iGCSE Biology (0610)-9.2 Heart - iGCSE Style Questions Paper 4

Question

Fig. 3.1 is a diagram of a section through a human heart.

(a) Draw an X on the septum in Fig. 3.1.

(b) Explain the reason for the difference between the thickness of the walls at B and at C in Fig. 3.1.

(c) A red blood cell enters the vena cava at A in Fig. 3.1. Explain how the red blood cell is moved from the vena cava to the aorta.

(d) An athlete measured her heart rate during a running race. She recorded it before the race, during the race and during her recovery. Her results are shown in Fig. 3.2.

(i) Suggest how the athlete could monitor the activity of her heart.

(ii) Calculate the percentage change in heart rate from the maximum heart rate reached during the race until the heart rate recorded at 18 minutes. Give your answer to three significant figures.

(iii) Explain why heart rate must increase during exercise.

▶️ Answer/Explanation

Solution

(a)

Answer: The X should be drawn on the wall separating the left and right sides of the heart (the septum).

Explanation: The septum is the muscular wall that divides the heart into left and right sides, preventing the mixing of oxygenated and deoxygenated blood.

(b)

Answer: The wall at B (left ventricle) is thicker than at C (right ventricle) because the left ventricle pumps blood at higher pressure to the whole body, while the right ventricle only pumps blood to the lungs.

Explanation: The left ventricle needs more muscular tissue to generate the force required to pump blood throughout the entire body. The right ventricle has a thinner wall because it only needs to pump blood to the nearby lungs, which requires less pressure. This structural difference reflects their different functional demands.

(c)

Answer: The red blood cell moves: from vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta.

Explanation: The journey begins when deoxygenated blood enters the right atrium through the vena cava. When the right atrium contracts, it pushes the blood through the tricuspid valve into the right ventricle. The right ventricle then contracts, sending blood through the pulmonary valve into the pulmonary artery to the lungs. In the lungs, the blood becomes oxygenated and returns via the pulmonary veins to the left atrium. The left atrium contracts, pushing blood through the mitral valve into the left ventricle. Finally, the powerful left ventricle contracts, sending oxygenated blood through the aortic valve into the aorta for distribution throughout the body. Valves prevent backflow at each stage.

(d)(i)

Answer: By using an ECG, measuring pulse rate, or listening to heart sounds with a stethoscope.

Explanation: Modern athletes might use smartwatches or fitness trackers that measure heart rate continuously. Alternatively, they could manually measure pulse at the wrist or neck, counting beats per minute. A doctor might use a stethoscope to listen to valve closures.

(d)(ii)

Answer: -48.9%

Explanation: From the graph: Maximum heart rate = 180 bpm at about 5 minutes; Heart rate at 18 minutes = 92 bpm. Percentage change = [(92 – 180)/180] × 100 = (-88/180) × 100 = -48.888…% ≈ -48.9% (to 3 significant figures). The negative sign indicates a decrease in heart rate during recovery.

(d)(iii)

Answer: Heart rate increases to deliver more oxygen and glucose to muscles and remove carbon dioxide and lactic acid faster.

Explanation: During exercise, muscles work harder and require more energy. The increased heart rate serves several crucial functions: 1) It delivers more oxygen to muscles for aerobic respiration, 2) It supplies more glucose (fuel for respiration), 3) It removes carbon dioxide (a waste product of respiration) more quickly, 4) It transports lactic acid (produced during anaerobic respiration) to the liver for processing, and 5) It helps regulate body temperature by increasing blood flow to the skin. This coordinated response ensures muscles can continue contracting efficiently during physical activity.

Question

Fig. 2.1 shows a cross-section of a human heart.

(a)(i) On Fig. 2.1, label with an R the position of the right ventricle.

(a)(ii) State the names of the structures labelled A and B on Fig. 2.1.

(a)(iii) Complete the sentence about blood vessel C. Blood vessel C transports blood from the ……………………. to the………………………

(b) Fig. 2.2 shows a cross-section of part of a heart that has an incomplete structure.

Explain how the incomplete heart structure shown in Fig. 2.2 may affect a person’s ability to transport oxygen.

(c) Fig. 2.3 shows how the body uses aerobic and anaerobic respiration during the first 120 seconds of vigorous physical activity. Between 0 and 20 seconds, the body also uses stored energy.

(c)(i) Describe the data shown in Fig. 2.3.

(c)(ii) State the balanced chemical equation for aerobic respiration.

(c)(iii) During anaerobic respiration an oxygen debt can build up. State the name of the chemical that causes this oxygen debt.

▶️ Answer/Explanation

Solution

(a)(i) R should be labeled on the right ventricle (lower right chamber of the heart).

(a)(ii)

A: Atrioventricular valve (e.g., bicuspid/mitral or tricuspid valve).
B: Semilunar valve (e.g., aortic or pulmonary valve).

(a)(iii) Blood vessel C (aorta) transports blood from the left ventricle to the body (systemic circulation).

Explanation: The aorta is the main artery carrying oxygenated blood from the heart to the body.

(b) The incomplete structure (e.g., a hole in the septum) allows mixing of oxygenated and deoxygenated blood. This reduces oxygen delivery to tissues because the blood pumped to the body is less oxygenated.

Explanation: Septal defects compromise the heart’s efficiency in separating oxygen-rich and oxygen-poor blood.

(c)(i) Key observations from Fig. 2.3:

Aerobic respiration energy increases gradually, plateauing at 80% by 100 seconds.
Anaerobic respiration peaks at 80% at 20 seconds, then declines to a steady 20%.
Both contribute equally (50% each) at 60 seconds.

(c)(ii) Balanced equation for aerobic respiration: \[ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O \]

(c)(iii) The chemical causing oxygen debt is lactic acid (produced during anaerobic respiration in muscles).

Explanation: Lactic acid accumulates when oxygen is insufficient, requiring post-exercise oxygen to metabolize it.

iGCSE Biology (0610)-9.2 Heart – iGCSE Style Questions Paper 4

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