Theory question 104
Sense Organs(a) What is a sensory cell?
(b) State one function each of the following parts of the mammalian eye: (i) lens (ii) vitreous humour (iii) optic nerve.
(c) (i) List four structures which protect the eye from injury (ii) Explain briefly how each of these structures performs its function.
(d) Explain why a person in a dark room is dazzled for some seconds when he is suddenly exposed to bright sunlight.
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(a) A sensory cell (receptor) is a specialised cell that detects a particular stimulus and changes it into nerve impulses
(b)(i) Lens: focuses (refracts) light onto the retina; changes shape for accommodation
(ii) Vitreous humour: keeps the eyeball firm and its shape; refracts light
(iii) Optic nerve: carries impulses from the retina to the brain
(c) Any four with function: eyelids – close to keep out dust and objects; eyelashes – trap dust and shade the eye; eyebrows – stop sweat running into the eyes; tear (lachrymal) glands – tears wash and moisten the eye and kill germs (lysozyme); bony orbit/eye socket – protects the eyeball from blows; conjunctiva – thin transparent layer protecting the cornea
(d) In the dark the pupil is wide and rhodopsin (visual purple) has built up in the rods, so the eye is very sensitive; sudden bright light floods the retina and over-stimulates it; it takes a few seconds for the iris to narrow the pupil and for the rods' pigment to be bleached and the cones to take over (light adaptation)
In (d) mention both the pupil and the retina's sensitivity.