Osmosis = passage of water from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
Partially permeable = Permeable to water molecules and a few other small molecules, not to larger molecules.
Water potential measured in units of pressure (kilopascals kPa).
Under standard conditions of temp and pressure (25C, 100kPa) pure water = water potential of 0.
- Addition of a solute to pure water = lowers water potential.
- Water potential = always less than 0 (negative).
- More solute added = more negative water potential.
- Water will move by osmosis, high to low w.p.
Finding water potential of cells or tissues = place them in series of solutions, no net gain or loss of water with solution with the same water potential.
Explanation of osmosis:
- Solution on left has low concentration of solute molecules, right has high conc. of solute molecules.