Principles of Diffusion and Osmosis

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Diffusion and Osmosis Across Dialysis Tubing
By Jasper Lee, Leo Zhao, Oliva Skopas, Alistair Dobson, and Alex Bell
11/15/13

Purpose: The purpose of this experiment was to demonstrate the principles of diffusion and osmosis, two processes that are essential for life, by using dialysis tubing (a semi-permeable membrane) to simulate the cell membrane and observe said processes.

Introduction: Diffusion is the movement of molecules from a higher concentration to a lower concentration. Imagine you had a glass of water and put a drop of food coloring in. The molecules of food coloring would move from the initial site of the drop, which has an high concentration of the coloring, to the rest of the water, which has a low concentration. Eventually, the food coloring will spread out so that the entire glass of water has an equal concentration of it. At this point, the glass of water is in dynamic equilibrium - that is, the average concentration of the food coloring throughout the water is the same. Molecules are always moving, so there will be times when the food coloring happens to converge on one spot and leads to a higher concentration. However, on average the concentration is relatively equal. Osmosis is similar to diffusion, in that it is the movement of molecules from a high to low concentration. However, there are two major differences. The first one is that osmosis is the movement of water exclusively - the movement of any other molecule besides it is not considered osmosis. The second one is that osmosis is the movement of water across a selectively permeable membrane. A selectively permeable membrane is one that allows certain molecules through and blocks others. Whether or not a molecule can pass through the membrane usu...

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...velop, decreasing the accuracy of the experiment. While the simulations was generally accurate, there were major limitations that sharply decreased the similarity between it and the cell.
Works Cited
Brooklyn College. "Fluid Mosaic Model of Plasma Membrane." Fluid Mosaic Model of Plasma Membrane. Brooklyn College, n.d. Web. 16 Nov. 2013. .
National Kidney Foundation. "Dialysis." The National Kidney Foundation: A to Z Health Guide. National Kidney Foundation, n.d. Web. 16 Nov. 2013. .
Schmidt, Andrea. "Concentration Gradients." Concentration Gradients. MIT, n.d. Web. 16 Nov. 2013. .

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