Ap Biology Lab 1 Report

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Lab 1 Diffusion, Osmosis, and Water Potential of Glucose

Problem: What effects will glucose have on diffusion, osmosis, and water potential?

Background: All living things have certain requirements they must satisfy in order to remain alive. These include exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and eliminating wastes. These tasks ultimately occur at the cellular level, and require that molecules move through the membrane that surrounds the cell. There are two ways that the molecules move through the membrane: passive transport and active transport. Diffusion is the movement of molecules from a region in which they are highly concentrated to a region in which they are less concentrated. Diffusion occurs when a system is not at equilibrium. Several factors affect how fast a molecule will diffuse. The first of these is the kinetic energy of the molecule, which is most frequently measured as the temperature of the system. The size of the molecule also affects how rapidly it will diffuse. Diffusion can occur through a cell membrane. The membrane allows small molecules like water (H2O), oxygen (O2), carbon dioxide (CO2), and others to pass through easily. It is said to be permeable to these molecules. Osmosis is a special case of diffusion. In this case, a large molecule like starch, is dissolved in water. The starch molecule is too large to pass through the cell membrane, so it cannot diffuse from one side of the membrane to the other. The water molecules can, and do, pass through the membrane. Hence, the membrane is said to be semi-permeable, since it allows some molecules to pass through but not others. However, on the side of the membrane with the starch, the starch molecules interfere with the movement of the water molecules, preventing them from leaving as rapidly as they enter. Thus, more water flows into the side with the starch than flows out, and the starch gets diluted.
If the starch is in a cell, the water



References: Reece, Jane. Campbell, Neil. Biology Seventh Edition. San Francisco: Pearson, 2005 http://www.biologycorner.com/bio1/diffusion.html# http://hyperphysics.phyastr.gsu.edu/hbase/Kinetic/diffus.htm l

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