Tropisms

• Define tropism

  The way a plant grows in response to a directional stimulus (+ or -)
• What is phototropism?

  Growth towards sunlight
• What is geotropism?

  Growth towards gravity

  (auxins accumulate at the lower side of the root tip, due to gravity, growth inhibited, downward growth)
• What is hydrotropism?

  Growth towards water
• Where in plant is phototropism always +?

  Stem
• Describe how phototropism works in shoots

  . Sunlight stimulates production of auxins in shoot tips

  . Auxins diffuse →,↓, towards shaded regions of plant

  . Stimulates cell growth

  . By activating TFs

  . At site of action

  . Positive phototropism
• Describe how phototropism works in roots?

  . Auxins produced at root tip

  . Inhibit growth

  . Negative phototropism - grows downwards
• What is the evidence for tropism?

  . Foil cap at shoot tip -> auxins are produced at tips

  . Agar block -> tropism is chemical/hormonal, as electrical impulses cant diffuse thru

  . Glass plate prevents auxins diffusing -> diffusion happens to elongate cell

  . Removal of auxin -> auxin makes plant grow