A-LevelBiologyControl and coordination9700/42 · May/June 2021 · Q19 Marks

(a) Fig. 1.1 is a diagram of part of a neurone membrane at resting potential. [Figure 1.1]

(a)(i)With reference to Fig. 1.1, name A, B, and D.[3]
(a)(ii)Substance C is required to make structure A function. Name substance C.[1]
(b)Some drugs can affect the functioning of neuromuscular junctions or cholinergic synapses. Table 1.1 lists three drugs and describes their action on neuromuscular junctions or cholinergic synapses. drug | action of drug ---|--- curare | blocks muscle cell membrane receptors at neuromuscular junctions nerve gas | inhibits acetylcholinesterase function in synapses alcohol | inhibits exocytosis of neurotransmitters in synapses Suggest and describe the immediate consequence of the action of each drug on a neuromuscular junction or cholinergic synapse.[5]

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Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[3] A – sodium potassium pump; CON if channel mentioned
[3] B - potassium ions ; A K+
[3] D - sodium ions; A Na+
[3] max 2 if no ref. to ions
[1] ATP;
[5] any five from: drugs could be in any order
[5] curare
[5] 1 less / no, ACh binds to receptors; I neurotransmitter
[5] 2 fewer / no, (ligand gated) Na+ channels open or fewer / no, Na+ can enter sarcomere / sarcoplasm or no / less, depolarisation of, sarcolemma / muscle cell membrane ;
[5] nerve gas
[5] 3 no / less, ACh broken down or ACh remains bound to receptor;
[5] 4 (ligand gated) Na+ channels remain open / Na+ continue to enter post synaptic neurone or permanent / AW, depolarisation (of post synaptic membrane); A sarcolemma
[5] alcohol
[5] 5 no / less, binding of, neurotransmitter / ACh, to receptors ;

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