The heart and cardiac cycleAQA A-Level Biology: Subtopic test

1. 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.

   (a)

   What is the position of the atrioventricular valve and of the aortic valve at this moment?

   [1 mark]

   • ABoth are closed
   • BBoth are open
   • CThe atrioventricular valve is open and the aortic valve is closed
   • DThe atrioventricular valve is closed and the aortic valve is open

   (b)

   What must happen for the aortic valve to open?

   [1 mark]

   • AThe pressure in the left atrium must exceed that in the left ventricle
   • BThe pressure in the aorta must rise above that in the left ventricle
   • CThe left ventricle must relax
   • DThe pressure in the left ventricle must exceed that in the aorta

   (c)

   Explain why blood does not flow back from the left ventricle into the left atrium while the ventricle contracts.

   [2 marks]

   Total for question 1: 4 marks

2. 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.

   (a)

   What was his cardiac output before training?

   [1 mark]

   • A143 cm³ min⁻¹
   • B510 cm³ min⁻¹
   • C5100 cm³ min⁻¹
   • D0.91 cm³ min⁻¹

   (b)

   What is his stroke volume after training, to the nearest cm³?

   [1 mark]

   • A5045 cm³
   • B93 cm³
   • C280 500 cm³
   • D0.011 cm³

   (c)

   Explain how his resting heart rate can fall without any fall in cardiac output.

   [2 marks]

   Total for question 2: 4 marks

3. 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.

   (a)

   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]

   (b)

   Explain the changes in the positions of the atrioventricular valve and the aortic valve between 0.10 s and 0.42 s.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Two studies investigated whether a diet high in saturated fat causes coronary heart disease (CHD). Study 1 followed 8000 adults for 12 years and found that CHD was more common in people who ate more saturated fat. However, the people who ate more saturated fat also smoked more and took less exercise. Study 2 followed 40 000 adults for 5 years and found no significant difference in the incidence of CHD between people who ate more and less saturated fat.

   (a)

   Evaluate the evidence from the two studies for a causal link between a diet high in saturated fat and CHD.

   [6 marks]

   (b)

   Suggest how a further study could be designed to give more reliable evidence of whether saturated fat causes CHD, and justify your choices.

   [6 marks]

   Total for question 4: 12 marks

End of questions