The heart and cardiac cycleAQA A-Level Biology: Mind map

Exam questions on The heart and cardiac cycle

1. In a resting adult, the pressures in the left atrium, left ventricle and aorta are recorded throughout the cardiac cycle. At one moment, contraction of the ventricles has just begun: the pressure in the left ventricle has risen above the pressure in the left atrium, but is still lower than the pressure in the aorta.
   Explain why blood does not flow back from the left ventricle into the left atrium while the ventricle contracts.2 marks
2. A man at rest has a heart rate of 68 beats per minute and a stroke volume of 75 cm³. After several months of endurance training, his resting heart rate falls to 55 beats per minute, while his resting cardiac output stays the same.
   Explain how his resting heart rate can fall without any fall in cardiac output.2 marks
3. One cardiac cycle in a resting person lasts 0.80 s. The ventricles begin to contract at 0.10 s, when the pressure in the left ventricle first exceeds that in the left atrium. The pressure in the aorta at this time is 10.7 kPa. The pressure in the left ventricle exceeds this at 0.18 s, reaches a maximum of 16.0 kPa at 0.28 s, and falls back below the aortic pressure at 0.42 s.
   Calculate the heart rate in beats per minute and the length of time for which the aortic valve is open during one cycle.3 marks