ALEVEL期中复习.docx

ALEVEL期中复习.docx

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ALEVEL期中复习

Review

1.WhatisSA/V?

WhatisSA?

WhatisV?

PleasecalculatetheSA/Vofa3cm*3cmsquareanditsSA/Vwhenitwascutinto27littlesquareswith1cmofthesidelength?

SA/Visthesurfaceareatovolumeratio.SAissurfacearea.Visvolume.

theSA/Vofa3cm*3cmsquare=3*3*6/（3*3*3）=2

theSA/Vofa1cm*1cmsquare=1*1*6/（1*1*1）=6

2.Pleasecalculatethemagnificationofthisimage,andthereallengthoftheinsect’sbody.

32mm*1000/100um=32083mm/320*1000=259um

3.Wehavelearnedaboutthecelltheory,doyouknowwhatisit?

Areallofthethreeideasofthetheorycorrect?

Basedonyourunderstandingandpresentation,whodidgreatcontributiontothedevelopmentofmicroscopeandthistheory?

（Ifyoudonotknow,askyourclassmateswhodidthispresentation）Leewenhoek,RobertHooker,Schleiden,Schwann,RobertBrown,Virchow,doyouknowthem?

Whatdidtheyfoundout?

Themajorprinciplesofthecelltheoryarethefollowing:

1.Allorganismaremadeofcells.2.Allexistingcellsareproducedbyotherlivingcells.3.Thecellisthemostbasicunitoflife.

RobertBrown（21December1773–10June1858）wasaScottish（苏格兰）botanist（植物学家）and palaeobotanist（古植物学家）whomadeimportantcontributionstobotanylargelythroughhispioneeringuseofthemicroscope.Hiscontributionsincludeoneoftheearliestdetaileddescriptionsofthe cellnucleus and cytoplasmicstreaming;theobservationof Brownianmotion（布朗运动）;earlyworkonplant pollination and fertilisation,includingbeingthefirsttorecognisethefundamentaldifferencebetween gymnosperms and angiosperms（裸子植物和被子植物）;andsomeoftheearlieststudiesin palynology（孢粉学）.Healsomadenumerouscontributionstoplanttaxonomy,includingtheerection（建立）ofanumberofplantfamiliesthatarestillacceptedtoday.

4.Whymanysmallcellsaremoreefficientthanonehugecell?

Isitbetterforacellassmallaspossible,ortheyneedtohaveapropersize?

Why?

Useexamplestotellmetheanswer.Ifyouarenotsure,askyourclassmatesdidthepresentation.

Thesizeofacellislimitedbyitsneedtoexchangematerialswithitsenvironment.Ifacellbecomestoolarge,itsdiffusiondistancebecomestoolongtobeefficientanditssurfaceareatovolumeratiobecomestoosmalltoallowthenecessaryexchange.However,itisnotbetterforacellassmallaspossible,becauseitmusthavenecessarycompositionsuchasnucleiandcytoplasm.

Forexample,SA/Vof1cmcubeis6butSA/Vof10cmcubeisonly0.6.Itmeansthevolumeincreasesmorerapidlythanthesurfaceareawhicheventuallycreatesaproblemforthecell.Waysofdealingwiththisaretoincreasethesurfaceareabyprotrudingextensions.Multicellularorganismsfacethesameproblem.Thisiswhy,forexample,wehavelungsandacircularsystem.

5.Pleaselistallthedifferencesbetweenprokaryoticandeukaryoticcells.

Prokaryotes

Eukaryotes

Diameterofcell

0.5-5um

40umandcommonly1000-10000timesthevolumeofprokaryotes

DNA

Circularandliesfreeinthecytoplasm.DNAisnaked.

Notcircularandiscontainedinanucleus.DNAisassociatedwithprotein,formingchromosomes.

Ribosomes

Smaller（18nmdiameter）

Larger（22nmdiameter）

ER

Notpresent

Present

Organelles

Veryfew

Manytypes

Cellwall

Present

Sometimespresent,e.g.Inplants

6.Pleaselistthedifferencesbetweenplantandanimalcells

Animalcells

Plantcells

nucleus

√

√

cytoplasm

√

√

Plasmamembrane

√

√

Endoplasmicreticulum

√

√

Golgiapparatus

√

√

ribosome

√

√

mitochondria

√

√

vacuole

√

√

Cellwall

×

√

chloroplast

×

√

centriole

√

×

Lysosome

√

√

√=present×=absent

7.IfIdrawa1mmeggin1cm,whatisthemagnitude?

Andiftheyolkoftheeggis0.5mm,whatwillbethesizeinmydrawing?

themagnitude=1cm/1mm=10.

thesizeoftheyolkinmydrawingshouldbe0.5mm*10=5mm.

8.Thecellmembrane,whatarethedifferentpartsinthemembrane?

Thehead?

Thetail?

Hydrophilic?

Hydrophobic?

Integralprotein?

Peripheralprotein?

Glycoprotein?

Cholesterol?

Theirfunctions?

Thecellmembraneconsistsofadoublelayerofphospholipidsinterspersedwithavarietyofothermolecules.Aphospholipidiscomposedofthreebasicparts:

achargedphosphategroup,glycerolandtwofattyacidchains.Together,theglycerolandthephosphategroupformthe“head”ofaphospholipid;thefattyacidchainsformthe“tail”.becausetheheadbearsacharge,itispolar.Recallthatwatermoleculesarealsopolar.Therefore,the“head”ishydrophilic.Incontrast,thefattyacidtailsarenonpolarandcannotformhydrogenbondswithwater.Asaresult,thenonpolartailsareattractedtoeachotherandrepelledbywater.

Othercomponents:

proteins（integral,peripheral,glycoprotein）,cholesterol.

Integralprotein（内在蛋白、整合蛋白）actaschannelproteins.

Peripheralprotein（外在蛋白、周边蛋白）canactasreceptors,enzymes,antigensandcarriers.

Glycoprotein:

theycanactasreceptorsorantigens.

Cholesterol:

itcanregulatethefluidityandstabilityofthemembrane.

9.Couldyoutellmethethreetypesoftransportationthroughthecellmembrane?

Whataretheirnames?

Whatarethedifferencesamongthem?

Whatarethethreetypesofpassivetransportation?

Whichtransportationneedsenergy?

Whichonesneedproteintocarrythesubstance?

Whatarethedifferentfunctionsofproteinsinfacilitateddiffusionandactivetransportation?

Diffusion

osmosis

activetransport

Simplediffusion

Facilitateddiffusion

Energy

Noneed

Noneed

Noneed

need

Proteinchannel

Noneed

need

Noneed

need

Concentration

high→low

high→low

high→low

low→high

10.Whydosomeofthemoleculescangothroughcellmembranebysimplediffusion,butsomeothersneedtogobythehelpofsomeproteins?

Thinkaboutpolarityofthemolecules,sizeofthemolecules,andtheconcentrationgradient.

Nonpolarandsmallmoleculessuchaswatermolecules,oxygenmoleculesandglycerolcangothroughcellmembranefromhighconcentrationgradienttolowconcentrationgradientwithoutthehelpofsomeproteins.However,polarandsmallmoleculessuchasaminoacidandglucoseneedtogobythehelpofsomeproteins.TheygofromhighconcentrationgradienttolowconcentrationgradientbyFacilitateddiffusionorbyactivetransportincontrast.

11.Whatarethethreemajorstagsofacellcycle?

Whichstageisthelongestone?

Whichistheshortest?

Whichstageisresponsiblefornucleusdivisionandwhichoneisforcelldivision?

Whathappensineveryphaseofinterphase（G1,S,G2）andmitosis（thefourphases）?

Youneedtobeabletoeasilyidentifyeveryphasesandknowthethingshappensineveryphase.

Thecellcycleistheperiodbetweenonecelldivisionandthenext.Ithasthreephases,namelyinterphase,nucleardivisionandcelldivision.

①Interphase:

G1+S+G2=90%ofthecellcycle.

G1:

growth,proteinsynthesis,increaseinthenumberofmitochondriaand/orchloroplast.

S:

DNAreplication.

G2:

growth,proteinsynthesis,preparationformitosis/cytokinesis.

②nucleardivision:

prophase,metaphase,anaphaseandtelophase.

Prophase:

nucleus,nucleolusdisappear;mitoticspindleforms;prophaseisthelongestphaseofmitosis.

Metaphase:

sisterchromatidslineupatmiddle;centrosomesareatoppositepolesofthecells;spindlefibersrunfromthecentrosomestothekinetochoresinthecentromeres.

Anaphase:

sisterchromatidsaresplitapart;thisistheshortestphaseofmitosis.

Telophase:

nucleiofnewcellsreform;chromatinuncoils.

③celldivision:

inanimalcells,celldivisioninvolvesconstrictionofthecytoplasmbetweenthetwonewnuclei,aprocesscalledcytokinesis（胞质分裂）.Inplantcellsitinvolvestheformationofanewcellwallbetweenthetwonewnuclei.

12.Whatarechromosome,chromatinandsisterchromatids?

Aretheysameincomposition?

Whataretheymadeof?

AchromosomeisonelongcontinuousthreadofDNAthatconsistsofnumerousgenesalongwithregulatoryinformation.Itistightlycondensed.IninterphaseDNAwrapsaroundhistonesloosely,whichiscalledchromatin.Asacellprogressesintomitosis,chromatinfurthercondenses.RecallthateachchromosomehasalreadybeencopiedduringthepreviousSstage.Thus,thechromosomelookssimilartoan“X”inwhichtheleftandrighthalvesaretwoidenticalDNAdoublehelixes.Onehalfofaduplicatedchromsomesiscalledachromatid.Together,thetwoidenticalchromatidsarecalledsisterchromatids.

13.Whatisstemcell?

Howdidyougrowfromasinglezygote?

Couldyoujusttellmethemajorprocesshappened,youmayneedtousethewordscelldivisionanddifferentiation.

Stemcellsareauniquetypeofbodycellthathavetheabilityto

（1）divideandrenewthemselvesforlongperiodsoftime,

（2）remainundifferentiatedinform,and（3）developintoavarietyofspecializedcelltypes.Whenastemcelldivides,itformseithertwostemcellsoronestemcellandonespecializedcell.

14.Iscelldivisionalwaysagoodthing?

Ifcelldivisionbecomeuncontrollable,whatdoesitmean？

Whatkindofillnesswillweget?

Cancersarecausedbyuncontrolledmitosis,possiblyastheresultofamutationinageneorgeneswhichcontrolcelldivision.Agentswhichcausecancerareknownascarcinogensandincludeionisingradiation,manychemicalsandviruses.Somecancershaveahereditarylink.

15.Ontheearth,morethan90%ofthesubstancesareorganicsubstances;couldyoutellmehowtodistinguishorganicsubstancesandinorganicones?

Pleasegivemeseveralexamplesoforganicsubstances.Whichelementisamustinorganicsubstances?

Carbonisoftencalledthebuildingblockoflifebecausecarbonatomsarethebasisofmostmoleculesthatmakeuplivingthings.Fourmaintypesofcarbon