Please enable JavaScript.

Coggle requires JavaScript to display documents.

Chapter 12 (Water Potential (can be increased in multiple ways (water can…

- - - - effect pressure has on water potential
        
        potential is measured in units of pressure
        
        megapascals or bars
      - more pressure on water, higher pressure potential
      - compressing is positive pressure
      - pressure potential is negative when water is under tension
    - - effects that solutes have on water potential
      - no solutes present in pure water
        
        osmotic potential is 0.0 MPa
        
        adding solutes decrease waters free energy
      - always negative
      - related to the #of particles present
    - - waters adhesion to non dissolved structures #
        
        such as cell walls
        
        membranes
        
        soil particles
      - adhesion only decreases waters free energy
      - always negative
- - - - molecule resides in cell wall
      - wall is permeable, molecule passes
        
        most small molecules can move easily
        
        moves through cell wall and intercellular spaces
        
        cell wall/intercellular is called apoplast
  - - - once in a guard cell. it cant leave
      - plasma be membrane is impermeable to K+
      - potassium pumping is possible, diffusion isnt
        
        loss of K+ affects adjacent cells
        
        water potential is less negative
      - water potential in guard cells more negative
  - - - due to more plasma membrane surface area
      - high-volume transport can occur
      - helps areas needing rapid transport
- - - - molecular pumps
      - active transport
    - - where water and nutrients are taken from
      - leaves are dominant sources in spring/summer
      - during other seasons, storage sites are sources
    - - polysaccharides arent permeable
      - sugars diffuse into conducting cells
      - sugars are polymerized into polysaccharides
      - this loads the phloem
  - - - plants control phloem sap
      - they decide where it goes at what rate
  - - - uncontrolled bleeding if phloem is cut
      - vascular bundles are broken constantly
        
        2 mechanisms seal broken seive elements
        
        p-protein
        
        swept into cell center
        
        becomes a tangled mass
        
        becomes to large and creates p-protein plug
        
        callose
        
        precipatates into a flocculent mass
        
        carried along w/ p-protein
        
        contributes to the plug
        
        done by chewing insects or large animals
- - - - membranes are of 3 types
        
        freely permeable
        
        allow all solutes to diffuse through
        
        little biological significance
        
        completely impermeable
        
        do not allow anything to pass through
        
        occur as isolation barriers
        
        differentially/selectively permeable
        
        allow only certain substances to pass through
        
        all lipid/protein cell membranes use this
      - diffusion through membranes is called osmosis #
      - molecular pumps
        
        most membranes have membrane-bound pumps
        
        use atp
        
        force molecules across membranes
- - - - water molecules interact strongly w/others
      - behaving as if bound together
      - when frozen, they are strongly bound
    - - molecules interact w/many substances
      - most substances in plants interact with water
      - adhesion allows most molecules to have shell of water
  - - - widely accepted model of practice
      - open stomata pores cause water loss
        
        apoplastic space is filled w/moisture saturated air
        
        water molecules diffuse from intercellular space
        
        this water loss is called transstomatal transpiration
      - some water is lost from the cuticle
        
        waxes and epidermis are hydrophobic
        
        pretty efficient at retaining water
        
        some water is lost through the cuticle
        
        this is called transcuticle transpiration
- - - - the only pure water in nature comes from rain
      - mountain streams are pretty pure
      - lakes, rivers, and other streams arent
  - - - fog
      - rain
      - dew
      - frost
      - humidity
      - air also pulls water out of plants
        
        motive force for transpiration
        
        seasons play a big part
    - - timing and regularity of precipitation
      - time between rains
      - amount of direct sunlight
      - ratio of sunny/rainy days
      - adaptations per plant
        
        different plants can access more or less water
        
        bigger the leaves, more water collects
- - - - some plants grow better in sandy soil
      - all depends on root depth
  - - - drought avoidance
        
        plants are known as desert ephemerals
        
        meaning short lived
        
        never reach full size
        
        small plants
        
        complete life cycle in 1-2 months
        
        seedlings are ready for next rainfall
        
        plants that avoid droughts and die
      - drought tolerance
        
        live through dry periods
        
        most are succulents
        
        high % of body is water storing cells
        
        stem succulents store water in pith and cortex
        
        survive by staying doormant