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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.