Theory question 101
Sense Organs(a) What is a sense organ?
(b) (i) State two main functions of the ear (ii) Explain the mechanism involved in one of the functions stated in (b) (i) above
(c) With the aid of a large labelled diagram illustrate the eye defect of short-sight and its correction
Show the model answer
(a) A sense organ is an organ with receptor cells that detect a particular stimulus (e.g. light, sound) and send impulses to the brain.
(b)(i) Hearing; balance (maintaining posture).
(ii) Hearing: sound waves enter the outer ear and make the eardrum vibrate; the ossicles (malleus, incus, stapes) pass and amplify the vibrations to the oval window; this sets the fluid in the cochlea vibrating, which stimulates sensory hair cells; impulses travel along the auditory nerve to the brain, which interprets the sound.
OR Balance: movement of the head moves the fluid (endolymph) in the semicircular canals, utriculus and sacculus; this bends sensory hairs in the ampullae, which send impulses through the auditory nerve to the cerebellum, which keeps the body balanced.
(c) Diagram 1: light rays from a distant object focused in front of the retina because the eyeball is too long (or the lens too thick/curved). Diagram 2: a concave (diverging) lens placed in front of the eye spreads the rays so they focus on the retina. Labels: eye lens, retina, point of focus, concave lens, light rays; title and neat labelling.
Short sight: image in front of the retina, corrected with a concave lens.