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  • Diffusion and Osmosis

    Life Science: Molecular

  • Vocabulary Diffusion

    Facilitated Diffusion
 Osmotic Pressure 

  • Cell Membrane The cell membrane is a semi-permeable lipid bilayer. – Semi-permeable means it lets some things pass

    through it. – Lipid means fat (phospholipid to be exact) – Bilayer means there are 2 layers

    Cell Membrane

  • Cell Membrane

    Cell Membrane

    The cell membrane maintains the internal environment of the cell, by moving molecules from one side to the other.

  • Phospholipid The cell membrane is composed phospholipids, which have hydrophilic heads and hydrophobic tails.

  • Cell membrane


    Protein channel Lipid bilayer

    Carbohydrate chains

    Lipid Bilayer

    Phospholipids spontaneously arrange into a double layered membrane in a fluid environment.

  • Fluid Mosaic Model

  • Membrane Proteins Proteins embedded within the membrane allow materials to move in and out of the cell.

  • Classes of membrane proteins – peripheral proteins

    • loosely bound to surface of membrane • ex: cell surface identity marker (antigens)

    – integral proteins • penetrate through the cell membrane • ex: transport proteins

    Membrane Proteins

  • Passive Transport Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.

  • Passive Transport In a cell... Diffusion moves small, uncharged molecules across the cell membrane until equilibrium is reached.

  • Facilitated Diffusion

    High Concentration

    Low Concentration

    Cell Membrane

    Facilitated diffusion is the movement of large or charged particles such as ions, sugars, and salts through protein channels across the cell membrane.

    High Concentration to Low Concentration

  • Passive Transport

  • Osmosis: Facilitated Diffusion Osmosis is the diffusion of water through a selectively permeable membrane. Many cells contain water channel proteins called aquaporins that allow water to pass directly through the membrane.

  • Osmosis: Facilitated Diffusion There is a net movement of water from low to high solute concentration, or high to low water concentration.

  • How Osmosis Works

  • The net movement of water into or out of a cell produces a force known as osmotic pressure.

    Osmotic Pressure

  • Osmotic Pressure Osmosis is a force that exerts a pressure on the more concentrated side of a cell membrane.

  • Solution Concentrations Tonicity is a measure of the osmotic pressure gradient of two solutions separated by a semipermeable membrane. • Hypertonic - Having a higher concentration than another

    solution. • Hypotonic - Having a lower concentration than another

    solution. • Isotonic - Having the same amount of dissolved solute as

    another solution.

  • Comparing Solutions • A cell placed in a hypertonic solution will decrease

    in volume. • A cell placed in a hypotonic solution will increase in

    volume. • A cell placed in an isotonic solution will not change

    in volume.

  • Hyper, Hypo, or Isotonic?

    Normal Red Blood Cell


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