Lec 3 Oct 5
-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+ : -70mV
little K+ outside of c