The amount of light entering into eye can be controlled and regulated by _____________.

The correct option is Iris.

To understand why the iris is responsible for controlling and regulating the amount of light that enters the eye, we can look at the anatomy and function of its key parts:

1. The Pupil: The pupil is the black, circular opening in the center of the colored part of the eye. It acts as a gateway or window through which light enters the inner chamber of the eye.

2. The Iris: The iris is the colored, ring-shaped muscular structure surrounding the pupil. The iris contains two sets of muscles: sphincter pupillae (circular muscles) and dilator pupillae (radial muscles). These muscles contract and relax to adjust the size of the pupil opening:
- In bright light: The circular muscles of the iris contract, causing the pupil to constrict (become smaller) to prevent too much light from entering and damaging the sensitive retina.
- In dim light: The radial muscles of the iris contract, causing the pupil to dilate (become larger) to allow more light to enter so that a clearer image can be formed.

3. Other structures: The cornea acts as the protective outer lens that refracts light, while the retina is the light-sensitive screen at the back of the eye where the image is formed. Neither of these structures actively regulates the intake of light.

Therefore, even though light passes through the pupil, it is the muscular action of the iris that controls and regulates the pupil's size, thereby controlling the amount of light entering the eye.