Plant Hormones

• Plant hormones

  Ensure plants grow in the right direction
• Auxin


  A plant growth hormone that controls growth
• Auxin's role in plant growth

  1. Produced in tips

  2. Moves backwards

  3. Stimulates cell elongation

  4. If tip removed, growth stops
• Auxin controls the growth of a plant in response to light (phototropism) and gravity (gravitropism or geotropism)
• Extra auxin promotes growth in the shoot


  Inhibits growth in the root
• Shoots grow towards light

  1. Tip exposed to light

  2. More auxin accumulates on shaded side

  3. Cells elongate faster on shaded side

  4. Shoot bends towards light
• Shoots grow away from gravity


  1. Shoot growing sideways

  2. Unequal distribution of auxin

  3. More auxin on lower side

  4. Lower side grows faster

  5. Shoot bends upwards
• Roots grow towards gravity

  1. Root growing sideways

  2. More auxin on lower side

  3. Extra auxin inhibits growth

  4. Cells on top elongate faster

  5. Root bends downwards
• In a root, the extra auxin inhibits growth