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Date May 2018 Marks available 2 Reference code 18M.3.HL.TZ1.4
Level Higher level Paper Paper 3 Time zone Time zone 1
Command term Describe Question number 4 Adapted from N/A

Question

The diagram shows one of the stages in neurulation.

Describe what happens next in neurulation.

[2]
a.

Explain the causes of spina bifida in vertebrates.

[2]
b.

Explain the process of neural pruning.

[2]
c.

Markscheme

a. neural plate moves/folds/bends inwards to form a groove 

b. cells multiply/edges increase in height 

c. borders/edges of neural plate join/form neural crest 

d. neural tube forms/separates from rest (of ectoderm)

a.

a. spine/spinal cord does not form properly
OR
incomplete closure of embryonic neural tube/ tissues around the neural tube do not fuse 

b. lack of folic acid/folate (B9 vitamin) in pregnancy 

c. genetic/family history 

d. exposure to certain medication/environmental conditions during pregnancy

b.

a. development of vertebrate nervous system results in overabundance of neurons/connections 

b. unused neurons/synapses are lost 

c. neurons destroy themselves by programmed/natural cell death/apoptosis 

d. removal of dendrites from neurons

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
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)
Option A: Neurobiology and behaviour

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