Auxin/Phototropism/Geotropism

• What is auxin and its role?

  • Plant hormone stimulating growth in shoots and inhibiting it in roots
• What is positive phototropism and how does it involve auxin?

  • A plant growing towards the light source shows positive tropism
  • Plant is exposed to light on one side
  • Auxin moves to the shaded side of the plant
  • It causes the cell there to elongate
  • As a result the shoot grows towards the light
  • plant receives more light meaning faster photosynthesis
• What is negative geotropism in shoots and how is auxin involved?

  • Negative geotropism is shoots growing away from gravity
  • Auxin moves to lower side of plant
  • This stimulates cells here to elongate making shoots bend and grow away from ground
  • This is beneficial as light levels are likely to be higher further form the ground
• What is positive geotropism in roots and how is auxin involved?

  • Postive geotropism is roots growing towards gravity
  • Auxin inhibits growth in roots
  • If the plant is horizontal auxin moves to lower part of the root
  • This stimulates growth on the upper part making roots bend and grow downwards
  • This is beneficial as there is likely to be increased water and nutrients lower down. This also provides stability for the plant
• What are the tropisms for shoots in a plant?

  • Positive phototropism (grow towards light source)
  • Negative geotropism (grow away from gravity)
• What is the tropism for roots in a plant?

  • Positive geotropism
• What does the hormone Giberellins and ethene control?

  • Giberellins= Starts germination of seeds
  • Ethene= Ripening of fruit