IB Biology SL C2.2 Neural signalling questions

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Question 1

Multiple choiceEasy1 mark

When an impulse reaches a neuron terminal, the presynaptic membrane depolarizes and neurotransmitter is released. Which ion movement acts as the intracellular signal for this release?

Show answer and explanation

Answer: C. Depolarization of the presynaptic membrane causes Ca²⁺ uptake into the neuron. Ca²⁺ acts as a signalling chemical inside the neuron and promotes neurotransmitter release. A: confuses K⁺ efflux, associated with repolarization, with the signal for neurotransmitter release. B: confuses Na⁺ influx, associated with depolarization, with the ion that signals release. D: reverses the direction: Ca²⁺ enters rather than leaves the presynaptic neuron. Remember: Ca²⁺ entry at the presynaptic membrane signals neurotransmitter release.

Question 2

Paper 2Medium16 marks

An electrical impulse was initiated at a point on the axon of a neuron. Detectors recorded the time at which the impulse reached different distances along the same axon. Figure 1 shows the results. Times and distances were recorded to the nearest 0.1 ms and 0.1 cm, respectively.

012345601234567891011Time from initiation to detection / msDistance from stimulation point along axon / cm
(a)

State what forms the cell body of a neuron, and give two differences between an axon and dendrites.

[3]
(b)

Use Figure 1 for parts (i) and (ii).

(i)

Describe the relationship between distance from the stimulation point and time of detection shown in Figure 1.

[2]
(ii)

Determine the average speed of the impulse along the axon. Give your answer in m s⁻¹.

[3]
(c)

Use the best-fit line in Figure 1 to estimate the time at which the impulse would be detected 7.0 cm from the stimulation point.

[2]
(d)

Explain how the arrangement of a neuron’s fibres can enable it to conduct impulses over long distances and along multiple branches.

[3]
(e)

A student concludes that Figure 1 proves that all neurons conduct electrical impulses at the same speed. Evaluate this conclusion using Figure 1.

[3]

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