Final answer:
The iris controls the amount of light entering the eye by adjusting the size of the pupil.
Step-by-step explanation:
The part of the eye that controls the amount of light entering the eye by adjusting the opening around the pupil is the iris.
The iris is the colored part of the eye that surrounds the pupil. It contains muscles that can contract or relax to adjust the size of the pupil. In bright light, the iris contracts, making the pupil smaller to limit the amount of light entering the eye. In dim light, the iris relaxes, making the pupil larger to allow more light to enter the eye.