The cardiac cycle — CCEA AS Biology Practice Questions

Question 1

Explain how pressure changes in the left side of the heart cause the atrioventricular and semilunar valves to open and close during one cardiac cycle.

Accepted Answer

During atrial systole the left atrium contracts and atrial pressure rises above ventricular pressure, so the bicuspid valve is pushed open and blood flows into the left ventricle. During ventricular systole the ventricle wall contracts, ventricular pressure rises above atrial pressure and the bicuspid valve closes, preventing backflow into the atrium. As the ventricle continues to contract, ventricular pressure rises above the pressure in the aorta, forcing the semilunar valve open so blood is ejected into the aorta. During diastole the ventricle relaxes and ventricular pressure falls below aortic pressure, so the semilunar valve closes and prevents blood returning to the ventricle.

Question 2

A student measured a heart rate of 72 beats per minute and a stroke volume of 70 cm³. Calculate the cardiac output in dm³ min⁻¹ and explain one change that would occur during exercise.

Accepted Answer

Cardiac output = stroke volume × heart rate = 70 cm³ × 72 = 5040 cm³ min⁻¹ = 5.04 dm³ min⁻¹. During exercise both heart rate and stroke volume increase, so cardiac output rises. This delivers oxygen and glucose to the respiring muscle faster and removes carbon dioxide and lactate more quickly, maintaining aerobic respiration.

The cardiac cycle: CCEA Biology practice questions

Sit the questions

Explain how pressure changes in the left side of the heart cause the atrioventricular and semilunar valves to open and close during one cardiac cycle.

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