考满分 toefl

1 .Listen to part of a lecture in a biology class.

听一段生物学课程的演讲

1 .OK, Just before the end of the last class, we started talking about trace metals, metals found in living organisms in very small quantities that serve important biological and important nutritive function in these organisms.

上堂课结束前，我们开始谈论微量金属，微量金属发现于生物体中，数量非常小，微量金属起重要的生物和营养功能在生命体中。

2 .And one trace metal that serves a nutritive function is zinc.

一个微量金属起营养功能的是锌。

1 .Zinc assists in a number of processes in humans, but we are going to focus on just one, one that applies to a number of organisms, not just humans.

锌有助于一些人体进程，但我们将重点放在一个上，一个适用于很多器官的，不只是人类。

2 .See, zinc plays a major role in carbon cycling, the conversion of various kinds of molecules with carbon, like carbon dioxide into other kinds of molecules with carbon that organisms can use.

锌在碳循环中起重要作用，各种带碳分子的转化，例如二氧化碳，转化成其他种类的器官可使用的带碳分子。

3 .So, take respiration, our bodies - our cells produce carbon dioxide when they break down sugars.

所以，以呼吸为例。我们的身体，我们的细胞产生二氧化碳当分解糖的时候。、

4 .We need to get CO2 out of our bodies, so the CO2 is converted into carbonic acid, which the blood is able to carry to the lungs.

我们需要去除身体中的二氧化碳，所以二氧化碳转化成碳酸，这样，血液把二氧化碳运输到肺部。

5 .Once the carbonic acid reaches the lungs, it's converted back into carbon dioxide, so that we can breathe it out.

一旦碳酸到达肺部，它转换回成二氧化碳，所以我们可以呼出二氧化碳。

1 .Now, this whole conversion process relies on a particular enzyme.

现在，这整个转换过程依赖于一种特定的酶。

2 .Um, who remembers what an enzyme is? Bob?

呃，谁记得什么是酶？鲍勃？

1 .Um, it's a protein, a specific kind of protein, one that speeds up chemical reactions.

呃，是一种蛋白质，一种特定的蛋白质，它加速化学反应。

1 .Exactly, different enzyme assists in different chemical reactions.

确实是。不同的酶协助不同的化学反应。

2 .Now, the one that speeds up the conversion of carbon dioxide has zinc in it.

我们说，加速二氧化碳转化的酶中具有锌。

3 .So this zinc enzyme is critical for getting CO2 out of our bodies through the lungs.

所以这种含锌酶对于通过肺排除我们身体中的二氧化碳是非常重要的。

4 .And it's also extremely important for plants.

它对于植物也是非常重要的

5 .Bob, can you tell us why?

鲍勃，你能告诉我们为什么？

1 .For making food, for photosynthesis?

为了制作食品，进行光合作用？

2 .Exactly! For photosynthesis.

确实。为了光合作用。

3 .Plants also convert carbon dioxide into different forms of carbon-containing molecules and the conversion process uses and relies on the very same enzyme that works in humans.

植物也将二氧化碳转化成不同形式的含碳分子，并且发生的转换过程依赖的酶就是与在人体中起作用的酶。

4 .So, zinc is also important for plants.

所以锌对植物也非常重要。

1 .OK, but zinc is scarce in certain environments, and it is particularly scarce in waters near the surfaces of rivers and lakes and shallower parts of oceans, which might make us wonder how plants could live there at all.

要。好。但是，锌在某些环境很稀缺。尤其是在河流，湖泊和海洋中较浅的部分的表面水中，这可能使我们想知道植物如何能在那里生长

2 .In fact there are a lot of marine plants that survive, that grow and reproduce in surface waters.

。事实上，那里有很多的海洋植物存活，生长和繁殖。

3 .In particular, there are a lot of diatoms.

尤其是有很多硅藻。

1 .Diatoms are microscopic, photosynthetic organisms and they are a major source of food for other organisms in the ocean.

硅藻是极小的光合生物。他们是海洋中其他生物体的一个主要食物来源

2 .There are a number of different types of diatoms and, well, diatoms play a very important role in the carbon cycling process, because they help make carbon available to other organisms in deeper parts of the ocean.

。硅藻有很多不同的种类，其在碳循环的过程中起非常重要的作用，因为它帮助较深部分海洋中的生物得到碳。

3 .The carbon that these diatoms use in photosynthesis is transferred to other parts of the ocean when the diatoms are eaten, say, by a fish that absorbs the carbon and then swims to another part of the ocean; or when the diatoms die and fall to the ocean floor.

硅藻在光合作用中使用的碳会转移到海洋的其他部分，当硅藻被吃掉，比方说，吸收的碳鱼吃掉，然后游到海洋的另一部分，或者硅藻死亡，下沉到海底。

1 .So, how do diatoms survive if zinc is so scarce?

那么如果锌是如此稀少，硅藻如何生存？

2 .Well, recently researchers discovered that a specific type of diatom makes a different enzyme that serves the same purpose.

嗯，最近研究人员发现，一种特定类型的硅藻，使不同的酶起同样的作用。

3 .But this enzyme doesn't contain zinc.

但是这种酶不包含锌。

4 .Instead, this new enzyme incorporates another trace metal - cadmium.

不同的是，这个新的酶结合另一种微量金属， 镉。

5 .Kelly, you've got a question?

凯里，你有问题吗？

6 .Yeah, I thought cadmium was toxic, didn't you say that?

是的，我以为镉是有毒的。你讲过的不是吗？

1 .It is poisonous to humans. Um, actually, we used to think that it was toxic to all biological life, that it didn't serve any biological purpose.

它对人类来说是有毒的。实际上，我们曾经认为它对所有生物都是有毒的，它没有任何到任何生物作用。

2 .But new study suggests that cadmium can actually substitute for zinc, that organism can use it instead of zinc when there is not enough zinc in their environment.

但是，新的研究表示，镉事实上可以替代锌，当生物体的环境中没有足够锌的时候，生物体可以用它来代替锌。

1 .Now the discovery of this cadmium-based enzyme is really important for a number of reasons: it's actually the first enzyme we discovered that uses cadmium.

但是，新的研究表明，镉实际上可以替代锌，有机体可以用它来代替锌当环境中没有足够的锌的时候。现在，这种基于镉的酶非常重要，有很多原因。他是我们首次发现的用镉的酶。.

2 .So it's possible that other not so typical trace metals may be used in chemical processes, that marine organisms might make enzymes from other trace metals when the essential one is scarce.

所以有可能其他不是很典型的微量金属可以用在化学过程中，这样海洋生物可以从其他微量金属得到酶当必须的酶很稀少的时候。

3 .And there're maybe other types of diatoms that use cadmium to cycle carbon.

可能还有其他类型的硅藻用镉来实现碳循环。

4 .But there is something else to think about, what is one of the most common greenhouse gases in our atmosphere, one of the major culprits in global warming?

但是，还有其它事情要考虑。考虑在我们的大气中最常见的温室气体，全球变暖的元凶。二氧化碳，是吧？

5 .Carbon dioxide, right?

二氧化碳，是吧？

1 .Now, if all these diatoms are taking carbon dioxide from the surface, converting it and transporting it to the bottom of the ocean, well maybe there's more to that whole process, that cycle, something that we overlooked.

现在，如果所有这些硅藻从表面吸收二氧化碳，将其转化和输送到海洋的底部，也许在整个过程，这个循环中，我们忽视了什么东西。

2 .So further research might tell us more about this warming cycles too.

所以，进一步研究也可能告诉我们更多关于变暖周期。