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Chapter 12: Transport (Water Potential (free energy can be increased by:…

- - - - ψπ: osmotic potential, effect that solutes have on water potential
        
        pure water osmotic potential is 0.0 MPa
        
        always negative
      - ψp: pressure potential, effect that pressure has on water potential
        
        water under pressure, pressure & water potential increase
      - ψm: matric potential, water’s adhesion to nondissolved substances
        
        always negative
        
        less important in living cells
        
        usual equation for living cells ψπ + ψp = ψ
- - - - occur as isolation barriers
    - - all lipid/protein cell membranes are this
- - - - if molecule secreted by active transport, origin cell probably impermeable to it in that area #impermeable because active transport pumps against concentration gradient
  - - - K+ actively transported into guard cells by surround cells
        
        K+ cannot leave due to impermeable plasma membrane
        
        K+ pumping possible, taken from surround cells
        
        water potential in guard cells becomes more negative
        
        thrown out of hydraulic equilibrium
        
        water diffuses out of surround cells into guard cells
        
        guard cells swell, bend, and push apart; opens stomatal pore
        
        1 more item...
        
        water potential in adj. cells becomes less negative
- - - - spring & summer: leaves dominant source
      - early spring: storage sites; tubers, corms, wood & bark parenchyma, fleshy taproots
      - some species sugars actively transported into sieve elements
      - other species, phloem loaded by polymer trap mechanism
        
        conducting cell membrane permeable to mono/disaccharides, not polysaccharides
        
        simple sugars diffuse into conducting cells & polymerized into polysaccharides
        
        sugar accumulated in cell & osmotic/water potential becomes more negative
        
        hydraulic disequilibrium b/t sieve elements & surrounding cells
        
        water diffuses into sieve elements
        
        instead of expanding, vacuolar membrane disintegrates & mixes w/ some cytoplasm (phloem sap)
        
        protoplasm squeezed into next cell through sieve pores
        
        massive loading causes pressure to build quickly, large volume of material flows from source
        
        pressure can be as high as 2.4 MPa
        (human blood pressure about 0.016 MPa) #megapascals unit pressure is measured in
  - - - water in upper tracheary elements must lift weight of entire water column
        
        for every 10 meters of height leaf water potential must be at least 0.1 MPa more negative than root water potential
      - due to tension on these molecules pressure potential is negative
        
        as water moves into leaf mesophyll xylem water potential becomes more negative
      - upper treachery ele, become negative & draw water up from xylem
        
        xylem draw water from root cortex, root cortex from root epidermis
        
        water potential of root epidermis & root hairs more negative than soil, water moves into root
    - - this water loss influences water movement through xylem
    - - to overcome friction & gravity leaf water potential must be 0.2 MPa more negative than root water potential for every 10 meters