Chapter 33, Problem 21A

Summary Introduction

Introduction:

Eyes help us to see things. Eyesight provides a person able to see. The outer light travels through a transparent cell called the cornea. The cornea focuses the light through an opening called the pupil. The pupil is functioned by muscles in the eyes called iris. The retina is present after the iris which projects the image onto the retina. The retina has photoreceptors called rods and cones. Rods are the reasons for the vision of dim lights whereas cones are responsible for the vision of bright lights.

Answer to Problem 21A

Correct answer:

The correct answer is option (a) rods.

Explanation of Solution

Explanation/justification for the correct answer:

Option (a) rods. Eyesight contains two types of photoreceptors. They are rods and cones. Rods are responsible for the vision of dim light. So, in a movie theatre where only a few dim emergency lights emerge, rods can help in finding the way to exit. Therefore, the correct answer is option (a).

Explanation for incorrect answer:

Option (b) cones. Cones receive bright light. As in a movie theatre where only the dim light emerges, cones adapt the vision of bright light. So, this is an incorrect option.

Option (c) Rods and cones are equally important. Rods are responsible for dim light vision, whereas cones are responsible for bright light vision. So in the situation mentioned above where only dim light emerges, rods will be most important for finding the way to exit. So, this is an incorrect answer.