stimuli

• what is a stimuli?

  a detectable change in environment
• what are the cells that detect stimuli?


  receptors
• why do organisms respond to stimuli?


  to increases survival rate
• what is taxes?

  simple response when an organism moves towards or away from a stimuli
• what is positive taxis?


  when an organism goes towards a stimuli
• what is negative taxis?


  when an organism moves away from a stimuli
• what are two examples of taxes?

  • earth warms - negative phototaxis to go towards soil
  • bacteria - positive chemotaxis to go towards chemicals
• what is kinesis?


  simple response by changing speed and changing the rate of direction
• whats and example of kineses?


  woodlice, when they are in damp areas, the increases the rate of changing directions so they stay there

  when they are in dry conditions , the move in a straight line to get out
• what is a tropism ?


  plants response to a stimuli
• what is plant growth controlled by?

  specific growth factors such as IAA
• what is IAA?


  (indoleacetic acid) auxin controls cell elongation in shoots and inhibits growth in its roots
• where is IAA made?


  in the tip or roots and shoots and diffuses into the cells
• describe phototropism in the tips?

  • IAA diffuses towards the shade which causes cell elongation on the shaded side so the plant bends and grows towards the light
• roots negative phototropisms


  • high concentration of IAA inhibits cell elongation causing roots to elongate on the lighter side, the roots bends away from the light