劍橋雅思10Test3閱讀Passage2原文翻譯(yi)Autumn leaves，今天(tian)中(zhong)國教育在線就來為大家分析(xi)這個問(wen)題(ti)。

Autumn leaves

秋葉變紅的原理

劍橋雅思10 Test3 Passage2閱讀原文翻譯

A部分

One of the most captivating natural events of the year in many areas throughout North America is the turning of the leaves in the fall.The colours are magnificent,but the question of exactly why some trees turn yellow or orange,and others red or purple,is something which has long puzzled scientists.

在北(bei)美許(xu)多地區，一(yi)(yi)(yi)年之(zhi)中最引人注(zhu)目的(de)自(zi)然(ran)現象之(zhi)一(yi)(yi)(yi)就(jiu)是秋天(tian)里(li)樹葉的(de)變化。其(qi)顏(yan)色(se)絢麗奪目。但究竟為什(shen)么一(yi)(yi)(yi)些樹木變成黃色(se)或橙色(se)，而其(qi)他(ta)卻(que)變成紅色(se)或紫色(se)？這一(yi)(yi)(yi)問題長期以來都困擾著(zhu)科(ke)學家。

B部分

Summer leaves are green because they are full of chlorophyll,the molecule that captures sunlight and converts that energy into new building materials for the tree.As fall approaches in the northern hemisphere,the amount of solar energy available declines considerably.For many trees—-evergreen conifers being an exception-the best strategy is to abandon photosynthesis*until the spring.So rather than maintaining the now redundant leaves throughout the winter,the tree saves its precious resources and discards them.But before letting its leaves go,the tree dismantles their chlorophyll molecules and ships their valuable nitrogen back into the twigs.As chlorophyll is depleted,other colours that have been dominated by it throughout the summer begin to be revealed.This unmasking explains the autumn colours of yellow and orange,but not the brilliant reds and purples of trees such as the maple or sumac.

夏天(tian)的(de)(de)葉(xie)(xie)子(zi)是綠(lv)色的(de)(de)，因為它們充滿了葉(xie)(xie)綠(lv)素。葉(xie)(xie)綠(lv)素文章來自(zi)老烤鴨雅思是一(yi)(yi)種捕獲陽光并(bing)將該(gai)能量轉化(hua)為新(xin)的(de)(de)樹木(mu)增(zeng)長材料(liao)的(de)(de)分(fen)子(zi)。隨(sui)著北(bei)半球秋(qiu)(qiu)天(tian)的(de)(de)到來，可(ke)利用的(de)(de)太陽能數量大大減(jian)少。對于許多(duo)樹木(mu)來說-常綠(lv)針葉(xie)(xie)樹除外(wai)-最佳(jia)策(ce)略是放棄光合(he)作用直到春天(tian)來臨。因此，與其保留冬季(ji)里十分(fen)多(duo)余的(de)(de)葉(xie)(xie)子(zi)，樹木(mu)選擇節省其寶貴(gui)的(de)(de)資源(yuan)而拋(pao)棄它們。但(dan)在棄置(zhi)這(zhe)(zhe)些葉(xie)(xie)子(zi)之前(qian)，樹木(mu)會分(fen)解其中的(de)(de)葉(xie)(xie)綠(lv)素分(fen)子(zi)，并(bing)將里面(mian)含有的(de)(de)寶貴(gui)的(de)(de)氮元素運(yun)回枝干。隨(sui)著葉(xie)(xie)綠(lv)素的(de)(de)枯竭，夏季(ji)里被它主導的(de)(de)顏(yan)色開始顯(xian)現(xian)出來。這(zhe)(zhe)一(yi)(yi)顯(xian)露(lu)過程解釋了秋(qiu)(qiu)天(tian)里出現(xian)的(de)(de)黃色和橙色，但(dan)卻無法解釋諸(zhu)如楓樹或漆樹之類的(de)(de)樹木(mu)所呈現(xian)的(de)(de)艷麗(li)的(de)(de)紅(hong)色和紫色。

C部分

The source of the red is widely known:it is created by anthocyanins,water-soluble plant pigments reflecting the red to blue range of the visible spectrum.They belong to a class of sugar-based chemical compounds also known as flavonoids.What’s puzzling is that anthocyanins are actually newly minted,made in the leaves at the same time as the tree is preparing to drop them.But it is hard to make sense of the manufacture of anthocyanins—why should a tree bother making new chemicals in its leaves when it’s already scrambling to withdraw and preserve the ones already there?

紅色(se)(se)的(de)(de)來源(yuan)廣(guang)為(wei)人知：它(ta)是由花(hua)(hua)青(qing)素(su)（一種可(ke)(ke)反射可(ke)(ke)見光譜中紅色(se)(se)到藍色(se)(se)范圍的(de)(de)水溶(rong)性植物(wu)色(se)(se)素(su)）產(chan)生的(de)(de)。它(ta)們屬于一類(lei)糖基化合(he)物(wu)，也被稱為(wei)類(lei)黃(huang)酮。令人費解的(de)(de)是，花(hua)(hua)青(qing)素(su)實(shi)際上是新合(he)成(cheng)的(de)(de)，是在(zai)樹木準備將樹葉丟棄(qi)的(de)(de)同時(shi)在(zai)里面產(chan)生的(de)(de)。但是，很難理解合(he)成(cheng)花(hua)(hua)青(qing)素(su)的(de)(de)意(yi)義-為(wei)什么樹木在(zai)急(ji)于收回并保存原本(ben)存在(zai)于樹葉中的(de)(de)化學物(wu)質時(shi)，還(huan)要在(zai)里面再制造出新的(de)(de)來呢？

D部分

Some theories about anthocyanins have argued that they might act as a chemical defence against attacks by insects or fungi,or that they might attract fruit-eating birds or increase a leaf’s tolerance to freezing.However there are problems with each of these theories,including the fact that leaves are red for such a relatively short period that the expense of energy needed to manufacture the anthocyanins would outweigh any anti-fungal or anti-herbivore activity achieved.

一些有關花(hua)青素的理(li)論認為，它(ta)們(men)可能是作為抵御昆蟲或真(zhen)菌(jun)攻擊的化(hua)學防(fang)御，或者(zhe)說，它(ta)們(men)可能會吸(xi)引以(yi)果實維(wei)生的鳥(niao)類或者(zhe)提(ti)升樹葉對寒冷的耐受(shou)性。但是，這些理(li)論都存在(zai)問題，例如樹葉變紅的時間如此(ci)之短，以(yi)至于制造花(hua)青素所需要耗(hao)費的能量會超過任何抗真(zhen)菌(jun)或防(fang)食草動(dong)物行為所取(qu)得的收益。

E部分

It has also been proposed that trees may produce vivid red colours to convince herbivorous insects that they are healthy and robust and would be easily able to mount chemical defences against infestation.If insects paid attention to such advertisements,they might be prompted to lay their eggs on a duller,and presumably less resistant host.The flaw in this theory lies in the lack of proof to support it.No one has as yet ascertained whether more robust trees sport the brightest leaves,or whether insects make choices according to colour intensity.

還有一(yi)種理論(lun)(lun)認(ren)為(wei)(wei)，樹木(mu)產生鮮(xian)(xian)艷的(de)(de)紅色是(shi)為(wei)(wei)了讓(rang)那些食草昆(kun)蟲相信，它(ta)們(men)十(shi)分(fen)健(jian)康強壯，能(neng)(neng)夠輕松的(de)(de)發起(qi)抵(di)御(yu)侵擾的(de)(de)化學防御(yu)。如果昆(kun)蟲會(hui)注意(yi)到這(zhe)些現(xian)象，它(ta)們(men)可(ke)能(neng)(neng)會(hui)將(jiang)卵產在顏色更(geng)為(wei)(wei)暗淡，不(bu)太(tai)可(ke)能(neng)(neng)進行抵(di)抗(kang)的(de)(de)宿主(zhu)上。這(zhe)一(yi)理論(lun)(lun)的(de)(de)缺陷在于缺乏證(zheng)據(ju)支持。尚無人能(neng)(neng)夠確定，更(geng)健(jian)壯的(de)(de)樹木(mu)是(shi)否(fou)會(hui)產生最鮮(xian)(xian)艷的(de)(de)葉子，又或者(zhe)昆(kun)蟲是(shi)否(fou)根據(ju)顏色強度來進行選擇。

F部分

Perhaps the most plausible suggestion as to why leaves would go to the trouble of making anthocyanins when they’re busy packing up for the winter is the theory known as the‘light screen’hypothesis.It sounds paradoxical,because the idea behind this hypothesis is that the red pigment is made in autumn leaves to protect chlorophyll,the light-absorbing chemical,from too much light.Why does chlorophyll need protection when it is the natural world’s supreme light absorber?Why protect chlorophyll at a time when the tree is breaking it down to salvage as much of it as possible?

樹(shu)葉為(wei)什(shen)么(me)會在忙(mang)于(yu)為(wei)冬季做準備的(de)時(shi)候還不嫌麻煩的(de)生產葉綠(lv)素。這(zhe)一(yi)現象最合(he)理的(de)解(jie)釋是一(yi)種(zhong)被(bei)稱為(wei)“光(guang)屏障”的(de)假說。它聽起來有些自相(xiang)矛盾。因為(wei)這(zhe)種(zhong)假說背(bei)后的(de)想法(fa)是，秋天里樹(shu)葉產生的(de)紅色素是為(wei)了防止葉綠(lv)素這(zhe)種(zhong)吸光(guang)物(wu)質吸收太(tai)多的(de)陽光(guang)。為(wei)什(shen)么(me)葉綠(lv)素作為(wei)自然界的(de)吸光(guang)能(neng)(neng)手還需要保(bao)護呢(ni)？為(wei)什(shen)么(me)要在樹(shu)木分(fen)解(jie)葉綠(lv)素以拯(zheng)救盡可(ke)能(neng)(neng)多的(de)營養物(wu)質時(shi)去保(bao)護它呢(ni)？

G部分

Chlorophyll,although exquisitely evolved to capture the energy of sunlight,can sometimes be overwhelmed by it,especially in situations of drought,low temperatures,or nutrient deficiency.Moreover,the problem of oversensitivity to light is even more acute in the fall,when the leaf is busy preparing for winter by dismantling its internal machinery.The energy absorbed by the chlorophyll molecules of the unstable autumn leaf is not immediately channeled into useful products and processes,as it would be in an intact summer leaf.The weakened fall leaf then becomes vulnerable to the highly destructive effects of the oxygen created by the excited chlorophyll molecules.

雖然葉(xie)(xie)綠(lv)素經過(guo)精巧的(de)(de)(de)(de)演變來捕捉太陽光中(zhong)(zhong)的(de)(de)(de)(de)能(neng)量(liang)，但它有時也(ye)會(hui)被過(guo)多的(de)(de)(de)(de)陽光所傷(shang)害(hai)，尤其(qi)(qi)是在(zai)干(gan)旱(han)、低(di)溫、或者營養缺乏的(de)(de)(de)(de)時候(hou)。此外，秋(qiu)天(tian)里(li)，當樹(shu)葉(xie)(xie)正忙于拆解(jie)其(qi)(qi)內部結構為冬天(tian)做準備的(de)(de)(de)(de)時候(hou)，對陽光過(guo)度(du)敏感的(de)(de)(de)(de)問題(ti)會(hui)更加嚴(yan)重(zhong)。不穩定的(de)(de)(de)(de)秋(qiu)葉(xie)(xie)中(zhong)(zhong)，葉(xie)(xie)綠(lv)素分子(zi)所吸收(shou)的(de)(de)(de)(de)能(neng)量(liang)并不會(hui)被立刻輸(shu)送到有用(yong)的(de)(de)(de)(de)產(chan)品或過(guo)程中(zhong)(zhong)，就(jiu)像(xiang)夏天(tian)里(li)完好無損(sun)的(de)(de)(de)(de)葉(xie)(xie)子(zi)里(li)所發生的(de)(de)(de)(de)那樣。這時候(hou)，衰弱的(de)(de)(de)(de)落葉(xie)(xie)十分容易受到活躍的(de)(de)(de)(de)葉(xie)(xie)綠(lv)素分子(zi)所產(chan)生的(de)(de)(de)(de)氧氣的(de)(de)(de)(de)破(po)壞(huai)。

H部分

Even if you had never suspected that this is what was going on when leaves turn red,there are clues out there.One is straightforward:on many trees,the leaves that are the reddest are those on the side of the tree which gets most sun.Not only that,but the red is brighter on the upper side of the leaf.It has also been recognised for decades that the best conditions for intense red colours are dry,sunny days and cool nights,conditions that nicely match those that make leaves susceptible to excess light.And finally,trees such as maples usually get much redder the more north you travel in the northern hemisphere.It’s colder there,they’re more stressed,their chlorophyll is more sensitive and it needs more sunblock.

即(ji)使你從未(wei)懷(huai)疑過這就是(shi)樹葉變紅時所發生的(de)(de)(de)(de)事(shi)情，也仍然存在(zai)許多提示線索(suo)。最簡單明了的(de)(de)(de)(de)一條(tiao)是(shi)：在(zai)許多樹木上(shang)，最紅的(de)(de)(de)(de)葉子(zi)出(chu)現在(zai)光照(zhao)最多的(de)(de)(de)(de)那(nei)一側。不僅如此，葉子(zi)上(shang)部的(de)(de)(de)(de)紅色(se)會更(geng)加鮮亮。幾十(shi)年來，如下事(shi)實都(dou)廣為(wei)人知，產生鮮艷紅色(se)的(de)(de)(de)(de)最佳條(tiao)件(jian)(jian)為(wei)干燥(zao)、陽光充足的(de)(de)(de)(de)白天(tian)和寒(han)(han)冷(leng)(leng)的(de)(de)(de)(de)夜晚。這些條(tiao)件(jian)(jian)恰好與那(nei)些使葉子(zi)容易遭受過度陽光損害的(de)(de)(de)(de)條(tiao)件(jian)(jian)相匹配。最后(hou)，在(zai)北半球越往北去，楓樹之類的(de)(de)(de)(de)樹木就會變得越紅。那(nei)里(li)更(geng)加寒(han)(han)冷(leng)(leng)，它們要承受更(geng)多的(de)(de)(de)(de)壓力，它們的(de)(de)(de)(de)葉綠(lv)素更(geng)加敏感，需要更(geng)多的(de)(de)(de)(de)光屏障。

I部分

What is still not fully understood,however,is why some trees resort to producing red pigments while others don’t bother,and simply reveal their orange or yellow hues.Do these trees have other means at their disposal to prevent overexposure to light in autumn?Their story,though not as spectacular to the eye,will surely turn out to be as subtle and as complex.

然而，至(zhi)今仍未被完(wan)全(quan)理解的是，為(wei)什(shen)么一(yi)些樹(shu)木會選擇產(chan)生紅色素，而其他的則嫌麻煩，只是顯露出其橙色或(huo)者黃(huang)色而已(yi)。難道(dao)這些樹(shu)木在拋棄葉子的時候(hou)擁有其他手(shou)段來防止過度暴露于(yu)秋天的陽光之下嗎？它們的故事雖然不那(nei)么引人注目，但肯定也同(tong)樣微妙和(he)復雜(za)。

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