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  • 1. Diffusion and Osmosis
  • 2. Outline• Learn the concepts of: – Diffusion, osmosis, semi-permeable membrane, isotonic, hypertonic, & hypotonic• Explore diffusion in a colloid – Relationship between diffusion & size 1 4 2• Explore diffusion & osmosis in a 3 dialysis bag – Dialysis bag experiment – Semi-permeable membrane – Water, glucose, starch• Plant/animal cells exposure to water – Hypertonic Env. – Hypotonic Env. – Isotonic Env.
  • 3. Diffusion• Solute molecules moving from an area of high concentration to an (water) area of low concentration – Random motion drives diffusion – Movement is based on kinetic energy (speed), charge, and mass of molecules 1 2 4 – Equilibrium is reached when there is an even distribution of solute molecules 3
  • 4. Osmosis• Diffusion of water through a semi- permeable membrane – Semi-permeable: permeable to solvents (WATER), but not to large molecules – High [water] to low [water]• Dissolved molecules (i.e. glucose, starch) are called solutes• REMEMBER: Water = solvent Glucose, Starch = solutes
  • 5. Diffusion Rates of Various Dyes• How do different MW solutions migrate through a 2 colloid? 1 3• Colloid – suspension of large, insoluble particles in a fluid medium 6 4 – Agar plate 5• Measure the rate of diffusion of various dye (differ in MW)• Measure diameter at T90  3 known(s) (crystal violet, malachite (minutes) green, potassium permanganate)  3 unknowns Part 1 pg. 82
  • 6. Diffusion Rates of Various Dyes• How do different MW solutions migrate through a colloid?• Standard Curve – Y-axis: molecular weight (MW) – X-axis: distance migrated ? (mm) Inverse Relationship • Higher MW, slower diffusion • Lower MW, faster diffusion
  • 7. Dialysis Bag Experiment• Dialysis Bag – Semi-permeable membrane – Water, glucose, & starch Dialysis bag Glucose• What passes through the dialysis bag? Iodine – Glucose (Benedict’s Test) Starch – Starch (Iodine Solution) T0 T80• Time Course Experiment – Every 10 minutes, measure the amount of glucose & starch present in the beaker Weigh Weigh Part 2 pg. 83
  • 8. Dialysis Bag Experiment - Results Lab Manual, page 84
  • 9. Dialysis Bag Experiment - ControlsNegative control for dialysis bag experiment (performed by TA)• Instead of using dialysis tubing, I will be using a plastic bag.• I will determine the weight, Benedict‘s result, & iodine results attime 0 and 80 minutesBiochemical test controls (in pairs)• set up test control of iodine test w/ glucose and starch• set up test control of Benedict‘s test w/ glucose and starch Iodine Benedict’s Glucose ? ? Starch ? ?
  • 10. Effect of Water on Cells• Hypertonic Environment – High [solute], low [water]• Hypotonic Environment – High [water], low [solute] Hypertonic Hypotonic• Isotonic Environment – [water] = [solute] Isotonic Part 3 pg. 85
  • 11. Osmosis in Living Cells Cellulose in cell wall
  • 12. Osmosis in Red Blood Cells• Observe sheep RBCs via a wetmount of the sample Isotonic• Aliquot one drop the followingsolutions with a ½ drop of RBC to Crenationa slide 0.9% saline 10% NaCl Predictions? Hypertonic Distilled water• Record observation in the tableon page 85 Hypotonic
  • 13. Osmosis in Plant Cells Plasmolysis• Observe Elodea leaves via a wetmount of the sample• Aliquot two drops the followingsolutions with a new Elodea leafto a slide. Incubate for 10 Hypertonicminutes @ room temp. 10% NaCl Predictions? Distilled water• Record observation in the tableon page 85 Hypotonic
  • 14. Plan of attack . . . Set-up Part I – Molecular Weight Diffusion in Colloid  Incubate for 90 minutes Set up Part II – Dialysis Bag  Time course: 80 minutes (time-point every 10 minutes) Part III – Osmosis in Living Cells
  • 15. AnimationsDialysis Bag Experiment• Cell••
  • 16. Transportation of Molecules• Passive Transport -Movement of molecules across a semi-permeable membrane - no energy required• Active Transport -Movement of molecules across a semi-permeable membrane against a concentration gradient with a protein - ENERGY – ATP• Facilitated Diffusion -Movement of molecules across a semi-permeable membrane with a protein - no energy required
  • 17. Effect of Water on RBC