Transport in the xylem of the plant

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  • Transport in the xylem of the plant
    • Transpiration is the inevitable consequence of gas exchange in the leaf
      • loss of water vapour
        • guard cells - control the aperture of the stoma and can adjust from wide open to fully closed
          • exception - liverworts
    • the cohesive property of water and the structure of the xylem vessels allow transport under tension
      • lignin - strenghten the walls of the xylem
        • pressure much lower than atmospheric one
      • water molecules are polar
        • cohesion between molecules
        • attraction to hydrophilic parts of the xylem
          • adhesion
            • water can be pulled up
              • cohesion between molecules
    • the adhesive property of water and evaporation generate tension forces in leaf cell walls
      • to replace water evaporated
        • from the xylem vessels
      • the force of adhesion between water and cell walls is strong enough to **** water out of the xylem
        • low pressure
          • pulling force - transpiration pull
    • active uptake of mineral ions in the roots causes absorption of water by osmosis
      • the solute concentration in the root cells is greater than the one in the soil
      • mineral ions are taken by active transport
    • Plants transport water from roots to leaves to replace losses from transpiration
      • apoplast pathway - water moves through cell walls
      • symplast pathway - water moves through cytoplasm


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