BIOL107 Lecture Notes - Lecture 8: Paramecium, Dynamic Equilibrium, Plasmolysis
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Diffusion is the tendency for molecules to spread evenly into available space. Each molecule moves randomly, but diffusion of a population of molecules may be directional. Dynamic equilibrium, as many molecules cross membrane in one direction as in the other. Free movement across the membrane down a concentration gradient (high to low) Movement of water is sub-class of passive diffusion (osmosis) The tonicity is the ability of a surrounding solution to cause cells to gain or loser water. Solute concentration is the same as that inside cell. Solute concentration greater than that inside cell - cell loses h2o. May lead to shriveling of an animal cell. Solute concentration is less than that inside the cell - cell gains h2o. Plant cell in hypotonic solution swells until wall opposes uptake; it is turgid (firm) Plant cell in isotonic environment, not net movement of water, : it is flaccid (limp)