CAIE A Level Biology 9700 · Transport in mammals
In a healthy mammalian heart, the aortic valve opens about 0.05 s after the start of ventricular systole. In a heart where the Purkyne tissue has been partially damaged, this interval increases to 0.10 s and the maximum rate of pressure rise in the left ventricle is significantly reduced.
Explain these observations with reference to the roles of the sinoatrial node, atrioventricular node and Purkyne tissue in coordinating the heartbeat.
6 marks, so the mark scheme is looking for about 6 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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