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Transport processes (water potential (it is the chemical potential of…

- - - - freely permeable membrane: allow all solutes to pass freely across the membrane
      - completely impermeable: do not allow anything to pass
      - selectively permeable: only allows selective substances to pass.
- - - - similar function to that of the guard cells
      - they can either accumulate or expel potassium and thus adjust the turgidity and water potential of the cell
    - - these are the molecular pumps which helps in transport of the molecules
      - the number of transfer cells depends on the surface area of the plasma membrane
    - - during night time, the guard cells are in hydraulic equilibrium because of which the water entering the cell and leaving the cell is of same rate
      - at sunrise, potassium is pumped into guard cells which increases solute concentration finally leading stomatal pore to open
  - - - water transport through xylem
        
        cohesion tension hypothesis of water transport is the mostly accepted hypothesis
        
        water in plant is lost by transstomatal transpiration and transcuticular transpiration
        
        a vessel having cavitation means the vessel can never conduct water again
      - control of water transport by guard cells
        
        bulk water movement through xylem is influenced primarily by water loss in the atmosphere
        
        whenever the soil has adequate amount of water, water loss is actually advantageous.
        
        for healthy and turgid plants, light often controls the guard cell water relation.
        
        water stress ; release of abscisic acid that prevents water loss.
      - properties of water
        
        movement of water through xylem depends on the properties of water
        
        liquid water is cohesive
        
        water adheres firmly to soil particles
        
        water is heavy and lifting it to the top of a tree needs a lot of energy
    - - phloem is responsible for the transport of sugar
      - in some plants sugars are actively transported by sieve elements while in some it is transferred by polymer trap mechanism
      - the actual amount of sugar and other nutrients transported per hour by phloem is called mass transfer.
      - sinks are sites that receives the transported phloem sap