CAIE A Level Biology 9700 · Control and coordination
The Venus fly trap (Dionaea muscipula) captures prey using modified leaves that form a trap. Each lobe of the trap bears several sensory hairs. When an insect touches a single sensory hair, an action potential is generated but the trap does not close. Only if a second hair is touched (or the same hair is stimulated again) within about 20 seconds does the trap snap shut. Explain why the trap closes only after repeated stimulation of the sensory hairs.
4 marks, so the mark scheme is looking for about 4 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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