Investigating Osmosis Through Living Membranes

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| Investigating Osmosis Through Living Membranes | Introduction: Diffusion is the tendency of molecules or ions to move from an area where they are in higher concentration to an area where they are in lower concentration, that is, down or along their concentration gradient (Marieb 2013). Osmosis is a special case of diffusion defined as the diffusion of a solvent, such as water, through a selectively permeable membrane (Marieb 2013). Osmosis occurs whenever the water concentration differs on the two sides of a membrane. Take a U-shaped container filled with a solution and separate the container into left and right compartments by a permeable membrane. Normally, net diffusion of both solute and water occurs until the concentration of water (and solute) is the same on both sides of the membrane (equilibrium). When the membrane is impermeable to solutes it creates a different result. In this situation, water diffuses from the side with lower solute concentration to the side with higher solute concentration. This continues until its concentration is the same on the two sides of the membrane. The movement of water leads to dramatic changes in the volumes of the two compartments. Osmosis in red blood cells affects the tonicity of the cells. Tonicity refers to the ability of a solution to change the shape or tone of cells by altering the cells’ internal water volume (Marieb 2013). Changes in the concentration of water on either side of the cell membrane result in a net loss or gain of water by the cell (Marieb 2013). If cells are exposed to a solution that has the same solute/water concentration as inside the cells, the solution is said to be isotonic. In an isotonic solution, cells retain their normal size and shape because the same volume of water moves into and out of the cell. If cells are exposed to a solution that contains higher concentration

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