Plant Hormones

• What are the 3 examples of plant hormones?

  Auxin, ethene, gibberellin
• What does auxin control?


  Growth of tips of shoots and roots
• Where is auxin produced?

  In the tips of shoots and roots
• What does auxin do and what does this stimulate?


  Diffuses backwards to stimulate cell elongation
• Where does auxin promote growth?


  shoots
• Where does auxin inhibit growth


  Roots
• What growth responses of a plant are auxins involved in?

  Response to light - phototropism, response to gravity - gravitropism/geotropism
• Are the shoots positively or negatively phototropic?


  Positive (grow towards light)
• Why are shoots that particular phototropic?

  - Side that's in the shade accumulates more auxins

  - causing cells on shaded side to elongate faster

  - so shoot bends towards light
• Are shoots positively or negatively gravitropic?


  Negatively
• Why are shoots negatively gravitropic?


  - when shoot grows sideways, gravity produces unequal distribution of auxin in the tip

  - there is more auxin in lower side

  - this causes lower side to grow faster, bending shoot upwards
• Are roots positively or negatively phototropic?

  Negatively
• Explain why the roots are this phototropic?

  - If root gets exposed to light, more auxin accumulates on the shaded side

  - auxin inhibits cell elongation on shaded side so root bends downwards back into ground
• Are roots positively or negatively geotropic?

  Positively
• Explain why they are this geotrope?

  - root growing sideways will have more auxin on lower side

  -in a root, extra auxin inhibits growth meaning cells on top elongate faster and root bends downwards
• What does gibberellin do?


  Stimulates seed germination, stem growth and flowering
• Which other hormone does gibberrelin work with to to help the plant to grow tall?


  Auxins
• Which part of the plant does gibberellin stimulate to grow?


  Stems
• What does ethene control?


  Shedding of leaves and ripening of fruit
• What produces ethene?


  Aging leaves
• How does ethene cause the shedding of leaves?


  - Stimulates cells that connect leaf to rest of the plant to expand

  - this breaks cell walls and causes leaf to fall off plant
• What inhibits shedding of leaves?


  Auxins
• What are auxins produced by and what do they do?


  - produced by young leaves

  - as leaves get older, they produce less auxin, leading to leaf loss
• What else does ethene stimulate?


  Enzymes that cause fruit to ripen
• How are plant hormones used in daily life?

  Selective herbicides, growing from cuttings in rooting powder, producing seedless fruit, controlling dormancy