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ID:40383666
大小:1.24 MB
页数:5页
时间:2019-08-01
《Transport in Flowering Plants》由会员上传分享,免费在线阅读,更多相关内容在学术论文-天天文库。
1、BioFactsheetJanuary2001Number82TransportinFloweringPlantsThisFactsheetcoverstherelevantASsyllabuscontentofthemajorexaminationboards.BystudyingthisFactsheetcandidateswillgainaknowledgeandunderstandingof:·theneedfortransportsystemsinfloweringplants.·thedistributionofxylemandphloeminroot,stema
2、ndleaf.·thestructureofxylemandphloeminrelationtotheirfunctions.·theuptakeofwaterandthetranspirationstream.·theeffectofchangingenvironmentalfactorsontranspiration.·themass-flowmodeltoexplaintranslocation,includingthe‘energy-requiring’natureoftheprocess.·theexperimentalevidencesupportingthema
3、ss-flowmodel.Transportsystemsintermsofsizeandsurfaceareatovolumeratio.Fig2.TransversesectionofdicotyledonousstemSubstancessuchasglucosemoleculesandnitrateionsmovenaturallyfromaregionofhigherconcentrationtooneoflowerconcentrationbydiffusion.impermeablephloemWaterdiffusesthroughaselectivelype
4、rmeablemembranefromaregionofvascularouterepidermiscambiumbundlehigherwaterpotentialtooneoflowerwaterpotential,aprocessknownasxylemosmosis.Thesevitalprocessesareessentialbutadequateonlyforthetransportofmoleculesandionsovershortdistanceswithinalivingsystem.Diffusionbyitselfisnotsufficient;iti
5、softentooslow,possiblyinthewrongdirectionandinadequateoverlongerdistances.Theevolutionofcortexfloweringplantshasseenthedevelopmentofefficienttransportsystemswhichhaveenabledplantstocolonisetheland,toincreasetheirsizeandtodevelopanerecthabit.Xylemandphloemenablethemovementofwater,organicmole
6、culesandionsoverlongdistances.Distributionofxylemandphloeminroot,stemandleaf.Fig3.VerticalsectionofdicotyledonousleafXylemtissuetransportswateranddissolvedmineralsaltsabsorbedfromthesoilbytherootsystem.Itconductsthedilutesolutionupthestemandimpermeableintotheleaves.Phloemtissuetransportsorg
7、anicsubstancesupanddowncuticleaplant,takingthemoleculesfromwheretheyaremade(leaves)toareasupperwheretheyareused(growingpoints/flowers)orstored(roots,seeds,epidermisfruits).palisadeRemember-transportofwaterandionsinthexylemisusuallyreferredmesophylltoasco
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