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1、2010年12月英语六级模拟试题及答案 PartⅡReadingComprehension(SkimmingandScanning)(15minutes) MainEnergiesfortheBody Abalanceddietisonethatprovidesanadequateintakeofenergyandnutrientsformaintenanceofthebodyandthereforegoodhealth.Adietcaneasilybeadequatefornorma
2、lbodilyfunctioning,yetmaynotbeabalanceddiet. Carbohydrates Carbohydratesarearapidsourceofenergy,theyarethebody'sfuel.Thebulkofabalanceddietshouldbemadefromcarbohydrates.Ifeateninanexcessofthedietaryrequirementscarbohydratesareeasilystoredasfatsinthecells
3、,althoughcarbohydrateisthefirstsourceofenergyinthebody.Anaverageadultrequiresabout12,000kJofenergyaday,mostofthisissuppliedbytherespirationofcarbohydratesinthecells. Carbohydratesareusedprincipallyasarespiratorysubstrates,i.e.tobeoxidizedtoreleaseenergyfo
4、ractivetransport,macromoleculesynthesis,celldivisionandmusclecontraction.Carbohydratesaredigestedintheduodenumandileumandabsorbedasglucoseintocells.Sourcesofcarbohydratessuchasstarcharerice,potatoes,wheatandothercereals.Sugarsarealsocarbohydrates,sourcesof
5、sugarsarerefinedsugar-sucrose,whichisafoodsweetenerandpreservativeandfruitsugars-fructose.Ifthedietlackscarbohydratestoresoffataremobilizedandusedasanenergysource. Proteins Proteinisnotadirectsourceofenergyinthebody,itisusedprimarilyforgrowthandrepairofb
6、odytissueswhileremaininganenergysourceasalastresort.Proteinsfulfillawidevarietyofrolesinthebody.Theyarebrokendowninthestomachandintestinestoaminoacidswhicharethenabsorbed.Thebodycanonlyform8aminoacidstobuildproteinsfrom,thedietmustprovideEssentialAminoAcid
7、s(EAAs)whicharesynthesizedintoproteinswhichcanbestructural,i.e.collageninbone,keratininhair,myosinandactininmuscle;metabolicenzymes,hemoglobin,protectiveantibodiesandcommunicativehormones. Sourcesofproteinincludemeat,fish,eggsandpulses.Thedietneedstoprovi
8、de8EAAsasthebodyisunabletosynthesisproteinswithoutthesemolecules.2otheraminoacidsaresynthesizedfromEAAssoifthedietlackstheoriginalEAAstheseothertwowillnotbepresenteither.Phenylalanineisconvertedtotyrosineandm
