Lecture 14 - BIO 202 Notes Lecture 14: Osmosis, transport...

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BIO 202 Notes Lecture 14: Osmosis, transport across membranes Chapter 7: Membrane Structure and Function 1. 7.3 Passive transport is diffusion of a substance across a membrane with no energy investment 1. Diffusion: molecules of any substance spread out evenly into the available space 1. A result of heat (or thermal motion) which is molecular energy 2. Diffusion of a population of molecules may be directional 2. Concentration gradient: higher vs. lower concentrations 1. In the absence of other forces, a substance will diffuse down its concentration gradient 2. Substances are unaffected by the concentration differences of other substances 3. Passive transport: diffusion of a substance across a biological membrane 1. Cell does not have to expend energy 4. Effects of Osmosis on Water Balance 1. Osmosis: the diffusion of water across a selectively permeable membrane 1. Depends on difference in free water concentration 1. i.e. water clusters around hydrophilic substances 1. may no longer be small enough to cross a membrane 2. not free water 2. Water Balance of Cells Without Walls 1. Behavior of a cell in a solution depends on both solute concentration and membrane permeability 2. Tonicity: ability of a solution to cause a cell to gain or lose water 1. Partly depends on its own concentration of nonpenetrating solutes (cannot cross the membrane) relative to that the cell’s concentration 3. Isotonic to the cell: no net movement of water 4. Hyptertonic to the cell: net movement of water out of the cell 1. Cell loses water, shrivels up, and dies 5. Hypotonic to the cell: net movement of water into the cell 1. Cells swells and lyses (bursts) 6. Animals must live isotonic environments 1. Seawater is isotonic to many marine invertebrates 2. Cells of most terrestrial animals are bathed in an isotonic extracellular fluid
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This note was uploaded on 10/13/2008 for the course BIO 202 taught by Professor Dean during the Fall '08 term at SUNY Stony Brook.

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Lecture 14 - BIO 202 Notes Lecture 14: Osmosis, transport...

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