Investigation 4:Diffusion and Osmosis Lab Overview You will investigate diffusion and osmosis in a model membrane system You will investigate the effect of solute concentration on water potential as it relates to living plants.

Diffusion & Osmosis

Investigation 4: Diffusion & Osmosis Description A. Diffusion: dialysis tubing filled with starch-glucose solution in beaker filled with KI solution (demo) B. Osmosis: dialysis tubing filled with different molarity sucrose solution in beaker filled with distilled water C. Water Potential potato cores in different concentrations sucrose solutions

Investigation 4: Diffusion & Osmosis Concepts semi-permeable membrane diffusion osmosis solutions hypotonic hypertonic isotonic water potential

Molarity C6H12O6 = glucose Sucrose = 2 glucose C6H12O6 + C6H12O6 = C6H12O6 - H2O = C12H22O11 so Using the periodic table, you can calculate molar mass of sucrose ~(342g)

So to make 500 ml of solution……. 342 x 1.0 x .5 0.2 M = 342 x .2 x .5 etc

Prepare dialysis bags…… Add sucrose solutions to bags Mass carefully Place in distilled water for 30 minutes Re-mass Calculate the % change in mass

Final Mass-Initial Mass Initial Mass To Calculate the % change in mass: Final Mass-Initial Mass Initial Mass X 100

Diffusion and Osmosis

Concentration Effect

Water Movement Water moves along energy gradient From high energy to low energy What forces cause water to move? Pressures Gravity Forces created by organisms Osmotic gradients Matric forces (adsorption) These forces are all components of water potential

Water potential is abbreviated with the Greek symbol Psi, Y So, what is water potential? energetic state of water availability of water potential energy - capacity for water to do work (exert a force over a distance) Water potential is abbreviated with the Greek symbol Psi, Y

Water potential How does water move? Why does water move? 1. Downhill Pressure potential 2. Hose, straw 3. Fresh – salty Osmotic potential 4. Sponge Matric potential Water potential describes water concentration Water moves down gradients of water potential,

Components of Water Potential Pressure potential: pushing (positive pressure, like the hose) or sucking (negative pressure, like a straw) Major factor moving water through plants Osmotic, or Solute potential: reduction in water potential due to the presence of dissolved solutes Dissolved substances dilute pure water, so salty water has lower water potential (lower concentration) than pure water Matric potential: reduction in water potential due to the presence of matric forces (tendency for water to adhere to surfaces) Matric potential dominates soil water

Water 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 potential Water potential is the measure of free energy of water in a solution Water always moves to a more negative water potential.

Water 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 Potato Yp = 0 (open beaker) so Y = Ys

To Calculate Ys 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 (0.0831 liter bars/mole °K T = Temperature °K (273 + °C)

Data Table M 1.0 0.8 0.6 0.4 0.2 0.0 % Change In Mass Period 1 Gr 1 Class Av 1.0 0.8 0.6 0.4 0.2 0.0

Data Table

Lab 1C: Class Averaged Data over Years Contents in Beaker % Change in Mass Distilled Water 21.4 0.2 M Sucrose 6.9 0.4 M Sucrose - 4.5 0.6 M Sucrose - 12.8 0.8 M Sucrose - 23.0 1.0 M Sucrose - 23.5

LinearFit for: Data Set Percent Change in Mass

So lets say the line of best fit crosses the x axis at 0.36…….. Ys = -iCRT Ys = -(1.0)(0.36 mole/liter)(0.0831 liter bar/mole ° K)(295 ° K) -8.83 bars This equals the entire Y of the cell

So, how does it matter to life? Water moves along a pressure gradient…

Stoma of pea plant (Vicea sp) Leaf water loss Occurs through plant leaves – driven by vapor pressure difference between leaves and air (pressure potential) Regulated by stomata – small holes in leaves that allow gas exchange In most plants, stomata open during the day to allow CO2 uptake This is when H2O loss through transpiration occurs Stoma of pea plant (Vicea sp) SEM, 3250X

Plant stomata open and close, thereby regulating CO2 uptake and associated water loss Stomatal resistance H2O, Latent heat CO2 Photo- synthesis When stomata open… Water from soil Stoma Leaf interior Outside air

Water movement to root Moves along water potential gradient Root has lower water potential than soil Rate depends on hydraulic conductivity and path length

Water movement through stem Driving force is difference in water potential between leaf and root Resistance depends on path length and stem structure Like sucking water up through a straw

Evapotranspiration Evaporation from leaf surfaces Transpirational water loss to the atmosphere Evaporation from soil Water transport through the plant Water uptake by plant roots

Water in the soil-plant-atmosphere continuum Yt = - 30 MPa What happens at night? Water moves along a gradient of decreasing water potential Stomata close – which term does this affect? How would water potential gradient respond? Leaves Yt = - 1.5 MPa Surface roots Yt = - 1.1 MPa Surface soil water Yt = - 0.8 MPa

Osmosis Lab 1E Plasmolysis Watch This!

Investigation 4: Diffusion & Osmosis Conclusions water moves from high concentration of water (hypotonic=low solute) to low concentration of water (hypertonic=high solute) solute concentration & size of molecule affect movement through semi-permeable membrane 2004-2005

Investigation 4: Diffusion & Osmosis ESSAY 1992 A laboratory assistant prepared solutions of 0.8 M, 0.6 M, 0.4 M, and 0.2 M sucrose, but forgot to label them. After realizing the error, the assistant randomly labeled the flasks containing these four unknown solutions as flask A, flask B, flask C, and flask D. Design an experiment, based on the principles of diffusion and osmosis, that the assistant could use to determine which of the flasks contains each of the four unknown solutions. Include in your answer: a description of how you would set up and perform the experiment; the results you would expect from your experiment; and an explanation of those results based on the principles involved. Be sure to clearly state the principles addressed in your discussion.