Leaves Turn Color托福聽力原文翻譯及問題答案

Leaves Turn Color托福聽力原文翻譯及問題答案

一、Leaves Turn Color托福聽力原文：

NARRATOR:Listen to part of a lecture in a botany class.

FEMALE PROFESSOR:It's autumn,and as you know,in most parts of the United States the leaves on the trees are changing color from green…to yellow,orange,and lots of other colors.So this'll be a great time to talk about how and why some of these leaves turn one color in particular—and that's bright red.Well,before we discuss why leaves turn red,first let's,um—look,I know this is very old material,but just to play it safe—let's first go over why leaves are usually green.It’s chlorophyll,right?

Leaves get their green color from chlorophyll—the chemical that's responsible for photosynthesis.The chlorophyll in the leaves collects energy from the Sun,in the form of sunlight,and it converts this energy into sugar,which is food for the plant.It's chlorophyll that makes leaves green most of the time.Now,the classic explanation for why leaves change color is this.

In autumn,the leaves start preparing for the winter and stop synthesizing new chlorophyll.Since chlorophyll is sensitive to sunlight and to cold temperatures—both of which you get in autumn—the existing chlorophyll in the leaves breaks down.And since it's not being replaced by the new chlorophyll,the green color of the leaves gradually fades away.As this happens,the other pigments present in the leaf become visible.According to the classic theory,this is true for the red pigment as well.It was there in the leaf all along but it was hidden by the green chlorophyll.OK,so that's the classic explanation,and it's partially right.Why do I say“partially”?

Well,it's probably true for pigments like yellow or orange,but it doesn't seem to hold for the red pigment.Let's back up a bit.Just what produces this red color in leaves?It's a red pigment called anthocyanin.

Here's where the classic explanation doesn't seem to apply to red.What's interesting is that during the summer,there was very little if any anthocyanin in the leaves,but in the weeks before a tree is about to drop its leaves,the production of anthocyanins increases significantly.In other words,unlike those other pigments,anthocyanins are not just unmasked by the breakdown of chlorophyll in autumn;they're actually created at this time.

So that raises a question.Why would a tree produce more anthocyanin just before dropping its leaves?Why does the tree spend so much of its resources doing this just before the leaves fall off?On the surface,this doesn't make sense.It'd be like spending money to,I don't know,to have your old car repainted when you know the car's not going to last more than a couple of months.All this extra anthocyanin in the autumn seems like a waste.

But remember,nature is very economical with its resources,so that means anthocyanin must be serving some function that's important for the tree.Today there are some theories about what that function might be.

One of them involves predatory insects;another involves fungi.You know,the more I read about these theories and the related research,it always created more questions for me than answers.So I was really glad to learn about a totally different theory…a new one.It seemed to come with research and data that give a full explanation.So here it is.

Remember I said the chlorophyll breaks down?Well,in autumn,a whole lot of other chemical constituents of the leaf break down as well.I don't mean they're totally destroyed,'cause actually they break down into other,different chemicals that the tree can reabsorb from the leaves and reuse later.

Now,this reabsorption process is very important for the tree,and—here's the key—it's sensitive to light,meaning that too much exposure to sunlight can interfere with this process.So where does anthocyanin fit in here?

Well,anthocyanin's more stable than chlorophyll.It's not harmed as easily by the Sun or the cold.So it's still working long after the chlorophyll breaks down.But what does it do?

The theory is that anthocyanin protects the reabsorption process from the sunlight.For example,if you look closely at a red leaf on a tree,you'll notice that most of the red pigment is on the upper side of the leaf,the side facing the Sun.This new theory suggests that what the anthocyanin is doing there on top is shielding the rest of the leaf from the sunlight…and more importantly,allowing those important chemicals to be reabsorbed by the tree.

二、Leaves Turn Color托福聽力中文翻譯：

旁白：聽植物學(xué)課上的部分講座。

女教授：現(xiàn)在是秋天，你知道，在美國的大部分地區(qū)，樹上的葉子正在從綠色變?yōu)辄S色、橙色和許多其他顏色。所以，這將是一個很好的時間來討論這些樹葉如何以及為什么會變成一種特別的顏色，那就是鮮紅色。好吧，在我們討論為什么樹葉會變成紅色之前，首先讓我們，嗯，看，我知道這是一種非常古老的材料，但為了安全起見，讓我們先看看為什么樹葉通常是綠色的。是葉綠素，對吧？

葉子的綠色來自葉綠素，這是一種負(fù)責(zé)光合作用的化學(xué)物質(zhì)。葉片中的葉綠素以陽光的形式從太陽收集能量，并將這種能量轉(zhuǎn)化為糖，糖是植物的食物。正是葉綠素使樹葉大部分時間變綠?，F(xiàn)在，樹葉為什么會變色的經(jīng)典解釋是這樣的。

秋天，樹葉開始為冬天做準(zhǔn)備，并停止合成新的葉綠素。由于葉綠素對陽光和寒冷的溫度都很敏感，這兩種情況在秋天都會發(fā)生，因此葉片中現(xiàn)有的葉綠素會分解。由于它沒有被新的葉綠素所取代，葉子的綠色逐漸消失。當(dāng)這種情況發(fā)生時，葉片中的其他色素變得可見。根據(jù)經(jīng)典理論，紅色素也是如此。它一直存在于葉子中，但被綠色葉綠素所掩蓋。這是經(jīng)典的解釋，部分正確。為什么我說“部分”？

嗯，對于黃色或橙色之類的顏料來說可能是這樣，但對于紅色顏料來說似乎不成立。讓我們后退一點。究竟是什么使樹葉呈現(xiàn)紅色？這是一種叫做花青素的紅色顏料。

這就是經(jīng)典解釋似乎不適用于紅色的地方。有趣的是，在夏天，樹葉中幾乎沒有花青素，但在樹木即將落葉的前幾周，花青素的產(chǎn)量顯著增加。換句話說，與其他色素不同的是，花青素不僅在秋天被葉綠素的分解所掩蓋；它們實際上是在這個時候創(chuàng)建的。

這就提出了一個問題。為什么一棵樹在落葉之前會產(chǎn)生更多的花青素？為什么這棵樹要在葉子掉下來之前花費這么多的資源來做這件事？表面上看，這毫無意義。我不知道，當(dāng)你知道你的舊車用不了幾個月的時候，這就像花錢重新油漆一樣。秋天所有這些額外的花青素似乎都是浪費。

但請記住，大自然的資源非常經(jīng)濟，這意味著花青素必須具有對樹木非常重要的功能。今天有一些關(guān)于這個函數(shù)可能是什么的理論。

其中一種涉及捕食性昆蟲；另一個涉及真菌。你知道，我對這些理論和相關(guān)研究讀得越多，它總是給我?guī)砀嗟膯栴}，而不是答案。所以我真的很高興了解到一個完全不同的理論…一個新的理論。它似乎有研究和數(shù)據(jù)可以提供充分的解釋。就是這樣。

記得我說過葉綠素會分解嗎？在秋天，樹葉的許多其他化學(xué)成分也會分解。我不是說它們完全被破壞了，因為它們會分解成其他不同的化學(xué)物質(zhì)，樹木可以從樹葉中重新吸收，然后再利用。

現(xiàn)在，這種重吸收過程對樹木非常重要，關(guān)鍵是它對光很敏感，這意味著太多的陽光照射會干擾這一過程。那么花色素苷在這里的位置呢？

花色素苷比葉綠素更穩(wěn)定。它不容易受到陽光或寒冷的傷害。因此，在葉綠素分解后，它仍能工作很長時間。但是它有什么作用呢？

理論上，花青素可以保護再吸收過程免受陽光的傷害。例如，如果你仔細(xì)觀察樹上的一片紅葉，你會發(fā)現(xiàn)大部分的紅色素都在葉子的上側(cè)，即面向太陽的一側(cè)。這一新理論表明，花青素在樹頂上的作用是保護葉片的其余部分免受陽光照射……更重要的是，讓這些重要的化學(xué)物質(zhì)被樹重新吸收。

三、Leaves Turn Color托福聽力問題：

Q1:1.What is the main purpose of the lecture?

A.To explain how the red pigment in leaves breaks down

B.To show that leaf color varies based on the tree species

C.To introduce a theory about why leaves turn a particular color

D.To explain how chlorophyll protects trees in autumn

Q2:2.What does the professor imply when she explains why leaves are green?

A.She wants to correct a common misconception about the topic.

B.She thinks the students are probably already familiar with the material.

C.She believes the process is too complicated to discuss in depth.

D.She knows that students are often confused about the functions of chlorophyll

Q3:3.What does the professor mean when she says that the classic theory is partially right?

A.It describes what happens in the summer but not what happens in autumn

B.It describes what happens in tree leaves but not what happens in leaves of other plants

C.It explains how pigments are synthesized but not how they break down.

D.It explains some cases of color change in tree leaves but not all cases.

Q4:4.Why does the professor mention painting a car?

A.To question why a large amount of anthocyanin is produced just before leaves fall

B.To explain why most leaves turn red instead of other colors

C.To remind students how cooler temperatures affect the color of leaves

D.To show how anthocyanin absorbs sunlight to produce food for trees

Q5:5.The professor mentions theories about why leaves turn red that involve predatory insects and fungi.What is her opinion about those theories?

A.They are based on careful research.

B.They do not completely explain the phenomenon.

C.They have not received enough attention.

D.They have been proved to be incorrect.

Q6:6.According to the professor,why does anthocyanin appear on the upper side of some leaves?

A.To help chlorophyll absorb the sunlight

B.To maximize the leaf's utilization of sunlight

C.To accelerate the breakdown of chlorophyll

D.To protect an important process from the sunlight

四、Leaves Turn Color托福聽力答案：

A1:正確答案：C

A2:正確答案：B

A3:正確答案：D

A4:正確答案：A

A5:正確答案：B

A6:正確答案：D

>> 雅思 托福 免費測試、量身規(guī)劃、讓英語學(xué)習(xí)不再困難<<