You walk from bright sunlight into a dim room. What happens to your pupil?
AIt becomes smaller
BIt becomes larger
CIt stays the same size
DIt closes completely
Answer & Solution
Correct answer: B. It becomes larger
1. The iris controls how much light reaches the retina by changing the size of the pupil.
2. In dim conditions the eye needs to admit more light, so the pupil must widen.
3. That widening happens because the radial muscles of the iris contract.
4. At the same time the circular muscles relax, allowing the opening to enlarge.
5. The reverse happens in bright light: circular muscles contract and the pupil narrows to protect the retina.
_Source: NECTA CSEE 2021 Biology 033, Question 1: Multiple Choice, item (vi)_
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