Lab 1- Osmosis and Diffusion Abstract

In this lab three different experiments were performed. For experiment 1A, the purpose of the experiment was to determine the direction of diffusion of small molecules. In exercise 1B, the purpose of the experiment was to determine the relationship between solute concentration and the movement of water through a membrane by osmosis. In the final part of the experiment, the purpose was to determine the water potential of potato cells.

Experiment 1A was performed as a class. In experiment one 1A, the solution with 15% glucose and 1 % starch was tested for the presence of glucose. This solution was then place in the bag and after tying off the ends of the bag the color of the solution was recorded. Also, a 250 ml beaker was filled with distilled and 4 ml of Lugol’s solution was added to the distilled water. The color was again recorded and the solution was also tested for glucose and the result was recorded. Following that, the bag was placed in the beaker and after 30 minutes the finally color of the solution in the bag and beaker were recorded. Then both were tested for the glucose again. The result was that the bag initially tested positive for glucose. However a second test was not taken. The beaker did not test positive for glucose initially. Again the beaker was also not tested a second time. The color of the bag was originally colorless and then it became an orange color. The beaker originally was an orange color, but then after 30 minutes was more colorless. In the second experiment, 6 dialysis tubes were created and each was filled with 15 ml of different solutions. The first dialysis tube was filled with distilled water, the second with 0.2 M sucrose, the third with 0.4 M sucrose, the fourth with 0.6 M sucrose, the first with 0.8 M sucrose, and the sixth with 1.0 M sucrose. The initial mass of each bag was then found and recorded in grams. After the initial mass was recorded, each bag was placed into an empty 250 ml beaker and each beaker was filled two third full with distilled water. They were then left to sit for 30 minutes. After 30 minutes each bag was removed and then the mass of each bag was determined again. These masses were again recorded and then the mass difference and percent change in mass was calculated out. Our results showed a 4.52 % mass difference in the dialysis bag with distilled water, a 4.61 % difference in the dialysis bag with 0.2 M sucrose, a 9.47% difference in the bag with 0.4 M sucrose, a 6.20 % difference in the bag with 0.6 M sucrose, a 15.40 % difference in the bag with 0.8 M sucrose, and a 18.11% difference in the bag with 1.0 M sucrose. In the final experiment, or exercise 1C, four cylinders or potatoes were cut out using a cork borer. The mass of the four cylinders was recorded and then placed into the beaker. The beaker was filled with distilled water and a plastic wrap was placed over the beaker to prevent evaporation. The potatoes were left submerged in the beaker over night. The next day the cores were removed from the beakers and the mass was again determined. Our initial mass was 3.73 grams. The final mass was 4.31 grams. The mass difference was .61 grams and the percent change in mass was 16.35%.

This experiment is useful because it shows which direction substances will flow or diffuse. The way in which substance flow is important because it allows our bodies to function properly. For example, in the body the protein albumin regulates blood volume by maintaining the osmotic pressure of the blood compartment.

Mindy WuPeriod 2

February 17, 2008