these decomposing bacteria use up (respire) the dissolved oxygen in the water, reducing oxygen levels so much that fish and other aquatic animals die from lack of oxygen.

    Examiner tip: This process, called eutrophication, kills fish through oxygen depletion caused by decomposing bacteria — not through direct toxicity of the fertiliser itself.

25. 25.

    State four components of a balanced human diet, other than water, and state one function of each.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that carbohydrates provide energy. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that proteins provide materials for the growth and repair of tissues. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that fats (lipids) provide a concentrated store of energy and thermal insulation. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: States that vitamins and minerals are needed in small amounts for specific body processes, e.g. vitamin C for healthy skin/connective tissue, or calcium for strong bones and teeth; or states that fibre aids the movement of food through the digestive system and prevents constipation. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: A balanced diet requires the right combination and proportion of all these nutrient groups together, not just a large total quantity of food — a diet can be high in calories yet still be unbalanced.

    Marking points

    • States that carbohydrates provide energy.
    • States that proteins provide materials for the growth and repair of tissues.
    • States that fats (lipids) provide a concentrated store of energy and thermal insulation.
    • States that vitamins and minerals are needed in small amounts for specific body processes, e.g. vitamin C for healthy skin/connective tissue, or calcium for strong bones and teeth; or states that fibre aids the movement of food through the digestive system and prevents constipation.

    Examiner tip: A balanced diet requires the right combination and proportion of all these nutrient groups together, not just a large total quantity of food — a diet can be high in calories yet still be unbalanced.

Original, unofficial practice questions from SubjectScout — not official past-paper questions.