2.1 Responding to Change
- The NERVOUS SYSTEM has RECEPTORS which detect STIMULI.
- The receptors are found in the SENSE organs e.g eye, ear, tongue, nose and skin.
- Light can stimulate receptors in the eye and ELECTRIC IMPULSES then pass to the brain along NEURONS (nerve cells).
- The brain and spinal cord form the CENTRAL NERVOUS SYSTEM (CNS).
- NERVES contain neurons.
- SENSORY NEURONS carry impulses from the receptors to the CNS.
- MOTOR NEURONS carry impulses from CNS to effector organs (muscle or glands). The muscle responds by contracting. The glands react by releasing chemicals.
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2.2 Reflex Actions
- REFLEX ACTIONS are rapid, automatic responses to stimulus. These protect us from damage.
- Main Steps are...
- A RECEPTOR detects STIMULUS (sharp pain).
- A SENSORY NEURON transmits the impulses to the CNS.
- A RELAY NEURON passes the impulses on.
- A MOTOR NEURON is stimulated
- The impulse passes on to an EFFECTOR (muscle or gland)
- Action is taken (the response)
- At the junction between the receptor to the effector is a REFLEX ARC.
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2.3 Hormones and the Menstrual cycle
- The MENSTRUAL CYCLE takes 28 days, with ovulation abput 14 days into the cycle.
- This cycle is cintrolled by 3 hormones.
- FOLLICLE STIMULATED HORMONE (FSH) is made in the PERTUITARY GLAND and causes the egg to mature and oestrogen to be produced.
- OESTROGEN is produced by the OVARIES and stops further production of FSH. It stimulates the womb lining to develop to recieve fertilised egg. It also stimulates the production of LH.
- LUTEINISING HORMONE (LH) is made by the pirtuitary gland and stimulates the mature egg to be released from the ivary (OVULATION)
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2.4 The artificial control of fertility
- The CONTRACEPTIVE PILL may contain oestrogen and progesterone.
- It prevents the production of FSH so no eggs mature.
- If a woman cannot produce mature eggs then FSH and LH can be given. This is known as 'fertility treatment'
- Contraceptive pills have helped to reduce famiily size which reduces poverty. Also it allows women to plan their pregnancy.
- Fertility drugs help infertile couples who are having IVF.
- Contraceptive pill can cause side effects. Some poeple object to its use due to ethical or religious reasons.
- Expensive process, unethical when older women have babies by IVF. Extra embryos may be stored or destroyed.
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2.5 Controlling conditions
- The body controls its INTERNAL ENVIRONMENT these include:
- Water Content
- Ion content
- Blood sugar level
- Water is constantly leaving our body in RESPIRATION and as sweat. Also we lose water in our urine (which is produced by the KIDNEYS)
- We also lose ions in our sweat and URINE.
- We must keep our body temperature constant, otherwise the ENZYMES in our body will not work properly or denature.
- The sugar in the blood is the energy source for cells. The level of sugar is controlled by the PANCREAS.
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2.6 Hormones and the control of plant growth
- Plants respond to light, gravity and moisture.
- Plants shoots lean towards the light. This is called PHOTOTROPISM.
- Roots grow towards gravity. This is called GRAVITROPISM. Roots also grow towards water.
- AUXIN is the hormone which controls Phototropism and Gravitropism.
- Unequal distribution of auxin causes unequal growth. This leads to the bending of the shoot or root.
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2.7 Using hormones
- It is important to evaluate the advantages and disadvantages of using hormones to control reftility.
- Contraceptive pills help to prevent pregnancy.
- Other women use hormones to help them become pregnant.
- Sometimes hormone treatment is used to help older women become pregnant. This may involve using an egg donor who is goven hormones to produce extra eggs.
- Can be used by farmers and gardeners.
- Weed killers are used to kill unwanted plants on lawns.
- When cuttings are taken from plants, hormones are used to encourage roots to grow before the cutting is planted.
- If plant hormones are used incorrectly they can cause damage to the environment.
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