May/June 2026 Paper 12

2026 · 40 questions · 40 parts · 40 marks

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21Stem Cells DifferentiationMedium1 mark
The graph shows how the number of stem cells in the brain changes as a person ages.
Figure 21, a graph of the number of stem cells in the brain (y-axis, 0 to 2.5 x 10$^{5}$) against age in years (x-axis, 0 to 100); the curve starts at about 2.4 x 10$^{5}$ stem cells at age 0 and falls steeply, levelling off close to zero by around age 80-100.
Which events will decrease in the brain due to the change in the number of stem cells as a person ages?