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biology 0610printed 183 · PDF 183
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printed 183 · PDF 183
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183
● Most refraction of the light entering in the eye is done by the cornea. The
lens makes fine adjustments.
● The light coming from long distance objects needs less bending as light
rays are diverging slightly. However light from nearby objects needs a lot of
bending as light rays are diverging sharply.
● The shape of the lens is changed to alter the amount of bending of the light.
The thicker the lens the more the bending. Adjusting the shape of the lens
according to the light is known as accommodation.
● The lens is held by suspensory ligaments. These ligaments are controlled
by the ciliary muscles which alter the tension of the ligaments and change
the shape of the lens.
● When this muscle contracts, the ligaments loosen and the lens gets thicker.
When this muscle relaxes, the ligaments are tightened and the lens becomes
Thinner.
Hormones
● Animals use chemicals to transmit information around the body. These
chemicals are known as hormones.
● Hormones are made in specialised glands called endocrine glands.
● The hormones are carried around the body via blood plasma.
● Each hormone targets specific organs called target organs.
● Adrenal glands secrete adrenaline which prepares the body for vigorous
action. These adrenal glands are found above each kidney. It makes your
heart beat faster, increases the breathing rate and widens the pupils as well.
● Pancreas secrete insulin which reduces the concentration of glucose in
blood. They also secrete glucagon which increases glucose concentration in
blood.
● Testis secrete testosterone which causes the development of male
secondary sexual characteristics.
● Ovary secretes oestrogen which causes the development of secondary