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  • Diffusion and

    Osmosis

  • The Cell Membrane

    The cell membrane is:

    Selectively permeable

    Permeable = Pass through (Latin)

    Cell membrane = Gate-Keeper that determines what can and cant enter the cell.

  • The Gate Keeper: The Cell

    Membrane

    Who comes in for the

    party?

    Small molecules like

    water, carbon dioxide,

    or oxygen can easily

    pass through the

    pores of the

    membrane.

    Who gets bounced?

    Large molecules like glucose

    Charged molecules

    like salts.

  • Molecule Movement

    Recall cells are small because they need to

    obtain sufficient nutrients and dispose of their

    wastes.

    This is done by the cell membrane by three

    means:

    1. Diffusion

    2. Osmosis

    3. Active Transport (Senior Science)

  • Definitions.

    Solution = A homogenous, liquid mixture of two or more substances.

    Solvent = The dissolving agent of a solution. Water is the most versatile solvent known.

    Solute = Substance that is dissolved in a solution.

  • Diffusion

    The process by which molecules tend to move

    from an area of higher concentration to an area

    of lower concentration.

    Concentration= amount of substance in a given volume.

    Think of the perfume example (high low)

    Think of the food-dye example (high low)

  • Why Diffusion?

    Kinetic molecular theory.

    Molecules are always moving

    Collisions occur between molecules, which causes the molecules to move away from one another.

    If there is space these molecules want to spread out evenly.

  • What direction will the molecules move?

  • Diffusion and the Cell

    Movement of molecules by diffusion is how the cell fulfills its needs.

    Nutrients: Low concentration in the cells, high concentration outside of the cells.

    What direction will the nutrients diffuse?

    From outside the cell to inside the cell.

    High to Low Concentration!!

  • Diffusion and the Cell

    Wastes: High concentration in the cell, low outside of the cell.

    What direction will the wastes move?

    From inside the cell to outside the cell.

    High to Low concentration

  • A special case of diffusion:

    Osmosis

    Water moves through the pores of the cell

    membrane like other molecules.

    The movement of water from a high

    concentration to a low concentration (thru a

    semi-permeable membrane) is called: Osmosis

    Osmosis = movement of water (the solvent)

    Diffusion = movement of dissolved materials (the solutes)

  • Osmosis is the movement of water (red dots) through a semipermeable membrane to a higher concentration of

    solutes (blue dots).

  • Activity Predicting

    Movement of Water This U tube has a

    selectively permeable membrane separating side A and B.

    Side A has a 40% solution of sugar and side B has a 60% solution of sugar.

    Which side has more water?

    Which way will the water move?

    Selectively Permeable Membrane

  • Osmosis a cure for the flu?

    Who here has taken penicillin to combat sickness?

    Penicillin weakens bacterial cell walls

    Water is at higher conc. outside the cellwhich way will water move?

    With a weak cell wall, the bacterial cell swells andPOP!

  • **Summary**

    Both osmosis and diffusion involve the movement of molecules from an area of high concentrations to a area of low concentrations.

    Osmosis = movement of water (the solvent)

    Diffusion = movement of dissolved materials (the solutes)

  • Water Balance

    The cell membrane doesnt actually control the movement of water.

    The environment around the cell determines the direction of water movement.

    For example, a cell is placed in a salt water tide pool. The sun evaporates some water.

    The concentration of water inside the cell is higher than outside.

    What happens?

    Water leaves the cell. Possible shrinking of the cell.

  • Water Balance

    On the contrary imagine it rains.

    A higher concentration of water outside the cell is the result.

    What happens?

    Water moves into the cell

    Possible swelling of the cell.

  • Water Regulation

    Without other mechanisms the cell would burst or shrivel.

    Plant vacuoles store water even when the environment is dry.

    The cell wall is rigid to prevent bursting or shriveling.

    Animals can increase or decrease their amount of water intake and outtake (Urine concentration/amount of water that is drank)

  • Hypertonic Solution More water inside cell than outside

    Plasmolysis

    Plasmolysis

    Cells shrink

    and die

  • Iso-osmotic Solution same concentration of water inside and outside cell

    Animal cell

    Plant cell

    No net gain or

    loss of water

  • Hypotonic Solution more water

    outside cell than inside

    Cytolysis

    cell swells and

    bursts

    Builds up turgor

    pressure cell

    becomes stiff,

    keeping plant

    upright

  • What would happen to a cell placed in pure water?

    90% water

    10% solute100% water

    Cells are about 90% water.

    Human Red Blood Cell Before: After

  • What would happen to a cell

    placed in a 20% salt solution?

    90% water

    10% solute

    Cells are about 90% water.

    80% water

    Human Red Blood Cell Before: After

  • Potatoes and Corn Starch..

    Finish your Experiments

    Remember Unit Test on Friday

    Microscopes & Cells

    Structures/Functions

    Cellular Respiration/Photosynthesis

    Cell Size

    Osmosis/Diffusion

    Single Celled Organisms.

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