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Transport Processes, the random motion of particles across a concentration…

- - - - plant cells can never burst because cell walls are strong enough to resist breakage
      - ex of turgid cell
      - growing cells have weak deformable walls that cannot resist pressure, this allows them to grow in size rather than burst
        
        growth can be stopped by either strengthening the cell wall or stopping the import of solutes
    - - the point at which the protoplast has lost just enough water to pull slightly away from the wall is called incipient plasmolysis
      - if the cell has not reached equilibrium and continues to lose water the protoplast can detach completely and shrink
        
        this is called plasmolysis
- - - - in glands apoplast is mostly intercellular space through which molecules move easily
      - in parenchymatous tissues primary walls are thin and the contact is extensive
        
        diffusion back into the cell is probably but if the original molecule was secreted by active transport this is not likely
        
        active transport is probably the most common mechanism for movement of water sugar and other nutrients between parenchyma cells within cortex pith and leaf mesophyll #
      - in nonglandular regions the apoplast is mostly cell walls
- - - - within sinks sugars are actively unloaded from sieve elements into surrounding cells making the sap more dilute.
      - because sap is under pressure it can bleed if phloem is cut
      - P-proteins can seal sieve elements by making a plug
        
        conifers dont have p protein
    - - as seive tube cells are loaded with sugars osmotic potential becomes more negative and water diffuses into the sieve elements
      - since sieve elements have large holes in their walls pressure causes protoplasm to squeeze into the next cells pushing photosynthate
      - phloem loading occurs amongst numerous vascular bundles
- - - - all but lipids interact with water - cellulose enzymes DNA and sugars have a shell of water molecules rather fimly attached to them
  - - - when stomata are open they lose water
      - air has a tremendous ability to absorb water this loss is called transstomatal transpiration
      - transcuticular transpiration is loss through the thick cuticle covering
      - as transpiratoin causes stomata to lose water their water potential becomes more negative
      - the gradient of water potentials reaches a tracheid or vessel member
      - as water moves out of tracheary elements into mesophyll parenchyma cells the water potential within the xylem water column becomes more negative
      - as water molecules leave xylem they do not leave a hole they pull the rest of the water with it all the way from the roots
      - for every 10 meters leaf water potential must be .1 MPa more negative than root water potential to overcome the weight of water