| Date | May 2017 | Marks available | 2 | Reference code | 17M.3.SL.TZ1.4 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Outline | Question number | 4 | Adapted from | N/A |
Question
The photomicrographs below show time lapse images of a migrating neuron in the grey matter of the cerebrum of an embryo. The time lapse images were taken at one hour intervals. The cell body is the rounded bright area towards the rear of the migrating neuron.
Calculate the rate of movement of the neuron cell body between 0 and 5 h. Working should be shown, giving the units.
Suggest a reason for the migration of neurons in the embryonic nervous system.
Outline neural pruning.
Markscheme
a. cell moves 25−28mm
OR
71−93μm
b. speed range is 71−93 μm in 5 hours
c. answer in the range 14−19 μm/h or μm h−1
a. «neural migration» positions cell types from different origins into specific locations
b. «neural migration» allows formation of connections/synapses
c. allows for differentiation of cell types/types of neuron
a. neural pruning is the removal of synapses/dendrites/ neural connections
b. caused by lack of use
c. it occurs during brain development/between birth and end of puberty
d. allows new neural connections/makes nervous system more efficient /plasticity
