A-LevelBiologyControl and coordination9700/42 · Oct/Nov 2022 · Q96 Marks
Voltage-gated channels are involved in the generation of an action potential. Fig. 9.1 is a diagram of the voltage-gated channels of sodium ions and potassium ions in the membrane of an axon. The channels are shown in three different states, 1, 2 and 3. [Figure 9.1] Fig. 9.2 is a diagram of different phases of an action potential in an axon. The phases are labelled A, B, C, D, E, F and G. [Figure 9.2]
- (a)Complete Table 9.1 to match each of the listed phases of the action potential with the appropriate state of the voltage-gated channels: 1, 2 or 3.[3]
- (b)Many neurones are surrounded by myelin sheaths. Describe and explain the role of the myelin sheath in the transmission of an action potential.[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.
- [3]
- phase of action potential | state of voltage-gated channels
- A | 2
- C | 1
- E | 3
- F | 3
- G | 2
- 5 correct = 3 marks
- 3/4 correct = 2 marks
- 1/2 correct = 1 mark
- [3] any three from:
- 1 Schwann cells, wrap around the axon / form the myelin sheath;
- 2 insulates (axon) / prevents movement of ions ;
- 3 depolarisation / action potentials, can only occur at nodes (of Ranvier);
- 4 ref. to long(er) local circuits / (nodes are) 1–3 mm apart;
- 5 action potentials, move by saltatory conduction / jump from node to node;
- 6 speed of transmission is, fast(er) / 100 m s-1 ;
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