B1 2.1 Responding to change
- The nervous system uses electrical impulses to enavle you to react quickly to your surroundings and coordinate what you do.
- Cells called receptors detect stimuli (changes in the environment).
- Like all animal cells, light receptor cells and other receptors have a nucleus, cytoplasm and cell membrane.
- Impulses from receptors pass along sensory neurons to the brain or spinal cord (CNS). Impulses are sent along motor neurons from the brain (CNS) to the effector organs.
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B1 2.2 Reflex actions
- Some responses to stimuli are automatic and rapid and are called 'relex actions'.
- Reflex actions run everyday bodily functions and help you to avoid danger.
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B1 2.3 Hormones and the menstrual cycle
- Hormones control the release of an egg from the ovary and the build-up of the lining of the womb in the menstrual cycle.
- Some of the hormones involved are FSH from the pituitary gland and oestrogen from the ovary.
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B1 2.4 The artificial control of fertility
- Hormones can be used to control fertility.
- Oral contraceptives contain hormones, which stop FSH production so no eggs mature.
- FSH can be used as a fertility frug for women, to stimulate eggs to mature in their ovaries. These eggs may be used in IVF treatments.
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B1 2.5 Controlling conditions
- Humans need to maintain a constant internal environment, controlling levels of water, ions and blood sugar, as well as temperature.
- Homeostasis is the result of the coordination of your nervous system, your hormones and your body organs.
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B1 2.6 Hormones and the control of plant growth
- Plants are sensitive to light moisture and gravity.
- Plant responses are brought about by plant hormones (auxin).
- The responses of roots and shoots to stimuli such as ligt and gravity are the result of the unequal distribution of plant hormones.
- We can use plant growth hormones as weed killers and as rooting hormones on cuttings.
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B1 2.7 Using hormones
- There are benefits and problems associated with the use of hormones to control fertility and these must be evaluated carfully.
- Plant hormones are very useful as weed killers but their use can damage the environment.
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