Paper 1 Q1 — Why acetylcholinesterase must be fast

Neurophysiology — role of high turnover number in resetting the synapse

What the examiners said

“A small number of candidates found it difficult to explain the high turnover number of acetylcholinesterase and some appeared to suggest that acetylcholinesterase was responsible for the impulse itself. Not all appreciated the importance of the breakdown of the neurotransmitter in relation to the generation of an action potential.”

Try the question (reconstruction)

Acetylcholinesterase has a very high turnover number at the synapse. Why is rapid breakdown of acetylcholine essential?

Examiner report: “Some wrongly suggested the enzyme generates the impulse rather than terminating the signal.”

Explore — clearing the cleft

Set the enzyme turnover rate. Watch how quickly acetylcholine is cleared and the membrane repolarises. Too slow, and signals blur into one continuous depolarisation.

Enzyme turnover rate: high

High turnover = the synapse resets fast enough to transmit separate impulses. The enzyme ends signals; it does not create them.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H3 Biology 9816 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

Made by lookang, using Claude Fable 5. More resources: iwant2study.org