Plant tropism

• What is phototropism?

  The growth response towards or away from light
• What is gravitropism/geotropism?

  The growth response with or against gravity
• Shoots will grow towards light - a positive tropism

  Shoots will grow against gravity - a negative tropism
• Benefits of the positive tropism?

  -Shoots

  • must grow upwards, away from gravity and towards the light so that the leaves are held out into the sunlight
  • the more light, better can photosynthesise
  • flowers need to be held up in the air, where insects, birds or wind can pollinate them.
• Benefits of positive tropism?

  -Roots

  • though need to grow downwards into the soil in order to anchor the plant in the and absorb water and minerals from between the soil particles.
• What is auxin?

  hormone and growth regulating chemicals in plants and it is made in the tip of the shoot and root.
• What is the role of auxin?

  cell elongation for growth

  auxin diffuse more shaded area

  effect: cells absorb water and elongate
• What is the role in shoot?

  more auxin more growth

  auxin absorbs more water
• How do plants grow to the light? (light exposed directly and equally on the top)

  - auxin is made in the tip of the shoot

  -causing the shoot cells to enlarge

  -when light is directly overhead, auxin diffuses equally down the shoot

  -shoot grows straight up
• How do plants grow to the light?(unilateral light)-light exposed at one side

  -when light is directional, the auxin moves more to the shaded side of the shoot

  -the cell on the shaded side elongate more than the cells on the lighted side

  -the shoot grows towards the light
• Unequal growth of stem sides results in bending system
• Shoots grow away from gravity so they show negative gravitropism.

  • the shoot will lay horizontally
  • auxin made in cells at the tip of horizontal shoot
  • auxin diffusing to the lower side (gravity pulls the auxin to diffuse down to the lower side)
  • auxin accumulating on the lower surface of the shoot
  • cells on the lower surface elongate faster, therefore the shoot bend upwards as it grows
• What is the apparatus that is for the experiment for gravitropism or geotropism in a shoot?

  Clinostat