(a) Photoreceptors are cells that are sensitive to light. They are of two types – rods and cones. These are present in the retina. Cones help in distinguishing colours. There are three types of cone cells – those responding to green light, those responding to blue light, and those responding to red light. These cells are stimulated by different lights, from different sources. The combinations of the signals generated help us see the different colours.

(b) Vestibular apparatus is located in the internal ear, above the cochlea and helps in maintaining body balance. Crista and macula are the sensory spots of the vestibular apparatus controlling dynamic equilibrium.

(c) Pupil is the small aperture in the iris that regulates the amount of light entering the eye. Cornea, aqueous humour, lens, and vitreous humour act together and refract light rays, focussing them onto the photoreceptor cells of the retina.