IGCSE Biology 0610 Paper 4: Human Transport, Heart, Blood and Circulation

Level: Year 10-11 (IGCSE) | Subject: Biology 0610 | Time: 75 minutes | Total: 100 marks | Parts: 28

Paper at a glance

Paper	Time	Marks	Calculator
Paper 4 (Extended, structured)	1 h 15 min	75	Not allowed

Questions

Question 1 (17 marks) – Heart structure and the cardiac cycle

(a) Describe the path of blood from the right atrium to the aorta and state the position of two valves. (3 marks)

(b) A person at rest has a heart rate of 72 beats per minute and a stroke volume of 70 cm3. Calculate the cardiac output in cm3 per minute. If the end-diastolic volume is 120 cm3 and the end-systolic volume is 50 cm3, work out the stroke volume and the ejection fraction. (4 marks)

(c) An ECG is recorded at a paper speed of 25 mm/s and two neighbouring R waves are 20 small squares apart (1 mm each). Calculate the interval between beats in seconds and the heart rate in beats per minute. (3 marks)

(d) Explain why the wall of the left ventricle is thicker than that of the right ventricle. (4 marks)

(e) Explain the advantage of a double circulation to a mammal. (3 marks)

Question 2 (17 marks) – Blood vessels and blood flow

(a) Compare the structure of an artery with that of a vein and give one feature of each that suits its function. (3 marks)

(b) The aorta has a cross-sectional area of 3 cm2 and blood flows at 28 cm per second. Calculate the flow rate in cm3 per second and per minute. If the total cross-sectional area of the capillaries is 3000 cm2, work out the average blood speed in them. (4 marks)

(c) Plaque in a coronary artery reduces its effective radius from 2 mm to 1.5 mm. Flow is proportional to the fourth power of the radius. Calculate the flow as a percentage of the original value and the percentage reduction. (4 marks)

(d) Explain how the slow flow in capillaries aids exchange of materials. (3 marks)

(e) Explain the roles of vasodilation in the skin and vasoconstriction in internal organs during exercise. (3 marks)

Question 3 (17 marks) – Blood components and oxygen transport

(a) State three features of red blood cells that suit them for carrying oxygen. (3 marks)

(b) A person has a haemoglobin concentration of 15 g per 100 cm3 and each gram of haemoglobin binds 1.34 cm3 of oxygen. Blood volume is 5 dm3. Calculate the oxygen carried by 100 cm3 of blood and the total carried by the whole blood volume. (4 marks)

(c) A patient has a haemoglobin concentration of only 9 g per 100 cm3. Calculate this as a percentage of the normal 15 g per 100 cm3 and explain two symptoms that may appear. (3 marks)

(d) During vigorous exercise the oxygen dissociation curve shifts to the right. Explain the cause and the advantage. (4 marks)

(e) A person has about 250 x 10 to the power nine platelets per dm3. Describe the role of platelets in clotting. (3 marks)

Question 4 (17 marks) – Gas exchange, exercise and heart rate

(a) Inhaled air contains 21% oxygen and exhaled air 16%. Ventilation is 6 dm3 per minute. Calculate the volume of oxygen absorbed by the lungs each minute in cm3. (4 marks)

(b) During exercise the heart rate rises to 150 beats per minute and stroke volume to 110 cm3. Calculate the cardiac output in cm3 and dm3 per minute and how many times the resting value of 5040 cm3 per minute this is. (4 marks)

(c) A person aged 16 has a resting heart rate of 72 beats per minute. Using maximum heart rate equal to 220 minus age, calculate the maximum rate, the heart rate reserve and the target rate at seventy per cent intensity. (3 marks)

(d) Explain the mechanism that makes breathing faster and deeper during exercise. (3 marks)

(e) Explain why breathing stays rapid for a while after exercise stops. (3 marks)

Question 5 (16 marks) – Tissue fluid, lymph and control of the blood

(a) Blood pressure in a capillary is 35 mmHg at the arteriole end and 15 mmHg at the venule end; plasma protein osmotic pressure is 25 mmHg. Calculate the net pressure at each end and state the direction of fluid movement. (4 marks)

(b) About 3 dm3 of fluid is filtered from capillaries each day and ninety per cent of it is reabsorbed. Calculate the volume reabsorbed and the volume that becomes lymph, in dm3 and cm3. (4 marks)

(c) Explain how the lymphatic system returns tissue fluid to the blood. (4 marks)

(d) Explain how the blood carries insulin and glucose so that blood glucose stays stable. (4 marks)

Question 6 (16 marks) – Circulatory health and medical technology

(a) Explain how atherosclerosis in a coronary artery leads to a shortage of oxygen in the heart muscle and to angina. (4 marks)

(b) One person has a blood pressure of 150/95 mmHg and another 120/80 mmHg. Calculate the pulse pressure of each and explain the health risk of the higher reading. (4 marks)

(c) Design an experiment to compare heart rate before and after exercise. State the variables to control, how heart rate is measured and why repeats matter. (4 marks)

(d) Evaluate the use of an artificial heart and of a heart transplant for treating heart failure. (4 marks)

Answers and marking notes

Question 1 – Heart structure and the cardiac cycle

(a) The right atrium contracts and blood passes through the tricuspid valve into the right ventricle (one mark); the right ventricle contracts and blood leaves through the pulmonary valve into the pulmonary artery towards the lungs (one mark); blood returns through the pulmonary vein to the left atrium, passes the bicuspid valve into the left ventricle and is pumped through the aortic valve into the aorta (one mark). [3 marks]

(b) Cardiac output = 72 x 70 = 5040 cm3 per minute (one mark); stroke volume = 120 – 50 = 70 cm3, which agrees with the given value (one mark); ejection fraction = 70 / 120 x 100 = 58.3% (one mark); so about sixty per cent of the end-diastolic volume is ejected and the rest stays in the ventricle (one mark). [4 marks]

(c) 20 mm / 25 mm per second = 0.80 s (one mark); heart rate = 60 / 0.80 = 75 beats per minute (one mark); the rhythm is regular and this rate is within the normal resting range (one mark). [3 marks]

(d) The left ventricle pumps blood around the whole body, a long distance (one mark); a higher pressure is needed, so a thicker muscle layer gives a stronger contraction (one mark); the right ventricle only pumps blood to the lungs, a short distance (one mark); a lower pressure is enough there, so a thinner wall matches the resistance of that circuit (one mark). [4 marks]

(e) Blood passes through the heart twice per circuit and can be re-pressurised after the lungs (one mark); the systemic circuit keeps a high pressure so oxygen and nutrients reach tissues quickly (one mark); the pulmonary circuit runs at lower pressure, protecting the lung capillaries (one mark). [3 marks]

Question 2 – Blood vessels and blood flow

(a) An artery has a thick wall with much muscle and elastic fibre, so it withstands high pressure and recoils to keep flow continuous (one mark); a vein has a thin wall and a wide lumen with valves that prevent backflow (one mark); venous pressure is low, so blood is pushed back by skeletal muscle contraction and the negative chest pressure on breathing in (one mark). [3 marks]

(b) Flow = 3 x 28 = 84 cm3 per second (one mark); per minute 84 x 60 = 5040 cm3, which matches the cardiac output (one mark); capillary speed = 84 / 3000 = 0.028 cm per second (one mark); a large total area means a low speed, so blood stays longer and exchange is more effective (one mark). [4 marks]

(c) Radius ratio = 1.5 / 2 = 0.75 (one mark); flow ratio = 0.75 to the power four = 0.316 (one mark); that is about 31.6% of the original (one mark); the reduction is 68.4%, so the heart muscle is short of oxygen and angina results (one mark). [4 marks]

(d) The capillary wall is one endothelial cell thick, so the diffusion distance is short (one mark); slow flow increases the time blood spends in the tissue, allowing more time for diffusion (one mark); the total surface area is large, so oxygen and glucose enter cells and wastes enter the blood effectively (one mark). [3 marks]

(e) Exercising muscle needs more oxygen, so sympathetic nerves constrict the vessels of internal organs and divert blood to muscle (one mark); skin vessels dilate, raising skin blood flow and heat loss (one mark); together they stop total peripheral resistance falling too far, which helps maintain blood pressure (one mark). [3 marks]

Question 3 – Blood components and oxygen transport

(a) The biconcave disc shape gives a large surface area to volume ratio for fast diffusion (one mark); mature cells have no nucleus or most organelles, leaving room for more haemoglobin (one mark); they contain much haemoglobin and each molecule binds four oxygen molecules (one mark). [3 marks]

(b) Oxygen per 100 cm3 = 15 x 1.34 = 20.1 cm3 (one mark); 5 dm3 is 5000 cm3, that is 50 units of 100 cm3 (one mark); total oxygen = 20.1 x 50 = 1005 cm3 (one mark); about 1 dm3 of oxygen, enough for resting metabolism (one mark). [4 marks]

(c) Percentage = 9 / 15 x 100 = 60% (one mark); the oxygen-carrying capacity falls, muscles are short of oxygen and the person tires easily (one mark); the body compensates by raising heart and breathing rates, so the person is breathless on exertion (one mark). [3 marks]

(d) Muscle respiration releases more carbon dioxide, so blood pH falls (one mark); temperature rises and organic phosphates inside red cells increase (one mark); the affinity of haemoglobin for oxygen falls, so more oxygen is released at the same partial pressure (one mark); the advantage is that active muscle gains more oxygen for respiration (one mark). [4 marks]

(e) When a vessel is damaged, platelets adhere to collagen and clump together (one mark); they release clotting factors that convert prothrombin to thrombin (one mark); thrombin converts fibrinogen to a fibrin mesh that traps blood cells and forms a clot to stop bleeding (one mark). [3 marks]

Question 4 – Gas exchange, exercise and heart rate

(a) The difference is 21 – 16 = 5 percentage points (one mark); oxygen absorbed per minute = 6 x 5 / 100 = 0.30 dm3 (one mark); that is 300 cm3 (one mark); this fits the resting metabolic rate, and both ventilation and uptake rise during exercise (one mark). [4 marks]

(b) Cardiac output = 150 x 110 = 16500 cm3 per minute (one mark); that is 16.5 dm3 per minute (one mark); the factor is 16500 / 5040 = 3.27 times (one mark); the rise comes from both rate and stroke volume, so muscle receives more oxygen (one mark). [4 marks]

(c) Maximum rate = 220 – 16 = 204 beats per minute (one mark); reserve = 204 – 72 = 132 beats per minute (one mark); target = 72 + 0.70 x 132 = 164.4, about 164 beats per minute (one mark). [3 marks]

(d) Muscles produce more carbon dioxide, so its concentration in the blood rises (one mark); the breathing centre in the medulla is stimulated by carbon dioxide and hydrogen ions (one mark); more impulses pass to the intercostal muscles and diaphragm, so breathing is faster and deeper, removing carbon dioxide and taking in more oxygen (one mark). [3 marks]

(e) During exercise muscle cannot get enough oxygen and respires anaerobically, forming lactic acid (one mark); the lactic acid builds an oxygen debt that must be repaid afterwards (one mark); so breathing and heart rate stay high to deliver oxygen to the liver to oxidise the lactic acid until the debt is cleared (one mark). [3 marks]

Question 5 – Tissue fluid, lymph and control of the blood

(a) At the arteriole end the net pressure is 35 – 25 = 10 mmHg outwards, so fluid is filtered into the tissue (one mark); at the venule end it is 25 – 15 = 10 mmHg inwards, so fluid is reabsorbed (one mark); blood pressure falls as blood travels along the capillary (one mark); so tissue fluid forms at the first end, most is reabsorbed at the second and the remainder becomes lymph (one mark). [4 marks]

(b) Reabsorbed = 3 x 0.90 = 2.7 dm3 (one mark); lymph = 3 – 2.7 = 0.3 dm3 (one mark); 0.3 dm3 = 300 cm3 (one mark); this fluid finally returns to the blood through lymph vessels, otherwise oedema develops (one mark). [4 marks]

(c) Lymph capillaries have closed ends and collect excess tissue fluid (one mark); the vessels contain valves that prevent backflow (one mark); there is no pump, so lymph is moved by skeletal muscle contraction and pressure changes in the chest during breathing (one mark); it finally enters the blood at the subclavian veins, maintaining blood volume and pressure (one mark). [4 marks]

(d) After a meal blood glucose rises and the insulin-secreting cells of the pancreas release insulin (one mark); insulin travels in the blood to the liver and muscles (one mark); it makes cells take up glucose and store it as glycogen, so blood glucose falls (one mark); when glucose is too low, glucagon is carried to the liver, where glycogen is broken down to glucose and blood glucose rises again (one mark). [4 marks]

Question 6 – Circulatory health and medical technology

(a) Plaque narrows the lumen of the coronary artery and reduces blood flow (one mark); the heart muscle gets oxygen from the coronary arteries, so supply falls below demand (one mark); the muscle respires anaerobically and lactic acid irritates pain receptors, causing angina (one mark); demand rises during exercise, so attacks usually occur then (one mark). [4 marks]

(b) Pulse pressure = 150 – 95 = 55 mmHg (one mark); the other person has 120 – 80 = 40 mmHg (one mark); both systolic and diastolic values are raised, so this is hypertension (one mark); persistent high pressure damages artery walls and raises the risk of atherosclerosis, stroke and kidney damage (one mark). [4 marks]

(c) Control the duration and intensity of exercise, room temperature, and the age and health of the subject (one mark); record a baseline resting rate after sitting quietly for five minutes (one mark); measure the pulse for 15 seconds and multiply by four immediately after a fixed period of exercise, or use a monitor, using the same method before and after (one mark); repeat several times and average to reduce random error and make the result reliable (one mark). [4 marks]

(d) A transplant gives a fully working heart and the patient can return to normal activity, but donor organs are scarce and patients may die while waiting (one mark); after transplant the patient needs long-term immunosuppressants, which raise the risk of infection (one mark); an artificial heart needs no donor and can be a bridge or long-term option, but it needs an external power supply (one mark); it carries risks of clotting and infection and is expensive, so each treatment suits different patients (one mark). [4 marks]

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