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Chapter5–MembraneStructureandFunctionExercise1–MembraneStructure(5.1)

Reviewtheanimalcellplasmamembranebylabelingthisdiagram.Labeltheitemsinboldfacetype:Startwiththecytoplasm,extracellularfluid,andafiberoftheextracellularmatrix.Inthemembrane,labelphospholipids,glycoprotein,glycolipid,carbohydratechain,hydrophobictails,hydrophilicheads,phospholipidbilayer,peripheralprotein,cholesterol,integralprotein,andfilamentsofthecytoskeleton.

Exercise2–MembraneProteins(5.1)

Labeleachmembraneproteinshownbelow.(SeeFigure5.3)

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Exercise3–Diffusion,Osmosis,andActiveTransport(5.2-5.3)

Reviewdiffusionandthefunctionofcellmembranesbymatchingeachofthephrasesontherightwiththeappropriatemechanismsfromthelistontheleft.Twoquestionsrequiremorethanoneanswer.

A. Diffusion ______ 1. Typeofdiffusionacrossabiologicalmembrane

B. Activetransport ______ 2. Movessolutesagainstconcentrationgradient

C. Osmosis ______ 3. Anyspreadofmoleculesfromareaofhighertolowerconcentration

D. Phagocytosis ______ 4. Diffusionwiththehelpofatransportprotein

E. Passivetransport ______ 5. ThreetypesofendocytosisF. Facilitateddiffusion ______ 6. EngulfingoffluidinmembranevesiclesG. Pinocytosis ______ 7. DiffusionofwateracrossselectivelypermeablemembraneH. Receptor-mediated

endocytosis______ 8. TransportmoleculesneedATPtofunction

I. Exocytosis ______ 9. Enablescelltoengulfbulkquantitiesofspecificlargemolecules ______ 10. Howoxygenandcarbondioxideenterandleavecells ______ 11. Twotypesofpassivetransport ______ 12. Engulfingofparticleinmembranevesicle ______ 13. Fusionofmembrane-boundvesiclewithmembrane,anddumpingof

contentsoutsidecell ______ 14. Howacellmightcaptureabacterium ______ 15. Helpedbyaquaporins

Exercise3–FacilitatedDiffusion(5.2)Osmosisisanimportantprocessthathasmanyeffectsonlivingthings.Testyourunderstandingofosmosisbypredictingineachofthefollowingcaseswhetherwaterwillenterthecell(In)orleavethecell(Out),orwhethertherewillbenonetmovementofwater(None).Assumethattheplasmamembraneispermeabletowaterbutnotsolutes.

____ 1. Cellisexposedtohypertonicsolution.

____ 2. Cellisplacedinsaltsolutionwhoseconcentrationitgreaterthancellcontents.

____ 3. Duetodisease,soluteconcentrationofbodyfluidoutsidecellislessthansoluteconcentrationofcells.

____ 4. Cellisinisotonicsolution.

____ 5. Single-celledorganismisplacedindropofpurewaterforexaminationundermicroscope.____ 6. Cellisimmersedinsolutionofsucroseandglucosewhoseindividualconcentrationsarelessthan

concentrationofsolutesincytoplasm,butwhosecombinedconcentrationisgreaterthanconcentrationofsolutesincytoplasm.

____ 7. Soluteconcentrationofcellisgreaterthansoluteconcentrationofsurroundingfluid.

____ 8. Cellisexposedtohypotonicsolution.

____ 9. Concentrationofsolutesincytoplasmisequaltosoluteconcentrationofextracellularfluid.

____ 10. Cytoplasmismoredilutethansurroundingsolution.

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Exercise4–MembraneStructureandFunctionsTrytopicturemembranesandtheirfunctionscloseupbycompletingthefollowingstory.

YourfirstmissionasaBionautrequiresyoutoenterabloodvesselandobservethestructureandfunctionsofcellmembranes.Youstepintothewater-filledchamberoftheMicrotron,whichquicklyshrinksyoutoasizemuchsmallerthenaredbloodcell.

Youtumblethroughthetunnel-likeneedleandintoabloodvesselinthearmofavolunteer.Huge,rubberyredbloodcellsslowlyglidepast.Floatingintheclear,yellowishbloodplasma,youswitchonyourheadlampandexaminetheepithelialcellsofthevesselwall.Theirplasmamembranesseemmadeofmillionsofsmallballoons.Thesearethepolar“heads”ofthe1_____________________moleculesthatmakeupmostofthemembranesurface.Throughthetransparentsurface,youcanseetheirflexible,2_____________________tailsprojectinginwardtowardtheinteriorofthemembrane,andbeyondthemaninnerlayerof3_____________________moleculeswiththeirtailspointingtowardyou.Hereandthereareglobular4_____________________moleculesembeddedinthemembrane;somerestlightlyonthesurface,butmostprojectallthewayintotheinteriorofthecell.Themembraneisindeeda5_____________________mosaic;theproteinsareembeddedlikethepiecesofapicture,butyoucanseethattheyarefreetomovearound.Youpushononeoftheproteins,anditbobslikeaniceberg.Someofthephospholipidsandproteinshavechainsofsugarmoleculesattachedtothem,forming6_____________________and7_____________________.Thesearethemoleculesthatactascell8_____________________tags.Younoticethatoneoftheproteinshasadimpleinitssurface.Justthenasmall,roundmoleculefloatingintheplasmanestlesinthedimple.Themoleculeisahormone,achemicalsignal,andthedimpledproteinisthe9______________________thatenablesthecelltorespondtoit.

Inyourlightbeam,youcanseethesparkleandshimmerofmanymolecules,largeandsmall,inthebloodandpassingthroughthecellmembrane.Oxygenismovingfromtheplasma,whereitismoreconcentrated,tothecellinterior,whereitislessconcentrated.Thismovementis10_____________________;whereitoccursthroughabiologicalmembrane,itiscalled11_____________________transport.Similarly,carbondioxideisflowingoutofthecell,downits12_____________________gradient,fromthecellinterior,whereitis13_____________________concentrated,totheblood,whereitis14_____________________concentrated.

Younotethatwatermoleculesarepassingthroughthemembraneequallyinbothdirections.Thetotalconcentrationofsolutesinthecellandinthebloodmustbeequal;thesolutionsmustbe15_____________________.Yousignalthecontrolteamtoinjectasmallamountofconcentratedsaltsolutionintotheblood,makingthebloodslightly16____________________relativetothecellcontents.Thiscauseswatertoflow17_____________________thecell,untilthetwosolutionsareagaininequilibrium.Thisdiffusionofwaterthrougha18_____________________permeablemembraneiscalled19_____________________.

Somesugarmoleculesfloatinginthebloodaresimpletoolargeandpolartopasseasilythroughtheplasmamembrane.Thesugarmoleculessimplybounceoff,unlesstheyhappentopassthroughporesinspecial20_____________________proteins.Thisisatypeofpassivetransport,becausethemoleculesmovedownaconcentrationgradientwithouttheexpenditureof21_____________________.Becausetransportproteinshelpout,itiscalled22_____________________diffusion.

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Yourchemscannerdetectsahighconcentrationofpotassiumionsinsidethecell.Transportproteinshereandthereinthemembraneareabletomovepotassiumintothecellagainsttheconcentrationgradient.Thismustbe23_____________________transport;thecellexpends24_____________________toprovideenergyto“pump”thepotassiumintothecell.

Suddenlythereisatugatyourfoot.Youlookdowntoseeyourflipperengulfedbyaripplingmembrane.Awhitebloodcellthesizeofabuildingquicklypinsyouagainstthevesselwall.Thephospholipidsofitsmembranearepressedagainstyourfacemask.Thecellisengulfingyou,protectingthebodyfromaforeigninvader!Takinginasubstanceinthiswayiscalled25_____________________,morespecifically26_____________________,ifthesubstanceisasolidparticle.Suddenlythepressurediminishes,andyouareinsidethewhitebloodcell,floatingfreeinamembrane-enclosedbag,or27_____________________.Anothersacisapproaching;itisa28_____________________,fullofdigestiveenzymes.Youmanagetogetyourlegsoutsideofthevacuoleandmoveitbacktowardtheinnersurfaceofthecellmembrane.Asthevacuolefuseswiththemembrane,youtearyourfeetfreeandswimawayfromthevoraciouscell,realizingthat29_____________________expelledyoualmostasfastasendocytosistrappedyou!

Youswimtotheexitpoint,andthecontrolteamremovesyoubysyringe.Youaresoonbackinthelab,restoredtonormalsize,andtellingyourcolleaguesaboutyourclosecall.Exercise5-CellCommunication(5.1)

Readpage90inthetextbookandlabelthefollowingdiagram.Answerthequestions.1. Ifyourcellsneededto

rapidlyrespondtoachangingenvironment,wouldyouwanttheeffecttobeshort-orlong-lived?

2. Giventheessentialroleofsignalingincellularandorganismalhealth,howmightdiseasesarisefromsignalingerrors?