Questions & Answers

Light sensitive cells of eyes are present in-
A) Cornea
B) Sclera
C) Choroid
D) Retina

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Hint: In eyes, the light sensitive cells are cones and rods. We must know the actual part of the eye where these cells are present to answer this question correctly.

Complete answer:
Eyes are sensory organs. They provide the ability of vision to animals, vision is the ability to be able to receive and process visual detail. Light is detected by eyes and is then converted into electro-chemical impulses shared via neurons with the brain. Higher organisms possess complex optical systems in which light is collected from the surrounding environment. Its intensity is regulated through a diaphragm which focuses it through an assembly of lenses which are adjustable and an image gets formed. The image is converted into a set of electrical signals which gets transmitted to the brain through complex neural pathways.

Brain is connected to the eye via the optic nerve which extends up to the visual cortex and other areas of the brain. Shapes and colours can be differentiated by complex eyes. Large areas of binocular vision to improve depth perception which involves in the visual fields of many organisms, especially predators while in other organisms, eyes are placed in such a manner in order to maximise the field of view; for example, rabbits and horses have monocular vision.

Among animals, the eye evolved around 600 million years ago, during the time of the Cambrian explosion. In higher animals, the eye works in such a manner that it allows light to enter and get projected onto a screen possessing a light-sensitive panel of cells. The screen is known as retina which is present at the rear of the eye.

The optic nerve transmits the signals to the brain. Eyes of such animals are typically almost spherical in shape, the eyes are filled with vitreous humour, a gel-like transparent substance. An iris is present with a focusing lens; the size of the pupil changes due to the relaxing or tightening of the muscles around the iris, it regulates the amount of light that enters the eye, thereby reducing the aberrations in absence of enough light.

Thus the correct answer is option ‘D’ i.e, Retina.

Note: Retina bears cone cells and rod cells. The cone cells detect colour and the rod cells which differentiate contrast in low light, these cells detect and convert light into neural signals creating vision.