Tropic Responses (Plants)

• How plants respond to their environment :

  • sense light - grow towards the sun and maximise photosynthesis
  • sense gravity - find more water and minerals
  • sense touch - climb around other objects
• Auxins : Control growth at the end of the shoots and the roots
• Auxins :

  • Are produced at the shoot/root
  • dissolved in the cells solution
  • diffuse backwards in the shoot/root
• Auxins stimulate growth in the shoot
• Auxins inhibit growth in the root
• Phototropism : response to light
• Gravitropism : Response to gravity
• Auxins accumulate on the shaded side and the lower side.
• Shoots are :

  • Positively phototropic (they grow towards the light)
  • Negatively gravitropic (grow away from the ground)
• Roots are :

  • Negatively phototropic (they grow away from the light)
  • Positively gravitropic (grow towards the ground)
• Auxin, Gibberellin, Ethene
• Uses of Auxins :

  • stimulates growth
  • leaves that have been cut off can grow into a new plant if we plant it in soil and give it rooting powder (which contains auxin)
  • kill weeds
• Uses of Gibberellin :

  • controlling dormancy - can grow more crops per year at the same time
  • inducing flowering - if used, plants can flower whenever. can also produce more flowers, and bigger flowers
  • growing larger fruit
• Uses of Ethene :

  • stimulates the ripening of fruit - can be controlled when it is being shipped
  • Ethene can be blocked whilst being transported so it doesn't ripen too early, and then exposed to Ethene when it arrives at its destination
  • Ethene stimulates an enzyme that causes the fruit to ripen