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 | Explain | Question number | 4 | Adapted from | N/A |
Question
The diagram shows one of the stages in neurulation.
Describe what happens next in neurulation.
Explain the causes of spina bifida in vertebrates.
Explain the process of neural pruning.
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. 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
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