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Potato IA Lab. This experiment tested osmosis when dealing with different concentrations of salt on the outside of the membrane.

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Introduction

Abstract: Osmosis is the diffusion of water across a semi-permeable membrane. This experiment tested osmosis when dealing with different concentrations of salt on the outside of the membrane. If there is a higher concentration of salt on the outside of the membrane, then water will move across the membrane to the outside in order to reduce the concentration of salt. This hypothesis was supported by the data from this experiment because it shows the weight of the potato cores decreased at higher levels of salt concentration. Introduction: The purpose of this experiment was to show the relationship between osmosis and the salinity in a solution. Water naturally diffuses across membranes from areas of lower salinity to areas of higher salinity. Osmosis is the net movement of water across a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane. (Bowen, 2000). When the concentration of dissolved salt is greater outside the semi-permeable membrane, the solution is hypertonic and water will diffuse across the membrane from the inside to the outside in order to reduce the salinity outside the membrane (Gross, De Zeeuw & Simpao, 2001). "Water molecules are able to pass through most biological membranes, so salinity imbalances within biological systems are naturally corrected via the diffusion of water across semi-permeable membranes to equalize salt concentrations on both sides of the membrane" (Gross, De Zeeuw & Simpao, 2001). ...read more.

Middle

The thermometer was then used to record any variations in temperature between the cups. The 1 cm diameter corer was used to create cores in the potato longer than 2 cm. A knife and a ruler were used to create 2 cm cores. This was repeated until 45 cores were created. The cores were separated into groups of 3 and weighed on a triple beam balance. Then, 3 cores were placed in all 15 cups. The cups were placed off to the side for 48 hours. After sitting for 48 hours, the thermometer was used to measure the temperature of the solution and any variations were recorded. All 15 cups were then drained in the sink. The 3 cores in each cup were blotted to remove excess moisture and weighed on a triple beam balance. The weight was recorded for each cup, noting the change between beginning and ending weight. Data: 0.0 M Salt Tests Weight Before (g) Weight After (g) Change (g) % Change Test 1 3.6g 3.7g +.1g 2.7% Test 2 3.6g 3.0g -.6g -16.6% Test 3 3.5g 3.8g +.3g 8.6% Test 4 3.6g 3.8g +.2g 5.6% Test 5 3.6g 3.0g -.6g -16.6% Average 3.6g 3.5g -.6g -3.3% 0.5 M Salt Tests Weight Before (g) ...read more.

Conclusion

This experiment could have been improved by using a more accurate scale. An electronic scale might have been able to measure the salt more precisely. Also, the excess moisture of the potatoes was taken off after they sat in the solution by blotting them on a paper towel. There was no way to measure this, and some potato cores may have had more moisture taken off than others, skewing results. However, I do not believe this would have affected the results enough to change the conclusion that the hypothesis was supported by this experiment. I would be interested to test how different types of salt, such as sea salt or kosher salt, affect the osmosis in potato membranes. I would like to redo my first group of 0.0 M solution because 2 of the results from those cups were abnormal and unexpected. While 3 of the cups gained a little bit of weight (approximately .2 g), 2 of the cups lost .6 g of weight. This seems very inconsistent and it leads me to believe that I made an error in my tests. Acknowledgements: I would like to thank my mother for purchasing the potatoes, cups, and distilled water. I would also like to thank my friends for their support. Literature Cited: Gross, C., De Zeeuw, J., & Simpao, T. (2001, April 27). Awesome Osmosis. Retrieved from http://marinediscovery.arizona.edu/lessonsS01/blennies/2.html Bowen, R. (2000, July 02). Portrait of a cell. Retrieved from http://www.vivo.colostate.edu/hbooks/cmb/cells/pmemb/osmosis.html ...read more.

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