Shoot and root growth

• 1. Shoots grow towards light

  • When a shoot tip is exposed to light, more auxin accumulates on the side that's in the shade than the side that's in the light
  • This makes the cell grow (elongate) faster on the shaded side, so the shoot bends towards the light
• 2. Shoots grow away from gravity

  • When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side
  • This causes the lower side to grow faster, bending the shoot upwards
  • The distribution of auxin in response to gravity means that the shoot should always grow in the right direction even in the absence of light
• 3. Roots grow towards gravity

  • When a root is growing sideways, more auxin will accumulate on it's lower side
  • In a root, the extra auxin inhibits growth
  • This means the cells on top elongate faster, and the roots bends downwards