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Transport Processes (Transport, Diffusion, and Membranes (Three types of…

- - - - Water leaves cells and enters cells at the same rate – equilibrium
      - Small water potential, less pressure potential
    - - High pressure potential, low water potential #
      - Figure 12-15
      - This makes the guard cell turgid and swell which allows the opening of the stomata
  - - - Cells at these joints called motor cells
    - - When cells are shrunken it causes the plant to close up, the potassium expelled out of cells
  - - - Larger the membrane, more pumps it can hold and vice versa
    - - Plasma membrane pressed against this wrinkly cell inside wall and allows for greater surface area
- - - - Move upward most easily through tracheids
    - - Upper tracheary elements lift this weight and there is tension on these water molecules, pressure potential is a negative number
      - Vertical xylem the weight of water counteracts its tendency to rise to areas of more negative water potential
    - - This water loss is called transstomatal transpiration
    - - Cellulose, DNA, enzymes, sugars, soil, etc
      - Interact with polymers of cell walls of tracheids and vessel elements, prevents water being drawn upward
    - - Molecules above the cavitation point are drawn upward and those below rush downward
      - Tracheid or vessel element can never conduct water again
      - Water column acts like a broken cable
    - - If hits vessel element it can expand and perforate the entire vessel
      - Occasionally embolisms can be healed
      - If hits tracheid only that one will lose water
      - FIGURE 12-25
  - - - Osmotic and water potential become more negative, water diffuses into sieve elements #
        
        This build up in pressure causes the protoplasm to leak out of sieve members into the next cell, creating phloem sap
      - Phloem is loaded by the polymer trap mechanism in some species – conducting cell membranes are permeable to monosaccharides and disaccharides
      - In both, parenchyma and companion cells are important in loading the phloem
      - STM/CC complex is a conducting cell and several companion cells
      - Sugars are actively transported into sieve elements
        
        Figure 12-17
        
        As sugars are accumulated the sieve member’s protoplasm becomes concentrated
    - - Mass transfer divided by cross-sectional area of phloem = specific mass transfer
    - - P-protein gets swept into the cell center where it becomes a tangled mass and forms a P-protein plug
        
        Figure 12-18
      - Callose – precipitates into a mass and is carried to broken sieve areas which helps leaking