Tropisms

• Tropism= a growth in response to a stimulus
• Phototropism

  = Growth of plants in response to light which comes from one direction only.

  • Maximises light for photosynthesis
  • Auxins produced in the tip diffuse down the shoot on the shaded side, so those cells elongate so shoot grows towards the light.
• Geotropism

  = Growth of plants in response to gravity.

  • Auxins build up on the lower side of the root because of gravity which inhibits cell growth, the cells at the top aren't inhibited so continue to elongate and grow so root grows downwards.
• Tropisms cane be negative or positive.