老托福閱讀真題passage11

老托福閱讀真題及答案：PASSAGE11Plantsaresubjecttoattackandinfectionbyaremarkablevarietyofsymbioticspeciesandhaveevolvedadiversearrayofmechanismsdesignedtofrustratethepotentialcolonists.Thesecanbedividedintopreformedorpassivedefensemechanismsandinducibleoractivesystems.Passiveplantdefensecomprisesphysicalandchemicalbarriersthatprevententryofpathogens,suchasbacteria,orrendertissuesunpalatableortoxictotheinvader.Theexternalsurfacesofplants,inadditiontobeingcoveredbyanepidermisandawaxycuticle,oftencarryspikyhairsknownastrichomes,whicheitherpreventfeedingbyinsectsormayevenpunctureandkillinsectlarvae.Othertrichomesarestickyandglandularandeffectivelytrapandimmobilizeinsects.Ifthephysicalbarriersoftheplantarebreached,thenpreformedchemicalsmayinhibitorkilltheintruder,andplanttissuescontainadiversearrayoftoxicorpotentiallytoxicsubstances,suchasresins,tannins,glycosides,andalkaloids,manyofwhicharehighlyeffectivedeterrentstoinsectsthatfeedonplants.ThesuccessoftheColoradobeetleininfestingpotatoes,forexample,seemstobecorrelatedwithitshightolerancetoalkaloidsthatnormallyrepelpotentialpests.Otherpossiblechemicaldefenses,whilenotdirectlytoxictotheparasite,mayinhibitsomeessentialstepintheestablishmentofaparasiticrelationship.Forexample,glycoproteinsinplantcellwallsmayinactivateenzymesthatdegradecellwalls.Theseenzymesareoftenproducedbybacteriaandfungi.Activeplantdefensemechanismsarecomparabletotheimmunesystemofvertebrateanimals,althoughthecellularandmolecularbasesarefundamentallydifferent.Both,however,aretriggeredinreactiontointrusion,implyingthatthehosthassomemeansofrecognizingthepresenceofaforeignorganism.Themostdramaticexampleofaninducibleplantdefensereactionisthehypersensitiveresponse.Inthehypersensitiveresponse,cellsundergorapidnecrosis—thatis,theybecomediseasedanddie—afterbeingpenetratedbyaparasite;theparasiteitselfsubsequentlyceasestogrowandisthereforerestrictedtooneorafewcellsaroundtheentrysite.Severaltheorieshavebeenputforwardtoexplainthebasisofhypersensitiveresistance.1.WhatdoesthepassagemainlydiscussThesuccessofparasitesinresistingplantdefensemechanismsTheoriesonactiveplantdefensemechanismsHowplantdefensemechanismsfunctionHowtheimmunesystemofanimalsandthedefensemechanismsofplantsdiffer2.Thephrase"subjectto"inline1isclosestinmeaningtosusceptibletoclassifiedbyattractivetostrengthenedby3.Theword"puncture"inline8isclosestinmeaningtopiercepinchsurroundcover.4.Theword"which"inline12referstotissuessubstancesbarriersinsectsWhichofthefollowingsubstancesdoestheauthormentionasNOTnecessarilybeingtoxictotheColoradobeetleresinstanninsglycosidesalkaloids6.Whydoestheauthormention"glycoproteins"inline17tocompareplantdefensemechanismstotheimmunesystemofanimalstointroducethediscussionofactivedefensemechanismsinplantstoillustratehowchemicalsfunctioninplantdefensetoemphasizetheimportanceofphysicalbarriersinplantdefenseTheword"dramatic"inline23couldbestbereplacedby(A)striking(B)accurate(C)consistent(D)appealingWhereinthepassagedoestheauthordescribeanactiveplant-defensereaction(A)Lines1-3(B)Lines4-6(C)Lines13-15(D)Lines24-27Thepassagemostprobablycontinueswithadiscussionoftheorieson(A)thebasisof