『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 19 Lec 3听力练习，Official 19 Lec 3原文答案解析，Official 19 Lec 3听力原文练习音频翻译。

托福TPO/Official 19 Lec 3听力原答案解析-音频翻译【新东方在线】

Narrator: Listen to part of a lecture in a marine biology class.

教授：好的，今天我们继续前面关于北美地区海盐沼泽地带的植物的讨论。

Professor: Ok, today we are going to continue our discussion of plant life in coastal salt marshes of North America.

海盐沼泽是植物最难以生存的环境之一。

Salt marshes are among the least inviting environments for plants.

那些地方的水盐分含量高，没有遮光物，并且起起落落的潮汐一直使沼泽处于被淹没的状态，所以，海碱地带的植物类型非常的单一，但”大米草“是个例外，它在生长茂盛。

The water is salty, there is little shade and the ocean tide comes in and out, constantly flooding the marsh, so the variety of plants found in salt marshes is limited, but there is a plant genus that thrives there, the Spartina.

事实上，大米草是在盐沼地发现的主要的植物。

In fact, the Spartina genus is the dominant plant found in salt marshes.

生活在地势低的盐沼地的一般叫做“海泽琴弦草”。

You can find one type of the Spartina, Saltmarsh Cordgrass, growing in low marsh areas.

生活在地势高的叫做“海蒲草”。

In higher marsh areas, you are likely to find a Spartina commonly called Salt-meadow Hay.

这样的话，为什么大米草属的植物的生活范围能够覆盖所有其它植物不能适应的地带呢？

So how is the Spartina able to survive in an environment that would kill most plants?

嗯，这是因为，这个属的植物通过各种方式适应了海盐沼的环境。

Well, it is because salt marsh grasses have found ways to adapt to the conditions there.

首先，它们能够承受高度的盐水环境。

First of all, they are able to withstand highly saline conditions.

这里涉及到一项非常有趣的适应机能，即逆渗透。

One really interesting adaptation is the ability to reverse the process of osmosis.

Typically, the process of osmosis works...

嗯，当水穿过植物的细胞壁时，一般来说，是含有盐分低的一方进入到含有盐分高的一方中去。

Well, when water moves through the wall of a plant cell, it will move from the side containing water with the lowest amount of salt into the side containing the highest amount of salt.

所以，同学们可以假设一株一般的植物，突然被放置到盐水中，会发生什么呢？植物中含有的水分的盐含量非常低，所以这些水分就会被吸引到盐分高的海水中去。

So imagine what would happen if a typical plant suddenly found itself in salt water, the water contained in the plant cells, that is water with very little salt would be drawn out toward the seawater, water with a lot of salt.

所以，我们看到的将会是植物的水分很快丢失，并且很快脱水。

So you can see the fresh water contained in the plant will be removed and the plant will quickly lose all its water and dehydrate.

但大米草属的植物是怎样的呢？它们会允许一部分海水进入它们的细胞，从而把盐分带入到植物中，形成一个比周围海水含盐度更高的盐溶液。

But what about the Spartinas, well, they allow a certain amount of salt to enter their cells, bringing the salt content of the water within the plant, to a slightly higher concentration than that of the surrounding seawater.

这样的话，海水不仅不能抽走它的水分，反而还要进入到它的体内，这就是所谓的“反渗透”，这种能力增加了细胞的强度。

So instead of fresh water moving out of the plant cells, salt from the seawater enters, reverse osmosis, and this actually strengthens the cells.

它们适应环境的另一项能力是排除超量盐分的能力。

Another adaptation to the salty environment is the ability to excrete excess salt back to the environment.

这个能力解释了为什么它在阳光下看起来总是闪闪发亮的。

That's why you might see a Spartina shimmering in the sunlight.

但是，反光的不是海水中蒸发水分而形成的盐结晶，虽然这个想法不错。

What's reflecting the light is not salt from seawater that has evaporated, although that's a good guess.

实际上，反射光的，是植物内部的盐结晶。

But it is actually the salt that came from within the plant.

下一次到了海边的沼泽地带，你可以找一两株这样的植物，在你亲朋面前秀一下。

You can really impress your friends and family with that little tidbit the next time you are in a salt marsh.

但是，适应盐沼地带过量的盐分并非它们生存所面临的唯一挑战。

But coping with salt is not the only challenge for plants in the salt marsh.

因为那儿的泥土非常紧密，而且含氧量极低，所以，大米草还得长出氧气管，空气可以从这些管道的微小开口透入，而这些管道中专门为氧气提供了直接入口，从叶面经过茎部把氧气输送到需要氧气的根部。

Soil there is dense and very low in oxygen, so Spartinas have air tubes, air enters through tiny openings on the leaves, the tubes provide direct pipe line for oxygen, carrying it down the leaves through the stems and into the roots, where it is needed.

如果你拔起一株大米草，你甚至还能发现一些粘在根部的红色泥土，这些土壤的颜色是由氧气和土壤中的硫化铁发生反应形成的，这个反应生成氧化铁，俗称“铁锈”。

If you pull up a Spartina, you might even notice some reddish mud on some of the roots, this is caused by oxygen reacting with iron sulfide in the soil, and it produces iron oxide or rust.

尽管大米草为了适应环境衍生出诸多化学和物理方面的生存机制，使它们能够在盐水中茁壮成长，并为它们的根系提供氧气。

Now, although the Spartinas have adapted several chemical and physical mechanisms that allow them to thrive in salt water and to feed oxygen to their roots.

依然还存在其它它们需要适应的环境问题，即潮汐的撕扯和飓风的暴力。

There is yet another aspect of the harsh environment that they have to adapt to, the force of tides and occasional violent storms.

风和海水时时刻刻都在抓扯着它们。

Wind and water are constantly crashing into these plants.

所以，正如同学们能够设想到的那样，大米草有一种把自己固定在泥土中的本领。

So as you might have guessed, they have developed a means of solidly anchoring themselves into the soil.

这是怎么做到的呢？它们长出一种叫做“地茎”的水下根系。

How? Well, they have tough sort of underground stems called rhizome.

一株草的根茎从泥土中长出，并且和附近植株的根茎铰链在一起，形成一种群落，群落中的植物就能同生共死。

Rhizomes from one plant grow through the muddy soil and interlock with those of other nearby plants, the plants form a kind of colony, a community that will survive or perish together.

它们单独在海中是无法存活的。

Because alone, as single plants, they cannot survive.

当然，这些领地上的植株还需要灵活性良好、能够接受潮水的冲击随意弯折而不断开的分枝。

Of course the plants in these colonies also need tough resilient stems above the soil, stems that can bent a lot but not break as water constantly crashes into them.

所以，除了相互铰链的地下根系外，它们还有另一种适应机制……嗯，我们还是回到反渗透吧。

So in addition to the interlocking underground rhizomes, they have yet another adaptation, and it is ... well, we are back to reverse osmosis again.

通过调节渗透压而保证细胞的饱和状态，大米草从而经受住了海底的巨大压强不会轻易被折断，这似乎使我们觉得大米草看上去就是简单的沼泽草类，但实际上，它们是化学，物理学和结构工程学等的交相辉映下的奇迹，正是如此，使得它们能够在别的植物无法忍受的环境中生存，甚至兴旺。

By adjusting the osmotic pressure so that the cells are always fully inflated, the plant is able to withstand great pressure before snapping, so Spartinas may look like simple marsh grass, but they are really a wonder of chemistry, physics and structural engineering that allows them to survive and even thrive in an environment in which most other plants will wilt and die within hours.

What is one result of reverse osmosis in the spartina?

Why does the professor mention reddish mud on the roots of a spartina?

In what way are rhizomes important for spartinas?

What can be inferred about the process that prevents spartinas from breaking in violent storms?

Narrator 
Listen to part of a lecture in a marine biology class. 
Professor 
Ok, today we are going to continue our discussion of plant life in coastal salt marshes of North America. Salt marshes are among the least inviting environments for plants. The water is salty, there is little shade and the ocean tide comes in and out, constantly flooding the marsh, so the variety of plants found in salt marshes is limited, but there is a plant genus that thrives there, the Spartina. In fact, the Spartina genus is the dominant plant found in salt marshes. You can find one type of the Spartina, Saltmarsh Cordgrass, growing in low marsh areas. In higher marsh areas, you are likely to find a Spartina commonly called Salt-meadow Hay. So how is the Spartina able to survive in an environment that would kill most plants? well, it is because salt marsh grasses have found ways to adapt to the conditions there. 
First of all, they are able to withstand highly saline conditions. One really interesting adaptation is the ability to reverse the process of osmosis. Typically, the process of osmosis works... Well, when water moves through the wall of a plant cell, it will move from the side containing water with the lowest amount of salt into the side containing the highest amount of salt. so imagine what 
would happen if a typical plant suddenly found itself in salt water, the water contained in the plant cells, that is water with very little salt would be drawn out toward the seawater, water with a lot of salt. So you can see the fresh water contained in the plant will be removed and the plant will quickly lose all its water and dehydrate. But what about the Spartinas, well, they allow a certain amount of salt to enter their cells, bringing the salt content of the water within the plant, to a slightly higher concentration than that of the surrounding seawater. So instead of fresh water moving out of the plant cells, salt from the seawater enters, reverse osmosis, and this actually strengthens the cells. 
Another adaptation to the salty environment is the ability to excrete excess salt back to the environment. That’s why you might see a Spartina shimmering in the sunlight. What’s reflecting the light is not salt from seawater that has evaporated, although that’s a good guess. But it is actually the salt that came from within the plant. Pretty cool, eh? You can really impress your friends and family with that little ? the next time you are in a salt marsh. 
But coping with salt is not the only challenge for plants in the salt marsh. Soil there is dense and very low in oxygen, so Spartinas have air tubes, air enters through tiny openings on the leaves, the tubes provide direct pipe line for oxygen, carrying it down the leaves through the stems and into the roots, where it is needed. If you pull up a Spartina, you might even notice some reddish mud on some of the roots, this is caused by oxygen reacting with iron sulfide in the soil, and it produces iron oxide or rust. 
Now, although the Spartinas have adapted several chemical and physical mechanisms that allow them to thrive in salt water and to feed oxygen to their roots, there is yet another aspect of the harsh environment that they have to adapt to, the force of tides and occasional violent storms. Wind and water are constantly crashing into these plants. So as you might have guessed, they have developed a means of solidly anchoring themselves into the soil. How? They have tough sort of underground stems called rhizome, rhizomes from one plant grow through the muddy soil and interlock with those of other nearby plants, the plants form a kind of colony, a community that will thrive and perish together. Because alone as single plants, they cannot survive. 
Of course the plants in these colonies also need tough resilient stems above the soil, stems that can bent a lot but not break as water constantly crashes into them. So in addition to the interlocking underground rhizomes, they have yet another adaptation, and it is ... well, we are back to reverse osmosis again, by adjusting the osmotic pressure so that the cells are always fully inflated, the plant is able to withstand great pressure before snapping, so Spartinas may look like simple marsh grass, but they are really a wonder of chemistry, physics and structural engineering that allows them to survive and even thrive in an environment in which most plants will wilt7 and die within hours.

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