The function of the iris in the eyes of a frog is to

The function of the iris is to ....

Select the correct option:
$(1)$ There are no photoreceptor cells slightly above the posterior pole of the eyeball,hence it is called the blind spot.
$(2)$ Rod cells contain a purple-red protein called rhodopsin.

Only rods are present in the eyes of one of the following animals:

The purple-red protein rhodopsin,which is present in the light-sensitive rod cells of the human eye,is a derivative of:

Ciliary muscles are found in the ........