Objective: In this lab we observed osmosis across a semi permeable membrane. Through this experiment, we were able to see the concept of osmosis in action as the water moved from areas of low solute (sucrose) across a membrane areas of higher solute concentration. Another concept we learned in this lab was how tonicity of a solution can affect osmosis into and out of a cell.
Materials and Methods: For the first part of this lab, we got a piece of dialysis tubing and used a clamp-to-clamp one end of the tube to make a bag. We then filled the bag with 0.5 M sucrose and put a pipette in the open end to measure the movement of water into the bag. We then put the bag of sucrose into a beaker of distilled water and recorded the change in volume in the pipette over 2.5 minute time intervals for 10 minutes. We then got a new dialysis bag and repeated the same experiment again, except we used a 1.5M sucrose solution. We put together the entire class’ data into excel and calculated the average and standard deviation for each time period in each concentration, and then generated a graph using the averages. For the second part of the experiment, we used dog red blood cells to observe the effects of tonicity on osmosis and in turn what happens to cells in different solutions, isotonic, hypertonic, and hypotonic. For this experiment, we observed normal dog red blood cells under a microscope. Next, we added one drop of blood and one drop of solution A to a test tube, mixed and then put on a slide with cover lens and observed the effects of osmosis due to the tonicity of the saline solution and the effects on the cell. We repeated the experiment for solution B and C and then determined which solution corresponded with the appropriate tonicity of isotonic, hypertonic, and hypotonic based on our observations.
Results: In the experiment with the dialysis bag, we observed a steady increase in volume of 0.01mL ever 2.5 minutes for the sucrose bag with a concentration of 0.5M. When we repeated the experiment with the 1.5M concentration of sucrose
