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  • 1. Cell Membranes Osmosis and Diffusion
  • 2. 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
  • 3. Phospholipid Bilayer
  • 4. Fluid Mosaic Model
  • 5. Blood-Brain Barrier
    • Allows some substances into the brain, but screens out toxins and bacteria
    • Substances allowed to cross include:
      • water, CO 2 , Glucose, O 2 , Amino Acids, Alcohol , and antihistamines. HIV and bacterial meningitis can cross the barrier .
  • 6. 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.
  • 7. Methods of Transport Across Membranes
    • 1. Diffusion
    • 2. Osmosis
    • 3. Active Transport
  • 8. Methods of Transport Across Membranes
    • Diffusion -passive transport - no energy expended
    • Osmosis - Passive transport of water across membrane
    • 3. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP
  • 9. 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 demo
  • 10. Diffusion
  • 11. Osmosis
  • 12. 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.
  • 13. Plant and Animal Cells put into various solutions
  • 14. Types of Transport
  • 15. Today’s Lab
    • We are using dialysis tubing as the cell membrane - It is selectively permeable
    • The solute is either the eosin starch solution or the sugar solution
    • What is the solvent?
  • 16. 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 I 3 - (triiodine ion) which is soluble.
    • I 3 - combines with the amylose and the starch molecule turns blue-black.
  • 17. Test for Starch Elmhurst College Website
  • 18. Test for Chloride ions
    • Indicator for presence of chloride ions is silver nitrate, AgNO 3
      • A white precipitate, AgCl, forms if chloride is present.
  • 19. Test for Sulfate ions
    • Indicator for the presence of sulfate ions is Barium chloride, BaCl
      • Barium sulfate, BaSO 4 - forms a white precipitate
      • BaCl + NaSO 4 ----> BaSO 4 + NaCl
  • 20. 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
  • 21. 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.
  • 22. This powerpoint was kindly donated to is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.