The diagram below shows how the iris and pupil of a human eye appear under
different conditions.
(a) Name the structures labeled X and Y
(b) (i) State the condition that leads to the change in appearance shown in
the diagram labeled B
(ii) Describe the changes that lead to the appearance of the iris
and pupil as shown in the diagram labeled B
(iii) What is the significance of the changes described

Answer:

a)
- X: pupil
- Y: Circular muscle
b i)
- Dim light/ low light
intensity/ darkness
ii)
- Circular muscles in iris relax, while radial muscles contract. The
pupil becomes bigger allowing more light to enter the eye.

iii)
- Allows one to visualize or see objects under dim light.

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