The function of iris in the eyes of frog is to

Options

A. Move lens forward and backward
B. Refract light rays
C. Bring about movement of eyelids
D. Alter the size of pupil.

Answer

### Step-by-Step Solution:

1. **Understanding the Iris**: The iris is the colored part of the eye that surrounds the pupil. It plays a crucial role in controlling the amount of light that enters the eye.

2. **Components of the Iris**: The iris contains smooth muscle cells that can contract or relax. These muscles are responsible for changing the size of the pupil.

3. **Function of Rhodopsin**: The smooth muscle cells in the iris contain a pigment called rhodopsin. This pigment is sensitive to light and plays a role in the contraction of the iris in response to varying light conditions.

4. **Regulating Light Entry**: When light levels change, the iris adjusts the size of the pupil. In bright light, the iris contracts, making the pupil smaller to reduce the amount of light entering the eye. Conversely, in dim light, the iris relaxes, allowing the pupil to enlarge and let in more light.

5. **Conclusion**: Therefore, the primary function of the iris in the eyes of a frog is to alter the size of the pupil, thereby regulating the amount of light that enters the eye.

### Final Answer:
The function of the iris in the eyes of the frog is to alter the size of the pupil.

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