HKDSE Biology Practice Paper: Transport In Humans

HKDSE Biology Practice Paper: Transport in Humans

2026-11-03

HKDSE Biology: Transport in Humans

HKDSE Biology practice paper on transport in humans: 12 questions, 100 marks, 75 minutes, with full answers, marking points and A4 printing.

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Paper details　Level: S6 | Subject: Biology | Time: 75 minutes | Marks: 100 | Questions: 12

Section A (Questions 1 to 4, 26 marks)

Read each question and write the correct answer with an explanation. Show working and units for any calculation.

#	Question	Answer and marking notes
1	List the four main components of blood and give one function of each.	Plasma carries water, nutrients, hormones and waste; red blood cells carry oxygen using haemoglobin; white blood cells defend against pathogens; platelets take part in clotting. Marking: one mark for each component with its function.
2	Describe the full path of blood starting from the right atrium and returning to the right atrium in a double circulation, and state the positions and roles of the two atrioventricular valves.	Right atrium, right ventricle, pulmonary artery, lungs, pulmonary vein, left atrium, left ventricle, aorta, body, vena cava, back to the right atrium. The tricuspid valve sits between the right atrium and ventricle and the bicuspid valve between the left atrium and ventricle, both preventing backflow. Marking: path 3, valve positions 2, role 1.
3	An athlete has a stroke volume of 70 mL and a heart rate of 75 beats per minute at rest, and 110 mL at 150 beats per minute during exercise. Find the cardiac output in both cases and the factor by which it rises.	At rest the cardiac output is 70 × 75 = 5250 mL per minute, or 5.25 L per minute. During exercise it is 110 × 150 = 16 500 mL per minute, or 16.5 L per minute. The factor is 16.5 divided by 5.25 = 3.14. Marking: each calculation 3, factor 2.
4	Compare arteries, veins and capillaries in wall thickness, lumen size, valves and blood flow speed, and relate each structure to its function.	Arteries have thick elastic walls, a narrow lumen, no valves and fast flow, carrying blood away from the heart. Veins have thinner walls, a wide lumen, valves and slower flow, carrying blood back. Capillaries are one cell thick with a tiny lumen, no valves and the slowest flow, which suits exchange. Marking: structure of each vessel 2 each, functional comparison 2.

Section B (Questions 5 to 8, 32 marks)

Answer the following questions with working, units and evidence drawn from the data given.

#	Question	Answer and marking notes
5	Explain why the oxygen dissociation curve of muscle shifts to the right during vigorous exercise, and state the physiological advantage of the shift.	Exercise raises muscle temperature and carbon dioxide and lowers pH, so the affinity of haemoglobin for oxygen falls and the curve shifts right. At any given oxygen partial pressure more oxygen is released to the muscle, matching the faster breathing and heart rate. Marking: three causes 1 each, significance 4.
6	Explain how tissue fluid forms and how the lymphatic system returns the excess fluid to the blood.	At the high pressure end of a capillary, water and small solutes are forced out through the wall by hydrostatic pressure to form tissue fluid. Most is reabsorbed at the low pressure end, while the rest enters lymph capillaries as lymph, travels through lymph vessels and nodes, and returns via the subclavian vein. Marking: formation 3, reabsorption 1, return route 3.
7	A red blood cell measures 30 mm across in a micrograph while its true diameter is 0.012 mm. Find the magnification, and the number of cells that could lie across a field of view 1.5 mm in diameter.	Magnification = image size divided by actual size = 30 divided by 0.012 = 2500 times. Across the field, 1.5 divided by 0.012 = 125 cells fit. Marking: formula 2, consistent units 3, magnification 3, count 2.
8	Describe the process of blood clotting and the role of platelets, and explain why a person with haemophilia bleeds for longer.	When a vessel is damaged platelets stick to the wound and release clotting factors that convert prothrombin to thrombin. Thrombin converts fibrinogen to fibrin, and the mesh traps blood cells to form a clot. A person with haemophilia lacks a clotting factor, so the chain is blocked and bleeding lasts longer. Marking: platelet role 2, thrombin 2, fibrin 2, haemophilia 2.

Section C (Questions 9 to 12, 42 marks)

Write fuller answers using correct scientific terms and support them with examples from Hong Kong or daily life.

#	Question	Answer and marking notes
9	A study followed 10 000 adults for 10 years. Among 5 000 smokers 350 developed coronary heart disease, and among 5 000 non smokers 140 did. Find both incidence rates and the relative risk, explain how atherosclerosis of the coronary arteries leads to the disease, and list three modifiable risk factors.	Smokers: 350 divided by 5000 × 100 per cent = 7.0 per cent. Non smokers: 140 divided by 5000 = 2.8 per cent. Relative risk = 7.0 divided by 2.8 = 2.5. Fatty plaques narrow the coronary arteries and a thrombus may block them, so heart muscle is starved of oxygen and dies. Modifiable factors include smoking, high blood pressure and high blood cholesterol, and obesity or inactivity are also accepted. Marking: both rates 2 each, relative risk 1, mechanism 3, factors 2.
10	Define systolic and diastolic pressure, and explain why long term high blood pressure raises the risk of a stroke.	Systolic pressure is the peak arterial pressure when the ventricles contract, and diastolic pressure is the lowest pressure when they relax. Sustained high pressure damages and stiffens artery walls and encourages thrombus formation, so a blocked or ruptured vessel in the brain causes a stroke. Marking: both definitions 3 each, stroke mechanism 4.
11	Design an experiment to study the effect of exercise on heart rate. Give the measuring steps, the variables to control and how to reduce error.	Recruit 20 students of similar age and record resting heart rate after 5 minutes of sitting. Each performs the same stair climbing for 3 minutes, then heart rate is recorded immediately and every minute until it returns to rest. Control exercise intensity, duration, room temperature and body position, use the same meter and the same recorder, and average three repeats to cut error. Marking: design 4, controls 4, measurement 3.
12	Explain why large mammals need a circulatory system, and compare the open circulatory system of an insect with the closed system of a mammal.	Volume rises with the cube of body length while surface area rises only with the square, so a large animal has a small surface area to volume ratio and diffusion alone cannot supply every cell, hence a circulatory system is needed. An insect has an open system of haemolymph at low pressure and slow flow, relying on tracheae to deliver air directly, whereas a mammal has a closed system at high pressure and fast flow that transports materials more efficiently. Marking: ratio 4, diffusion limit 3, insect comparison 4.

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