考满分 toefl

1 .<-NARRATOR:->Listen to part of a lecture in a botany class.

旁白：听一段植物学课程。

1 .<-FEMALE PROFESSOR:->OK, last time we talked about photosynthesis, the process by which plants use light to convert carbon dioxide and water into food.

教授：好了，上次我们讲了光合作用，即植物用光把二氧化碳和水转化成食物的过程。

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

今天我想讲讲光影响植物的另一种方式。

3 .I'm 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; plus, depending on the wavelength, we see different colors.

我相信你们从物理课上都知道了光是怎样做微观运动的，只有在光的波长达到一定范围时，我们才能看见光；还有，根据波长不同，我们看到的颜色也不同。

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

植物也能分辨出不同波长的光。

5 .Now I don't want to confuse you-it's not like plants have eyes-plants don't see in the sense that humans or animals do-but they do have photoreceptors.

我不想把你们搞糊涂，不是说植物有眼睛—植物不像人或动物一样能看到光，但植物有光感受器。

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

光感受器是通过发出化学信号对光线做出反应的细胞。

2 .And the organism- the plant- reacts to this signal; in fact, the signals that plants get from their photoreceptors sometimes cause significant reactions.

生物体，或说植物，会对信号产生反应；事实上，光感受器发出的信号有时候会让植物产生剧烈反应。

1 .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.

很多种植物是季节性的，它们感知冬去春始的一种方式就是感应光的变化。

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

成年植物开花的时间基于植物感受到的光量而定。

3 .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.

某些植物如果感受到过强的光时，是不会开花的，还有一些只会在感受到一定的光量时才会开花。

4 .Of course, these aren't conscious reactions-these plants just automatically respond to light in certain ways.

当然，这些都不是有意识的反应——这些植物会以特定的方式自动对光线做出反应。

1 .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.

植物也能分辨出人眼无法看到的特定波长的光，具体来说，一种称为远红的波长。

2 .[realizing that the name is actually inappropriate] Although why they call it "far-red"... I mean, it's not really 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.

尽管他们称其为“远红”……我是说，它根本不是红色的。这种光在光谱上处于红外谱段。我们看不见这种光，但植物能感受到这种不同的波长。

1 .OK, now I need to mention another thing about photosynthesis.

好了，现在我要提到光合作用的另一方面。

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

我没有解释不同波长的光是怎么影响光合作用的。

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

植物吸收光进行光合作用时，它只吸收某些波长的光，反射别的光。

1 .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.

植物吸收绝大多数接触到的红光，但只吸收了部分到达它们的远红光，它们反射了剩余部分。

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

记住这点，这和我将要讲的实验有关。

1 .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.

这个精彩的实验显示，植物不仅能感受到某些特定波长的光并作出反应，还能感应到不同光之间波长比的变化。

2 .This experiment was called the Pampas experiment.

这个实验称为潘帕斯实验。

1 .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 sensed with their photoreceptors.

实验背后的思想是，植物的光感受器能感受到红光与远红光的比率变化，且植物会对此作出反应。

2 .Some biologists hypothesized 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.

一些生物学家提出假设，如果一种植物被另一种植物（的影子）遮住了，前者会停止生长——这是由植物感受到的红光与远红光的不寻常比率引起的反应。

3 .OK, imagine there are two plants, one below the other.

好了，想象有两种植物，一种在另一种下面。

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

在高处的植物会吸收绝大部分的红光来进行光合作用，但反射绝大部分的远红光。

5 .That would lead to the plant in its shade sensing an unusual ratio-there would be less red light and more far-red light than normal.

这会让被影子遮挡住的植物感应到不寻常比率。红光比正常情况少了，而远红光多了。

6 .What that ratio signifies is important-a ratio of less red light to more far-red light would cause a reaction from the plant: it would stop growing taller-because that plant could sense it wasn't going to get enough sunlight to provide the energy to grow large.

这个比率有重要意义—更少的红光与更多的远红光产生的比率会导致植物作出反应：植物会停止长高，因为会感觉到它没有足够的阳光来提供能量来生长。

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

为了测试这个假说，研究人员用了一些电子灯，嗯……事实上他们用的是发光二极管，即LED灯。

1 .These light-emitting diodes could simulate red light.

这些发光二极管能模拟红光。

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

他们把这些LED灯放在被影子遮住的植物周围。

3 .The LEDs produced light that the plants sensed as red-but, unlike sunlight, the light from these LEDs did not support photosynthesis.

LED灯发出的光会被植物感知成红光—和阳光不同的是，这些LED灯发出的光不能用作光合作用。

4 .So the plants sensed a 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.

那么这些植物感应到了红光和远红光的合适比率并作出反应，继续长高，但事实上，这些植物并没有从光合作用中得到足够的能量来维持这样的生长。

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

因为植物没得到足够的能量来维持生长，大多数被影子遮挡的植物很快就死了。