The eye is made up of several parts: the cornea, pupil, iris, lens, and retina. Each has an important function. You can see and put together a model of the eye in the Institute's Bioscience Exhibit.
Ask the students Have you ever seen a picture of yourself where your eyes are red? This happens when the camera's flash reflects off the retina - or back wall - of your eye.
The iris is the muscle that lets the proper amount of light through the pupil and into the eye. It opens when there is little light and closes when there is a lot. The students can illustrate this for another.
Have partners face one another. Let one close his/her eyes for a count of 10 seconds, then open them. What does the partner observe?
The pupil is large, then becomes small. When the eye was shut, the iris relaxed trying to get more light into the pupil. When the eye opened, there was a flood of light - the iris shut the pupil down, trying to limit the light coming in.