Experimental evidence for phototropisms

• What conclusions did Darwin make to his experiment?

  1. Growth stimulus is produced in tip
  2. Growth stimulus is transmitted to zone of elongation
  3. Cells on shaded side grow faster than ones on lit side

  
• What did the boysen-jenson experiment conclude?

  • Materials which aren’t permeable to water can stop the curvature response in some circumstances
  • Materials which are permeable to water don’t interfere with curvature response

  
• What did went’s experiment conclude?

  1. angle of curvature is related to the number of tips used
  2. Number of tips relates to the concentration of auxin in the agar block
  3. Curvature response is due to a chemical which moves from the tip and affects cell elongation

  
• How do plants grow in the dark?

  • Rapidly (more so than in light)
  • Because gibberellins involved in extreme elongation at internodes (where hormones are stimulated from) and levels fall when exposed to light
  • Growth slows when exposed to light to use resources elsewhere like for synthesising leaves
  • Gardeners use this to force growth