Answer the following questions briefly:
Explain how the human eye adapts itself to bright light and dim light.
Topic: Adaptation of the eye to light
Answer
In BRIGHT light the circular muscles of the IRIS contract, making the PUPIL SMALLER, so less light enters and the retina is protected. The CONES, which need bright light, are stimulated and give colour vision.
In DIM light the radial muscles of the iris contract, making the PUPIL LARGER, so more light enters. The RODS, containing rhodopsin, are stimulated and give black-and-white vision.
Two mechanisms are involved, and a full answer gives BOTH: the IRIS adjusting the SIZE OF THE PUPIL, which controls how much light enters the switch between CONES (bright light, colour) and RODS (dim light, black and white)
Most candidates give only the pupil and lose the second half.
A way to keep the receptors paired: Cones for Colour, Rods for the dark — and Rhodopsin with Rods, both beginning with R. Rhodopsin is made from VITAMIN A, which is why a deficiency causes NIGHT BLINDNESS.