CAIE A Level Biology 9700 · Control and coordination
Two sensory neurones of the same diameter are isolated from a mammal. One is myelinated and the other is unmyelinated. When a stimulus of the same strength is applied to each neurone, the action potential travels more rapidly along the myelinated neurone. Explain how the structure of the myelinated neurone allows this more rapid transmission.
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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