Water transport in plants

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  • Created by: adele_26
  • Created on: 15-05-16 16:24
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  • Water Transport in Plants
    • Transpiration
      • The loss of water vapour from the leaves and stems.
        • O2 moves out of leaves down a concentration gradient by diffusion out the Stomata.
          • Affected by Light, Temperature, Humidity, Wind.
      • Roots - leaves
        • enters roots via osmosis and is transported up xylem to leaves.
        • Evaporates from mesophyll cells along diffusion gradient.
      • Cohesion-tension theory
        • Water is cohesive- attracted to other H2O molecules so pulled up Xylem.
        • Water evaporated at leaves- creates tension, pulling water up column.
        • Water is adhesive- attracted to walls of xylem vessels.
    • Translocation
      • Transport of organic compounds in Phloem from source to sink.
        • Symplast route
          • Through cytoplasm into sieve tubes via diffusion through plasmodesmata.
            • Water follows sucrose- creates pressure and moves sucrose through Phloem (mass flow).
        • Apoplast Route
          • Sucrose travels through cell walls into companion cells and sieve elements.
            • Water also moves in via osmosis = build up of turgor pressure.
              • Water carrying assimilates moves into sieve-tube elements and molve up or down plant to areas of low pressure by mass flow.
          • In companion cells, sucrose moved into cytoplasm in active process.
            • Hydrogen ions pumped out using ATP and return down conc. gradient via co-transport protein.
        • Sucrose unloaded at any point into cells- diffusion.
          • Concentration gradient maintained.
        • Loss of solutes in Phloem = rise in water potential.
          • Water moves out by osmosis- some used in transpiration stream.
    • Symplast pathway
      • Through living parts of cell- Cytoplasm.
      • Cytoplasms connect through plasmodesmata
      • Water moves via Osmosis
    • Apoplast Pathway
      • Through non-living parts (Cell walls).
      • Water diffuses through cell walls- can carry solutes.
      • From area of high hydrostatic pressure to low (mass flow).
      • When water gets to epidermis, it's pathway is blocked by the casparian strip and enters symplast pathway.


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