Question

Number of rod cells in eye is
a) 120 million
b) 80 million
c) 60 million
d) 180million

Answer 1

Hint: Rod cells are the photoreceptor cells. They function in dim light and are mainly responsible for night vision.

Complete Answer:
1. Sclera: The white protective layer in the eye is called sclera. It is the outermost covering.
2. Cornea: The front transparent part of the sclera is called cornea. Light enters the eye through the cornea.
3. Iris: A dark muscular tissue and ring-like structure behind the cornea are known as the iris. The colour of the eye is indicated by the colour of the iris.
4. Pupil: A small opening in the iris is known as a pupil. Iris controls the size of the pupil. It is concerned with the amount of light exposure to the eye.
5. Lens: A transparent structure present behind the pupil is called a lens. By the action of ciliary muscles, to focus light on the retina, it changes its shape. To focus distant objects, the lens becomes thinner and to focus nearby objects it becomes thicker.
6. Retina: It is a light-sensitive layer in the eye. It consists of many nerve cells. Images formed by the lens into electrical impulses with the help of retina. Through optic nerves the electrical impulses obtained are then transmitted to the brain.

Rod cells:
- They are the photoreceptor cells of the retina of the eye that can function in lower light or dim light whereas Cone cells are the type of photoreceptor cells of retina that can function in bright light.
- Rods are usually found concentrated at the outer edge of the retina and are used in peripheral vision.
- There are approximately 120 million rod cells in the human eye.
- Rod cells are more sensitive compared to cone cells and are responsible for night vision.

Hence the correct answer is (a) 120 million.

Note: Rod cells are located across the retina except at the centre part of fovea whereas the cone cells are present in the fovea centralis.