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Diffusion and Osmosis: Investigating the Processes of Diffusion and Osmosis in a Model Membrane System and the Effect of Solute Concentration on Water Potential as it Relates to Living Plant Tissues

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Introduction

Diffusion and Osmosis: Investigating the Processes of Diffusion and Osmosis in a Model Membrane System and the Effect of Solute Concentration on Water Potential as it Relates to Living Plant Tissues Mike Karp Partner: Elizabeth Moran Mead AP BIO 10/24/04 Abstract The purpose of this experiment was to understand the principles of diffusion, osmosis, and water potential. In the first section of this lab, we measured the diffusion of small molecules through dialysis tubing, an example of a selectively permeable membrane. The dialysis tubes were filled with 15% glucose and 1% starch. They were placed into a beaker with H2O and IKI. We analyzed the diffusion of glucose by recording color and presence of glucose in both the bag and the beaker. Next, we studied osmosis by investigating the relationship between solute concentration and the movement of water through a selectively permeable membrane. We were able to do this by filling dialysis tubes with distilled water and different molar concentrations of sucrose. We then placed the tubes into beakers filled with distilled water for 30 minutes. By recording the initial mass, the final mass after taking the tube out of the water, and calculating the mass difference and percent change in mass, we discovered how much osmosis took place. In the final exercise of the lab, we used potato cores placed in different molar concentrations of sucrose in order to determine the water potential of potato cells. This enabled us to explore what is meant by the term "water potential." ...read more.

Middle

Table 1.4 shows the initial and final mass of the potato cores in the different solution as well as the mass difference, percent change in mass, and class average percent change in mass. Table 1.5 shows the class data for the potato core results. Graph 1.1 shows the class average for the percent change in mass of the dialysis bags. The independent variable is the solution. The dependent variable is the percent change in mass of the dialysis bags. Graph 1.2 is the class average for the percent change in mass of the potato cores at different molarities of sucrose. The independent variable is the sucrose molarity within the beaker. The dependent variable is the percent increase or decrease in mass of the potato cores. Table 1.1 Initial Contents Solution Color Presence of Glucose Initial Final Initial Final Bag 15% glucose & 1% starch Cloudy clear Royal Blue Yes Yes Beaker H2O & IKI Amber Brown Amber Brown No Yes Calculations Table 1.2: Dialysis Bag Results - Individual Data Contents in Dialysis Bag Initial Mass (g) Final Mass (g) Mass Difference (g) Percent Change in Mass 0.4 M Sucrose 21.30 23.31 2.01 9.437 0.6 M Sucrose 21.65 25.18 3.53 16.305 Table 1.3: Dialysis Bag Results - Group Data Contents in Dialysis Bag Initial Mass (g) Final Mass (g) Mass Difference (g) Percent Change in Mass a) 0.0 M Distilled Water 21.87 21.84 -.03 -.137 b) 0.2 M Sucrose 16.58 17.40 .82 4.946 c) ...read more.

Conclusion

The higher the molarity of the sucrose in the bag, the more water diffused across the membrane from the beaker into the bag. This explains the increase in the mass of the bag from the initial to the final measurement. In exercise 1C, the potato was put in a solution of increasing molarity. Since the potato was hypotonic to the solution, water left the potato by osmosis and the potato shrunk in size. This was reflected by the increasingly negative percent change in its mass. There are believed to be no great errors that occurred during the experiment except in the 0.8 M and 1.0 M sucrose in the potato core lab. The percent change does not follow the trend it is supposed to follow. Experimental error could have been incorrectly weighing the mass of the cylinders. One would be able to identify an error by seeing a great change between intervals in the percent change in mass of the two experiments. As the molarity increases in exercise 1B, the percent change in mass should increase. As the molarity increases in exercise 1C, the percent change in mass should decrease. Future experiments could include testing a variety of molarities not used during this experiment or a different solution than sucrose. The results of this experiment are very significant. They help explain how cells of an organism can survive under changing conditions. Cells need to be able to obtain nutrients and rid themselves of waste. By osmosis and diffusion, this can be accomplished. ...read more.

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