plant hornones

• plants can respond to change in the

  external environment
• plant responses are usually slower than

  animal responses
• plant responses

  roots and shoots growing away from a particular stimulus

  plants flowering at a particular time

  ripening of fruits
• when a part of a plant responds by growing in a particular direction it's called

  tropism
• growth of shoots

  gravity > grow away = negative gravitropic ( geotropic )

  light > grow towards = positive phototrophic
• growth of roots

  gravity > grow towards = positive gravitropic ( geotropic)

  light > grow away = negative phototrophic
• tropisms are controlled by a group of plant hormones called

  auxins
• plant responses

  to light

  • more light reaches one side of the shoot
  • more auxin is sent down to the shaded side of the shoot
  • this results in cells on the shaded side elongating more
  • the shoot therefore bends towards the light
• in roots auxin moves to the bottom of the roof and causes less elongation so the root grows

  downwards
• gibberellins are

  important for initiating seed germination
• ethene

  controls cell division and ripening of fruits
• auxins are used as

  weed killers

  rooting powders

  promoting growth in tissue culture
• ethene is used for

  control of ripening food during transport
• gibberellins are used for

  promoting flowering for demand

  increase food size