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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
(iii) What is the significance of the changes described in (b) (ii) above?

Answer Text:
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.