S5 Biology Practice Paper: Circulation, Blood And Gas Exchange (100 Marks)

S5 Biology Practice Paper: Circulation, Blood and Gas Exchange (100 marks)

2026-11-12

Biology – Transport and Gas Exchange

S5 Biology paper: 6 questions, 16 parts, 100 marks, 60 minutes. Cardiac output, cardiac cycle, haemoglobin, alveolar gas exchange, tissue fluid and mean arterial pressure.

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Section A – Cardiac Output and Circulation

Answer all three parts. Total 16 marks. A student has a resting heart rate of 70 beats per minute and a stroke volume of 70 mL.

#	Question	Answer and marking notes
1	Find the resting cardiac output, expressed both in mL per minute and in L per minute.	Answer: Cardiac output = heart rate x stroke volume = 70 x 70 = 4900 mL per minute = 4.9 L per minute. (Marks: formula 2, value 2, units 2)
2	During exercise the heart rate rises to 140 beats per minute and stroke volume to 110 mL. Find the cardiac output and how many times the resting value it is.	Answer: Cardiac output = 140 x 110 = 15400 mL per minute = 15.4 L per minute, which is 3.14 times the resting value, an increase of about 214.3 percent. (Marks: value 2, ratio 2, percentage 1)
3	Assume a total blood volume of 5.0 L. Using the resting cardiac output, how many seconds does one complete circulation take, and how does this change during exercise?	Answer: Time = 5.0 divided by 4.9 = 1.02 minutes, about 61.2 seconds; during exercise cardiac output rises so the circulation time is shorter. (Marks: calculation 3, seconds 1, explanation 1)

Section B – Heart Structure and Cardiac Cycle

Answer all three parts. Total 18 marks. A person has a resting heart rate of 60 beats per minute and a ventricular systole lasting 0.3 s.

#	Question	Answer and marking notes
4	Find the duration of one cardiac cycle, and the duration and percentage of ventricular diastole.	Answer: Cycle = 60 divided by 60 = 1.0 s; ventricular diastole = 1.0 – 0.3 = 0.7 s, which is 70 percent of the cycle. (Marks: cycle 2, diastole 2, percentage 2)
5	Explain how the atrioventricular valves and semilunar valves ensure one-way blood flow.	Answer: During ventricular diastole the atrioventricular valves open and the semilunar valves close, so blood flows from the atria into the ventricles. During ventricular systole the pressure rises, the atrioventricular valves close to prevent backflow into the atria, and the semilunar valves open so blood is ejected into the aorta and pulmonary artery. (Marks: atrioventricular valves 3, semilunar valves 3)
6	Explain why the wall of the left ventricle is thicker than that of the right ventricle.	Answer: The left ventricle pumps blood into the systemic circulation, which has a higher resistance, so it must generate a higher pressure (systolic about 120 mmHg). The right ventricle pumps into the pulmonary circulation at a lower resistance (about 25 mmHg), so the left ventricular muscle layer is thicker. (Marks: systemic pressure demand 3, pulmonary comparison 3)

Section C – Blood, Haemoglobin and Oxygen Transport

Answer all three parts. Total 18 marks. A person has a haemoglobin concentration of 150 g per litre and a blood volume of 5.0 L.

#	Question	Answer and marking notes
7	Find the total mass of haemoglobin and the volume of oxygen it can carry when fully saturated (1 g of haemoglobin binds about 1.34 mL of oxygen).	Answer: Total haemoglobin = 150 x 5.0 = 750 g; oxygen carried = 750 x 1.34 = about 1005 mL, that is about 1.0 L. (Marks: total 3, oxygen volume 3)
8	Carbon monoxide binds haemoglobin about 250 times more strongly than oxygen does. Explain why inhaling carbon monoxide can be fatal.	Answer: Carbon monoxide occupies the oxygen-binding sites and forms a stable compound, so far less haemoglobin is available to carry oxygen. The oxygen content of the blood falls, the tissues (especially brain and heart muscle) become short of oxygen, and unconsciousness or death may follow. (Marks: binding sites 3, reduced transport 2, tissue effect 1)
9	People living at high altitude have more red blood cells. Explain this adaptation using oxygen partial pressure and the oxyhaemoglobin dissociation curve.	Answer: At high altitude the air pressure is low, so alveolar oxygen partial pressure is lower and the saturation of haemoglobin falls. More red blood cells raise the total amount of oxygen carried, so the tissues still receive enough oxygen. (Marks: low partial pressure 3, curve and saturation 2, compensation 1)

Section D – Alveolar Gas Exchange

Answer all three parts. Total 16 marks. The total alveolar surface area is about 70 square metres and the body surface area is 1.8 square metres.

#	Question	Answer and marking notes
10	Find how many times the alveolar surface area is compared with the body surface area.	Answer: Ratio = 70 divided by 1.8 = 38.9 times. (Marks: formula 3, value 3)
11	In emphysema the alveolar walls break down and the surface area is reduced. Using the principle of diffusion, explain the effect on gas exchange.	Answer: The rate of diffusion is proportional to surface area, so a smaller area means less oxygen and carbon dioxide diffuse per unit time, blood oxygen falls, and the patient must breathe faster to compensate. (Marks: diffusion and area 3, effect 2)
12	Given a breathing rate of 15 per minute, a tidal volume of 0.5 L and an anatomical dead space of 0.15 L, find the minute ventilation and the alveolar ventilation.	Answer: Minute ventilation = 15 x 0.5 = 7.5 L per minute; alveolar ventilation = 15 x (0.5 – 0.15) = 5.25 L per minute. (Marks: ventilation 2, dead space 2, value 1)

Section E – Tissue Fluid, Lymph and Oedema

Answer both parts. Total 16 marks. Blood volume is 5.0 L, plasma is 55 percent of blood volume, and tissue fluid is about 11 L.

#	Question	Answer and marking notes
13	Find the plasma volume and how many times the tissue fluid volume is compared with it.	Answer: Plasma = 5.0 x 55 percent = 2.75 L; tissue fluid is 11 divided by 2.75 = 4.0 times the plasma volume. (Marks: plasma 4, ratio 4)
14	About 20 L of fluid is filtered from the capillaries each day and 17 L is reabsorbed. Find the volume returned by the lymph vessels each day and explain why a blocked lymph vessel causes oedema.	Answer: Lymph return = 20 – 17 = 3 L per day; if the lymph vessels are blocked, tissue fluid cannot return to the blood and accumulates in the tissue spaces, causing oedema. (Marks: calculation 4, mechanism 4)

Section F – Blood Pressure and Vessel Resistance

Answer both parts. Total 16 marks. A person has a blood pressure of 120 over 80 mmHg.

#	Question	Answer and marking notes
15	Using the formula (systolic + 2 x diastolic) divided by 3, find the mean arterial pressure and state its physiological meaning.	Answer: Mean arterial pressure = (120 + 2 x 80) divided by 3 = 280 divided by 3 = 93.3 mmHg; it represents the average pressure driving blood through the organs and is an index of tissue perfusion. (Marks: calculation 5, meaning 3)
16	If the radius of a vessel is halved, by what factor does the resistance change (resistance is inversely proportional to the fourth power of the radius)? State the effect of arterial hardening on blood flow.	Answer: Resistance factor = (1 divided by 0.5) to the power 4 = 16 times; hardening narrows the lumen and reduces elasticity, so resistance rises, blood flow falls at the same pressure, and the workload of the heart increases. (Marks: factor 4, effect 4)

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