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Osmose and diffusion Selective permeability Review: the cell membrane controls the exchanges done between the exterior of the cell and the interior of the cell. If the cell membrane lets only certain substances go in or go out of the cell, we say it is has selective permeability. Only certain molecules are allowed in or out of the cell Diffusion • • • • Diffusion is the movement of particles of solute. From an area of high concentration to low concentration It is by diffusion that particles enter and exit the cell. The semi-permeable membrane lets the solute particles travel through because they are small. Examples of diffusion • The yellow food coloring that we put in water diffuses until it is equal all over the water: • When someone cooks, the smell disperses all over the house. • It goes from most concentrated (the kitchen) to least concentrated (a bedroom) Osmosis -The cell is composed of 70% of water -Molecules of water are small and can pass through the cell membrane. -Osmosis is the movement of the water, which is the solvent. If the solute if too big to go through the cell membrane, the water will go through instead. -The movement of the water is determined like diffusion: -Most concentrated area of water to an area of less water -This is done to dissolve the area that doesn’t have enough water. The sugar molecule is too big to go through the membrane, so the water will go through. Interesting web sites! http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_diffu sion_works.html http://www.wiley.com/legacy/college/boyer/0 470003790/animations/membrane_transport/ membrane_transport.htm Animal Cell Plant cell Result: Hypotonic Isotonic Hypertonic Here, there is not enough water inside the cell, so the water from the outside goes in. Here the concentrations are equal: ideal situation Here there is not enough water outside of the cell, so the water must must come out. The cell inflates The cell’s shape does not change The cell shrivles.