Question

Adaptation of eyes in dark is due to
A. Depletion of vision pigments in rods
B. Depletion of vision pigments in cones
C. Repletion of vision pigments in rods
D. Repletion of vision pigments in cones

Answer 1

Hint: Adaptation by the eyes refers to the ability of the eyes to adjust to various levels of light intensity with the help of pupils, rod cells and cone cells.

Complete answer:
When we move from an area of high light intensity to a dark area, our eyes adjust the vision accordingly.
One of the factors which adjust the light intensity is the pupil of the eye, which is the opening which lets light in. Pupils dilate or open up more in dark conditions to let more light in.

Once the light is in, two receptors, rods and cones which are responsible for vision take the role. Once stimulated, the photopigments in these cells break down, producing a flood of signals resulting in the glare.
Cone cells are responsible for light vision and rod cells are responsible for black and white vision. Cones are less sensitive to light and their response time to stimuli are faster than that of rods.
Rod cells contain a biological pigment called rhodopsin, which is highly photosensitive. When exposed to light, rhodopsin will get immediately photobleached. And they will take a while to regenerate and regain the sensitivity.
The high light intensity will photo bleach the rhodopsin present in the rods and when shifted to darkness, initially blackness is seen because of this. In a while, the rhodopsin will regenerate and the sensitivity of the retina increases over time which will enable the vision in dark.
Also cones are more numerous, approximately 120 million whereas the number of cones are 6 million.

Hence, the correct answer is option (C)

Note: Cone cells are of three types which are red (60%), green(30%) and blue(10%) cones.