Osmosis & Diffusion Lab - Dialysis TubingBackgroundThe movement of molecules through a cell membrane is termed osmosis or diffusion. Such movement is principally possible because nutritive molecules are smaller than membrane micropores. If the molecules are too large, no molecular transfer, or diffusion occur.Thus, some membranes may transmit selectively and are termed semi-permeable membranes. In the following experiment, cellophane dialysis tubing serves as an excellent representation of the cell membrane. The enclosed tube may, for the purpose of this experiment, be considered a single living cell in greatly enlarged form.MaterialsGlucose Solution, Starch Solution, Iodine Solution, Glucose Test Strips, Dialysis Tubing, String, 400 ml Beaker, 10 mL Graduated Cylinder, Scissors, RulerProcedureMeasure ...view middle of the document...
Pour this into the tubing as well.Tie the second end of the tubing in an overhand knot and rinse it under the faucet. Set your "cell" on a clean surface.Fill the 400 ml beaker ¾ full with tap water. Add 10 drops of Iodine solution and stir well. (Iodine will turn blue-black in the presence of starch).Test the solution in the beaker for the presence of glucose by dipping a glucose test strip into it. After 30 seconds, compare the color on the strip to the color chart on the side of the bottle. Complete the Initial Status information on your data table.Place the artificial cell (the sealed tubing with solutions) into the beaker of solution and allow it to remain undisturbed for 15-20 minutes.Remove the tubing from the beaker and record your observations in the data table for final status of the solution and the bag.Retest the solution in the beaker and in the bag with a new glucose test strip and record this data in your table.Data Name __________________
Initial Solution Color
Final Solution Color
Initial Presence of Glucose
Final Presence of Glucose
15 % Glucose & 1% Starch
H2O + KI
Analysis of ResultsWhich substance(s) are entering the bag and which are leaving the bag?What experimental evidence supports your answer?Explain the results you obtained. Include he concentration differences and membrane pore size in your discussion.Quantitative data uses numbers to measure observed changes. How could this experiment be modified so that quantitative data could be collected to show that water diffused into the dialysis tubing?Based on your observations, rank the following by relative size, beginning with the smallest: glucose molecules, water molecules, KI molecules, membrane pores, and starch molecules.What results would you expect if the experiment started with glucose and KI solution inside the bag and only starch and water outside? Why?