B1 Revision~ Coordination and Control

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2.1 Responding to Change

  • 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'
  • Advantages
  • 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.
  • Disadvantages
  • 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 
  • Temperature
  • 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


In Women

  • 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.

In plants

  • 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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