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 in (b) (ii) above?

Answer:

a)
Answer
- 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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