3.6.1.1 Survival and response

• Types of stimuli:

  • Light
  • Heat
  • Pressure
  • Sound
  • Gravity
• Why might organisms need to move?

  • Avoid predation
  • Find food/water
  • Favorable habitat
  • Find a mate
  • Avoid competition
  • prevent water loss
• Stimulus: A change in the internal or external environment
• Taxis: A directional response to a directional stimulus.

  • Organism moves whole body towards or away from stimulus
• Kinesis: Non-directional response to a non-directional stimulus.

  • Whole body moves (rate of movement or turns)
  • Unfavorable area = more turns
  • Intensity of stimulus is proportional to the intensity of response
• Tropism: Directional growth in response to a directional stimulus. Plant root/shoot grows towards or away from a stimulus

  • Tips of root/shoots make the auxin IAA (Indoleacetic acid)
  • IAA moves to surrounding cells through diffusion or active transport - for further travel it moves through the phloem
  • IAA promotes cell elongation in shoots
  • IAA inhibits cells elongation in roots
• Geotropism - movement due to gravity
• Phototropism - growth in response to light