Plant Hormones

• What is a tropism?

  A tropism is a plant's response to a stimulus
• What is phototropism?

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

  Gravitropism is a plant's response to gravity
• What is auxin?

  Auxin is a hormone controlling plant growth
• How do plant shoots show positive phototropism?

  • Light causes auxin to move to shaded side
  • Shaded side cells grow more, bending towards light
  • Increases photosynthesis rate
• How do plant shoots show negative gravitropism?

  • Auxin accumulates on lower side in horizontal shoot
  • Lower side cells grow more, bending away from gravity
  • Increases light availability for photosynthesis
• How do plant roots show positive gravitropism?

  • Auxin accumulates on lower side in horizontal root
  • Lower side cells grow less, bending towards gravity
  • Increases water and nutrient availability
• What are gibberellins?

  Gibberellins are hormones involved in seed germination
• What is ethene?

  Ethene is a hormone involved in cell division
• What are the uses of auxins?

  • Weedkillers: cause rapid plant growth and death
  • Rooting powder: promotes quick new plant growth
  • Tissue culture: stimulates root and shoot growth
• What are the uses of ethene?

  • Controls food ripening in the food industry
  • Allows fruit to ripen just before sale
• What are the uses of gibberellins?

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