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时间:2018-12-09
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1、第九篇AnEssentialScientificProcess一个至关重要的科学过程Alllifeontheearthdependsupongreenplants.Usingsunlight,theplantsproducetheirownfood.Thenanimalsfeedupontheplants.Theytakeinthenutrientstheplantshavemadeandstored.Butthat’snotall.Sunlightalsohelpsaplantproduceoxygen.Someoftheoxygenisusedbytheplant,buta
2、plantusuallyproducesmoreoxygenthanituses.Theexcessoxygenisnecessaryforanimalsandotherorganismstolive.Theprocessofchanginglightintofoodandoxygeniscalledphotosynthesis.Besideslightenergyfromthesun,plantsalsousewaterandcarbondioxide.Thewatergetstotheplantthroughitsroots.Thecarbondioxideentersth
3、eleavesthroughtinyopeningscalledstomata.Thecarbondioxidetravelstochloroplasts,specialcellsinthebodiesofgreenplants.Thisiswherephotosynthesistakesplace.Chloroplastscontainthechlorophyllsthatgiveplantstheirgreencolor.Thechlorophyllsarethemoleculesthattraplightenergy.Thetrappedlightenergychange
4、swaterandcarbondioxidetoproduceoxygenandasimplesugarcalledglucose.Carbondioxideandoxygenmoveintoandoutofthestomata.Watervaporalsomovesoutofthestomata.Morethan90percentofwateraplanttakesinthroughitsrootsescapesthroughthestomata.Duringthedaytime,thestomataofmostplantsareopen.Thisallowscarbondi
5、oxidetoentertheleavesforphotosynthesis.Asnightfalls,carbondioxideisnotneeded.Thestomataofmostplantsclose.Waterlossstops.Ifphotosynthesisceased,therewouldbelittlefoodorotherorganicmatterontheearth.Mostorganismswoulddisappear.Theearth’satmospherewouldnolongercontainoxygen.Photosynthesisisessen
6、tialforlifeonourplanet.练习:1.Inthefirstparagraph,theword“excess”means.B extra.2.Whichofthefollowingdoesnotmovethroughaplant’sstomata?D Food.3.Inthetitle,thetermEssentialScientificProcessreferstoA photosynthesis.4.ThispassageisprimarilydevelopedbyA explainingaprocess.5.Anothergoodtitleforthisp
7、assagewouldbeC HowPhotosynthesisWorks.第二十二篇RealWorldRobots现实世界中的机器人Whenyouthinkofarobot,doyouenvisionashiny,metallicdevicehavingthesamegeneralshapeasahumanbeing,performinghumanlikefunctions,andrespondingtoyourquestionsinamonotonevoiceaccentuatedbyh
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