Question

For the synthesis of the rhodopsin, which of the following foods is needed?
a. Mango
b. Rice
c. Carrot
d. Tomatoes

Answer 1

Hint: Rhodopsin (also known as visual purple) is a light-sensitive protein. It is essential for vision, especially in dim light. It is a biological pigment found in the rods of the retina. Vitamin A is a precursor of rhodopsin, that helps us to see at night.

Complete answer:
The human eye is a complex camera-like structure. It has several parts: cornea, iris, pupil, lens and retina. Retina is the innermost, softest, transparent neurosensory layer of the eyeball sensitive to the light. The retina contains millions of light sensitive cells called photoreceptors. There are two types of photoreceptors cells:-

Rods: They are more sensitive to light of low intensity. They are suitable for night vision but the image formed is diffused, lacking in details.

Cones: They are sensitive to light of high intensity. They are more suited for day vision and they produce a sharp image with the fine details.

The rods of the mammalian eye contain an extremely photosensitive substance called rhodopsin or visual purple. It is a compound of opsin or scotopsin (protein) and retinene (pigment). During bright light, it disappears or reduces to a state which is unfit for visual sensation. It breaks up into opsin and retinene in dim light and stimulates sensory impulses in rods.

In darkness opsin and retinene recombine to form rhodopsin with the help of ATP. Retinene is a derivative of vitamin A. In this way the rods are prepared to respond to light again. This cycle of breakdown and resynthesis of rhodopsin goes on continuously.

Vitamin A is a precursor to the formation of the photopigment rhodopsin, which is located in the rods. Vitamin A promotes good eyesight, especially in dim light. Carrots, fish, spinach, lettuce, broccoli, sweet potato etc. are food rich in vitamin A.

Mangoes and tomatoes contain high levels of Vitamin C whereas rice is a source of protein and contains various vitamins but do not contain Vitamin A.

Hence, the correct answer is option (C).

Note: Rhodopsin cannot be synthesized inside the human body. It is made up of a protein opsin and a pigment known as retinene which is a derivative of vitamin A. The food sources that are rich in vitamin A like carrots, spinach, sweet potatoes, lettuce etc. are important for the synthesis of rhodopsin.