Plant Hormones (Triple)

• Plants produce hormones to coordinate and control growth and responses to light (phototropism) and gravity (gravitropism or geotropism). Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.
• This shows shoots shined with light from one side only and it grows towards the light

  
• Scientists removed the tips of the shoots and found that the shoots didn't grow towards the light. Scientists suggested that shoot tips produce a plant hormone called auxin

  
• Scientists covered the tips of the shoots with foil to block out the light, the shoots didn't grow towards the light - this tells us the tips are sensitive to light

  
• Scientists used foil to cover the lower parts of the shoots and the shoots grew towards the light - this tells us the lower parts of shoots aren't sensitive to light

  
• Auxin is produced at the tip of the shoot and it triggers cell growth. Light causes auxin to concentrate on the darker side of the shoot tip, auxin now spreads down the shoot so cells on the darker side grow faster than cells on the lighter side, causing the shoot to grow towards the light

  
• 1. This shows shoots shined with light from one side only and it grows towards the light
  2. Scientists removed the tips of the shoots and found that the shoots didn't grow towards the light. Scientists suggested that shoot tips produce a plant hormone called auxin
  3. Scientists covered the tips of the shoots with foil to block out the light, the shoots did not grow towards the light - this tells us the tips are sensitive to light
  4. Scientists used foil to cover the lower parts of the shoots and the shoots grew towards the light - this tells us the lower parts of shoots are not sensitive to light

  
• Plant roots grow towards the force of gravity - this is called gravitropism or geotropism and also involves auxin
• Auxin is produced in the root but gravity causes the auxin to concentrate on the lower side. In roots, auxin inhibits cell growth so the lower side grows more slowly than the upper side, causing the roots to grow towards the force of gravity

  
• Gibberellins are important in starting the germination of seeds
• Ethene controls cell division and ripening of fruits