A-LevelBiologyControl and coordination9700/42 · May/June 2018 · Q815 Marks

Describe how an action potential arriving at a presynaptic neurone can result in the release of acetylcholine into the synaptic cleft.

(a)Describe how an action potential arriving at a presynaptic neurone can result in the release of acetylcholine into the synaptic cleft.[4]
(b)Lidocaine is a local anaesthetic drug which blocks voltage-gated Na⁺ channels in the postsynaptic membrane of a synapse. Explain the effect of lidocaine action on the postsynaptic neurone.[2]
(c)(i)Fig. 8.1 is a diagram of a neuromuscular junction. [Fig. 8.1] With reference to Fig. 8.1, name structures A, B and C.[3]
(c)(ii)Outline the importance of structure A in the transmission of nerve impulses.[2]
(c)(iii)Explain why the structures labelled C are needed in a neuromuscular junction.[4]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[4] any 4 of: 1 (presynaptic) membrane depolarised ; 2 calcium (ion) channels open / (presynaptic membrane becomes) more permeable to Ca²⁺; 3 Ca²⁺ move in (to presynaptic, neurone / knob) ; R membrane 4 causes vesicles (of ACh) to move towards (presynaptic) membrane ; 5 vesicle fuses with (presynaptic) membrane / exocytosis ;
[2] any 2 of: 1 no Na⁺ enter (postsynaptic neurone) ; 2 no depolarisation of (postsynaptic) membrane ; 3 no, action potentials / impulses (transmitted) ;
[3] A - myelin sheath / Schwann cell; B - sarcolemma; C - mitochondria ;
[2] any 2 of: 1 insulates axon / prevents movement of ions / AW ; 2 increases speed (of impulses); 3 saltatory conduction / described ;
[4] 1 produces / releases, ATP ; any 3 of mp2-5: 2 (for) production / recycling, of ACh ; 3 (for) production / movement, of vesicles or exocytosis; 4 (for) contraction of sarcomere ; 5 (for) sodium potassium pumps / active transport ;

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