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biology 0610printed 182 · PDF 182
328 pagesrevision 46933
printed 182 · PDF 182
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182
● There are two kinds of receptor cells in the retina. Rods are sensitive to quiet dim
light but they do not respond to colour. Cones are able to distinguish between colours
but they only function in bright light.
● The coloured part of the eye is the iris. In the middle of the iris is a small
circular gap called the pupil.
● The size of the pupil influences the amount of light entering and reaching the retina.
● In low light intensities the iris pulls back and makes pupil larger but in high light
intensities the iris closes in and makes pupil smaller.
● To adjust size of pupil iris contains two types of muscles. Circular muscles
are arranged in circles around the pupil. Radial muscles run outwards from
the edge of the pupil.
● When circular muscles contract they make pupil get smaller. When radial
muscles contract they make pupil dilate or get larger. This is called the iris
reflex or the pupil reflex.
● The circular muscles and radial muscles are antagonistic muscles meaning that
when one contracts the other relaxes.
Focusing Light
● Bending light rays is called refraction.