A-LevelBiologyControl and coordination9700/42 · May/June 2019 · Q110 Marks
(a) Fig. 1.1 is an electron micrograph showing a cross-section of a myelinated neurone. [Figure 1.1] Name A and B. A B
- (a)Name A and B. A B[2]
- (b)Explain what is meant by saltatory conduction and describe its effect on the transmission of a nerve impulse.[3]
- (c)A type of sea snail, Conus purpurascens, produces a toxin that blocks calcium ion channels in the presynaptic knob of a cholinergic synapse. The presence of this toxin results in no action potentials in the postsynaptic neurone. Explain why the presence of this toxin results in no action potentials in the postsynaptic neurone.[5]
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Mark scheme
Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.
- [2] A - Schwann cell / myelin sheath;
- B - axon / axoplasm / cytoplasm ;
- [3] 1 action potential / impulse, ‘jumps' from node to node;
- 2 local circuits, set up between nodes / longer; A local currents
- 3 fast / increases speed (of transmission of impulse);
- [5] any five from:
- 1 no calcium ions enter (the presynaptic knob) ;
- 2 (so) vesicles do not, move towards / fuse with, presynaptic membrane ;
- 3 no, exocytosis / release, of ACh ; R exocytosis of vesicles
- 4 ACh does not diffuse across (synaptic) cleft;
- 5 no binding with receptor (protein) on postsynaptic membrane ;
- 6 sodium (ion) channels do not open ;
- 7 sodium ions do not enter (postsynaptic) neurone ;
- 8 no depolarisation (of postsynaptic membrane);
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