Plant hormones

• Tropism is plants growing towards or away from a stimulus, such as light or gravity, due to a change in concentration of auxin
• Positive tropism is plant growing towards a stimulus
• Negative tropism is a plant growing away from a stimulus
• Plant stems do positive phototropism, they grow towards light
• Plant roots do negative phototropism, they grow away from light
• Auxin controls the growth of plants by promoting cell division and cell elongation
• In a HIGH concentration of auxin:

  • causes cells in stems to grow more
  • causes cells in roots to grow less
• Geotropism is a plant's response to gravity
• Roots do positive geotropism and grow in the direction of gravity
• Stems do negative geotropism and grow against gravity
• If a root is placed horizontally, the bottom side contains more auxin and grows less, causing got to do positive geotropism
• If a stem is placed horizontally, the bottom sides contain more auxin and grow more, causing it to do negative geotropism
• Investigating the effect of light on the growth of seeds:

  IV- placing plants in light and dark conditions, different colours of light, light intensity, direction of light

  DV- mean height of seedlings

  CV- number of seeds on each dish, volume of water, temperature they are kept at
• Gibberellins initiate seed germination
• Low concentrations of gibberellin increase the speed of germination, stimulating cell elongation and causing them to grow taller
• Uses of gibberellins:

  • end seed dormancy
  • promote flowering
  • increase fruit size
• Ethene is a hydrocarbon gas that speeds up ripening in bananas and other fruit, controlling cell division during plant growth
• Uses of auxin:

  • weedkillers
  • rooting powders
  • promoting growth