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  • B1.2
    • Responding to change
      • The nervous system has receptors to detect stimuli.
        • The receptors are found in sense organs, the eye, nose, mouth, ear and skin.
      • The brain and spinal cord form the central nervous system (CNS)
      • Nerves contain neurons. Sensory neurons carry impulses from receptors to the CNS.
      • Motor neurons carry impulses from the CNS to effector organs which may be muscles or glands.
        • The muscles respond by contracting.
          • The glands respond by secreting chemicals.
    • Reflex actions
      • 1) A receptor detects a stimulus.
      • 2) A sensory neuron transmits the impulse to the CNS.
      • 3) A relay neuron passes the impulse on.
      • 4) A motor neuron is stimulated.
      • 5) The impulse passes to an effector (muscle or gland).
      • 6) Action is taken (the response).
    • Controlling Conditions
      • The body carefully controls its internal environment.
        • Water content
        • Ion content
        • Temperature
        • Blood sugar level
    • Hormones and Menstrual Cycle
      • FSH is made by the pituitary gland and causes the egg to mature and oestrogen to be produced.
      • Oestrogen is produced by the ovaries and inhibits the further production of FSH.
        • It stimulates the production of LH and also stimulates the womb lining to develop to receive the fertilised egg.
      • LH is made by the pituitary gland and stimulates the mature egg to be released from the ovary.
    • Artificial control of fertility
      • The contraception pill may contain oestrogen and progesterone.
        • The pill prevents the production of FSH so no eggs mature.
      • Advantages
        • Contraceptive pills have helped to reduce family size which helps reduce poverty.
        • It allows women to plan their pregnancy.
        • Fertility drugs can help couples who are having IVF
      • Disadvantage
        • Side effects
        • Ethical or religious reasons
          • Older women having babies
          • Extra embryos being destroyed or stored
        • IVF is an expensive process.
    • Control of Plant Growth
      • Plant shoots grow towards light. This response is phototropism.
      • Roots grow down towards gravity. This response is gravitropism.
        • Roots also grow towards water.
      • Auxin is the hormone that controls phototropism and gravitropism


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