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biology 0610printed 184 · PDF 184
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female sexual characteristics and helps control menstrual cycle.
● There are some differences between the nervous system and endocrine
system. Nervous system is made up of nerves while the endocrine system is
made up of glands.Nervous system transmits information in the form of
electrical impulses but the endocrine system transmits information in the
form of chemicals. Nervous system transmits impulses along neurons but in
the endocrine system chemicals are carried via blood plasma. Nervous
system acts fast while the endocrine system acts slow. Effect of the nervous
system is short termed while the effect of the endocrine system is long
termed.
Coordination in Plants
● Plants also respond towards stimuli. They do this by changing their rate or
direction of growth.
● Growth towards a stimulus is said to be a positive response but growth away
from a stimulus is said to be a negative response. These growth responses
are called tropisms.
● Growth responses to light are called phototropism.
● Growth responses to gravity are called gravitropism.
● Normally in a plant shoots grow towards light so they are positively
phototropic. On the other hand, roots are negatively phototropic. Generally
grow away from gravity so they are negatively gravitropic while roots are
positively gravitropic.
● Plants also use chemicals for transporting information.These are known as
plant hormones. One important one is auxin.
● Auxin is made at the tip of the shoot. Then it diffuses down to the rest of the
shoot. Auxin makes the cells get longer. More the auxin, the faster they
elongate. Without it they will not grow.
● When light shines on one side of the shoot, auxin diffuses to the shady side
and causes the cells there to grow and elongate faster. This causes the shoot
to grow towards the light source.
● Same with gravitropism, if a shoot is kept on its side the auxin accumulates at
the bottom and causes cells there to grow and eventually makes the shoot
grow