Biology 3.7 Osmosis

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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.


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