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					Water and its relation
        to
Osmosis & Diffusion
   Living cells contain aqueous
   (water) solution and they are
 surrounded by aqueous solutions
Ø If the concentration of dissolved
 substances (solutes) is not the same
 inside and outside the cell –

  l   A process called osmosis occurs
Ø Osmosis:
the movement of water molecules from an
  area with less solutes (low concentration) to
  an area with more solutes in the solution
  (high concentration)
Ø   The water passes through the semi-permeable
    membrane until the concentration of the
    solutes is the same on both sides.
Ø Osmosis is the
 movement of water
 (red dots) through
 a semi permeable
 membrane to a
 higher
 concentration of
 solutes (blue dots).
        What are semi-permeable
             membranes?
Ø   Those membranes that allow the solvent (liquid),
    but not the solutes to pass from one side of the
    membrane to another

Ø   EX: egg, cellophane, and cell membranes

Ø   In these membranes the pores are large enough
    for water to pass through but too small for other
    compounds to pass
                Examples
Ø Sailor died from dehydration due to the
  high concentration of salt in the seawater.
Ø After drinking the seawater the high
  concentration of salt caused the water to
  travel out of his cells.
Ø This caused the cells to dehydrate or
  shrink
How do we
 get pickles?
Ø Living cells contain aqueous solutions –
  intracellular fluid
Ø The cells are also surrounded by an
  aqueous solution-
  intercellular fluid
Ø Cells function and survive by keeping
  the concentration within and around the
  cell approximately the same.
Ø   If the concentration of solute in the fluid
    surrounding the cell is higher than inside the
    cell the solution is hypertonic
Ø   Water will travel out of the cell through the
    membrane - crenation
Red Blood Cells in a Hypertonic
          Solution
              Hypertonic Solution
Ø   The word "HYPER"
    means more, in this case
    there are more solute
    (salt) molecules outside
    the cell, which causes
    the water to be sucked in
    that direction.
Ø If the concentration of the solute outside the
  cell is less than inside the cell it is called a
  hypotonic solution.
Ø Hemolysis will occur – additional water will
  travel into the cell causing it to swell and
  rupture.
Red Blood Cells in a Hypotonic
          Solution
            Hypotonic Solution
Ø   The word "HYPO"
    means less, in this
    case there are less
    solute (salt)
    molecules outside the
    cell, so water will
    move into the cell.
Ø   When the fluids have the same concentrations
    they are called isotonic
Ø   EX: when fluids are administered to a patient
Red Blood Cells in an Isotonic
          Solution
              Isotonic Solution
Ø   If the concentration of
    solute (salt) is equal
    on both sides, the
    water will move back
    in forth but it won't
    have any result on the
    overall amount of
    water on either side.
Ø   "ISO" means the
    same
          What is Diffusion?
Ø Diffusion is the natural tendency of
  molecules to flow from higher
  concentrations to lower concentrations
Ø The rate of diffusion depends on the
  weight of the molecules—heavy molecules
  diffuse more slowly than light molecules.
       Diffusion of Gases
Ø A bottle of perfume opened in one
 corner of a room would slowly fill the
 room




Ø Molecules disperse from a concentrated
 source, the newly opened bottle, until
 they are evenly distributed throughout
 the room
Ø Smell of freshly baked cookies
         Diffusion of Liquids
Ø When two fluids mix together without any
  help from us.
Ø We can explain this using the idea that
  particles move.
Ø Instead of the particles moving around
  and mingling with particles of the same
  material, they move around and mingle
  with particles of the other material as well
      How Diffusion of Liquid in
           Liquid Works
Ø Add a drop of food coloring in a container
  of water.



Ø The color will “diffuse” or disperse
  throughout the entire sample until the
  sample is a uniform color.

     http://paer.rutgers.edu/pt3/movies/mixing2.mov
     How Diffusion of Solid in
         Liquid Works
Ø The solute (solid) dissolving in the solvent
  is also an example of diffusion.
Ø The water “attacks” the solute which
  eventually dissolve.
Ø What are ways that this process in
  increased?
How Diffusion of Solid in
    Liquids Works
Diffusion across a Membrane
Selectively Permeable membranes –

 Living membranes alter what may pass
 through at any given time
Diffusion of CO2 and O2 in the Lung
Kidney Dialysis
               Review
Ø Osmosis:the movement of water
 molecules from an area of low solute
 concentration to an area of high solute
 concentration.

Ø Thewater passes through the semi-
 permeable membrane until the
 concentration of the solutes is the same
 on both sides.
Ø Diffusionis the natural tendency of
 molecules to flow from higher
 concentrations to lower concentrations

Ø Movement  may be of molecules or ions
 across a semi-permeable membrane

Ø Depends  on molecular size, ionic charge,
 and molecular solubility (ability of solute
 to dissolve in solvent)
Diffusion or Osmosis?

           1% salt (low concentration) in
           the bag
           10% salt (high concentration)
           surrounding the bag


           Which way does the water
           move?
Diffusion or Osmosis?

           Iodine solution in the bag
           Starch solution surrounding
           the bag.


           What do you predict will
           happen?
Lab Set-up

				
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posted:3/13/2014
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