Mass transport in plants

• Describe the cohesion tension theory

  • water evaporates from the leaf through the stomata
  • lowers water potential of leaf cells
  • water drawn out of xylem
  • Creates tension, pulling water up in xylem
  • cohesion, between water molecules so maintains continuous Column of water
  • adhesion of water molecules to walls of xylem pulling wars inwards resulting in tension
• Describe how xylem vessels structure is related to their function

  • long hollow tubes with no end walls so continuous water column
  • tubes contain no cytoplasm or organelles so no obstruction to continuous water column
  • lignin so provides support
  • pits in walls so allows lateral movement of water when vessel blocked
  • lignin so waterproof prevents water loss