Mass Transport in Plants

Mass Transport in Plants

Overview:

• Why do plants need water?
  • fills vacuole and makes cells turgid so plant is supported
  • reactant in photosynthesis
  • required for hydrolysis reactions
  • transport medium for ions from roots to leaves
  • solvent
• Why do plants need sucrose?
  • in growing areas sucrose is hydrolysed to glucose so can be used in respiration or converted to cellulose
  • sucrose is condensed to starch for storage in storage organs
  • transports better than glucose as it is less reactive so less likely to be used up along the way

Transport in Xylem Vessels:

• Overview -
  • xylem vessels transport water and dissolved ions from the roots up through the stem and leaves of the plant
  • end walls are broken down into dead tissue to form hollow pipes used to carry water in a continuous, unbroken column
  • vertical cell walls are thickened with lignin to withstand tension
  • lignin is waterproof to keep water inside

• Cohesion -
  • known as tension theory of water transport
  • transpiration occurs as water evaporates from the leaf mesophyll cells and water vapour diffuses into the air via stomata
  • water is drawn from the xylem vessels, to replace that lost from transpiration
  • water enters the xylem at the roots
  • water molecules are held together by many weak hydrogen bonds, creating cohesion between the water molecules
  • the transpiration  "pull" stretches the column of water molecules as negative presssure is created since it is under tension
  • lignin withstands the tension so as vessels become narrower, the walls do not collapse
  • adhesion of water molecules to walls helps the column remain unbroken and rise upwards

• Factors…