『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 45 Passage 2阅读练习：According to paragraph 3, why do most deciduous wind-pollinated trees produce their pollen in the spring?真题题目及答案解析，TPO/Official 45 Passage 2阅读原文范文音频翻译

托福TPO/Official 45 Passage 2阅读原文According to paragraph 3, why do most deciduous wind-pollinated trees produce their pollen in the spring?题目答案及解析-新东方托福官方网校手机版

花粉是一种由开花植物产生的粉状物质，含有雄性生殖细胞，通常由昆虫或鸟类从一株植物传播到另一株植物，但有些植物依靠风来传播花粉。

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.

缺点是风显然对花粉的传播位置没有特定的方向。

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

这就像试图通过爬上屋顶，把一大把信件抛向空中，希望其中一封能落到朋友的花园里，以此来把信送到村子另一端的朋友手中。

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.

对于构成温带森林的相对较少的优势树种来说，由于在花粉传播范围内有许多同种个体，这是一种相当安全的赌注。

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.

如果村子里有很多人都在屋顶上扔信，你的朋友肯定会收到一封。

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，每种树种的个体数量很少且分布广泛，风将花粉吹到另一个个体的机会非常渺茫，因此动物作为花粉传播者是更安全的选择。

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.

即使在多风的环境中，热带地区的高大树木通常也不是靠风授粉的。

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

类似地，在温带森林中，由昆虫授粉的树木往往以单独、分散的个体形式生长。

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

由于风媒花不需要吸引昆虫或其他动物，它们不再需要明亮的花瓣、花蜜和香味。

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

这些在最好情况下是浪费，在最坏情况下则会阻碍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尽可能传播得更远，树木们演化出各种各样的适应方式。

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

大多数风媒传粉的落叶树（每年秋天都会落叶）在树枝上没有叶子的春天产生花粉，以减少周围表面与柱头（花朵接收花粉的部分）“竞争”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.

常绿针叶树不会落叶，从春季开花中获得的收益较少，事实上，有些树在秋季或冬季开花。

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.

一旦花粉被风带走，花粉的命运显然取决于风的变化，但并非一切都听天由命。

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.

小颗粒可能会被吹得更远，但它们也更容易被吹过等待的柱头，因为较小的颗粒往往会被困在柱头周围快速流动的空气中。

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.

但柱头会产生湍流，从而减慢柱头周围的空气速度，可能有助于花粉粘附在柱头上。

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

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

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.