Diffusion

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					  Cell Membranes
Osmosis and Diffusion
      Functions of Membranes
1. Protect cell
2. Control incoming and outgoing substances
3. Maintain ion concentrations of various
  substances
4. Selectively permeable - allows some
  molecules in, others are kept out
Phospholipid Bilayer
Fluid Mosaic Model
      Blood-Brain Barrier
• Allows some substances into the
  brain, but screens out toxins and
  bacteria
• Substances allowed to cross include:
   water, CO2, Glucose, O2, Amino Acids,
   Alcohol, and antihistamines. HIV and
   bacterial meningitis can cross the
   barrier.
                Solutions
• Solutions are made of solute and a
  solvent

• Solvent - the liquid into which the solute
  is poured and dissolved. We will use
  water as our solvent today.

• Solute - substance that is dissolved or put
  into the solvent. Salt and sucrose are
  solutes.
 Methods of Transport Across
        Membranes
1. Diffusion

2. Osmosis

3. Facilitated Diffusion

4. Active Transport
 Methods of Transport Across
        Membranes
1. Diffusion -passive transport - no energy
       expended
2. Osmosis - Passive transport of water
       across membrane
3. Facilitated Diffusion - Use of proteins to
      carry polar molecules or ions across
4. Active Transport- requires energy to transport
             molecules against a concentration
             gradient – energy is in the form of
             ATP
              Diffusion
• Movement of molecules from an area of
  high concentration to an area of low
  concentration.

• Movement from one side of a membrane
  to another, un-facilitated
Diffusion
Osmosis
    Tonicity is a relative term
• Hypotonic Solution - One solution has a
  lower concentration of solute than
  another.
• Hypertonic Solution - one solution has a
  higher concentration of solute than
  another.
• Isotonic Solution - both solutions have
  same concentrations of solute.
Plant and Animal Cells put into
       various solutions
Types of Transport
     Membrane Permeability
• Solute is eosin-starch-chloride solution
• Solvent is Water
• Indicator for presence of starch is IKI
• Starch is made of amylose and amylopectin –
  amylopectin is insoluble
• Iodine is not very soluble in water, but with KI
  it forms a I3- (triiodine ion) which is soluble.
• I3- combines with the amylose and the starch
  molecule turns blue-black.
Test for Starch
       Test for Chloride ions
• Indicator for presence of chloride ions is
  silver nitrate, AgNO3

  – A white precipitate, AgCl, forms if chloride
    is present.
        Test for Sulfate ions
• Indicator for the presence of sulfate ions
  is Barium chloride, BaCl
  – Barium sulfate, BaSO4 - forms a white
    precipitate
  – BaCl + NaSO4 ----> BaSO4 + NaCl
              Living Cells
• Beet cubes will be used to see the result of
  boiling and adding alcohol to a live
  membrane.
• Yeast cells are used to see effects of heat
• Fern gametophytes are used to see result
  of putting live cells in solutions of varying
  tonicity
                 Osmosis
• We will make an osmometer to see
  osmosis
• Sugar solution in a dialysis tube is used to
  simulate a cell membrane.
• Various concentrations of solute may be
  used around the room.

				
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