Plant growth hormones

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  • Created by: alexda
  • Created on: 08-05-14 17:29
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  • Plant growth hormones
    • Plants can respond to stimuli (e.g. light, gravity or moisture) by regulating their growth.
    • A tropism is a plants growth response. A positive tropism is growing towards a stimulus.
      • Phototropism is the growth of a plant in response to light. Shoots are positively phototropic because they grow towards light.
        • 1. When a shoot tip is exposed to light, more auxin accumulates on the shaded side.
        • 2. This makes the cells elongate and divide faster on the shaded side so the shoot bends towards the light.
        • 3. This enables plants to absorb more light for photosynthesis which provides sugar - needed for growth.
      • Gravitropism is the growth of a plants in response to gravity. Roots are positively gravitropic because they grow towards the full of gravity.
        • 1. When a root is growing sideways gravity produces an unequal distribution of auxin in the tip with more auxin on the lower side.
    • Auxin is a plant hormone that controls growth at the tips of shoots and roots. Auxin promotes growth in the shoot but high concentrations inhibit growth in the roots.
    • Gibberellin stimulates seed germination, stem growth and flowering.


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