In the human eye, why does the pupil ENLARGE in dim light and CONSTRICT in bright light?
AIt is a sign of emotion only
BThe iris muscle automatically adjusts pupil size so the retina receives an optimal amount of light — more in dim conditions, less in bright conditions, protecting the retina
CThe pupil is too small to actually change size
DThe lens controls this; the pupil is fixed
Answer & Solution
Correct answer: B. The iris muscle automatically adjusts pupil size so the retina receives an optimal amount of light — more in dim conditions, less in bright conditions, protecting the retina
The iris is muscular and reflexively controls pupil size based on light intensity. In low light, the iris relaxes and the pupil widens so more light reaches the retina. In bright light, the iris contracts to reduce pupil opening — protecting the retina from over-stimulation and improving image clarity. This is called the pupillary reflex.
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