2Diffusion and Osmosis Overview You will investigate diffusion and osmosis in a model membrane systemYou will investigate the effect of solute concentration on water potential as it relates to living plants.
14Water Potential In Potato Cells Osmosis is a special type of diffusion. It is the movement of water molecules through a selectively permeable membrane from a region of higher water potential to an area of lower water potentialWater potential is the measure of free energy of water in a solutionWater always moves to a more negative water potential.
15Water Potential = Yp + Ys Where there is no % change in mass, the solution in the beaker has the same water potential as the potato cells.(Y = Yp + Ys) = (Y = Yp + Ys)Beaker PotatoYp = 0 (open beaker) so Y = Ys
16To Calculate Ys See page 13 of the lab Ys = -iCRT i = Ionization constant (sucrose is 1.0 because it does not ionize).C = Molar Concentration (from line of best fit where the line crosses the x axis)R = Pressure Constant ( liter bars/mole °KT = Temperature °K (273 + °C)
17So lets say the line of best fit crosses the x axis at 0.36…….. Ys = -iCRTYs = -(1.0)(0.36 mole/liter)( liter bar/mole ° K)(295 ° K)-8.83 barsThis equals the entire Y of the cell