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  • Osmosis
    • osmosis is the diffusion of water molecules down a water potential gradient (high to low) through a selectively permeable membrane
    • Water Potential (psi- ?)
      • measure of the ability of water molecules to move and is measured in kilopascals (KPa)
      • plant:            ? = solute potential + pressure potential (? s+ ? p) animal:            ? = solute potential (?=?s)
      • All solutions have a negative ?  because polar molecules attract the water molecules so they cannot move elswhere
      • pure water has 0KPa
    • Pressure Potential
      • the solutes in vacuole draw water in by osmosis, this causes the vacuole to expand and push on the cell wall. cell wall = inelastic so exerts an outward pressure
    • managing water balance
      • Hypotonic
        • solution has a lower solute conc than the cell. so cell has lower ? than solution
        • animal cell: water will diffuse into the cell and possibly cause it to burst because they have no cell wall
        • Plant cell: water will diffuse into cell causing it to become turgid as water entering causes the vacuole expands and pushes on the cell wall creating pressure
      • Isotonic
        • solution has an equal conc of solute and water potential as cell
        • Animal cell: the cell will be a normal size and not gain or lose any water (no net movement)
        • Plant cell: cytoplasm is begining to pull away from cell wall (incipient plasmolysis) because there's not enough water to push the cell contents against the wall
      • hypertonic
        • solution has higher solute conc than the cell. so cell has higher water potential than solution
        • Animal cell: water will diffuse out of the cell and shrivel up
        • plant cell: water will diffuse out of cell and will become floppy as there's no pressure on the cell wall. it does retain its shape though


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