responses in plants

• what are auxins?

  • plant hormones - control growth at tips of shoots and roots - move through plant in solution
  • produced at tips and diffuse backwards - stimulate the cell elongation process - occurs in cells just behind the tips
  • promote growth in shoot - inhibit growth in root
  • do growth responses of plants to light and gravity
• auxins and phototropic?

  • positively phototrophic - shoot tip exposed to light - accumulates more auxin in side of shade than side of light
  • cell elongates faster on shaded side - shoot bends towards light
  • negative phototrophic - shoot exposed to some light - more auxin accumulated on shaded side
  • auxin inhibits cell elongation on shaded side - root bends downwards back into the ground
• auxins and geotropism?

  • negative geotropism - shoot grows sideways - gravity produces an unequal distribution of auxin in tip - more auxin on lower side
  • lower side to grow faster - bending the shoot upwards
  • positive geotropism - root growing sideways - more auxin on lower side
  • in root the extra auxin inhibits growth - cells on top elongate faster and root bends downwards