CAIE A Level Biology 9700 · Control and coordination
In the Venus fly trap (Dionaea muscipula), the modified leaves close rapidly when prey touches the trigger hairs. The plant does not close after a single touch but only if two touches occur within about 20 seconds.
Explain how the Venus fly trap achieves this rapid closure after repeated stimulation, and contrast this mechanism with the slower actions of auxin in cell elongation (acid growth) and gibberellin in barley seed germination.
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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