MCHow Diffusion WorksHiaw0品0国PlayPauseAudioTextMolecules dissolvedin a solution are in constant randommotion due totheirkinetic energy. One result of this motion is that dissolvedmoleculesbecomeevenlydistributedthroughoutthesolutionCopyrightTheMcGraw-Hill Companies,Inc
Osmosis-DiffusionofWater(PassiveTransport)Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or displayMembranesacGlassSolutewithsolutiontubeWaterContainerwithwaterPore.b.AstheH,odiffusesintothesac,thevolumea..Insetshowsaclose-upoftheosmoticprocess.c.Evenasthesolutionbecomesdiluted,thereThegradientgoesfromtheoutercontainerincreasesandforcestheexcesssolutionintowillstillbeosmosisintothesac.Equilibriumthetube,whichwill rise continually(higherconcentrationofH,O)tothesac(lowewillnotoccurbecausethesolutionscanneveconcentrationofH,O).Somewaterwilldiffusebecomeequal. (Why?)theoppositedirectionbutthenetgradientfavorsosmosisintothesac.17
Osmosis - Diffusion of Water (Passive Transport) 17 Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display. Glass tube Membrane sac with solution Solute Water Container with water Pore Even as the solution becomes diluted, there will still be osmosis into the sac. Equilibrium will not occur because the solutions can never become equal. (Why?) As the H2O diffuses into the sac, the volume increases and forces the excess solution into the tube, which will rise continually. Inset shows a close-up of the osmotic process. The gradient goes from the outer container (higher concentration of H2O) to the sac (lower concentration of H2O). Some water will diffuse the opposite direction but the net gradient favors osmosis into the sac. a. b. c
Responseto solutions of differentosmoticcontentFExCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or displayCellswithIsotonic SolutionHypotonicSolutionHypertonicSolutionCell WallCell wallCellmembraneCellmembraneWaterconcentrationisequalinsideandNetdiffusionofwaterisintothecell:thisWaterdiffusesoutofthecellandoutsidethecell,thus rates ofdiffusionshrinksthecell membraneawayfromswellstheprotoplastandpushesittightlyagainstthewall.Wall usuallypreventsthecell wall;processisknownasareequal inbothdirections.cellfromburstingplasmolysis.CellsLackingEarlyCellWallEarlyCell membraneLatee(osmolysis)LateRatesofdiffusionareequalDiffusionofwaterintothecellcausesWaterdiffusingoutofthecell causesinbothdirections.ittoswell,andmayburstitifnoittoshrinkandbecomedistorted18mechanismexiststoremovethewaterDirectionofnetwatermovement
18 Response to solutions of different osmotic content Early Early Direction of net water movement. Cell membrane Late (osmolysis) Late Cells with Isotonic Solution Hypotonic Solution Hypertonic Solution Cell Wall Cells Lacking Cell Wall Cell membrane Cell wall Cell membrane Water concentration is equal inside and outside the cell, thus rates of diffusion are equal in both directions. Net diffusion of water is into the cell; this swells the protoplast and pushes it tightly against the wall. Wall usually prevents cell from bursting. Water diffuses out of the cell and shrinks the cell membrane away from the cell wall; process is known as plasmolysis. Rates of diffusion are equal in both directions. Diffusion of water into the cell causes it to swell, and may burst it if no mechanism exists to remove the water. Water diffusing out of the cell causes it to shrink and become distorted. Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
FacilitatedDiffusion(PassiveTransport)Copyright The McGraw -HillCompanies, Inc. Permis sion required for reproduction or displayInsideInsideOutsideOutsidecellcellcellcell(a)b
Facilitated Diffusion (Passive Transport) 19 Outside cell Inside cell Outside cell (a) (b) Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display. Inside cell