plant hormones (triple)

• Phototropism


  Plants growing towards light
• How phototropism works


  1. Shoot tips produce auxin hormone

  2. Auxin concentrates on darker side of shoot tip

  3. Cells on darker side grow faster

  4. Shoot grows towards light
• Removing shoot tips prevents phototropism
• Covering shoot tips with foil prevents phototropism
• Covering lower parts of shoots does not prevent phototropism
• Auxin


  Plant hormone produced at shoot tips that triggers growth towards light
• Gravitropism/Geotropism


  Roots growing towards the force of gravity
• How gravitropism works


  1. Auxin produced in roots

  2. Gravity causes auxin to concentrate on lower side

  3. Lower side grows more slowly

  4. Root grows towards gravity
• Gibberellins


  Plant hormones important for seed germination
• Ethylene


  Plant hormone that controls cell division and fruit ripening