stimulus and response ✅

•  It was suggested that the movement of the maggots might have been influenced by the Earth’s magnetic field. Suggest one simple way of repeating the investigation which would avoid this possibility.

  • rotate box
  • place magnets around box
• The muscle is a effector in a simple reflex arc
• Effect of gravitropism on IAA

  IAA moves to underside therefore roots grow downwards and shoots grow upwards
• TROPISM= Directional response of plant to a stimulus and respond by regulating growth
• RP- Using choice chamber to investigate response

  eg. light on woodlice

  • divide petridish into compartment for light intensity
  • cover one Half in dark card and put damp filter paper in both halves
  • place mesh over and put woodlice in centre
  • After 10 mins take lid off and record where they are

  Can be repeated investigating humidity too by using damp filter paper and a drying agent
• Role of auxin


  stimulate growth of shoots and inhibit growth of roots
• effect of phototropism on IAA

  • IAA moves to shady side in both
  • SHOOTS= therefore grow /bend towards light
  • ROOTS= therefore Bend away from the light
• positive tropism= growth towards stimulus

  (vice versa)
• • Gibberellins stimulate seed germination and flowering.
  • Abscisic acid (ABA) helps plants respond to environmental stress and is involved in stomatal closure.
  • Cytokinins stimulate cell division and cell differentiation.
  • Ethene stimulates flowering and fruit ripening.
• Auxins promote cell elongation in shoots but have the opposite effect in roots
• tip produces IAA
• How does IAA actually work?

  enters the nucleus of plant cells and binds to the promoter regions of DNA. It then acts as a transcription factor, activating or inhibiting the transcription of genes which code for proteins involved in cell elongation and growth.
• How is IAA transported?

  transported around the plant in the phloem then moves shorter distances within the plant (from cell to cell) by diffusion and active transport.
• how is IAA moved from cell to cell

  diffusion and active transport
• TAXIS= organism moves towards or away from a directional stimulus. eg light
• KINESIS=movements in response to a non-directional stimulus. EG humidity