CAIE A Level Biology 9700 · Transport in mammals
The heartbeat is coordinated by a sequence of electrical impulses passing through specialised cardiac muscle tissue. The sinoatrial node (SAN), atrioventricular node (AVN), and Purkyne tissue each play distinct roles in this process. A key feature is the delay that occurs at the AVN.
Explain how the SAN, AVN, and Purkyne tissue coordinate the contraction of the atria and ventricles, and why the delay at the AVN is essential for efficient heart 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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