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Diffusion and Osmosis The Cell Membrane • Is the gatekeeper • Regulates what comes • in and out of the cell They are semipermeable; allow certain molecules and ions in and out • Found in both plant and animal cells Cell Wall • Found only in plant cells and bacteria cells • Main function is support • Have holes to allow stuff in and out Diffusion • The movement of molecules from an area of high concentration to an area of low concentration • Molecules tend to “spread out” and equalize • Requires no energy Equilibrium When molecules are evenly spread throughout a space Osmosis • The diffusion of water across a membrane • The cell membrane is selectively permeable and water is one of the lucky ones! • Watch the animation http://www.stolaf.edu/people /giannini/flashanimat/transp ort/osmosis.swf Rule for Osmosis •If the area outside the cell has more salt – then water will be sucked out of the cell •If the area inside the cell has more salt-then water will be sucked into the cell U - Tube Cells In Different Solutions Isotonic Solutions • “ISO" means the same • Amount of dissolved material is the same inside and outside the cell – Animal cells do well in this type of solution Hypotonic Solutions • “Hypo" means less • Amount of dissolved material is less outside the cell • Cells without a cell wall will swell and may burst in this solution • Cells with a cell wall will swell, but once firm the cell wall prevents any more water from entering the cell – Plant cells like this solution! Hypertonic Solutions • “Hyper" means more • Amount of dissolved material is more outside the cell • Cells without cell walls will shrink or die • Cells with cell walls will shrivel; the membrane will pull away from the cell wall • No cells like this solution and in both cases they may die So don’t be hyper! 1. Why is the water moving toward the left side of the beaker? 2. Which side of the beaker is hypertonic? WORD LIST •Diffusion •Osmosis •Selectively permeable •Equilibrium •Hypertonic •Hypotonic •Isotonic Know all of these words for the test
