B11: Hormonal co-ordination: plants

• Tropism


  Response of a plant to a stimulus
• Phototrophism


  a plant’s response to light
• Gravitropism


  A plant’s response to gravity
• Auxin


  A plant hormone that controls growth
• Positive phototropism

  When one side of the shoot is in light, auxin moves to the shaded side, and the shoot then bends towards the light, allowing photosynthesis to happen faster
• Negative gravitropism


  Auxin accumulates at the shoot, and the cells on the lower side of the shoot grow more, causing the plant to bend away from gravity direction, allowing more light to be available for photosynthesis
• Positive gravitropism


  Auxin accumulates in the lower side, so cells grow less, and the roots grow towards gravity, so more water and nutrients are available to the plant roots
• Gibberellins


  A type of plant hormone involved in seed germination
• Ethene


  A type of plant hormone, involved in cell division and ripening
• Uses of auxins


  -Weed killers: cells grow at a rapid rate, causing the plant to die

  -Rooting power: causes new plants to grow quickly

  -Tissue culture: grows roots and shoots
• Uses of Ethene


  Controls fruit ripening
• Uses of Gibberellins


  -Terminating seed dormancy

  -Promoting flowering

  -Increase size of fruit