CAIE A Level Biology 9700 · Control and coordination
A student investigates the effect of increasing stimulus intensity on the frequency of action potentials in a sensory neurone. She observes that even with a very strong stimulus, the maximum frequency reaches a plateau at approximately 500 impulses per second. Explain why the refractory period limits the maximum frequency of action potentials in a neurone.
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.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.