Plant Hormones

• Plants growing towards light is called phototropism
• Investigations into phototropism:

  • There are some shoots and light is shone from one side only
  • The shoots grow towards the light
  • The scientists removed the tips of the shoots, and they no longer grew towards the light.
  • They found that the tips produced a hormone called auxin
  • The scientist then covered the tips with foil to prevent light and the plants didn't grow towards the light
  • This tells us that the tips were sensitive to light
  • This was further proven my covering the bottom part in foil and the plants grew towards the light
• Investigating phototropism:

  1. Auxin is produces at the tip of the root, and in shoots, triggers cell growth
  2. Light causes auxin to concentrate on the darker side of the shoot
  3. Cells on the darker side grow faster than cells on the lighter side
  4. This means that the shoot grows towards the light.
• Plant roots grow in accordance with gravity, in a process known as geotropism or gravitropism.
• Geotropism / Gravitropism:

  • Auxin is produced in the root
  • Gravity causes auxin to concentrate on the lower side
  • In roots, auxin inhibits cell growth
  • The lower side now grows more slowly than the upper side
  • The roots now grow towards the force of gravity
• Gibberellins are important to start the germination of seeds
• Ethene controls cell division and the ripening of fruits