老托福閱讀真題passage11

1、老托福閱讀真題及答案：passage11老托福閱讀真題及答案：passage114/4老托福閱讀真題及答案：passage11老托福閱讀真題及答案：PASSAGE11Plantsaresubjecttoattackandinfectionbyaremarkablevarietyofsymbioticspeciesandhaveevolvedadiversearrayofmechanismsdesignedtofrustratethepotentialcolonists.Thesecanbedividedintopreformedorpassivedefensemechanismsandindu

2、cibleoractivesystems.Passiveplantdefensecomprisesphysicalandchemicalbarriersthatprevententryofpathogens,suchasbacteria,orrendertissuesunpalatableortoxictotheinvader.Theexternalsurfacesofplants,inadditiontobeingcoveredbyanepidermisandawaxycuticle,oftencarryspikyhairsknownastrichomes,whicheitherpreven

3、tfeedingbyinsectsormayevenpunctureandkillinsectlarvae.Othertrichomesarestickyandglandularandeffectivelytrapandimmobilizeinsects.Ifthephysicalbarriersoftheplantarebreached,thenpreformedchemicalsmayinhibitorkilltheintruder,andplanttissuescontainadiversearrayoftoxicorpotentiallytoxicsubstances,suchasre

4、sins,tannins,glycosides,andalkaloids,manyofwhicharehighlyeffectivedeterrentstoinsectsthatfeedonplants.ThesuccessoftheColoradobeetleininfestingpotatoes,forexample,seemstobecorrelatedwithitshightolerancetoalkaloidsthatnormallyrepelpotentialpests.Otherpossiblechemicaldefenses,whilenotdirectlytoxictothe

5、parasite,mayinhibitsomeessentialstepintheestablishmentofaparasiticrelationship.Forexample,glycoproteinsinplantcellwallsmayinactivateenzymesthatdegradecellwalls.Theseenzymesareoftenproducedbybacteriaandfungi.Activeplantdefensemechanismsarecomparabletotheimmunesystemofvertebrateanimals,althoughthecell

6、ularandmolecularbasesarefundamentallydifferent.Both,however,aretriggeredinreactiontointrusion,implyingthatthehosthassomemeansofrecognizingthepresenceofaforeignorganism.Themostdramaticexampleofaninducibleplantdefensereactionisthehypersensitiveresponse.Inthehypersensitiveresponse,cellsundergorapidnecr

7、osisthatis,theybecomediseasedanddieafterbeingpenetratedbyaparasite;theparasiteitselfsubsequentlyceasestogrowandisthereforerestrictedtooneorafewcellsaroundtheentrysite.Severaltheorieshavebeenputforwardtoexplainthebasisofhypersensitiveresistance.1.WhatdoesthepassagemainlydiscussThesuccessofparasitesin

8、resistingplantdefensemechanismsTheoriesonactiveplantdefensemechanismsHowplantdefensemechanismsfunction(D)HowtheimmunesystemofanimalsandthedefensemechanismsofplantsdifferThephrasesubjecttoinline1isclosestinmeaningto(A)susceptibleto(B)classifiedby(C)attractiveto(D)strengthenedbyThewordpunctureinline8i

9、sclosestinmeaningto(A)pierce(B)pinch(C)surround(D)cover.Thewordwhichinline12referstotissuessubstancesbarriersinsects5.WhichofthefollowingsubstancesdoestheauthormentionasNOTnecessarilybeingtoxictotheColoradobeetleresinstanninsglycosidesalkaloids6.Whydoestheauthormentionglycoproteinsinline17tocomparep

10、lantdefensemechanismstotheimmunesystemofanimalstointroducethediscussionofactivedefensemechanismsinplantstoillustratehowchemicalsfunctioninplantdefensetoemphasizetheimportanceofphysicalbarriersinplantdefenseTheworddramaticinline23couldbestbereplacedby(A)striking(B)accurate(C)consistent(D)appealing8.Whereinthepassagedoestheauthordescribeanactiveplant-defensereaction(A)Lines1-3Lines4-6Lines13-15Lines24-27Thepassagemostprobablycontinueswithadiscussionoftheorieson(A)thebasi