| A | B |
|---|
| the eye is | a sense organ |
| receptor cells | are found in the retina |
| cone cells | are sensitive to the colour of light |
| different cone cells | detect different colours |
| cone cells | generate impulses in sensory neurones |
| The optic nerve | carries impulses to the brain |
| rod cells | detect differences in light intensity |
| rod cells work | in dim light |
| cone cells work | in bright light |
| ciliary muscles | alter the shape of the lens |
| cornea | a clear, colourless covering that focuses light |
| iris | the coloured part of the eye |
| retina | a layer of rods and cones |
| the retina is found | at the back of the eye |
| pupil | a 'hole' - the black circle at the front of the eye |
| light enters the eye | through the pupil |
| the amount of light entering the eye | is controlled by muscles in the iris |
| when the pupil constricts | its diameter decreases |
| when the pupils dilate | its diameter increases |
| the fatter the lens | the more it bends |
| the thinner the lens | the less it bends |
| refraction | bending light |
| most focussing is done by | the retina |
| the lens | fine tunes focussing |
| ciliary muscles | change the shape of the lens |
| near objects | require a fat lens |
| distant objects | require a thin lens |
| a fat lens is | more convex |
| a thin lens is | less convex |
| short-sighted people | cannot see distant objects |
| long-sighted people | cannot see near objects |
| short-sightnedness requires | a diverging lens |
| long - sightedness requires | a converging lens |
| diverging lenses | spread light out |
| converging lenses | bend light inwards |
| a short sighted eyeball | is too long |
| a long sighted eyeball | is too short |
| in a short sighted eye | the image is formed in front of the retina |
| in a long sighted eye | the image is formed behind the retina |
| perfect sight means | the image is formed on the retina |
| cataract | protein build up inside the lens |
| symptom of cataracts | a cloudy lens |
| colour blindness happens when | some cones do not work properly |
