Question

Which one of the following is the correct difference between the rod cells and the cone cells of our retina?
(A) Overall function: rod cells- vision in poor light, Cone cells- colour vision and detailed vision in bright light.
(B) Distribution- Rod cells- more concentrated in the centre of the retina, cone cells-Evenly distributed all over the retina
(C) Visual acuity: rod cells- high, cone cells – low.
(D) Visual pigment contained: rod cells- iodopsin, cone cells- rhodopsin.

Answer 1

Hint: Photoreceptors in the retina are classified into two groups, named after their physical morphologies. Rod cells are highly sensitive to light and cone cells are capable of detecting a wide spectrum of light photons.

Complete answer:

Point of difference	RODS	CONES
Number	More numerous, 125 millions in. each eye	Less than rods, 7 millions in each eye
Pigment	Rhodopsin	Iodopsin
Sensitivity	Sensitive to light	Less sensitive to light
Vision	Dark light	Bright light
Visual pigment	Only one, black-white	3 visual pigment, to differentiate colors
location	periphery of retina	center of retina
Speed of response to light	Slow response: long integration time	Fast response: short integration time
Visual acuity	Poor; many rods share common neuron connection to brain	Good; each cone cell has its own neuron connection to brain
Light level	Scotopic	Photopic

Thus, the correct answer is option A, rod cells- vision in poor light, Cone cells- colour vision and detailed vision in bright light.

Additional information: Photoreceptors, the structures responsible for vision. The retina is a membrane containing sensory receptors that lines the internal aspect of the posterior wall of the eyeball, deep to the choroid layer and superficial to the vitreous humor. It is composed of epithelial, glial and neural cells, which are organised into 10 distinctive layers in which a specialised group of receptors can be found.

Note:- Rod cells function in night vision whereas cone cells function in day vision. A typical human being has three different types of cones that divide up visual color information into red, green, and blue signals.