Question

 If you walk from a dark room into sunlight and back again into dark room, how would your pupils alter in size? What makes this happen?

Answer 1

 Initially, in a dark room, the pupil is large so as to allow a large amount of light into the eye. When we go out into sunlight, we feel glare in our eyes as the pupil is large. Gradually, the pupil contracts, and we are able to see clearly. On moving back from sunlight to a dark room again, we are not able to see the surroundings clearly, because the pupil is small. Gradually, the pupil expands, which then improves our vision. This action of the pupil is controlled by the iris, which automatically adjusts the size of the pupil according to the intensity of light that the eye receives.