Plant Hormones

• What is auxin?

  a plant hormone that controls growth near the tips of shoots and roots in response to light (phototropism) and gravity (geotropism)
• What happens when a shoot tip is exposed to light?

  auxin accumulates on the side that’s in the shade so the cells elongate faster, so the shoot bends towards the light
• What happens when a shoot is growing sideways?

  Gravity produces an unequal distribution of auxin in the tip (more on the lower side) so it grows faster and bends the shoot upwards
• What happens when a root is growing sideways?

  Gravity produces an unequal distribution of auxin on its lower side, (in roots auxin inhibits growth) so the cells on top elongate faster and the root bends downwards
• Steps to investigating plant growth response

  1. Put 10 cress seeds in three different petri dishes find with moist filter paper,
  2. Shine lights from different directions onto different dishes
  3. Leave for a week to observe the response (they will grow towards the light)
• what? What are the three plant hormones that have commercial uses?

  auxins, gibberellin, ethene
• what are three commercial uses of auxins ?

  Killing weeds, growing from cuttings with rooting powder, growing cells in tissue culture
• What are three commercial uses of gibberellin?

  Controlling dormancy, inducing flowering, growing larger fruit
• What is one commercial used of Ethene?

  Stimulate the ripening of fruit
• Gibberelling causes plants stems to grow
• What is a phototropism?

  A response to the stimulus of light
• What is Geotropism?

  Growth in response to gravity