Plant Hormones

• What is a tropism?


  A tropism is the response of a plant to a specific stimulus.
• What is phototropism?


  Phototropism is the response of a plant’s shoot or root to light.
• What is gravitropism?


  Gravitropism is the response of a plant’s shoot or root to gravity.
• What is auxin?


  Auxin is a hormone which controls the growth of a plant’s shoots and roots.
• How does auxin affect plant growth?


  When auxin is unevenly distributed in a growing plant, the rate of growth will also be unequal.
• How do plant shoots show positive phototropism?


  • One side of the shoot is in the light, causing auxin to move to the shaded side.
  • At the shaded side, the cells are stimulated to grow, bending the shoot towards the light.
  • This allows photosynthesis to occur at a faster rate.
• How do plant shoots show negative gravitropism?


  • In a horizontal shoot, auxin accumulates in the lower side due to gravity.
  • Cells on the lower side grow more, causing the shoot to bend away from gravity.
  • This allows more light for photosynthesis.
• How do plant roots show positive gravitropism?


  • In a horizontal root, auxin accumulates in the lower side, causing cells to grow less.
  • The root bends in the direction of gravity.
  • This allows more water and nutrients to be available to the roots.
• What are gibberellins?

  Gibberellins are a type of plant hormone involved in seed germination.
• What is ethene?


  Ethene is a type of plant hormone involved in cell division and ripening.
• What are the uses of auxins?


  • Weedkillers: auxin causes rapid growth, leading to plant death.
  • Rooting powder: auxin promotes quick growth of new plants.
  • Tissue culture: auxin promotes growth of roots and shoots.
• What are the uses of ethene?


  • Control of food ripening in the food industry.
  • Allows fruit to be ripened just before sale.
• What are the uses of gibberellins?


  • Termination of seed dormancy.
  • Promotion of flowering.
  • Increase of fruit size.