CAIE A Level Biology 9700 · Transport in mammals
Explain the sequence of events by which the sinoatrial node (SAN) initiates and coordinates the heartbeat, including the roles of the atrioventricular node (AVN) and Purkyne tissue. In your answer, explain why the delay of the impulse at the AVN is important for efficient cardiac function.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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