Leaves Turn Color托福听力原文翻译及问题答案

Leaves Turn Color托福听力原文翻译及问题答案

一、Leaves Turn Color托福听力原文：

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托福听力中文翻译：

旁白：听植物学课上的部分讲座。

女教授：现在是秋天，你知道，在美国的大部分地区，树上的叶子正在从绿色变为黄色、橙色和许多其他颜色。所以，这将是一个很好的时间来讨论这些树叶如何以及为什么会变成一种特别的颜色，那就是鲜红色。好吧，在我们讨论为什么树叶会变成红色之前，首先让我们，嗯，看，我知道这是一种非常古老的材料，但为了安全起见，让我们先看看为什么树叶通常是绿色的。是叶绿素，对吧？

叶子的绿色来自叶绿素，这是一种负责光合作用的化学物质。叶片中的叶绿素以阳光的形式从太阳收集能量，并将这种能量转化为糖，糖是植物的食物。正是叶绿素使树叶大部分时间变绿。现在，树叶为什么会变色的经典解释是这样的。

秋天，树叶开始为冬天做准备，并停止合成新的叶绿素。由于叶绿素对阳光和寒冷的温度都很敏感，这两种情况在秋天都会发生，因此叶片中现有的叶绿素会分解。由于它没有被新的叶绿素所取代，叶子的绿色逐渐消失。当这种情况发生时，叶片中的其他色素变得可见。根据经典理论，红色素也是如此。它一直存在于叶子中，但被绿色叶绿素所掩盖。这是经典的解释，部分正确。为什么我说“部分”？

嗯，对于黄色或橙色之类的颜料来说可能是这样，但对于红色颜料来说似乎不成立。让我们后退一点。究竟是什么使树叶呈现红色？这是一种叫做花青素的红色颜料。

这就是经典解释似乎不适用于红色的地方。有趣的是，在夏天，树叶中几乎没有花青素，但在树木即将落叶的前几周，花青素的产量显著增加。换句话说，与其他色素不同的是，花青素不仅在秋天被叶绿素的分解所掩盖；它们实际上是在这个时候创建的。

这就提出了一个问题。为什么一棵树在落叶之前会产生更多的花青素？为什么这棵树要在叶子掉下来之前花费这么多的资源来做这件事？表面上看，这毫无意义。我不知道，当你知道你的旧车用不了几个月的时候，这就像花钱重新油漆一样。秋天所有这些额外的花青素似乎都是浪费。

但请记住，大自然的资源非常经济，这意味着花青素必须具有对树木非常重要的功能。今天有一些关于这个函数可能是什么的理论。

其中一种涉及捕食性昆虫；另一个涉及真菌。你知道，我对这些理论和相关研究读得越多，它总是给我带来更多的问题，而不是答案。所以我真的很高兴了解到一个完全不同的理论…一个新的理论。它似乎有研究和数据可以提供充分的解释。就是这样。

记得我说过叶绿素会分解吗？在秋天，树叶的许多其他化学成分也会分解。我不是说它们完全被破坏了，因为它们会分解成其他不同的化学物质，树木可以从树叶中重新吸收，然后再利用。

现在，这种重吸收过程对树木非常重要，关键是它对光很敏感，这意味着太多的阳光照射会干扰这一过程。那么花色素苷在这里的位置呢？

花色素苷比叶绿素更稳定。它不容易受到阳光或寒冷的伤害。因此，在叶绿素分解后，它仍能工作很长时间。但是它有什么作用呢？

理论上，花青素可以保护再吸收过程免受阳光的伤害。例如，如果你仔细观察树上的一片红叶，你会发现大部分的红色素都在叶子的上侧，即面向太阳的一侧。这一新理论表明，花青素在树顶上的作用是保护叶片的其余部分免受阳光照射……更重要的是，让这些重要的化学物质被树重新吸收。

三、Leaves Turn Color托福听力问题：

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托福听力答案：

A1:正确答案：C

A2:正确答案：B

A3:正确答案：D

A4:正确答案：A

A5:正确答案：B

A6:正确答案：D

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