Water Potential Notes

Water Potential

• $Water Potential$

  • A measure of the free energy of water is less than when it has to surround solutes
  • The force responsible for the movement of water in a system
  • Symbol: Psi or ψ
  • measured in bars or megapascals

• 2 components of Water Potential

  • Solute Potential (Osmotic Potential)
  • Determined by solute concentration
  • Always negative
  • Pressure potential
  • Results from the exertion of pressure on cell walls as water moves in or out
  • Can be negative or positive

• %%Water Potential of Pure Water= 0%%

Adding solute decreases water potential

• Making it negative
• %%Open Breakers and Animals= 0 pressure potential%%
• %%Water moves from high to low water potential%%

Animal Cells

• Water movement depends only on solute concentration
  • No Cell Wall
• Hypertonic: Water moves out of the cell
  • Cell Shrinks
• Hypotonic: Water moves into the cell
  • Lysis: Cell Swells and Bursts

Plant Cells

• %%The cell wall can exert pressure and prevent lysis%%
  • When the pressure in the cell becomes large enough
• Flaccid: Limp
  • Isotonic solution
  • Vacuole does not exert pressure on the cell wall
• Turgid: Firm
  • Hypotonic solution
  • Vacuole exerting pressure on the Cell wall
• Plasmolysis
  • Hypertonic Solution
  • Plant cell shrinks from the cell wall