『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 28 Lec 3听力练习：What is the lecture mainly about?原文题目答案解析，TPO/Official 28 Lec 3听力原文范文音频翻译。

托福TPO/Official 28 Lec 3听力原文What is the lecture mainly about?-新东方托福官方网校手机版

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

教授:上一次，我们讨论了光合作用，通过这个过程，植物用光将二氧化碳和水转化成食物。

Professor: OK. Last time we talked about photosynthesis, the process by which plants use light to convert carbon dioxide and water into food.

今天我想说说另一个光影响植物的方式。

Today I want to talk about another way light affects plants.

我很确定从物理课上，你们都知道了光是怎么用微观的方式传播着，并且我们只能看见在一定波长范围内的光。

I am sure you all know from physics class about how light moves in microscopic waves and that we can only see light when the wavelength of that light is in a specific range.

另外，取决于不同的波长，我们看见不同的颜色。

Plus, depending on the wavelengths, we see different colors.

好的，植物也可以区分不同波长的光。

Well, plants are also capable of distinguishing between different wavelengths of light.

植物并不能像人类或者动物那样看得到，但是他们有光感受器。

Plants don't see in the sense that humans or animals do, but they do have photoreceptors.

光感受器是通过传出化学信号来对光做出反应的细胞。

Photoreceptors are cells that respond to light by sending out a chemical signal.

并且，生物体、植物会对这种信号做出反应。

And the organism, the plant, reacts to this signal.

事实上，这些从它们光感受器中获得的信号有时候会引起巨大的反应。

In fact, the signals that plants get from their photoreceptors sometimes cause significant reactions.

它们获知冬天已经离去而春天已经到来的一种方法，就是感觉光线的变化。

And one way they know when winter is ending and spring is beginning is by sensing the change in light.

一个成熟植物开花的时间也取决于他感受到的光量。

The time when an adult plant flowers is based on the amount of light the plant senses.

某些植物种类如果感觉到太多光线就不会开花，而有些只有感觉到一定量的光才会开花。

Certain plant species won't flower if they sense too much light and some plants will only flower if they sense a specific amount of light.

当然，这些并不是有意识的反应。

Of course, these aren't conscious reactions.

这些植物只是用特定方式对光自动地做出反应。

These plants just automatically respond to light in certain ways.

植物能够区分人类肉眼无法看见的特定波长的光。

Plants are also able to distinguish between specific wavelengths of light that the human eye cannot even see!

Specifically there's a wavelength called far-red.

尽管我们称它为远红外的….我的意思是，它并不是红色的。

Although why they call it far-red … I mean, it is not really red.

It lies in the infrared range of the spectrum.

我们看不见它，但是植物可以感觉到它是一个不同的波长。

We can't see it, but plants can sense it as a different wavelength.

好的，现在我需要提一下光合作用。

OK. Now I need to mention another thing about photosynthesis.

我没有解释过不同波长的光是怎么影响光合作用的。

I didn't explain how different wavelengths of light affect photosynthesis.

当一个植物吸收光去进行光合作用，它只吸收某些波长的光，而把其他一些反射掉。

When a plant absorbs light for performing photosynthesis, it only absorbs some wavelengths of light and reflects others.

植物会将大多数碰到它的红光都吸收掉，但是只吸收部分红外光线。

Plants absorb most of the red light that hits them, but plants only absorb some of the far-red light that hits them.

要记住这个，因为这个会和我要讨论的一个实验相关。

Remember this, because it's going to be relevant in an experiment I want to discuss.

这个吸引人的实验显示了，植物不仅可以察觉到某些波长的光线并作出反应，而且可以感觉到一个波长和另一个波长之间比例的变化，并作出反应。

This fascinating experiment showed that plants not only detect and react to specific wavelengths of light, plants can also detect and react to changes in the ratio of one wavelength to another.

这个实验就被称作为蒲苇实验。

This experiment was called the Pampas experiment.

蒲苇实验背后的理念和植物用它们的光感受器感觉到的红光和红外光线比例变化而做出的反应相关。

The idea behind the Pampas experiment had to do with the response of plants to changes in the ratio of red light to far-red light that the plants sense with their photoreceptors.

有些生物学家们假设，一个植物如果在另一个植物的遮挡下会停止生长，这是被它感受到的异常红光和红外光线比例做引起的。

Some biologists hypothesize that a plant will stop growing if it's in the shade of another plant, a reaction that's triggered when it senses an unusual ratio of red light to far-red light.

好的，想象一下那里有两种植物。

在上面的植物会吸收掉大部分的红光去进行光合作用，但是反射掉了大部分的红外光线。

The plant on top would absorb most of the red light for photosynthesis, but reflect most of the far-red light.

那个会导致在阴暗处的植物感觉到异常的比例。

That would lead to the plant in its shade sensing an unusual ratio.

比起正常情况下，那里会有更少的红光和更多的红外光线。

There will be less red light and more far-red light than normal.

那个比例所表示的东西是很重要的。

更少红光和更多红外光线的比例会引起植物的反应。

A ratio of less red and to more far-red light would cause a reaction from the plant.

它会停止长高，因为植物会感觉到它不会获得足够的光线来获得能量去增长。

It would stop growing taller, because that plant could sense that it wasn't going to get enough sunlight to provide the energy to grow large.

为了测试他们的假设，研究人员用了一些电子光线，事实上，它们时发光二极管，也就是LED。

To test their hypothesis, researchers took some electrical lights, um… actually, they were light-emitting diodes, or LEDs.

These light-emitting diodes could simulate red light.

因此，他们将这些LED放到一些在阴影下的植物周围。

So they put these LEDs around some plants that were in the shade.

这些LED制造出让这些植物可以感觉为红色的光。

The LEDs produce light that the plants sensed as red.

但是，并不像太阳，LED的光并不支持光合作用。

But, unlike sunlight, the light from these LEDs did not support photosynthesis.

因此，这些植物感觉到了正常的红光和红外光线的比例，并且做出持续增长的反应，但事实上这些植物并没有从光合作用中获得足够的能量去支持这样的增长。

So the plants sensed the proper ratio of red light to far-red light and reacted by continuing to grow taller, while in reality these plants were not getting enough energy from photosynthesis to support all of that growth.

因为他们没有获得足够的能量去增长，在很短一段时间以后，在阴影部分的植物大部分都死了。

And because they weren't getting enough energy to support their growth, most of the shaded plants died after a short time.

According to the professor, what is one way that a plant reacts to changes in the number of hours of sunlight?

Why does the professor think that it is inappropriate for certain wavelengths of light to be named “far-red”?

What point does the professor make when she discusses the red light and far-red light that reaches plants?

According to the professor, how does a plant typically react when it senses a high ratio of far-red light to red light?

In the Pampas experiment, what was the function of the LEDs?

Narrator Listen to part of a lecture in a botany class. Professor OK. Last time we talked about photosynthesis, the process by which plants use light to convert carbon dioxide and water into food. Today I want to talk about another way light affects plants. I am sure you all know from physics class about how light moves in microscopic ways and that we can only see light when the wavelength of that light is in a specific range. Plus, depending on the wavelengths, we see different colors. Well, plants are also capable of distinguishing between different wavelengths of light. Now, I don’t want to confuse you. It is not like plants have eyes. Plants don’t see in the sense that humans or animals do, but they do have photoreceptors. Photoreceptors are cells that respond to light by sending out a chemical signal. And the organism, the plant, reacts to this signal. In fact, the signals that plants get from their photoreceptors sometimes cause significant reactions. And many plants are seasonal. And one way they know when winter is ending and spring is beginning is by sensing the change in light. The time when an adult plant flowers is based on the amount of light the plant senses. Certain plant species won’t flower if they sense too much light and some plants will only flower if they sense a specific amount of light. Of course, these aren’t conscious reactions. These plants just automatically respond to light in certain ways. Plants are also able to distinguish between specific wavelengths of light that the human eye cannot even see! Specifically there’s a wavelength called far-red. Although why they call it far-red … I mean, it is not red at all. It lies in the infrared range of the spectrum. We can’t see it, but plants can sense it as a different wavelength. OK. Now I need to mention another thing about photosynthesis. I didn’t explain how different wavelengths of light affect photosynthesis. When a plant absorbs light for performing photosynthesis, it only absorbs some wavelengths of light and reflects others. Plants absorb most of the red light that hits them, but plants only absorb some of the far-red light that hits them. They reflect the rest. Remember this, because it’s going to be relevant in an experiment I want to discuss. This fascinating experiment showed that plants not only detect and react to specific wavelengths of light, plants can also detect and react to changes in the ratio of one wavelength to another. This experiment was called the Pampas experiment. The idea behind the Pampas experiment had to do with the response of plants to changes in the ratio of red light to far-red light that the plants sense with their photoreceptors. Some biologists hypothesize that a plant will stop growing if it’s in the shade of another plant, a reaction that’s triggered when it senses an unusual ratio of red light to far-red light. OK. Imagine there are two plants. One below the other. The plant on top would absorb most of the red light for photosynthesis, but reflect most of the far-red light. That would lead to the plant in its shade sensing an unusual ratio. There will be less red light and more far-red light than normal. What that ratio signifies is important. A ratio of less red and to more far-red light would cause a reaction from the plant. It would stop growing taller, because that plant would sense that it wasn’t going to get enough sunlight to provide the energy to grow large.To test their hypothesis, researchers took some electrical lights, um… actually, they were light-emitting diodes, or LEDs. These light-emitting diodes could simulate red light. So they put these LEDs around some plants that were in the shade. The LEDs produce light that the plants sensed as red. But, unlike sunlight, the light from these LEDs did not support photosynthesis. So the plants sensed the proper ratio of red light to far-red light and reacted by continuing to grow taller, while in reality these plants were not getting enough energy from photosynthesis to support all of that growth. And because they weren’t getting enough energy to support their growth, most of the shaded plants died after a short time.