Lec 4.docx

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Biological Sciences
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Peter A.Bowler

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Lec 3 Oct 5 Water movement -Water moves from lower osmolarity to higher osmolarity (from higher water concentration to lower water concentration) Osmolarity: only makes sense in comparison to another solution Ho w about tonicity? -Describes behavior of a cell when placed in a solution and allowed to come to equilibrium -water is only going to move if there’s a difference in osmolarity -volume change of cell is caused by water movement across the membrane 5% dextrose in water—isomostic but hypotonic +hypotonic means water is moving into the cell (cell is swelling) +5% dextrose is in the cell +its hypotonic b/c 5% dextrose is permeable to the cell membrane and goes into the cell: this is modifying the osmolarity +-tonicity refers to the solution in relation to its effect on the cell When equilibrium is reached, which way will water have moved? -equal compartments of 1 M urea and 1 M glucose. -membrane is permeable to neither -now, membrane is permeable to water and urea (but not glucose) 1 OsM urea 1 M glucose water moves from left to right compartment to equalize its concentration and reach equilibrium, so water moves to the right towards glucose + urea that has moved How about movements of ions across membranes? +opposite charges attract +charges are attracted to opposite charge in electric field +voltage meter tells voltage of one point relative to the other point **commit this to memory!::: the inside of a “resting” cell is typically about -70 mV relative to the outside of the cell (ChECK WHAT TIMES OF IONS MOVE ACROSS MEMBRANE –NONPOLAR?) Which way will ions move across cell membranes? -K+ : cell K+ : -70mV - little K+ outside of c
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