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Biology LibreTexts

5: Diffusion and Osmosis

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    Diffusion and Osmosis

    (Adapted from


    Diffusion is the process by which molecules spread from areas of high concentration to areas of low concentration. This movement, down the concentration gradient, continues until molecules are evenly distributed. Osmosis is a special type of diffusion: the diffusion of water through a semipermeable membrane. The concentration of water is inversely related to the concentration of solute: more solute corresponds to less water and less solute corresponds to more water. This is important because osmotic vocabulary describes the solute and not the water. Hypertonic solutions contain a high concentration of solute and little water, relative to hypotonic solutions that have a low concentration of solute andtherefore a higher concentration of water. The term “isotonic” is used when two areas have an equalconcentration of solute: no net osmosis is occurring.