Control of heart rateEdexcel A-Level Biology B: Subtopic test

1. 1
   A 17-year-old runner has a resting heart rate of 62 beats per minute. During a 5 km race her heart rate rises to 170 beats per minute and the carbon dioxide concentration in her blood increases. After she finishes, both gradually return to normal.

   (a)

   In which region of the brain is the cardiac centre that controls heart rate?

   [1 mark]

   • ACerebellum
   • BMedulla oblongata
   • CHypothalamus
   • DCerebral cortex

   (b)

   Which receptors detect the increase in the carbon dioxide concentration of the runner's blood?

   [1 mark]

   • ABaroreceptors in the carotid sinus
   • BOsmoreceptors in the hypothalamus
   • CThermoreceptors in the skin
   • DChemoreceptors in the carotid bodies and aorta

   (c)

   Explain how the rise in carbon dioxide concentration in the runner's blood leads to an increase in her heart rate.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A woman stands up quickly from lying down and feels dizzy for a few seconds. Blood pools in her legs, so the blood pressure in her aorta and carotid arteries briefly falls. Within seconds her heart rate rises and her blood pressure returns to normal.

   (a)

   Where are the baroreceptors that monitor the woman's blood pressure located?

   [1 mark]

   • AIn the aortic arch and the carotid sinus
   • BIn the vena cava and the pulmonary veins
   • CIn the SAN and the AVN
   • DIn the medulla oblongata and the hypothalamus

   (b)

   Which sequence correctly describes the reflex that raises the woman's heart rate?

   [1 mark]

   • ABaroreceptors send fewer impulses to the cardiac centre; the parasympathetic nerve releases more acetylcholine at the SAN
   • BBaroreceptors send more impulses to the cardiac centre; the sympathetic nerve releases noradrenaline at the SAN
   • CBaroreceptors send fewer impulses to the cardiac centre; the sympathetic nerve releases more noradrenaline at the SAN
   • DBaroreceptors send more impulses to the cardiac centre; the parasympathetic nerve releases more acetylcholine at the SAN

   (c)

   Explain why the woman's heart rate falls back to normal once her blood pressure has been restored.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is walking home when a dog suddenly runs at her. Within seconds her heart rate rises from 70 to 120 beats per minute. The raised rate persists for several minutes after the dog has left.

   (a)

   Explain how the nervous system brings about the immediate rise in the student's heart rate.

   [3 marks]

   (b)

   Suggest why the student's heart rate remains raised for several minutes after the dog has left. Include the role of adrenaline in your answer.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A patient has received a donor heart. During the transplant operation the nerves that normally supply the heart, including the sympathetic nerve and the vagus (parasympathetic) nerve, were cut and have not reconnected. The donor heart's SAN is healthy. His resting heart rate is about 100 beats per minute, compared with a typical resting rate of about 70 beats per minute in a healthy adult. When he starts to exercise, his heart rate rises more slowly than in a healthy person and also takes longer to fall afterwards.

   (a)

   Explain the three observations about the patient's heart rate: the high resting rate, the slow rise during exercise and the slow fall afterwards.

   [6 marks]

   (b)

   The patient sometimes feels dizzy when he stands up quickly. Explain why he is more likely to do so than a healthy person, and suggest one piece of advice for him, justifying your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions