Question

(b) How do you see an object and its colour?

Answer 1

Part 1: Mechanism of vision

• Light rays of visible wavelength enter the cornea & lens and are focused on the retina.
• Photoreceptors in the retina are composed of opsin & retinal, In dark, retinal and opsin interact with each other.
• Light induces the dissociation of retinal and opsin from each other causing a change in the structure of opsin/
• This further causes change in the permeability of the membrane.
• Change in permeability generates an action potential which is transmitted by optic nerves to the visual cortex area of the brain.
• These impulses are analysed & an image is formed on the retina which is recognised on the basis of earlier memory & experience.

Part 2: Colour vision

• Retina has cone cells which help in the colour vision.
• There are three types of cones found in the human eye, namely, red, green and blue cones.
• Each type of cone is sensitive to a particular wavelength of light.
• When light of different wavelengths stimulates more than one type of cone cells simultaneously, it results in the detection of different colors.