Why?

TransportinCells

How dowatermoleculesmovein andoutofcells?

Wateraccountsforover70% ofthehuman body.Ifwaterlevelsarenotregulatedandmaintainedin an organismtheconsequencescanbedisastrous.Cellsandtissuesmayswell,bloodcellsburst,orthebrain mayexpandsomuchitpushesontheskull,leadingtobraindamageanddeath.Sowhatexactlyisthe processthatallowsorganismstoregulateandmaintaintheirwatercontent?

Model1–MovementofWaterInandOutof Cells

1. Asolutionconsistsofasoluteandasolventmixedtogether.Forthesolutionin Model1 identify andprovidethesymbolforthe

a.solute.

b. solvent

.

2. Considerthesizeofthesugarandwatermoleculesin Model1.Whichmoleculesin thediagram in Model1 areabletomovethroughtheselectivelypermeablemembrane?

3. Completethetablebelowbycountingthemoleculesin Model1.

InsidetheCell / OutsidetheCell
Numberofsugarmolecules
Numberofwatermolecules
Ratioofwatertosugar

4. Whichsolutionin Model1 ismoreconcentrated—thesolutioninsidethecelloroutsideofthe cell?Explainyouranswerin termsoftheratioofsolutetosolventparticles.

5. Considerthearrowsindicatingmovementofwateracrossthemembrane.

a.Inwhichdirectionarewatermoleculesmoving—intooroutofthecell?

b. Aremorewatermoleculesmovingintooroutofthecell?

c. Isthenet directionofwatermovementintooroutofthecell?

6. Circlethecorrectwordbelowtoindicatethechangein theconcentrationofthesugarsolution oneachsideofthemembrane aswatermoleculesmove.

a.Thesolutioninsidethecellwillbecome(more/less)concentratedwiththenet movementof water.

b. Thesolutionoutsidethecellwillbecome(more/less)concentratedwiththenet movementof water.

7. Applyingwhatyoualreadyknowabouttherandommovementofmolecules,whatwilleventu- allyhappentotheconcentrationonbothsidesofthemembrane?

8. Thedefinitionofdiffusionisthemovementofmoleculesacrossamembranefromanareaof highconcentrationtoanareaoflowconcentration. Accordingtothisdefinition,isthecellin Model1 undergoingdiffusion?Explain.

9. Inthecelldiagramin Model1, whereisthehigherconcentrationofwater—insideoroutsideof thecell?

10. Isthecellin Model1 undergoingdiffusionifyouconsidertheconcentrationofwateroneither sideoftheselectivelypermeablemembrane?Explain.

ReadThis!

Osmosisisthemovementofwaterfromhighwaterconcentrationtolowwaterconcentration acrossa semi-permeablemembrane.

Model2–OsmosisinPlantandAnimalCells

Externalsolution:
Hypertonic / Isotonic / Hypotonic
Animal
Cell / A / B / C
Crenated / Normal / Lysed

Cellmembrane

Cellwall

Plant
Cell / D / E / F
Plasmolysed / Normal / Turgid

11. Usingyourknowledgeofcells,whichtypeofcellsin Model2—animalorplant—have

a.aselectivelypermeablemembrane?

b. apermeable,rigidcellwall?

12. Thearrowsin Model2 showmovementofwaterintoandoutofthecells.Whatdoesthethick- nessofthearrowindicate?

13. ForeachquestionusediagramsA–Fin Model2.Whichcellsshow

a.anet increasein water? b. anet decreasein water? c. nonet changein water?

14. Considerthedefinitionforosmosisandthenet movementofwaterfromadilutesolution(high concentrationofwater)toaconcentratedsolution(lowconcentrationofwater).

a.DescribetheconcentrationofthesolutionsurroundingcellsAandD(extracellular),relative totheconcentrationofthesolutioninsidecellsAandD(intracellular).

b. DescribetheconcentrationoftheextracellularsolutionofcellsCandF,relativetotheintra- cellularsolutionofcellsCandF.

c. DescribetheconcentrationoftheextracellularsolutionofcellsBandE,relativetothecon- centrationoftheintracellularsolutionofcellsBandE.

15.Usingthediagramsin Model2 andtheanswerstothepreviousquestion,developdefinitionsfor thefollowingwords.

a.Ahypertonic extracellularsolutionis .

b. Ahypotonicextracellularsolutionis .

c. Anisotonicextracellularsolutionis .

16. Considerthecellsin Model2 thatarein hypertonicsolutions.

a.Describewhathashappenedtotheplantcell.

b. Whatwordisusedtosummarizethesechangestotheplantcell?

c. Whatwordwouldbeusedifthecellwerefromananimal?

17. Considerthecellsin Model2 thatarein hypotonicsolutions.

a.Describethechangestotheplantcell.

b. Whatwordsummarizesthesechangestotheplantcell?

c. Whatwordwouldbeusedifthecellwerefromananimal?

18.When animalcellsarein ahypotonicsolutiontheycanundergolysis.However,plantcellsdo not,theyonlybecometurgid.

a.Definelysisbasedonthediagramin Model2.

b. Whatstructureontheplantcellpreventslysisfromoccurringin ahypotonicsolution?

ExtensionQuestions

19. Usingtheconceptofosmosis,explainwhywaterissprayedoverproducein agrocerystore.How mightthischangetheappearanceoftheproduce,andwhywouldthischangebedesirable?

20. Supposeyoumadealettucesaladin theafternoon,addedsaltandotherseasonings,andthenput thesaladin therefrigerator.When youtookthesaladoutoftherefrigeratorfordinner,thelet- tucelookedwiltedandsomewaterwasin thebottomofthebowl.Usetheprinciplesofosmosis toexplainwhathappened.

21. Inextremecases,itispossibletodiefromdrinkingtoo muchwater.Theconsumptionofseveral litersofwaterin ashortamount oftimecanleadtobrainedema(swelling)anddeath.Explain theeffectofingestinganextremelylargeamount ofwateratthelevelofthebraincells,including theroleofosmosisin thisprocess.

22. Thediagrambelowshowsasingle-celledorganismcalledParamecium,whichlivesin freshwater environments.Thisorganismcontainsaspecializedorganellecalledacontractilevacuolethat helpsmaintainosmoticbalance.Predicthowthisorganellemighthelptheorganismsurvive giventhatitisconstantlyimmersedin ahypotonicsolution.

FoodVacuoles

RadiatingCanal

ContractileVacuole

Nucleus

Oral Groove

Vestible

Oesophagus

Cilia