Doyouwanttoknowhowandwhyafallleafchangescolor?Wefirsthavetounderstandwhatleavesareandwhattheydo.

Leavesaretheworld’sfoodfactories.PlantstakewaterfromthegroundthroughtheirrootsandtakeCO2fromtheair.PlantsusesunlighttoturnwaterandCO2intoglucose(葡萄糖)akindofsugar.Plantsuseitasfoodforenergyandgrowing.

Achemicalcalled“chlorophyll”intheleavesgivesplantstheirgreencolour.Assummerendsandautumncomesthedaysgetshorterandshorterandtrees“know”tobegingettingreadyforwinter.

Duringwinterthereisnotenoughsunlightorwater.Treesrestduringthistimeandliveonthefoodtheystoreduringthesummer.Theybegintoshutdowntheirfood-makingfactories.Asthegreenchlorophylldisappearsfromtheleaveswebegintoseeyellowandorangeleaves.

Thebrightredsandpurplesweseeinleavesaremademostlyinautumn.Insometreeslikemaplessunlightandthecoolnightsofautumnturntheglucoseintheleavesintoaredcolour.Andwecanenjoythebeautifulredleavesduringautumn.

1.Whichshouldbeinthebox?

A.airB.sugarC.waterD.wind

2.Theunderlinedword“chlorophyll”means__________.

A.叶绿素B.脂肪C.蛋白质D.淀粉

3.Theleavesturnyellowbecausetheyareshortof(缺少)__________.

A.waterandCO2

B.glucoseandenergy

C.sunlightandwater

D.sunlightandCO2

4.WhichofthefollowingisNOTtrue?

A.Whenautumncomesthedaysgetshorterandshorter.

B.Duringwintertreesliveonthefoodtheystoreinsummer.

C.Duringwintersomeofyellowandorangecolorsarestillintheleaves.

D.Treesbegintostopmakingfoodinsummer.

5.Thispassagetellsus_____________.

A.theplantscangrowwellonlywiththesunlight

B.thereareallkindsofplantsontheearth

C.notallthecolorsoftheleavesarefromchlorophyll

D.mapleleaveschangethecolorasothertrees