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Biol 66-Lab 2

Biol 66-Lab 2. Diffusion, Osmosis, and Tonicity. Osmosis. The movement of water from a higher to lower water concentration. Two compartments separated by a semi-permeable membrane, such as a dialysis tubing

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Biol 66-Lab 2

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  1. Biol 66-Lab 2 Diffusion, Osmosis, and Tonicity

  2. Osmosis • The movement of water from a higher to lower water concentration. • Two compartments separated by a semi-permeable membrane, such as a dialysis tubing • Large molecules like glucose cannot move through membrane while water, a much smaller molecule, can and will

  3. Osmosis

  4. Osmosis Experiment • Use ring stand with the thistle tube • Obtain dialysis tubing, fold one end over twice (make folds the size of your finger) and seal the end with the orange plastic clip • Tie the other end to the rubber stopper on the thistle tube using thread • Fill dialysis tubing with the sucrose solution using long tube syringe. Make sure there are no air bubbles present. • Fill the beaker with distilled water and lower the dialysis tubing into the water until it is completely covered. Measure the height of the solution and begin the experiment.

  5. Osmosis Experiment • Start this experiment first as it takes some time to complete • Measure distance up the thistle tube every five minutes for the first thirty minutes, and every ten minutes there after until the solution has gone all the way up the thistle tube • Graph the results, and turn it in with the data sheet

  6. Diffusion • Passive movement of a substance down its concentration gradient from an area of high concentration to an area of low concentration • Diffusion is a function of: • Concentration gradient • Surface area over which diffusion occurs • Permeability of the substance • Temperature

  7. Diffusion • The instructor will perform this experiment at the front of the room • One beaker of warm water and one beaker of hot water will be set up • Potassium Permanganate will be dropped into both, and the difference in diffusion rate will be observed

  8. Solubility • Substances can have different solubilities depending on whether the substance prefers a polar or nonpolar environment • Some substances have polarity or charge and readily associate with the polar molecule water • Some substances are nonpolar, and thus are repelled by water. They will partition into a separate layer.

  9. Solubility • Perform experiment in the fume hood, which means one group at a time should perform this experiment. Wear gloves, goggles, and your lab coat • One person in the group should do the mixing and vortexing under the hood, another group member should bring the reagents in the order needed and pipette them into the tube • Waste should go into the chemical waste bottle in the hood

  10. Tonicity • Tonicity: (used with respect to a cell membrane): • isotonic: equal concentrations of osmotically active solute on both sides of membrane • Hypotonic: lower solute concentration outside membrane • Hypertonic: higher solute concentration outside membrane • Concept of Osmolarity • (# particles) x (molarity of solute) • Osmotic Pressure is proportional to Osmolarity

  11. Tonicity Experiment • This part of the lab deals with human blood. Wear gloves and a lab coat. Stay in the red taped square. • Set up small test tubes with each of the salt solutions available • Obtain blood by using the lancet, and pool the blood on a piece of parafilm • With a Pasteur pipette add a drop of blood to each of the salt solutions

  12. Tonicity Experiment • Cover tube with parafilm and vortex in hood. Alternatively, “tickle” the test tube and mix the contents • Place a drop of each on a microscope slide and observe the appearance of the red blood cells

  13. Homeostasis • Maintenance of a constant internal environment via negative feedback loops • We will examine this concept by looking at pulse rate, which is an example of a measurement in your body that is not a constant, but varies around a set point • We will examine this point by looking at how pulse rate changes over time in exercisers and non-exercisers (students self identify as regular exercisers or not)

  14. THE END

  15. Stoichiometry • Molarity (M)= # of moles of a solute/ liters of solution • Millimolarity (mM)= millimoles of solute/ liters of solution • Osmolarity (osM)= moles x the number of particles • Milliosmolarity (mOsm)= millimoles x the number of particles in solution

  16. Stoichiometry • 1 mole= 6.02x1023 particles • Molecular weight (MW) gives us the number of grams in one mole of the substance • Ex. The MW of water is 18, which means if you have 6.02x1023 water molecules they will collectively weigh 18 grams

  17. Stoichiometry • You add 12 grams of NaOH (MW=40) into 300 ml of water, what is the molarity of the solution made? • 12 grams x (1mol/40 grams) = 0.3 moles NaOH • 300ml (1L/1000ml) = 0.3 L water • M=moles/L • 0.3 moles/0.3L • You made a 1M solution of NaOH

  18. Stoichiometry • You add 10 grams of KCl (MW=64) to 500 ml of water, what is the milliosmolarity of the solution? • 10 grams KCl (1mole/64 grams) = 0.16 moles • 500ml of water(1L/1000ml) = 0.5L • 0.16 moles KCL/0.5L water = 0.31M • 0.31 M (1000mM/1M) = 312.5mM x 2 particles • =625 mOsm

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