CAIE A Level Biology 9700 · Transport in mammals
Explain how the sequence of electrical activity from the sinoatrial node (SAN) through the atrioventricular node (AVN) to the Purkyne tissue coordinates the contraction of the heart chambers, and discuss why the delay at the AVN is essential for efficient blood flow during the cardiac cycle.
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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