Cell Structure and Function 6 Remernber that these molecules are polar and will attract water molecules around themselves in the form of hydration shells' The second conclusion we may draw is that atthough all solutions began as isoosmotic to the cell, the particular solutes we used in this exercise were not present in the cell at those concentrations. For example, although the total concentration of all solutes in the red blood cell is equivalentto 0.3M, the cell does not contain 0.3M of pure urea as is contained in a 0.3M urea solution. Therefore urea molecules, because they are small enough to cross the cell membrane, would initially diffuse into the cell. This diffusion creates an increase in the amount of solutes within the cell. The cell contents now become hypertonic to the outside solution and water moves into the cell by osmosis' The uncontrolled entry of water ultimately lyses the cells. We can, therefore, say that although the red blood cells and the test solutions were initially isoosmotic
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