Water Potential  The free energy per mole of water  Calculated from two components: Solute potential (osmotic pressure) Pressure potential (turgor pressure)

Water Potential  What is solute potential? Dependent on solute concentration Also called the osmotic potential  What is pressure potential? Results from exertion of pressure on a solution Can be positive or negative (tension) Sometimes called turgor pressure

Water Potential  How does this affect movement of water? Water moves from area of higher water potential (higher free energy) to lower water potential (lower free energy)

Water Potential  Example: Open beaker of pure water = zero ○ Solute pressure and pressure potential zero Increase in pressure = increase in water potential Addition of solute lowers solute potential = decreases water potential

Water Potential  Solute potential is negative Equation of solute potential = - iCRT C = molar concentration Increase solute concentration, decrease solute potential

Water Potential  Example: Cell separated from pure water by selectively permeable membrane Potential is higher outside cell