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2. Coordination and Control
Biology Unit 1
2.1 Responding to change
How a nervous system works:
Receptor sensory neurone CNS (relay neurone) motor neurone effector (muscle
(contract) or gland (secrete chemical substance))
2.2 Reflex Actions
Reflex actions = automatic responses to stimuli (follow a reflex arc)
Synapses = junctions between nerves. Electrical impulses must cross synapses they do so
by releasing chemicals between the gap which attach to the surface of the next neuron.
2.3 Hormones/menstrual cycle
FSH: -Matures eggs -Stimulates ovaries to produce oestrogen
Oestrogen: -lining of uterus develops inhibits FSH production stimulates LH
LH: -stimulates release of egg
2.4 Artificial control of fertility
Oral Contraceptives = contain hormones that inhibit production of FSH so no eggs mature
1. Woman given FSH and LH to stimulate eggs to mature and be released.
2. Eggs fertilized with sperm outside body.
3. They develop into embryos.
4. Embyros inserted into mother's womb.
2.5 Controlling Conditions
Internal environment = conditions inside body. Balance = Homeostasis
Water (and ions):
Take in = food/drink
Lose = breathe out/sweat/urine (kidneys control this)
Temperature kept at 37'C:
Cool down = sweat
Warm up = shiver
Blood sugar levels:
Concentration kept constant by hormones made in the pancreas.
2.6 Control of Plant Growth
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TROPISM" Growth response to...
Gravity = Gravitropism (geotropism)
Light = Phototropism
Touch = Thigmotropism
Water = Hydrotropism
Effect of auxin:
Seed laid on side in dark. Auxin is spread equally through tissues.
Auxin gathers on the lower side of the shoot and root due to gravity.
Roots grow more (cells expand) on the side with the least auxin, making it bend and grow
towards the force of gravity. Then auxin becomes evenly spread again.…read more