Question 1
Paper 1A style
How does the sodium–potassium pump contribute to the resting potential of a neuron?
- It pumps two Na⁺ out and three K⁺ in by facilitated diffusion
- It pumps three Na⁺ out and two K⁺ in using energy from ATP
- It pumps Na⁺ and K⁺ into the neuron using energy from ATP
- It opens voltage-gated channels so Na⁺ diffuses out
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Answer: B [1]
Question 2
Paper 1A style
Why can a signal pass in only one direction across a typical synapse?
- The synaptic cleft is too wide for ions to diffuse back
- The postsynaptic neuron has no sodium–potassium pumps
- Only the presynaptic neuron releases neurotransmitter and only the postsynaptic membrane has its receptors
- Voltage-gated calcium channels are found only in the postsynaptic membrane
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Answer: C [1]
Question 3
Paper 1B style
The table shows the diameter and conduction speed of six nerve fibres. The values are typical values for practice. (a) Compare the conduction speeds of fibre C and fibre D. [2] (b) Calculate how many times wider fibre C is than fibre D. [1] (c) A larger study of 50 myelinated fibres found a correlation coefficient of r = 0.95 between diameter and conduction speed. State the type of correlation and calculate the coefficient of determination, R². [2] (d) Using the data, suggest one advantage of myelination in the nervous system of a vertebrate. [1]
| Fibre | Myelinated | Diameter / µm | Conduction speed / m s⁻¹ |
|---|---|---|---|
| A | No | 0.5 | 0.6 |
| B | No | 1.0 | 1.2 |
| C (squid giant axon) | No | 500 | 25 |
| D | Yes | 4 | 24 |
| E | Yes | 10 | 60 |
| F | Yes | 20 | 120 |
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- (a) speeds similar / C 25 m s⁻¹ and D 24 m s⁻¹ [1]
- (a) D achieves this with a much smaller diameter / C is non-myelinated and D is myelinated [1]
- (b) 500 ÷ 4 = 125 times [1]
- (c) (strong) positive correlation [1]
- (c) R² = 0.95² = 0.90 [1] Accept 0.9025.
- (d) fast conduction with narrow fibres, so many fibres fit in a small space / nerve OWTTE [1]
- Accept: rapid responses without needing giant axons.
Question 4
Paper 2A style
Describe how the arrival of an action potential at a presynaptic neuron leads to an excitatory postsynaptic potential at a synapse that uses acetylcholine.
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- depolarization of presynaptic membrane opens (voltage-gated) calcium channels [1]
- Ca²⁺ diffuses into presynaptic neuron [1]
- Ca²⁺ acts as a signal causing vesicles to fuse with presynaptic membrane / exocytosis [1]
- acetylcholine diffuses across the synaptic cleft [1]
- acetylcholine binds to (transmembrane) receptors on postsynaptic membrane [1]
- ion channels open and positive ions / Na⁺ diffuse into the postsynaptic cell [1]
- postsynaptic membrane depolarized [1]
- max 4