10 Coordination

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  • Coordination
    • Plant growth factors
      • light, gravity and water
      • plant growth factors
        • exert their influence by affecting growth
        • made by cells located throughout the plant
        • some affect the tissues that release them rather than distant cells
    • Chemical mediators
      • chemicals released from certain mammalian cells that have effect on cells on their immediate vicinity
        • histamine - stored in certain white blood cells and released as a response to an injury or allergen
          • causes dilation of small arteries and arterioles and increased permeability of capillaries, leading to localised swelling, redness and itching
        • prostoglandins - found in cell membranes and also cause dilation of small arteries and arterioles
          • causes increased permeability of capillaries, affect blood pressure and neurotransmitters, in doing so affecting pain sensation
    • Control of tropisms by IAA (indoleacetic acid)
      • IAA in shoot tip, causes elongation (increases growth)
        • e.g. IAA moves to shaded side of shoot which increases concentration therefore the shoot grows faster and elongates on the shaded side so the shoot grows towards light
      • IAA in root tip decreases growth; bends towards gravity
    • Principles of coordination
      • the nervous system
        • stimulate cells by secreting neurotransmitters directly onto them
        • rapid transmission
        • response is localised, rapid and short lived
        • effect is temporary
      • the hormonal system
        • produces chemicals that are transported in the blood plasma to their target cells which they then stimulate
        • relatively slow transmission
        • response is widespread, slow and long lasting

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