Control of heart rateAQA A-Level Biology: Subtopic test

1. 1
   A mammalian heart is removed from the body and placed in warm, oxygenated saline solution. All the nerves to it have been cut. The heart continues to beat rhythmically for several minutes.

   (a)

   Which term describes a heartbeat that is initiated within the heart muscle itself, without a nerve impulse?

   [1 mark]

   • ANeurogenic
   • BMyogenic
   • CAutonomic
   • DVoluntary

   (b)

   What is the role of the atrioventricular node (AVN)?

   [1 mark]

   • AIt delays the wave of excitation so that the atria finish contracting before the ventricles contract
   • BIt initiates the wave of excitation that spreads across the atria
   • CIt conducts the wave of excitation rapidly to the apex of the heart
   • DIt acts as a layer of tissue that conducts the wave directly from the atria to the ventricles

   (c)

   Explain why the wave of excitation is carried by Purkyne tissue down the septum to the apex of the heart before it spreads upwards through the ventricle walls.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A volunteer holds her breath for 30 seconds. During this time the carbon dioxide concentration of her blood rises and her heart rate increases from 70 to 85 beats per minute.

   (a)

   Where are the chemoreceptors that detect the change in her blood?

   [1 mark]

   • AIn the walls of the left ventricle and the vena cava
   • BIn the walls of the right atrium and the SAN
   • CIn the hypothalamus and the skin
   • DIn the walls of the carotid arteries and the aorta

   (b)

   Which change in her blood stimulates the chemoreceptors?

   [1 mark]

   • AA rise in blood pH
   • BA fall in blood temperature
   • CA fall in blood pH caused by the rise in carbon dioxide concentration
   • DA rise in blood pressure

   (c)

   Explain how the rise in carbon dioxide concentration leads to the increase in her heart rate.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Physiologists investigate how the autonomic nervous system controls the heart rate of an anaesthetised mammal at rest. With all nerves intact, the resting heart rate is 90 beats per minute. When the parasympathetic nerve to the sinoatrial node (SAN) was cut, the rate rose to 110 beats per minute. When the sympathetic nerve to the SAN was cut instead, the rate fell to 80 beats per minute. When both nerves were cut, the heart continued to beat at 100 beats per minute.

   (a)

   The blood pressure of this mammal suddenly rises. Describe how pressure receptors lead to a return of the heart rate towards normal.

   [3 marks]

   (b)

   Use the data to deduce the roles of the heart muscle and the autonomic nerves in controlling the resting heart rate.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A patient has had an artificial pacemaker fitted because her sinoatrial node (SAN) no longer produces regular impulses. The pacemaker delivers a small electrical impulse to the wall of her right atrium at regular intervals. Her atrioventricular node (AVN), bundle of His, Purkyne tissue and heart muscle are healthy. Her cardiologist explains that the pacemaker must also be able to increase her heart rate when she exercises, as a healthy SAN would.

   (a)

   Describe and explain how a healthy heart increases its rate when a person starts to exercise.

   [6 marks]

   (b)

   Explain how an impulse delivered by the pacemaker to the atrium leads to the coordinated contraction of the atria followed by the ventricles.

   [6 marks]

   Total for question 4: 12 marks

End of questions