Osmosis And Diffusion Essay

1698 words - 7 pages

Introduction: Osmosis and diffusion are two processes that occur constantly among cells.  When the concentration of a solution differs inside and outside of a cell the solution will diffuse through until it reaches equilibrium. Osmosis occurs in the cell’s permeable membrane.  In this lab, dialysis tubing is used to represent the selectively permeable membrane in a cell. Dialysis tubing is made from cellulose or cellophane to allow water or smaller molecules diffuse through it.   In selectively permeable membranes, solutions travel across their concentration gradients by osmosis. During osmosis, there are three diverse types of solutions that move across the gradient in different ...view middle of the document...

This experiment is proving that in a selectively permeable membrane enclosing a sucrose solution, water will diffuse into it.  This is because there is a low concentration of water inside the solution, so what moves in.  Proving that inside the dialysis bag is a hypotonic solution.   
Materials and Methods: 
Procedure 1A:
Take a 30-cm piece of dialysis tubing that has been soaking in water.  Tie off one end to form the bag.  Test the 15% glucose/1% starch solution for glucose.  Record the results.  Put 15 mL of the 15% glucose/1%starch solution in the bag and tie off the other end.  Record color.  Fill a 250 mL beaker with distilled water.  Add 4 mL of Lugol’s solution to the distilled water and record color.  Test the solution for glucose and record the results.  Next put the bag in the beaker with the solution.  Let this stand for 30 minutes or color change.  Record final colors in both bag and solution.  Test the beaker and the bag for the presents of glucose and record in data table. 
Procedure 1B:           
To start the experiment take 30-cm strips of precut dialysis tubing and make them into bags by tying knots in the end, and pour about 15-25 mL; though the amount of the solution won’t affect the outcome, of the following solutions into separate bags: a.) tap water, b.) 0.2 M sucrose, c.) 0.4 M sucrose, d.) 0.6 M sucrose, e.) 0.8 M sucrose, f.) 1.0 M sucrose. Then remove all the air from the bag and tie another knot at the end, but leave room for expansion of the contents.   Make sure to rinse each bag of possible excess sucrose.  Record the mass of each bag expressed in grams.  Fill 250- mL beakers with tap water and put one dialysis bag in each one.
Let them stand for 30 minutes before drying them and taking a second measurement. Take data and record it in a chart that includes the initial mass, final mass, mass difference, and Percent change of each solution.  Also record the percent changes from the rest of the experiments. 
Procedure 1C:
Pour 100 mL of a solution into a 250 mL beaker and cut 3 cm. thick slices of potatoes.  Use a cork borer to make four potato cylinders, not including potato skins.  Use four potatoes per beaker.  Keep potatoes covered until they are weighed to keep air from touching them.  Record the mass of potatoes.  Put the potatoes into the sucrose solution.  Cover the solution and let sit overnight.             
Following day, remove potatoes from the solution, blot excess solution, and weigh.  Record the final mass and the class data in table.  Graph all results. 
Results: The following results were recorded both in class and later on in a computer program. 
1A. Table 1.1
|  |  |Solution color |  |Presence of glucose |  |
|  |Initial Contents |Initial |Final |initial ...

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