Pupil response to light and dark

Steps:

• In darkness, pupils dilate to maximize light intake.
• When light turns on at 5 seconds, pupils constrict rapidly to reduce light entry.
• Light stays on for 5 seconds, maintaining constriction.
• When light turns off at 10 seconds, pupils dilate gradually back to original size.

Why A is correct:

• Graph A depicts initial large diameter, quick constriction at 5s, and slow dilation starting at 10s, matching the pupillary light reflex.

Why the others are wrong:

• B shows no initial dilation, ignoring dark adaptation.
• C depicts slow constriction and fast dilation, reversing actual response rates.
• D has immediate changes without timing alignment to light events.

Final answer: A