investigation 4:diffusion and osmosis lab overview you will investigate diffusion and osmosis in a...

Investigation 4:Diffusion Investigation 4:Diffusion and Osmosis Laband Osmosis Lab

OverviewOverview

You will investigate diffusion and You will investigate diffusion and osmosis in a model membrane osmosis in a model membrane systemsystem

You will investigate the effect of You will investigate the effect of solute concentration on water solute concentration on water potential as it relates to living potential as it relates to living plants.plants.

Diffusion & OsmosisDiffusion & Osmosis

Investigation 4: Diffusion & Investigation 4: Diffusion & OsmosisOsmosis DescriptionDescription

A. Diffusion: dialysis tubing filled with starch-glucose A. Diffusion: dialysis tubing filled with starch-glucose solution in beaker filled with solution in beaker filled with KI solution (demo)KI solution (demo)

B. Osmosis: dialysis tubing filled B. Osmosis: dialysis tubing filled with different molarity with different molarity sucrose sucrose solution in beaker filled with solution in beaker filled with distilled waterdistilled water

C. Water PotentialC. Water Potential potato cores in potato cores in

different concentrations sucrose solutionsdifferent concentrations sucrose solutions

Investigation 4: Diffusion & Investigation 4: Diffusion & OsmosisOsmosis

ConceptsConcepts semi-permeable membranesemi-permeable membrane diffusiondiffusion osmosisosmosis solutionssolutions

• hypotonichypotonic• hypertonichypertonic• isotonicisotonic

water potentialwater potential

MolarityMolarity CC66HH1212OO6 6 = glucose= glucose

Sucrose = 2 glucoseSucrose = 2 glucose CC66HH1212OO6 6 + C+ C66HH1212OO6 6 = =

CC66HH1212OO6 6 - H- H22O = CO = C1212HH2222OO1111 soso

Using the periodic table, you Using the periodic table, you can calculate molar mass of can calculate molar mass of sucrose sucrose

~(342g)~(342g)

So to make 500 ml of So to make 500 ml of solution…….solution…….

1.0 M =1.0 M =342 x 1.0 x .5342 x 1.0 x .5

0.2 M = 0.2 M = 342 x .2 x .5342 x .2 x .5

etcetc

Prepare dialysis bags……Prepare dialysis bags…… Add sucrose solutions to bagsAdd sucrose solutions to bags

Mass carefullyMass carefully

Place in distilled water for 30 Place in distilled water for 30 minutesminutes

Re-massRe-mass

Calculate the % change in massCalculate the % change in mass

Final Mass-Initial Final Mass-Initial MassMass

Initial MassInitial MassX 100

To Calculate the % change in mass:

Diffusion and Diffusion and OsmosisOsmosis

Concentration EffectConcentration Effect

Water MovementWater Movement

Water moves along energy gradientWater moves along energy gradient From high energy to low energyFrom high energy to low energy

What forces cause water to move?What forces cause water to move? PressuresPressures

• GravityGravity• Forces created by organismsForces created by organisms

Osmotic gradientsOsmotic gradients Matric forces (adsorption)Matric forces (adsorption)

These forces are all components of These forces are all components of water potentialwater potential

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,

Water potential Why does water move?How does water move?

1.

2.

3.

Downhill

Fresh – salty

Hose, straw

4. Sponge

Pressure potential

Osmotic potential

Matric potential

Water potential describes water concentration

Water moves down gradients of water potential,

Components of Water PotentialComponents of Water Potential

Pressure potential: pushing (positive pressure, like the Pressure potential: pushing (positive pressure, like the hose) or sucking (negative pressure, like a straw)hose) or sucking (negative pressure, like a straw) Major factor moving water through plantsMajor factor moving water through plants

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

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

Water Potential In Water Potential In Potato CellsPotato Cells

Osmosis is a special type of diffusion. It Osmosis is a special type of diffusion. It is the movement of water molecules is the movement of water molecules through a selectively permeable through a selectively permeable membrane from a region of membrane from a region of higherhigher water water potential to an area of potential to an area of lowerlower water water potentialpotential

Water potential is the measure of free Water potential is the measure of free energy of water in a solutionenergy of water in a solution

Water always moves to a moreWater always moves to a more negative negative water potentialwater potential..

Water PotentialWater Potential

= = pp + + ss

Where there is no % change in mass, the solution in the Where there is no % change in mass, the solution in the

beaker has the same water potential as the potato cells.beaker has the same water potential as the potato cells.

((= = pp + + ss) = () = (= = pp + + ss) )

BeakerBeaker Potato Potato

p p = 0 (open beaker) so = 0 (open beaker) so ss

To CalculateTo Calculate ss

s s = -iCRT= -iCRT

i = Ionization constant (sucrose is i = Ionization constant (sucrose is 1.0 because it does not ionize).1.0 because it does not ionize).

C = Molar Concentration (from line C = Molar Concentration (from line of of best fit where the line crosses best fit where the line crosses the x axis)the x axis)

R = Pressure Constant (0.0831 liter R = Pressure Constant (0.0831 liter bars/mole bars/mole °°KK

T = Temperature T = Temperature °°K (273 + K (273 + °°C)C)

Data TableData Table

% Change In Mass Period 1% Change In Mass Period 1

MM Gr Gr 11

Gr Gr 22

Gr Gr 33

Gr Gr 44

GGr r 55

Class Class Av Av

1.01.0

0.80.8

0.60.6

0.40.4

0.20.2

0.00.0

Data Table

Contents in BeakerContents in Beaker % Change in Mass% Change in Mass

Distilled WaterDistilled Water 21.421.4

0.2 M Sucrose0.2 M Sucrose 6.96.9

0.4 M Sucrose0.4 M Sucrose - 4.5- 4.5




Lab 1C: Class Averaged Data over Years

Sample Best Fit % Change in Mass of Potato Cores at Different Molarities of Sucrose

-25

-20

-15

-10

-5

0

5

10

15

0.0 0.2 0.4 0.6 0.8 1

Sucrose Molarity within Beaker

Pe

rce

nt

Ch

an

ge

Data Set Best Fit

LinearFit for: Data Set Percent Change in Mass

So lets say the line of best fit So lets say the line of best fit crosses the x axis at 0.36……..crosses the x axis at 0.36……..

s s = -iCRT= -iCRT

s s = -(1.0)(0.36 mole/liter)(0.0831 liter bar/mole = -(1.0)(0.36 mole/liter)(0.0831 liter bar/mole °° K) K)

(295 (295 °° K) K)

-8.83 bars-8.83 bars

This equals the entire This equals the entire of the cell of the cell

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

Leaf water lossLeaf water loss Occurs through plant leaves – driven by vapor pressure difference Occurs through plant leaves – driven by vapor pressure difference

between leaves and air (pressure potential)between leaves and air (pressure potential) Regulated by stomata – small holes in leaves that allow gas Regulated by stomata – small holes in leaves that allow gas

exchangeexchange In most plants, stomata open during the day to allow COIn most plants, stomata open during the day to allow CO22 uptake uptake

This is when HThis is when H22O loss through transpiration occursO loss through transpiration occurs

Stoma of pea plant(Vicea sp)

SEM, 3250X

H2O, Latent heat

CO2

Stoma

Leaf interior Outside air

Waterfromsoil

Photo-synthesis

Stomatalresistance

Plant stomata open and close, thereby regulating CO2 uptakeand associated water loss

When stomata open…

Water movement to rootWater movement to root Moves along water Moves along water

potential gradientpotential gradient Root has lower water Root has lower water

potential than soilpotential than soil Rate depends on Rate depends on

hydraulic conductivity hydraulic conductivity and path lengthand path length

Water movement through stemWater movement through stem

Driving force is difference in Driving force is difference in water potential between leaf water potential between leaf and rootand rootResistance depends on path Resistance depends on path length and stem structurelength and stem structureLike sucking water up Like sucking water up through a strawthrough a straw

Evaporation from leaf surfaces

Evaporation from soil

Transpirational water lossto the atmosphere

Evapotranspiration

Water transport through the plant

Water uptake by plant roots

Surface soil water t - 0.8 MPa

Surface roots t - 1.1 MPa

Leaves t - 1.5 MPa

Atmosphere t - 30 MPa

Water in the soil-plant-atmosphere continuum

Water moves along a gradient of decreasing

water potential

What happens at night?

Stomata close – which term doesthis affect?How would waterpotential gradientrespond?

Osmosis Lab 1E PlasmolysisOsmosis Lab 1E Plasmolysis Watch This!

2004-20052004-2005


ConclusionsConclusions water moves from high concentration of water moves from high concentration of

water (hypotonic=low solute) to low water (hypotonic=low solute) to low concentration of water (hypertonic=high concentration of water (hypertonic=high solute)solute)

solute concentration & solute concentration & size of molecule size of molecule affect movement affect movement through through semi-permeable semi-permeable membrane membrane


ESSAY 1992ESSAY 1992

A laboratory assistant prepared solutions of 0.8 M, 0.6 M, 0.4 M, and 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 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 randomly labeled the flasks containing these four unknown solutions as flask A, flask B, flask C, and flask D.A, flask B, flask C, and flask D.

Design an experiment, based on the principles of diffusion and osmosis, that 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 the assistant could use to determine which of the flasks contains each of the four unknown solutions.four unknown solutions.

Include in your answer:Include in your answer:

a.a. a description of how you would set up and perform the experiment;a description of how you would set up and perform the experiment;

b.b. the results you would expect from your experiment; andthe results you would expect from your experiment; and

c.c. an explanation of those results based on the principles involved. an explanation of those results based on the principles involved.

Be sure to clearly state the principles addressed in your discussion.Be sure to clearly state the principles addressed in your discussion.

investigation 4:diffusion and osmosis lab overview you will investigate diffusion and osmosis in a...

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