『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 45 Passage 2阅读练习，TPO/Official 45 Passage 2原文答案解析，TPO/Official 45 Passage 2阅读原文练习音频翻译。

托福TPO/Official 45 Passage 2阅读原文题目答案及解析-新东方托福官方网校手机版

花粉是由开花植物产出的、含有雄蕊生殖细胞的、外观呈粉末状的物质。花粉一般通过昆虫或鸟类，在植株间进行传播，但是一些植株也会依靠风去传播它们的花粉（这被称作是“风媒授粉”）。

Pollen, a powdery substance, which is produced by flowering plants and contains male reproductive cells, is usually carried from plant to plant by insects or birds, but some plants rely on the wind to carry their pollen.

风媒授粉通常被认为是一种非常原始的、又很浪费珍贵的花粉的传粉方式，但是这种方式又很常见，尤其是在高纬度地区。

Wind pollination is often seen as being primitive and wasteful in costly pollen and yet it is surprisingly common, especially in higher latitudes.

要知道，风特别擅长远距离传播花粉；花粉可以被风吹到几百千米远，而这么远的传播距离通常是只有鸟类才能做到的。

Wind is very good at moving pollen a long way; pollen can be blown for hundreds of kilometers, and only birds can get pollen anywhere near as far.

但是很明显，至于风会将花粉吹到哪里去，这是不确定的，同时这也是风媒授粉方式的缺陷。

The drawback is that wind is obviously unspecific as to where it takes the pollen.

刚刚所描述的内容就像是接下来这种情况：想象一下我们打算把一封信寄给住在村子另一边的朋友，我们爬上了屋顶、接着向空中扔出很多信件、然后希望其中的一封最终会飘落到朋友的花园里。（你觉得朋友会有多大的概率收到你的信件呢？）

It is like trying to get a letter to a friend at the other end of the village by climbing onto the roof and throwing an armful of letters into the air and hoping that one will end up in the friend’s garden.

当然，温带森林里面，在花粉传播的有效范围内，通常生长着大量的同品种树木，所以对于长在温带森林的树种来说，风媒授粉是一种比较稳妥的方式。

For the relatively few dominant tree species that make up temperate forests, where there are many individuals of the same species within pollen range, this is quite a safe gamble.

想象这个场景：如果很多村民都站在屋顶上往下扔出信件，那么你的朋友一定会收到其中的一封！

If a number of people in the village were throwing letters off roofs, your friend would be bound to get one.

相比之下，在热带地区，每一个种类的树木数量都非常地少、而且树木也是四处随机散落的，所以风将花粉从一棵树吹到另一棵相同种类的树的几率很小（几乎可以忽略不计），相反，对于热带地区的树木来说，通过动物们去传播花粉则是一种更为可靠的方式。

By contrast, in the tropics, where each tree species has few, widely scattered individuals, the chance of wind blowing pollen to another individual is sufficiently slim that animals are a safer bet as transporters of pollen.

所以，尽管热带的风比较多，但是热带地区的高大林木们一般也不会通过风来传播花粉。

Even tall trees in the tropics are usually not wind pollinated despite being in windy conditions.

同理可推，如果温带森林中的树木靠昆虫来传播花粉，（那么一定面积内、相同的林木数量多少就显得没有那么重要了，）那么林木们会趋向于分散得更加广泛。

In a similar way, trees in temperate forests that are insect pollinated tend to grow as solitary, widely spread individuals.

因为风媒授粉通常不需要吸引昆虫或者其他动物，所以它们不需要艳丽的花瓣、花蜜以及花香。

Since wind-pollinated flowers have no need to attract insects or other animals, they have dispensed with bright petals, nectar, and scent.

这些用来吸引昆虫和动物的特征对于风媒授粉的树种充其量来说只是浪费；往坏处说，甚至还会干扰花粉在空气中的传播。

These are at best a waste and at worst an impediment to the transfer of pollen in the air.

这就导致了风媒授粉的树木的花和柔荑花絮都是非常不不起眼的。（柔荑花絮就是密集的圆柱状、无瓣的小花团）

The result is insignificant-looking flowers and catkins (dense cylindrical clusters of small, petalless flowers).

当然，风媒授粉需要非常非常多的花粉粒。

Wind pollination does, of course, require a lot of pollen.

桦木和榛树的每个柔荑花序分别可以产生550万和400万颗花粉粒。

Birch and hazel trees can produce 5.5 and 4 million grains per catkin, respectively.

为了能让更多的花粉粒尽可能传播得更远，树木们演化出多种多样的适应方式（来增加授粉成功的几率）。

There are various adaptations to help as much of the pollen go as far as possible.

（首先，）为了减少同柱头（花中接受花粉的部位）“争夺”花粉的可能性（也就是，尽量减少花粉可以接触的其他非柱头表面的几率），大多数的落叶型风媒授粉树木（每年秋天落叶的树木）会在树枝仍是光秃秃的春天就产生它们的花粉。

Most deciduous wind-pollinated trees (which shed their leaves every fall) produce their pollen in the spring while the branches are bare of leaves to reduce the surrounding surfaces that “compete” with the stigmas (the part of the flower that receives the pollen) for pollen.

而常绿针叶林则不会落叶，所以这类树木如果在春天开花的话，那么它们产生的花粉数量会很少；除此之外，还会有一些常绿针叶林会在秋冬季节开花。

Evergreen conifers, which do not shed their leaves, have less to gain from spring flowering, and, indeed, some flower in the autumn or winter.

（其次，）花所在的树枝越高，其所产出的花粉也就越有可能传播得更远，这是因为高处的风比较大（而且是一阵一阵地狂吹），所以在花粉落地前，它们极有可能会被吹到更远的地方。

Pollen produced higher in the top branches is likely to go farther: it is windier (and gustier) and the pollen can be blown farther before hitting the ground.

除此之外，悬在空中的柔荑花絮（比如说榛树的花絮）则会将花粉粒紧紧抓住，直到风力增加到可以将柔荑花絮折弯的程度，才会将花粉粒释放到空气中，这样的话，就保证了只有在风刮得很猛烈时，花粉粒才会飘落到空中，也就能随着大风飘得更远。

Moreover, dangling catkins like hazel hold the pollen in until the wind is strong enough to bend them, ensuring that pollen is only shed into the air when the wind is blowing hard.

（最后，）对于风媒授粉来说，天气也是一个十分重要的因素。

为了避免过多的花粉粒粘附在湿乎乎的表面、或被雨水冲刷从而被沉淀到地表，所以通常在空气干燥的时候，花粉粒才会从雄蕊上飘落到空中。

Pollen is shed primarily when the air is dry to prevent too much sticking to wet surfaces or being knocked out of the air by rain.

但是，尽管有多样的适应方式（来增加授粉成功的几率），还是有很多花粉不能离开顶部的树枝，完成授粉；事实上，仅仅只有百分之零点五到百分之四十的花粉能从母体成功飘落，到达距离母体一百米开外的地方。

Despite these adaptations, much of the pollen fails to leave the top branches, and only between 0.5 percent and 40 percent gets more than 100 meters away from the parent.

但是，一旦当花粉飘到一百米之外的地方，它们中的相当一大部分就可以飘到一千米甚至更远的地方。

But once this far, significant quantities can go a kilometer or more.

所以实际上，在高海拔地区，花粉通常可以被传播至数千千米之外。

Indeed, pollen can travel many thousands of kilometers at high altitudes.

因为这些花粉在空气中四处漂浮，我们不难想到：使用风来授粉的树木便是我们过敏的主要来源了。

Since all this pollen is floating around in the air, it is no wonder that wind-pollinated trees are a major source of allergies.

一旦花粉被风吹到空中，它们能飘到哪里主要就取决于风（因为风是变幻莫测的），但是这一切也不是完全随机的（它们能飘到何处还会受到花粉粒大小的影响）。

Once the pollen has been snatched by the wind, the fate of the pollen is obviously up to the vagaries of the wind, but not everything is left to chance.

风承载的花粉粒通常是干干的、圆圆的、滑滑的，并且通常都会比以昆虫为媒介传播的花粉粒要小一些。

Windborne pollen is dry, rounded, smooth, and generally smaller than that of insect-pollinated plants.

比如说，小的花粉粒更容易飘得更远（导致周围可能没有同种植株），但这些小的花粉粒们也更容易掉落在等待授粉的柱头上，因为小的花粉粒更容易被卷入环绕在柱头周围的快速流动的空气中。

Small grains may be blown farther but they are also more prone to be whisked past the waiting stigma because smaller particles tend to stay trapped in the fast-moving air that flows around the stigma.

柱头也会产生震动，这会降低柱头周围空气的流动速度，并且会促进花粉粘附到柱头上（从而完成植株的授粉）。

But stigmas create turbulence, which slows the air speed around them and may help pollen stick to them.

The word “drawback” in the passage is closest in meaning to

Which of the following can be inferred from paragraph 1 about pollen production?

According to paragraph 1, wind-pollinated trees are most likely to be found

Paragraph 1 supports which of the following as the reason animals are a safer bet than wind as pollinators when the individual trees of a species are widely separated?

In paragraph 1, the author compares pollen moved by wind with letters thrown off roofs in order to

Paragraph 2 suggests that wind-pollinated plants do not have bright petals, nectar, and scent for which TWO of the following reasons? To receive credit, you must select TWO answers.

The word “respectively” in the passage is closest in meaning to

According to paragraph 3, why do most deciduous wind-pollinated trees produce their pollen in the spring?

According to paragraph 4, which of the following is NOT an adaptation that helps ensure that pollen travels as far as possible?

The word “significant” in the passage is closest in meaning to

The phrase “no wonder” in the passage is closest in meaning to

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

Look at the four squares  that indicate where the following sentence could be added to the passage. This level of volume is important to ensure that at least some of the pollen reaches a target tree, but dispersing the pollen is crucial as well.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Wind Pollination Pollen, a powdery substance, which is produced by flowering plants and contains male reproductive cells, is usually carried from plant to plant by insects or birds, but some plants rely on the wind to carry their pollen. Wind pollination is often seen as being primitive and wasteful in costly pollen and yet it is surprisingly common, especially in higher latitudes. Wind is very good at moving pollen a long way; pollen can be blown for hundreds of kilometers, and only birds can get pollen anywhere near as far. The drawback is that wind is obviously unspecific as to where it takes the pollen. It is like trying to get a letter to a friend at the other end of the village by climbing onto the roof and throwing an armful of letters into the air and hoping that one will end up in the friend’s garden. For the relatively few dominant tree species that make up temperate forests, where there are many individuals of the same species within pollen range, this is quite a safe gamble. If a number of people in the village were throwing letters off roofs, your friend would be bound to get one. By contrast, in the tropics, where each tree species has few, widely scattered individuals, the chance of wind blowing pollen to another individual is sufficiently slim that animals are a safer bet as transporters of pollen. Even tall trees in the tropics are usually not wind pollinated despite being in windy conditions. In a similar way, trees in temperate forests that are insect pollinated tend to grow as solitary, widely spread individuals. Since wind-pollinated flowers have no need to attract insects or other animals, they have dispensed with bright petals, nectar, and scent. These are at best a waste and at worst an impediment to the transfer of pollen in the air. The result is insignificant-looking flowers and catkins (dense cylindrical clusters of small, petalless flowers). Wind pollination does, of course, require a lot of pollen.  Birch and hazel trees can produce 5.5 and 4 million grains per catkin, respectively.  There are various adaptations to help as much of the pollen go as far as possible.  Most deciduous wind-pollinated trees (which shed their leaves every fall) produce their pollen in the spring while the branches are bare of leaves to reduce the surrounding surfaces that “compete” with the stigmas (the part of the flower that receives the pollen) for pollen.  Evergreen conifers, which do not shed their leaves, have less to gain from spring flowering, and, indeed, some flower in the autumn or winter. Pollen produced higher in the top branches is likely to go farther: it is windier (and gustier) and the pollen can be blown farther before hitting the ground. Moreover, dangling catkins like hazel hold the pollen in until the wind is strong enough to bend them, ensuring that pollen is only shed into the air when the wind is blowing hard. Weather is also important. Pollen is shed primarily when the air is dry to prevent too much sticking to wet surfaces or being knocked out of the air by rain. Despite these adaptations, much of the pollen fails to leave the top branches, and only between 0.5 percent and 40 percent gets more than 100 meters away from the parent. But once this far, significant quantities can go a kilometer or more. Indeed, pollen can travel many thousands of kilometers at high altitudes. Since all this pollen is floating around in the air, it is no wonder that wind-pollinated trees are a major source of allergies. Once the pollen has been snatched by the wind, the fate of the pollen is obviously up to the vagaries of the wind, but not everything is left to chance. Windborne pollen is dry, rounded, smooth, and generally smaller than that of insect-pollinated plants. But size is a two-edged sword. Small grains may be blown farther but they are also more prone to be whisked past the waiting stigma because smaller particles tend to stay trapped in the fast-moving air that flows around the stigma. But stigmas create turbulence, which slows the air speed around them and may help pollen stick to them.