Plant Hormones

• Auxins controls growth near the tips of shoots and roots
• A plants response to light is phototropism
• A plants response to gravity is gravitropism or geotropism
• When a shoot tip is exposed to light the auxins accumulate on the side with shade, which makes that sides cells grow and elongate faster, making the shoot bend towards the light
• When a shoot is sideways gravity creates an unequal distribution of auxins, causing the lower sides cells to grow and elongate, bending the shoot upwards
• When a plant is sideways in a root the auxins inhibit growth on the lower side, causing the top to elongate, bending the root downwards
• In a shoot auxins promote cell elongation
• In the root auxins inhibit growth
• Unequal distributions of auxin cause unequal growth rates in plant roots and shoots
• Gibberellins are important in initiating seed germination
• Ethene controls cell division and ripening of fruits
• Plant growth hormones are used in agriculture and horticulture
• Auxins are used for

  • Weed killers
  • Rooting powders
  • Promoting growth in tissue culture
• Ethene is used in the food industry to control ripening of fruit during storage and transport
• Gibberellins can be used to

  • End seed dormancy
  • Promote flowering
  • Increase fruit size
• Plant growth practical

  • Put 10 seeds inside 3 different petri dishes lined with moist filter paper
  • Shine one light from and the other lights from different directions
  • Leave the seeds for a week and observe the responses
• Control variables for plant growth practical

  • Number of seeds
  • Type of seed
  • Temperature
  • Water
  • Light intensity