Tropisms & Auxins

• What is the role of auxins in plants?

  Auxins control growth at the ends of the shoots and roots
• How do plants respond to stimuli in their environment?

  Plants respond to stimuli by growing towards or away from them
• Why do plants grow their shoots towards light?


  To maximize photosynthesis
• What is phototropism?


  Phototropism is a plant's growth response to light
• What is geotropism?


  Geotropism is a plant's growth response to gravity
• How do auxins behave in shoots when responding to light?


  Auxins accumulate on the shaded side, causing faster growth there
• What happens to the growth of shoots in response to gravity?


  Auxins accumulate on the lower side, causing the shoot to curve upwards
• How do auxins affect root growth in response to light?

  Auxins accumulate on the lower shaded side, inhibiting growth and causing the root to curve downwards
• What is the effect of auxins on root growth in response to gravity?


  Auxins accumulate on the lower side, inhibiting growth and causing the root to curve downwards
• What are the key differences between the responses of shoots and roots to light and gravity?

  • Shoots:
  • Positively phototropic (grow towards light)
  • Negatively geotropic (grow away from gravity)
  • Roots:
  • Negatively phototropic (grow away from light)
  • Positively gravitropic (grow towards gravity)
• What is the difference in auxin behavior between shoots and roots?


  In shoots, auxins stimulate growth; in roots, they inhibit growth
• How do auxins cause a shoot to curve towards light?


  By accumulating on the shaded side and stimulating faster growth there
• What happens when a root is exposed to light?

  Auxins accumulate on the lower side, inhibiting growth and causing the root to curve downwards
• How does the accumulation of auxins differ in shoots and roots when responding to gravity?


  In shoots, auxins accumulate on the lower side to promote upward growth; in roots, they accumulate on the lower side to inhibit growth