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Lab #5

Lab #5. Osmosis, Tonicity, and Measurements of Concentration. Diffusion and Concentration. Solute particles diffuse from regions of high concentration to regions of low concentration Proceeds until equilibrium reached. Lecture Text Fig 6.2. Diffusion and Membrane Transport.

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Lab #5

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  1. Lab #5 Osmosis, Tonicity, and Measurements of Concentration

  2. Diffusion and Concentration • Solute particles diffuse from regions of high concentration to regions of low concentration • Proceeds until equilibrium reached Lecture Text Fig 6.2

  3. Diffusion and Membrane Transport • Lipid bilayer determines what substances can readily pass through a cell membrane • if bilayer is permeable, simple diffusion • if bilayer is impermeable, no simple diffusion Fig 2.8

  4. Membrane Permeability • Size • the smaller the particle, the more permeable • small molecules (O2, CO2,H2O) can • large molecules (protein, DNA) cannot • Lipid Solubility • YES: non-polar molecules (O2, cholesterol), • NO: charged atoms/molecules (Na+, Cl-, HCO3-), large polar molecules (glucose)

  5. Osmosis • Net diffusion of water across a semi-permeable membrane • diffusion of the solvent, not the solute Fig 2.9; Lecture Text Fig 6.6

  6. Osmosis • For osmosis to occur: • the membrane must be permeable to water and impermeable to at least one of the solutes in the solution • there must be a difference in solute concentration between the two sides of the membrane

  7. Lab Exercise:Osmometer • Obtain thistle tube assembly • Remove stem • Fill bell with sucrose solution • Replace stem • Place in water • Mark meniscus Fig 2.10

  8. Measures of Concentration • g/dL or % • convenient, but does not indicate # molecules/volume solution • Molarity • moles solute/L solution • Molality • moles solute/kg solvent • Osmolality • moles of osm. active solutes/kg water • Tonicity • effect of differences in osmotic pressure on net movement of water

  9. Moles • Mole = 6.02 x 1023 particles • Mass of one mole of a substance = the atomic/molecular weight in grams • # moles = mass (g) / m.w. (g/mole)

  10. Molarity # moles solute / L solution Units = Molar (M) • 1 M = 1 mole/L solution Calculation • STEP 1: Determine # of moles solute (g/mw) • STEP 2: Divide # moles by solution vol. in liters

  11. Molality (m) • # moles solute / kg solvent • for water, 1 kg = 1 L • Units = molal (m) • 1 m = 1 mole/kg solvent • Calculated similar to molarity Lecture Text Fig 6.8

  12. Osmotic Concentration: Osmolality (Osm) • total # of moles of solute particles dissolved in a given volume of water • Units = Osmolal (Osm) • 1 Osm = 1 mole / kg water • osmolality depends on the number of solute particles, not the specific type of solute particles • Calculation • Determine total moles solutes (g/mw for each individual solute) • Divide by kg water Lecture Text Fig 6.9

  13. Osmolality and Dissociation • Ionic compounds dissociate in water • ionic bonds are broken • Increases the # of solute particles in the solution • e.g. NaCl  Na+ + Cl- • 1 m NaCl solution has an osmotic concentration of 2 Osm • Calculation • Determine # moles of each solute • Multiply # moles of ionic compounds by the number of particles created by dissociation • Add up total moles of particles • Divide by kg water Lecture Text Fig 6.10

  14. Tonicity • Comparison of differences in osmotic pressure between two solutions separated by a semi-permeable membrane • e.g., intracellular fluid and extracellular fluid • Effect of differences in osmotic pressure on osmotic movement of water

  15. Tonicity • if [osm]ECF = [osm]ICF • osmosis will not occur • extracellular fluid is isotonic • if [osm]ECF > [osm]ICF • water will flow out of the ICF into the ECF • extracellular fluid is hypertonic • if [osm]ECF < [osm]ICF • water will flow out of the ECF into the ICF • extracellular fluid is hypotonic

  16. Exercise:Tonicity of Erythrocytes • Observe cells in saline solutions of different concentrations • Hypotonic • Isotonic • Hypertonic

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