Tropic response

• Tropic responses


  The responses of plants to stimuli like light, water and gravity
• Tropisms


  • Directional - the plant either grows towards or away from a stimulus
• Gravitropism


  A response in which parts of a plant grow towards or away from gravity
• Shoots


  • Negatively gravitropic - grow upwards, away from gravity
• Roots


  • Positively gravitropic - grow downwards, towards gravity
• Phototropism


  A response in which parts of a plant grow towards or away from the direction of the light source
• Shoots


  • Positively phototropic - grow towards the light source
• Roots


  • Negatively phototropic - grow downwards, away from light
• Investigating gravitropism in shoots and roots


  Place seedlings in Petri dish with damp cotton wool, align radicals differently, leave to grow in dark for 2 days, observe directional growth
• Investigating phototropism in shoots


  Place potted seedlings in cardboard boxes, expose to single light source, observe stem growth direction
• Auxin


  A chemical produced in the tips of actively growing shoots that stimulates cell elongation or growth
• Auxin distribution in shoot in response to light

  Auxin is either destroyed on the light side or moves to the shaded side, causing unequal cell elongation and stem bending towards light
• Auxin distribution in shoot in response to gravity

  Auxin accumulates on the lower side, causing faster growth of lower cells and shoot bending upwards