Final answer:
The iris is the colored part of the eye that adjusts the size of the pupil to regulate the amount of light entering the eye.
Step-by-step explanation:
The colored part of the eye that contains muscles to contract or expand the pupil is the iris. The iris adjusts the amount of light entering the eye. It constricts the pupil in bright light to reduce the amount of light entering and dilates it in low light to allow more light in.
This muscle is essential for regulating vision in different lighting conditions. The cornea, on the other hand, is a protective layer on the front of the eye but does not play a role in adjusting the pupil size.
Understanding the iris's function is part of learning about the human eye structure, which has three layers: the fibrous tunic, the vascular tunic, and the neural tunic, housing the retina. Rods and cones, located in the retina, are responsible for detecting light and colors, respectively. Lastly, the lens of the eye focuses light onto the retina to create a clear image.