英语作文：秋天叶子为什么会变颜色.docx

英语作文：秋天叶子为什么会变颜色

经典英语作文：秋天叶子为什么会变颜色在日常的学习、工作、生活中，大家总免不了要接触或使用作文吧，作文根据写作时限的不同可以分为限时作文和非限时作文。那么问题来了，到底应如何写一篇优秀的作文呢？下面是小编为大家整理的经典英语作文：秋天叶子为什么会变颜色，希望能够帮助到大家。英语作文：秋天叶子为什么会变颜色1Whydoleaveschangecolorinthefall?asksPatriciaBrown,ofNewYorkCity.Autumnscooldaysaretrimmedwithdeepblueskiesandgoldenlight,andbrilliantleavesofyellow,orangeandred.Leaveschangingcolorinthefallareatreeswayofpreparingforlongwinter,ratherlikeweputupstormwindowsandpullwarmclothesandblanketsoutofstorage.Insummer,theleavesontreeslikepinoaksandsugarmaplesaregreenbecausetheyarechock-fullofthegreenpigmentchlorophyll.Treesneedsunlighttoproducechlorophyll.Inturn,chlorophyllusessunlightsenergytosplitwater(H2O)intohydrogenandoxygen.Meanwhile,leavesalsoabsorbcarbondioxidegasfromtheair.Theendproductsofleafchemistry:carbohydrates(homemadeplantfoodforthetree),andoxygen,releasedintotheair(thegasweneedtobreathe).Thewholeprocessiscalledphotosynthesis.Alongwithgreenchlorophyll,mostleavesalsocontainyellow,orangeandred-orangepigmentscelledcarotenoids.Treesdontneedlighttomakecarotenoids.Botanistscallthem"helperpigments,"becausecarotenoidsabsorbsomesunlightand(nicely)passtheenergyalongtochlorophyll.Wedontseemuchofthesedeputypigments(carotene,lycopene,andxanthophyll)insummer,becausetheyaremaskedbyabundantgreenchlorophyll.Buttheever-shorteningdaysoffallmeanlessdaylightandcolderweather.Theaveragetreeisrushingtosaveallthenutrientsitcanforitswinterhibernation.Nitrogenandphosphorusarepulledfromleavesforstorageinbranches.Alayerofcorkycellsgrowsbetweentheleavesstemsandtheirbranches,reducingtheleavessupplyofnutrientsandwater.Withdiminishedsunlight,water,andnutrients,chlorophyllsynthesisslows.Old,worn-outchlorophyllbreaksdownattheusualrate--ironically,sunlightdestroysit--soeachleafsstockgraduallydwindles.Andasthegreenfades,yellowandorangeemergefromhiding.Unlikethegreenandyellowpigments,redandpurplepigments(anthocyanins,partoftheflavonoidclass)actuallyforminleavesintheautumn,tintingleavesscarletandburgundy.Botanistshavelongwonderedwhyso