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1、韩苏：2014考研英语阅读每日一篇(36) 2014考研基础阅读每日一篇第三十六篇如约而至，呵呵，只要努力，就能成功，锲而不舍，金石可镂!我们一起做起来吧! Unit7科学世界 Text6正文 Mostgrowingplantscontainmuchmorewaterthanallothermaterialscombined.C.R.Darneshassuggestedthatitisaspropertotermtheplantawaterstructureastocallahousecomposedmainlyofbrick--
2、abrickbuilding.Certainitisthatallessentialprocessesofplantgrowthanddevelopmentoccurinwater.Themineralelementsfromthesoilthatareusablebytheplantmustbedissolvedinthesoilsolutionbeforetheycanbetakenintotheroot.Theyarecarriedtoallpartsofthegrowingplantandarebuiltintoessentia
3、lplantmaterialswhileinadissolvedstate.Thecarbondioxidefromtheairmayentertheleafasagasbutisdissolvedinwaterintheleafbeforeitiscombinedwithapartofthewatertoformsimplesugars--thebasematerialfromwhichtheplantbodyismainlybuilt.Activelygrowingplantpartsaregenerally75to90percen
4、twater.Structuralpartsofplants,suchaswoodystemsnolongeractivelygrowing,mayhavemuchlesswaterthangrowingtissues. Theactualamountofwaterintheplantatanyonetime,however,isonlyaverysmallpartofwhatpassesthroughitduringitsdevelopment.Theprocessesofphotosynthesis,bywhichcarbondi
5、oxideandwaterarecombined--inthepresenceofchlorophyll(叶绿素)andwithenergyderivedfromlight--toformsugars,requirethatcarbondioxidefromtheairentertheplant.Thisoccursmainlyintheleaves.Theleafsurfaceisnotsolidbutcontainsgreatnumbersofminuteopenings,throughwhichthecarbondioxideen
6、ters.Thesamestructurethatpermitstheonegastoentertheleaf,however,permitsanothergas--watervapor--tobelostfromit.Sincecarbondioxideispresentintheaironlyintracequantities(3to4partsin10,000partsofair)andwatervaporisnearsaturationintheairspaceswithintheleaf(at80F,saturatedairw
7、ouldcontainabout186partsofwatervaporin10,000partsofair),thetotalamountofwatervaporlostismanytimesthecarbondioxideintake.Actually,becauseofwindandotherfactors,thelossofwaterinproportiontocarbondioxideintakemaybeevengreaterthantherelativeconcentrationsofthetwogases.Also,no
8、tallofthecarbondioxidethatenterstheleafissynthesizedintocarbohydrates(碳水化合物). Text6习题 1.Agrowingplant
