| Date | November 2017 | Marks available | 4 | Reference code | 17N.3.SL.TZ0.07 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 07 | Adapted from | N/A |
Question
The diagrams illustrate changes in synapse density of the cerebral cortex from newborn to adult.
[Source: THE POSTNATAL DEVELOPMENT OF THE HUMAN CEREBRAL CORTEX, VOLUMES IVIII, by Jesse LeRoy Conel, Cambridge, Mass.: Harvard University Press, Copyright © 1939, 1941, 1947, 1951, 1955, 1959, 1963, 1967
by the President and Fellows of Harvard College. Copyright © renewed 1967, 1969, 1975, 1979, 1983, 1987, 1991.]
Explain the processes illustrated by the diagrams.
Markscheme
a. at birth neurons are mainly unconnected
b. after birth «up to 2 years» neurons start to make synapses/connections with other neurons
OR
up to 2 years the number of synapses/connections increases
c. «increase in synapses» occurs rapidly due to learning/new experiences
d. each neuron can make multiple synapses
e. brain makes many more connections than are required
f. «after 2 years/in adults» neural pruning causes the loss of unused neurons/synapses/connections
Do not accept more neurons are made
[Max 4 Marks]
