(a) The amount of light entering the eyes of a human is controlled by iris and pupil.
The iris automatically adjusts the size of the pupil according to the intensity of light received by the eye.
If the amount of light received by the eye is large (as during the daytime), then the iris contracts the pupil (makes the pupil small) and reduces the amount of light entering the eye. On the other hand, if the amount of light received by the eye is small (as in a dark room or during night), the iris expands the pupil (makes the pupil large) so that more light may enter the eyes. Thus, the iris regulates (or controls) the amount of light entering the eye by changing the size of the pupil.
(c) About 35 million people in the developing world are blind and most of them can be cured. About 4.5 million people with corneal blindness can be cured through corneal transplantation of donated eyes. Out of these 4.5 million, 60% are children below the age of 12. So, if we have got the gift of vision, why not pass it on to somebody who does not have it. People can be motivated to donate their eyes
after death by telling them about this good deed. They can be told that they will live in someone else body even after their death. For this awareness camps can be organised to tell the people about the benefits they will give to the blind.
