Plant transport systems

• when water scarce, guard cells:

  1. actively transport K+ ions out into epidermal cells
  2. water moves out as well through osmosis and guard cells become flaccid
  3. stomata closes so that water loss is minimal
• when water is available

  1. active transport of K+ ions into guard cells from epidermal cells
  2. guard cells gain water from osmosis and become turgid
  3. stomata is opened and transpiration occurs again
• Why does water follow the K+ ions?

  • K+ ions increase solute concentration or decrease solute concentration
  • water moves from an area of high concentration to low concentration
  • OR water moves from an area of high solute concentration to area of low solute concentration
• Translocation - movement of dissolved substances within the phloem
• epidermis


  has a thick, waxy cuticle that waterproofs the leaf surface, so that the loss of water and gas is reduced
• spongy mesophyll 


  are loosely packed with air pockets in between them to allow water vapour, O2 and CO2 to diffuse through