Question

As compared to rods, cones are _______ times less sensitive to light.
A. 100
B. 200
C. 300
D. 400

Answer 1

Rods and cones are the two photoreceptor cells present in human eyes. The retina is the photosensitive layer of our eyes where rods and cones are seen. The rods are adapted for dim light vision or twilight vision. It is also called scotopic vision. Cones are adapted for bright light vision or daylight vision. It is also called photopic vision. Colour vision is also the function of cone cells.

Complete answer:
The rod cells are active in dim light therefore their sensitivity to light should be very much high to get stimulated by a very small amount of light as compared to the cone cells. The cone cells are active in the daylight and their sensitivity will be much lesser than the rod cells because when the amount of light decreases very low, the cone cells will become inactive and the rod cells will start functioning. Therefore the sensitivity of cone cells is about 300 times lesser than the rod cells.
The images obtained by the rod cells are black and white in color. A photosensitive pigment called rhodopsin or visual purple is seen in the rod cells. It is a purplish red protein that contains a derivative of vitamin A. It consists of opsin and aldehyde. Rod cells are seen accumulated in the peripheral region of the retina. Rod cells are slightly larger than cone cells and have more light absorption area and therefore have increased sensitivity.
Images formed by the cone cells are colorful. Iodopsin or visual violet is the pigment seen in cone cells. There are three types of cone cells that possess characteristic photopigments that respond to blue, green, and red lights. Erythrolabe is the pigment adapted for red color absorption. The protein present in it is erythrosin. Chlorolabe is adapted for green color which contains protein chloropsis. Cyanolabe is adopted for blue light absorption which contains protein cyanopsin.

As compared to rods, cones are 300 times less sensitive to light. Thus option (C) is correct.

Note: Vitamin A is the precursor of rhodopsin pigment seen in rod cells. The deficiency of Vitamin A causes night blindness or nyctalopia. The cone cells contain only 3 color pigments. But the sensations of different colors can be produced by the combination of the three-cone cells in different ratios. When the red, green, and blue cone cells are stimulated equally white light is produced in the eyes.