『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 58 Passage 2阅读练习：What purpose does paragraph 2 serve in the passage as a whole?真题题目及答案解析，TPO/Official 58 Passage 2阅读原文范文音频翻译

托福TPO/Official 58 Passage 2阅读原文What purpose does paragraph 2 serve in the passage as a whole?题目答案及解析-新东方托福官方网校手机版

不同物种的生物时常进化出适应能力，使它们在资源上完全相互依赖。

Organisms of different species frequently evolve adaptations that make them utterly and specifically dependent on each other for resources.

例如，很多树木的根系中必须有菌根真菌，这种真菌对树木是不可或缺的，因为它们有助于树木从土壤中吸收矿物质。

For example, many trees must have mycorrhizal fungi living in their root systems, fungi that are indispensable to the tree because they facilitate mineral uptake from the soil.

反过来，真菌依靠树木进行光合作用;树木中的一些化学食物是它们唯一的能量来源。

In turn, the fungi rely on the trees to photosynthesize; they use some of the tree’s chemical food as their only energy source.

这种亲密的关系是共同进化的例子，通过这一关系，两类物种变得如此依赖彼此，以至于它们只有在对方的存在下茁壮成长。

Such intimate relationships are examples of coevolution through which two species become so interdependent that they can thrive only in each other’s presence.

第一眼看上去，矮松和矮松鸦之间的关系似乎不是共同进化的关系。

At first glance, the relationship between pinyon pine trees and the pinyon jay does not appear to be one of coevolution.

种子捕食者，特别是矮松鸦，被矮松产生的松果和种子所吸引。

Pinyon pines produce cones and seeds that attract seed predators, especially the pinyon jay.

当然，一粒种子包含着为下一代的植物胚芽。

A seed, of course, contains an embryonic plant for the next generation. 

有些植物的种子有毒，这明显是为了减少因为动物带来的损失。

Some plants have poisonous seeds, an obvious adaptation to reduce loss to animals.

然而，矮松有一系列的特点，这些特点相结合使得松鸦到访并获得矮松的种子。

Pinyons, however, have an array of characteristics that combine to encourage jays to visit the pines and help themselves to the seeds.

松果位于树上方且靠外的位置，里面的种子就在松鸦的视线中，本质上就是在邀请它们参与进来。

Cones are positioned upward and outward on the tree, so the seeds inside are in plain sight of the jays, essentially inviting them to partake.

矮松种子通常较大，并且每粒种子都蕴藏着很多能量。

Pinyon seeds are unusually large, and each seed is high in energy. 

它的皮很薄，这意味着像矮松鸦这样的鸟类不仅能吃下种子，还能消化它。

The seed coat is thin, meaning that birds such as pinyon jays can not only ingest the seeds but also digest them.

在许多植物中，不易消化的种皮能使种子安然无恙地通过鸟类的消化系统。

In many plants, an indigestible seed coat permits the seed to pass unharmed through the bird’s alimentary system.

可食用和不可食用的矮松种子的种皮有不同的颜色，这表明松鸦应该选择哪一种。

Pinyon seed coats differ in color between edible and nonviable seeds, signaling the jays as to which they should select.

矮松成功的生存策略似乎并非是吸引种子捕食者。

Attracting seed predators would not seem to be a successful survival strategy for pinyon pines.

然而，矮松松鸦的行为倾向于将超过其当前生存需要的种子掩埋。

However, pinyon jays are behaviorally adapted to bury any seeds in excess of their immediate survival needs.

这对松鸦来说是一种有用的行为，因为它们可以在冬天找回一些埋在地下的种子，而且对树木也有好处，因为没有找回的种子已经做好了发芽的准备。

This is a useful behavior for the jays, providing they can retrieve some of the buried seeds during winter, and good for the trees, as the unretrieved seeds are ready to germinate.

然而，要想让松鸦埋下种子，必须有远超它们直接需求的大量种子。

Still, for the jays to bury any seeds, there must be an abundance of seeds far beyond the jays’ immediate needs.

一棵树不可能产生这么多种子，但如果一个地区所有的矮松同时产生大量种子，这些种子就会“充斥市场”，这样就有远超当地松鸦的消费能力的矮松种子了。

One tree could never produce so many seeds, but if all the pinyons in a region produced heavy seed crops at once, they would indeed “flood the market” with vastly more pinyon seeds than the local population of jays could consume.

In fact, that is exactly what the pinyon pines do.

产生这么多种子需要大量的能量，这么多的能量导致矮松种群每年不可能产生这么多的种子。

It requires a great deal of energy to make so many seeds, so much energy that it is unlikely that a pinyon population could produce such a bumper seed crop every year.

然而，更重要的是，即使这些树每年可以产生大量种子，这对它们来说也是严重不利的。

More important, however, it would be to the severe disadvantage of the trees to produce large seed crops annually, even if they could.

这样做不仅可以让矮松种子数量多，而且可以预测。

Doing so would make the resource not only abundant but also predictable.

多年来，种子捕食者稳定地增加它们种群的数量，最终增长到可以吃掉所有的种子。

Seed predators could, over the years, steadily build their populations, eventually increasing so much that they could, indeed, consume virtually all of the seeds.

植物更能适应间歇性地产生大量种子。

It is much more adaptive for the plants to produce seed cornucopias intermittently.

首先，能量可以储存几年，然后用于生产松果和种子，确保有足够的能量生产大量种子作物。

First, energy can be stored for some years and then devoted to cone and seed production, ensuring adequate energy to produce a large seed crop.

第二，在种子产量低的年份，种子捕食者的数量将下降，大多因为饥饿、繁殖减少或迁移。

Second, seed-predator populations will decline in years of low seed production, either through starvation, reduced reproduction, or emigration.

在大多数地区，矮松大约每隔六年会产生大量种子。

Pinyons in most areas have a roughly six-year interval between heavy seed crops.

矮松鸦已经完全适应了矮松的循环，它们的繁殖也与之联系在一起。

Pinyon jays have so completely adapted to the cycle of the pinyons that their reproduction is tied to it.

大多数鸟类的性成熟是为了应对白天长度的变化。

Most species of birds mature sexually in response to changes in day length.

然而，于矮松鸦而言，日长只是刺激繁殖的一个因素。

In pinyon jays, however, day length is only one stimulus for reproduction.

另一个因素是矮松种子的获取。

The other cue is availability of pinyon seeds.

当种子充足时，矮松鸦在早春就繁殖，整个夏天持续繁殖，最早到冬至又重新进入繁殖状态。

When seeds are abundant, jays can breed very early in spring, continue breeding through summer, and reenter breeding condition as early as the winter solstice.

因此，由于矮松种子数量间接性大爆发，矮松鸦的数量也暂时增多。

So the jay population temporarily enlarges in response to one of the intermittent large crops of pinyon seeds.

但是松鸦数量的增加往往小于种子数量的增加。

But the increase in the population of jays is less than the increase in the size of the seed crop.

因此，许多种子被埋在地里随后发芽，这时种子发芽的数量比没有松鸦参与掩埋要多得多。

Thus many of the seeds of a bumper crop are buried and subsequently germinate, many more than would germinate without planting by the jays.

The word "indispensable" in the passage is closest in meaning to

According to paragraph 1, mycorrhizal fungi need to live in root systems of trees in order to

The word "partake" in the passage is closest in meaning to

According to paragraph 2, all the following are characteristics of pinyon pine seeds that make them attractive to seed predators EXCEPT:

What purpose does paragraph 2 serve in the passage as a whole?

It can be inferred from paragraph 4 that the reason the pinyon jay population in an area declines for several years in succession is that

According to paragraph 4 which of the following is a reason why pinyon pines do not produce a bumper seed crop every year?

What purpose does the discussion of paragraph 5 serve in the passage as a whole?

Look at the four squares  that indicate where the following sentence could be added to the passage. As a result, less energy will be needed to produce a crop of seeds large enough to flood the reduced market for them.  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

Pinyon Pines and Pinyon Jays Organisms of different species frequently evolve adaptations that make them utterly and specifically dependent on each other for resources. For example, many trees must have mycorrhizal fungi living in their root systems, fungi that are indispensable to the tree because they facilitate mineral uptake from the soil. In turn, the fungi rely on the trees to photosynthesize; they use some of the tree’s chemical food as their only energy source. Such intimate relationships are examples of coevolution through which two species become so interdependent that they can thrive only in each other’s presence. At first glance, the relationship between pinyon pine trees and the pinyon jay does not appear to be one of coevolution. Pinyon pines produce cones and seeds that attract seed predators, especially the pinyon jay. A seed, of course, contains an embryonic plant for the next generation. Why sacrifice it to an animal? Some plants have poisonous seeds, an obvious adaptation to reduce loss to animals. Pinyons, however, have an array of characteristics that combine to encourage jays to visit the pines and help themselves to the seeds. Cones are positioned upward and outward on the tree, so the seeds inside are in plain sight of the jays, essentially inviting them to partake. Pinyon seeds are unusually large, and each seed is high in energy. The seed coat is thin, meaning that birds such as pinyon jays can not only ingest the seeds but also digest them. In many plants, an indigestible seed coat permits the seed to pass unharmed through the bird’s alimentary system. Pinyon seed coats differ in color between edible and nonviable seeds, signaling the jays as to which they should select. Attracting seed predators would not seem to be a successful survival strategy for pinyon pines. However, pinyon jays are behaviorally adapted to bury any seeds in excess of their immediate survival needs. This is a useful behavior for the jays, providing they can retrieve some of the buried seeds during winter, and good for the trees, as the unretrieved seeds are ready to germinate. Still, for the jays to bury any seeds, there must be an abundance of seeds far beyond the jays’ immediate needs. One tree could never produce so many seeds, but if all the pinyons in a region produced heavy seed crops at once, they would indeed “flood the market” with vastly more pinyon seeds than the local population of jays could consume. In fact, that is exactly what the pinyon pines do. It requires a great deal of energy to make so many seeds, so much energy that it is unlikely that a pinyon population could produce such a bumper seed crop every year. More important, however, it would be to the severe disadvantage of the trees to produce large seed crops annually, even if they could. Doing so would make the resource not only abundant but also predictable. Seed predators could, over the years, steadily build their populations, eventually increasing so much that they could, indeed, consume virtually all of the seeds. It is much more adaptive for the plants to produce seed cornucopias intermittently. Doing so has several major advantages. First, energy can be stored for some years and then devoted to cone and seed production, ensuring adequate energy to produce a large seed crop. Second, seed-predator populations will decline in years of low seed production, either through starvation, reduced reproduction, or emigration. Pinyons in most areas have a roughly six-year interval between heavy seed crops. Pinyon jays have so completely adapted to the cycle of the pinyons that their reproduction is tied to it. Most species of birds mature sexually in response to changes in day length. In pinyon jays, however, day length is only one stimulus for reproduction. The other cue is availability of pinyon seeds. When seeds are abundant, jays can breed very early in spring, continue breeding through summer, and reenter breeding condition as early as the winter solstice. So the jay population temporarily enlarges in response to one of the intermittent large crops of pinyon seeds. But the increase in the population of jays is less than the increase in the size of the seed crop. Thus many of the seeds of a bumper crop are buried and subsequently germinate, many more than would germinate without planting by the jays.