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Date November 2020 Marks available 2 Reference code 20N.3.HL.TZ0.4
Level Higher level Paper Paper 3 Time zone TZ0 / no time zone
Command term Suggest Question number 4 Adapted from N/A

Question

The image on the left shows a developing neuron on the first day of culture (day 1). The image on the right shows the same neuron after one day (day 2).

[Source: The establishment of polarity by hippocampal neurons
in culture, CG Dotti, CA Sullivan and GA Banker, Journal of Neuroscience 1 April 1988, 8 (4) 1454–1468;
DOI: https://doi.org/10.1523/JNEUROSCI.08-04-01454.1988, Copyright ©1988 Society for Neuroscience.]

Describe the changes occurring in this neuron from day 1 to day 2.

[2]
a.

Suggest other processes that may occur during neural development.

[2]
b.

Suggest what can happen to neurons that are unused in the nervous system.

[1]
c.

Markscheme

a. branches (of dendrites/axons) formed
OR
new/more dendrites formed;

b. dendrites/axons grow/get longer;

a.

a. neural tube differentiation/formation;

b. neuron (may) migrate to other parts;

c. axon (may) extend beyond the neural tube/myelinates;

d. synapses develop;

e. neural pruning;

Do not accept “connection” instead of “synapse”.

b.

a. neural pruning;

b. neurons are destroyed / apoptosis

c.

Examiners report

Many candidates could describe at least one change occurring, but many used terminology for processes occurring at later stages that were not shown on the photographs.

a.

Most candidates suggested correctly at least one other process, and stronger candidates suggested two.

b.

The vast majority of candidates correctly suggested neural pruning.

c.

Syllabus sections

Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Core topics) » A.1 Neural development
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Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Core topics)
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