Osmosis

Osmosis

  • definition

    • net movement of water molecule from an area of high water potential to an area of low water potential through a partially permeable membrane

  • passive

  • osmosis

Water potential $$\psi$$

  • the tendency of water molecules to move from one region to another

    • water molecules used to dissolve solute are not free to move

  • pure water has highest water potential

    • water potential becomes more negative as amount of solute increases

  • measured in units of pressure (Pa/kPa)

  • water potential

Plant cell in pure water

  • higher water potential outside of cell

    • hypotonic solution

  • water moves into cell

  • cell swells and becomes turgid

  • cellulose cell wall prevents it bursting

  • turgid plant cell

Animal cell in pure water

  • higher water potential outside of cell

    • hypotonic solution

  • water moves into cell

  • cell swells and bursts

    • cytolysis

  • lysis of animal cell

Plant cell in conc. sugar solution

  • lower water potential outside of cell

    • hypertonic solution

  • water moves out of cell

  • cell loses turgor pressure and eventually plasma membrane pulls away from cell wall

    • plasmolysis

  • plasmolysis of plant cell

Animal cell in conc. sugar solution

  • lower water potential outside of cell

    • hypertonic solution

  • water moves out of cell

  • cell loses volume and shrivels

    • crenation

  • crenation of animal cell

Flaccid plant cells

  • plant cells should be turgid to give plant support

  • if cells start to lose water they will become flaccid

  • if they gain more water they can become turgid again

  • if they continue to lose water they will become plasmolysed

    • cell usually dies (same with lysed/crenated animal cells)