Control of the heartbeat and ECGsEdexcel International A Level Biology: Flashcards

Exam questions on Control of the heartbeat and ECGs

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.
   Explain why the heart continues to beat after its nerves have been cut.2 marks
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.
   Explain the importance of the delay in the impulse at the AVN.2 marks
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.
   Calculate the heart rate of patient A and state what it shows.3 marks