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Biol1020-10.9-diffusion - Diffusion of water molecules...

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9 October 2006 Diffusion: Tendency for molecules to spread into an available space Concerns net movement of molecules Net movement moves down a concentration gradient At equilibrium, net movement ceases but molecular movement does not. Diffusion increases randomness (leads to increase in entropy) Therefore, diffusion is spontaneous Diffusion is passive transport; the cell does not have to expend energy for diffusion to occur Aspects that control rate of diffusion: Size of molecule: Smaller molecules diffuse faster, large molecules diffuse slower Temperature Increase in temperature=increase in rate of diffusion Permeability of membrane Concentration gradient Steeper concentration gradient=more rapid diffusion Osmosis:
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Unformatted text preview: Diffusion of water molecules across a semi permeable membrane Facts: ♦ 60% of adults consist of water and 70% of kids consist of water ♦ Most cell membranes have small transmembrane proteins which create channels called “Aquaporins” Osmotic pressure: ♦ Amount of pressure used to create equilibrium. ♦ Animal cells Terrestrial animals (like humans…) • 3 compartments: ♦ heart and blood vessels=8% of water content ♦ interior of cells=67% of water content ♦ spaces between cells and blood vessels=25% of water content ♦ Plant cells Like to be hypotonic Cell wall holds/controls water Cell wall is permeable to everything, but keeps cell from “blowing up”...
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