Control of the heartbeat and ECGsEdexcel International A Level Biology: Subtopic test

1. 1
   A medical student keeps the heart of a mammal beating in warm, oxygenated saline solution after it has been removed from the body. All the nerves that normally supply the heart have been cut, yet the heart carries on beating regularly for several minutes.

   (a)

   What term describes cardiac muscle that can initiate its own contraction without nervous stimulation?

   [1 mark]

   • ANeurogenic
   • BMyogenic
   • CVoluntary
   • DSynaptic

   (b)

   Which structure acts as the pacemaker of the heart?

   [1 mark]

   • AAtrioventricular node
   • BBundle of His
   • CPurkyne fibres
   • DSinoatrial node

   (c)

   Explain why the heart continues to beat after its nerves have been cut.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a healthy heart, a wave of electrical activity spreads from the sinoatrial node (SAN) across the walls of both atria. A layer of fibrous tissue that does not conduct electricity separates the atria from the ventricles, so the wave cannot pass directly between them.

   (a)

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

   [1 mark]

   • AIt generates the impulse that starts each heartbeat
   • BIt conducts the impulse rapidly to the apex of the heart
   • CIt delays the impulse before it passes to the ventricles
   • DIt spreads the impulse through the walls of the atria

   (b)

   Why is it important that the ventricles contract from the apex (the bottom tip of the heart) upwards?

   [1 mark]

   • ABlood is squeezed upwards towards the arteries leaving at the top of the ventricles
   • BBlood is forced back into the atria
   • CThe valves between the atria and ventricles are forced open
   • DThe AVN is given time to recharge

   (c)

   Explain the importance of the delay in the impulse at the AVN.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A cardiologist records electrocardiograms (ECGs) from two patients, A and B. A normal resting heart rate is 60 to 100 beats per minute. Patient A: the time between successive R waves is constant at 0.50 s, and every QRS complex is preceded by a P wave. Patient B: the time between successive R waves varies irregularly between 0.30 s and 0.90 s, no distinct P waves can be seen and the baseline shows rapid, irregular, small waves.

   (a)

   Calculate the heart rate of patient A and state what it shows.

   [3 marks]

   (b)

   Suggest what the ECG of patient B shows about the activity of the heart and explain how this would affect the heart's function.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In a healthy heart each cardiac cycle starts in the wall of the right atrium, and the only electrical route from the atria to the ventricles is a specialised pathway of conducting tissue. A patient has fainting episodes. Her ECG shows P waves occurring regularly at 75 per minute and QRS complexes occurring regularly at 35 per minute, with no fixed relationship between the two. She is diagnosed with complete heart block, caused by damage to the atrioventricular node (AVN).

   (a)

   Describe how the normal electrical activity of the heart coordinates one heartbeat.

   [6 marks]

   (b)

   Explain how the ECG findings and the patient's fainting episodes are related to the damage to her AVN.

   [6 marks]

   Total for question 4: 12 marks

End of questions