B3.9 Plant hormones

• What effects do auxins have on plant roots?

  Inhibit cell/plant growth.
• What happens to auxins once they're produced?

  They diffuse backwards along the root or shoots.
• What is gravitropism (also known as geotropism)?

  A tropism in response to gravity.
• Which stimuli can plants detect?

  1. Light
  2. Gravity
  3. Touch
  4. (others like water)
• How do plant hormones act differently to human hormones?

  Plant hormones only act locally, whereas human hormones travel throughout our bodies.
• Are roots positively or negatively gravitropic (geotropic)? What does this mean?

  Roots are positively gravitropic, this means they will grow towards gravity (downwards).
• Where in a plant are auxins made?

  In the growing tips of the roots and shoots.
• Are roots positively or negatively phototropic? What does this mean?

  Roots are negatively phototropic, which means they will grow away from the light.
• What effect do auxins have on plant shoots?

  Stimulate cell/plant growth.
• What are auxins?

  They control growth at the tips and shoots of the roots. Auxins are produced in the tips and diffuses backwards to stimulate cell elongation.

  Auxins promote growth in the roots and inhibits growth at the roots
• Do auxins accumulate on the light or dark side of a shoot/root?

  Light breaks down auxin, so there will be more auxin on the dark side.
• Are shoots positively or negatively gravitropic (geotropic)? what does this mean?

  Shoot are negatively gravitropic, this means they will grow away from gravity (so upwards).
• What is a tropism?

  A tropism is a growth in response to a stimulus, which may lead to a change in the direction of a shoot or a root.
• What is a phototropism?

  A tropism in response to light.
• Do auxins accumulate on the top or bottom side of a shoot/root?


  Gravity pulls auxins downwards, so there will be more auxin on the lower side.
• Are shoots positively or negatively phototropic? what does this mean? 


  Shoots are positively phototropic, which means they will grow towards the light.
• What does it mean for a seed to germinate?

  Germination is the process by which a seed starts to grow and develop.
• What are 3 uses of auxins in agriculture and horticulture?

  1. In selective weedkillers.
  2. Growing from cuttings with rooting powder.
  3. To promote growth in tissue cultures.
• What are 3 uses of gibberellin ?

  1. To end seed dormancy.
  2. To promote flowering.
  3. To increase the size of fruits.
• What is ethene used for?

  Ethene stimulates fruit to ripen, so it can be used in the food industry to control ripening of fruit during storage and transport.
• Name 3 plant hormones.

  1. Auxins.
  2. Gibberellin.
  3. Ethene.
• Explain how auxins can be used in weedkillers.

  1. Auxins stimulates plant cells to divide and grow.
  2. If large amount of auxins are added to plants it can disrupt their growth process by overstimulating them.
  3. This can kill the plant.
• What is a 'selective' weedkiller?

  It only kills some types of plants, not all plants.
• What does it mean for a seed to be 'dormant'?

  Dormant is the period in which seeds are inactive and do not grow or develop.
• What is the effect of the widespread use of weedkillers on biodiversity?

  Widespread use of weedkillers will reduce biodiversity, as it kills plants.