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  1. 1. Cell Membranes Osmosis and Diffusion
  2. 2. Functions of Membranes <ul><li>1. Protect cell </li></ul><ul><li>2. Control incoming and outgoing substances </li></ul><ul><li>3. Maintain ion concentrations of various substances </li></ul><ul><li>4. Selectively permeable - allows some molecules in, others are kept out </li></ul>
  3. 3. Phospholipid Bilayer
  4. 4. Fluid Mosaic Model
  5. 5. Blood-Brain Barrier <ul><li>Allows some substances into the brain, but screens out toxins and bacteria </li></ul><ul><li>Substances allowed to cross include: </li></ul><ul><ul><li>water, CO 2 , Glucose, O 2 , Amino Acids, Alcohol , and antihistamines. HIV and bacterial meningitis can cross the barrier . </li></ul></ul>
  6. 6. Solutions <ul><li>Solutions are made of solute and a solvent </li></ul><ul><li>Solvent - the liquid into which the solute is poured and dissolved. We will use water as our solvent today. </li></ul><ul><li>Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes. </li></ul>
  7. 7. Methods of Transport Across Membranes <ul><li>1. Diffusion </li></ul><ul><li>2. Osmosis </li></ul><ul><li>3. Active Transport </li></ul>
  8. 8. Methods of Transport Across Membranes <ul><li>Diffusion -passive transport - no energy expended </li></ul><ul><li>Osmosis - Passive transport of water across membrane </li></ul><ul><li>3. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP </li></ul>
  9. 9. Diffusion <ul><li>Movement of molecules from an area of high concentration to an area of low concentration. </li></ul><ul><li>Movement from one side of a membrane to another, un-facilitated </li></ul><ul><li>diffusion demo </li></ul>
  10. 10. Diffusion
  11. 11. Osmosis
  12. 12. Tonicity is a relative term <ul><li>Hypotonic Solution - One solution has a lower concentration of solute than another. </li></ul><ul><li>Hypertonic Solution - one solution has a higher concentration of solute than another. </li></ul><ul><li>Isotonic Solution - both solutions have same concentrations of solute. </li></ul>
  13. 13. Plant and Animal Cells put into various solutions
  14. 14. Types of Transport
  15. 15. Today’s Lab <ul><li>We are using dialysis tubing as the cell membrane - It is selectively permeable </li></ul><ul><li>The solute is either the eosin starch solution or the sugar solution </li></ul><ul><li>What is the solvent? </li></ul>
  16. 16. Membrane Permeability <ul><li>Solute is eosin-starch-chloride solution </li></ul><ul><li>Solvent is Water </li></ul><ul><li>Indicator for presence of starch is IKI </li></ul><ul><li>Starch is made of amylose and amylopectin – amylopectin is insoluble </li></ul><ul><li>Iodine is not very soluble in water, but with KI it forms a I 3 - (triiodine ion) which is soluble. </li></ul><ul><li>I 3 - combines with the amylose and the starch molecule turns blue-black. </li></ul>
  17. 17. Test for Starch Elmhurst College Website
  18. 18. Test for Chloride ions <ul><li>Indicator for presence of chloride ions is silver nitrate, AgNO 3 </li></ul><ul><ul><li>A white precipitate, AgCl, forms if chloride is present. </li></ul></ul>
  19. 19. Test for Sulfate ions <ul><li>Indicator for the presence of sulfate ions is Barium chloride, BaCl </li></ul><ul><ul><li>Barium sulfate, BaSO 4 - forms a white precipitate </li></ul></ul><ul><ul><li>BaCl + NaSO 4 ----> BaSO 4 + NaCl </li></ul></ul>
  20. 20. Living Cells <ul><li>Beet cubes will be used to see the result of boiling and adding alcohol to a live membrane. </li></ul><ul><li>Yeast cells are used to see effects of heat </li></ul><ul><li>Fern gametophytes are used to see result of putting live cells in solutions of varying tonicity </li></ul>
  21. 21. Osmosis <ul><li>We will make an osmometer to see osmosis </li></ul><ul><li>Sugar solution in a dialysis tube is used to simulate a cell membrane. </li></ul><ul><li>Various concentrations of solute may be used around the room. </li></ul>
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