lab 7 diffusion and osmosis in cells - biology with mrs....

HonorsBiology DueTuesdayNovember8th!Unit3:Cells

Name:_________________________________________________Period:______

Lab 7: Diffusion and Osmosis in the Cell Part A: Relationship Between Cell Size and Diffusion Rate Diffusionisoneoftheveryimportantprocessesbywhichsubstancessuchasnutrients,waste,water,andoxygenaretransportedbetweenlivingcellsandtheirenvironmentthroughthecell’ssurface.Acellneedsalargesurfaceinordertocarryoutmetabolicfunctionsandasthecellgrowsitneedstocarryoutmoreandmorereactions.Asacellgrowsinsize(volume),thedistanceincreasesbetweenthecytoplasmatthecenterofthecellandthecellmembrane.Therateofchemicalexchangewiththesurroundingenvironmentmaybecometoolowtocarryoutalloftheneededreactions.Itmaynotbeabletoexcretewastequicklyenoughortakeinimportantnutrients.Thevolumeofacelldeterminesrequirementswhilesurfaceareadeterminessupply.Becausethissurfaceareatovolumeratioissoimportant,itssizeofthecellislimited.Therateofexchangeofmaterials(nutrients/waste)andenergy(heat)isafunctionofitssurfacearea.Inthisinvestigation,youwilluseagarcubestowhichtheindicatorbromothymolbluehasbeenadded.BTBisanacid/baseindicatorthatturnsyellowinthepresenceofanacidsuchasaceticacid(vinegar).Thusthesurfaceoftheagarcubeswillturnyellowimmediatelywhenputintoanacidsolution.Theacidwillcontinuetodiffusethroughthecubeandgraduallyturntheinsideofthecubeyellow.

Materials: Agar Bowl Vinegar(Acid) Ruler Spoon Scalpel(Sharp!) Timer PaperTowel Procedure:

1. Collectyourlabmaterialsandagarpiece.2. Accurately,cutthreeagarcubeswiththefollowingmeasurements:

a. 3cmx3cmx3cm(27cm3involume)b. 2cmx2cmx2cm(8cm3involume)c. 1cmx1cmx1cm(1cm3involume)

3. Placetheagarcubesinthebowl.Carefullypourvinegarinthebowluntilthecubesarecompletelycovered.Immediatelystartatimerfor10minutes.

4. After10minutes,usingthespoon,carefullyremovethecubesfromthebowlontoapapertowel,blottingthecubesdry.Becarefulnottosquishordeformyourcubes.

5. Cuteachcubeinhalf(carefulnottosquishordamagethecube!)6. Observetheinsideofthecubes.Measurethewidthoftheportionofthecubesthatremainsblue;thisisthevolumethat

wasnotpenetratedbythevinegar/acid.ItcanbeassumedthatthewidthofthisblueportionisthesameinLength,Width,andHeight.Therefore,usingLxWxH,youcancalculatethevolumeoftheunpenetratedsectionofeachcube.

7. Usethecalculationtablebelowtohelpyoutocompletethedatatable.8. Tocleanup,throwawayallyouragarandthepapertowelanddumpoutthevinegarfromthebowl.9. Refillyourvinegarflaskifneededandreplacethepapertowelforthenextperiod.

Helpful Calculations:

• Totalvolumeofeachcube:Volume(incm3)=LxWxH• Unpenetratedvolumeofeachcube(youonlyneedtomeasureone“side”ofthiscube):Volume(incm3)=LxWxH• Penetratedvolume(amountofcubethatturnedyellow)(incm3)=Totalvolume–Unpenetratedvolume• Percentdiffusion(percentofagarthatagardiffusedinto)=(Penetratedvolume/Totalvolume)x100=%

Data Table:

CubeSize TotalVolume(cm3)

UnpenetratedVolume(cm3)

PenetratedVolume(cm3)

PercentDiffusion(%)

1cm

2cm

3cm

HonorsBiology DueTuesdayNovember8th!Unit3:Cells

Graph and Data Analysis: Onthegraphbelow,graphthedata:Totalvolume(x-axis)vsPercentdiffusion(y-axis)1. Inthislab,theagarcubesrepresentlivingcells.

Whatdoesthevinegarrepresent?

2. Givenyourgraphanddata,whatisthemosteffectivesizedcubethatyoutestedformaximumdiffusion?Why?

3. Givenyourgraph,extrapolatewhatpercentdiffusionacellsmallerthan1cm3wouldexperience.Explainyouranswer.4. Givenyourgraph,extrapolatewhatpercentdiffusionacelllargerthan27cm3wouldexperience.Explainyouranswer.

5. Whydoorganismsgrowbyincreasingthenumberofcellsintheirbodies?Whynotsimplyincreasethesizeoftheirexistingcells?

Part B: Inquiry into Osmosis – The Diffusion of Water Aswehavediscussed,waterisamoleculethatisnecessaryforthefunctionsoflivingcells.Inparticular,watermakesupalargepartofthecytoplasminsidethecellmembrane.Whenwaterdiffusesintooroutofacell,itiscalledOSMOSIS.Themovementofwaterinandoutofacellislargelydeterminedbytheamountofsolutesbothinsideandoutsidethecell.Theinsideofacellisslightlysalty,approximately1%.Inamulticellularorganism,suchasyourself,thefluidthatsurroundscellsandthefluidthatmakesupyourbloodisalsoabout1%.Becauseoftheseequalpercentages,waterwillflowinandoutofthecellatequalrates.Whenacellisinasolutionthatisequallyslightlysalty,thesolutioniscalledISOTONIC,wheretheprefixiso-means“same”andthesuffix-tonicmeans“solution”.Whenacellisputinasolutionthathasasolutionthathasasaltpercentthatishigherthan1%,waterfrominsidethecellwillleavethroughthecellmembranetothehighersaltconcentration.Thiswillcausethecelltoshrink.ThissaltysolutioniscalledHYPERTONIC,wheretheprefixhyper-meanshighandagain-tonicmeanssolution.Lastly,whenacellisputinasolutionthathaslessthan1%saltorevenzeropercentsalt,waterfromoutsidethecellwillmoveintothecellcausingthecelltoswellandmaybeevenpop.ThislastsolutioniscalledHYPOTONIC,wheretheprefixhypo-meanslowand-tonicmeanssolution.Inthislab,youwillobservetheprocessofwatermovinginandoutofonioncells.Materials: Redonion Microscope Microscopeslide Coverslip 15%saltsolution Pure(nosalt)water Papertowel Procedure: Step1

1. Carefullypeelawaythecoloredlayerofthecellsfromtheredonion.Thisshouldonlybethethinpurplelayer.

2. Placethethin,purpleonionlayeronadrymicroscopeslide(shinysideup–NOWATER,NOCOVERSLIPYET.)

3. Viewtheonionskinonthelowestobjectivelens,4xobjective,andobservetheentireoniontissuetofindthemostpurplearea

4. Focusonthemost-purpleareawiththemediumpowerobjectivelens,10xobjective.5. ObservethecellsanddrawwhatONEonioncelllookslikeintheboxintheobservation

section.

HonorsBiology DueTuesdayNovember8th!Unit3:Cells

Step21. Removetheslidefromthemicroscopeandplace2smalldropsof15%saltwaterontotheonionskin.Placeacoverslipon

theslidestartingatanangleandgentlylayingovertheonionskin.2. Placetheslidebackunderthemicroscopeandfocusontheonioncellsagainunder4xandthenunder10x.Lettheonion

cellssitfor5minutes.3. Afterabout5minutes,observetheonioncellsanddrawwhatONEonioncelllookslikeintheobservationsectionafter

exposuretothissaltwater.Step3

1. Removetheslidefromthemicroscope.Removethecoverslipandsetitasidetobethrownaway.2. Useasmallcornerofacleanpapertowelanddabtheonionskintowickawaythesaltwater.Addapproximately2dropsof

thedistilledwateranddabawaythiswaterwithacleanpapertowelcorneragaintowickawayanyleftoversalt.3. Add2moredropsofdistilledwaterontotheonionskin.Gentlylayanewcoverslipovertheonioncellsandwater.4. Puttheslidebackunderthemicroscopeandfocusthecellsagainunder4xandthenunder10x.5. Lettheonioncellssitfor5minutes.6. Afterabout5minutes,observetheonioncellsanddrawwhatONEonioncelllookslikeintheobservationsectionafter

exposuretothissaltwater.7. Tocleanup,removeandthrowawaytheonionskin.Washanddrythemicroscopeslide.Throwawaythecoverslips.

Lastly,turnoffyourmicroscopeandputitawayasinstructed.Observations:

Analysis:

1. Basedontheinformationfromtheintroduction,whichsolutiondoyouthinkwouldbedeemedahypotonicsolutionfromthelab?Explain.

2. Basedontheinformationfromtheintroduction,whichsolutiondoyouthinkwouldbedeemedahypertonicsolutionfromthelab?Explain.

HonorsBiology DueTuesdayNovember8th!Unit3:Cells

Lab 7 Scores: Part A:

1 2 3 4

Labsheetwasturnedin,butanswerswerenot

completedordonotaddressthequestions.

Halfoftheitemshavebeencompletedorsomeitems

arenotthoroughorthoughtful.Improvements

areneededandsomeanswersneedtobe

reconsidered.

Mostitemshavebeencompletedthoroughlyand

thoughtfully.Someimprovementsmaybe

neededorsomeanswersmayneedtobereconsidered.

Allitemshavebeencompletedthoroughlyand

thoughtfully.Noimprovementsneeded.

Part B:

1 2 3 4

Labsheetwasturnedin,butanswerswerenot

completedordonotaddressthequestions.

Halfoftheitemshavebeencompletedorsomeitems

arenotthoroughorthoughtful.Improvements

areneededandsomeanswersneedtobe

reconsidered.

Mostitemshavebeencompletedthoroughlyand

thoughtfully.Someimprovementsmaybe

neededorsomeanswersmayneedtobereconsidered.

Allitemshavebeencompletedthoroughlyand

thoughtfully.Noimprovementsneeded.