『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 34 Passage 3阅读练习：What role does paragraph 5 play in the passage?真题题目及答案解析，TPO/Official 34 Passage 3阅读原文范文音频翻译

托福TPO/Official 34 Passage 3阅读原文What role does paragraph 5 play in the passage?题目答案及解析-新东方托福官方网校手机版

许多植物（至少有68个不同科的一种或多种）即使在没有开花的情况下也可以分泌花蜜，因为它们在茎、叶、叶茎或其他结构上带有花外蜜腺（产生花蜜的结构）。

Many plants—one or more species of at least 68 different families—can secrete nectar even when they have no blossoms, because they bear extrafloral nectaries (structures that produce nectar) on stems, leaves, leaf stems, or other structures.

这些植物通常出现在有大量蚂蚁的地方，大多数在热带地区，但也有些在温带地区。

These plants usually occur where ants are abundant, most in the tropics but some in temperate areas.

在北美东北部，有各种李子、樱桃、玫瑰、山楂、白杨和橡树。

Among those of northeastern North America are various plums, cherries, roses, hawthorns, poplars, and oaks.

像花蜜一样，花外蜜主要由水组成，其中糖的溶解糖含量高，在某些植物中还包含少量氨基酸。

Like floral nectar, extrafloral nectar consists mainly of water with a high content of dissolved sugars and, in some plants, small amounts of amino acids.

我们现在已经知道的是，某些植物的花外蜜会吸引蚂蚁和其他昆虫，但是大多数带有这些蜜腺的植物的进化史我们还不清楚。

The extrafloral nectaries of some plants are known to attract ants and other insects, but the evolutionary history of most plants with these nectaries is unknown.

尽管如此，大多数生态学家认为，所有花外蜜都会吸引昆虫来捍卫植物。

Nevertheless, most ecologists believe that all extrafloral nectaries attract insects that will defend the plant.

蚂蚁可能是植物中最常见、最有韧性的防御者。

Ants are probably the most frequent and certainly the most persistent defenders of plants.

由于高度活跃的工蚁需要大量能量，因此植物通过给蚂蚁提供丰富能量的花外蜜来满足这一需求。

Since the highly active worker ants require a great deal of energy, plants exploit this need by providing extrafloral nectar that supplies ants with abundant energy.

为了回馈这种帮助，蚂蚁守护着蜜腺，驱赶或杀死可能与蚂蚁争夺花蜜的入侵昆虫。

To return this favor, ants guard the nectaries, driving away or killing intruding insects that might compete with ants for nectar.

这些入侵者中有许多是草食性的，会吃掉植物的叶子。

Many of these intruders are herbivorous and would eat the leaves of the plants.

生物学家曾经认为，花外蜜的分泌具有纯粹的内部生理功能，而蚂蚁对分泌它的植物没有任何好处。

Biologists once thought that secretion of extrafloral nectar has some purely internal physiological function, and that ants provide no benefit whatsoever to the plants that secrete it.

这一观点和反对蚂蚁捍卫植物的“保护主义”假说已经争论了一百多年。然后在1910年，持怀疑态度的威廉·莫顿·惠勒（William Morton Wheeler）对这一争论进行了评论。

This view and the opposing “protectionist” hypothesis that ants defend plants had been disputed for over a hundred years when, in 1910, a skeptical William Morton Wheeler commented on the controversy.

他呼吁拿出证据证明保护主义的观点：蚂蚁的到来为植物提供了保护，并且在没有这种昆虫的情况下，相比有这种昆虫的时候，更多的物种将死亡或无法开花。

He called for proof of the protectionist view: that visitations of the ants confer protection on the plants and that in the absence of the insects a much greater number would perish or fail to produce flowers or seeds than when the insects are present.

芭芭拉·本特利（Barbara Bentley）于1977年审查了相关证据后，就确定了我们现在已有大量证据这一事实，从那时起，更多的观察和实验进一步证明了蚂蚁有益于植物。

That we now have an abundance of the proof that was called for was established when Barbara Bentley reviewed the relevant evidence in 1977, and since then many more observations and experiments have provided still further proof that ants benefit plants.

一个例子表明了，被吸引到花外蜜的蚂蚁如何保护牵牛花免受昆虫侵袭。

One example shows how ants attracted to extrafloral nectaries protect morning glories against attacking insects.

北美牵牛花的主要害虫主要实用牵牛花的花朵或果实，而不是叶子。

The principal insect enemies of the North American morning glory feed mainly on its flowers or fruits rather than its leaves.

以花为食的蚂蚱通过破坏花粉或柱头而间接阻碍了授粉和种子的产生，这些花冠或柱头负责接受花粉粒并让其在上面发芽。

Grasshoppers feeding on flowers indirectly block pollination and the production of seeds by destroying the corolla or the stigma, which receives the pollen grains and on which the pollen germinates.

没有色彩艳丽的花冠，花朵就不会吸引传粉者，也不会受精。

Without their colorful corolla, flowers do not attract pollinators and are not fertilized.

一只成年蚂蚱在一小时内会破坏掉大约2.5英寸长的大花冠。

An adult grasshopper can consume a large corolla, about 2.5 inches long, in an hour.

毛毛虫和种子甲虫直接影响种子生产。

Caterpillars and seed beetles affect seed production directly.

毛毛虫吞噬产生种子的卵巢，卵巢是生产种子的地方，而甲虫幼虫在​​挖果时会吃种子。

Caterpillars devour the ovaries, where the seeds are produced, and seed beetle larvae eat seeds as they burrow in developing fruits.

每个萼片底部的花外蜜会吸引几种昆虫，但其中96％是蚂蚁，这包括几种不同物种的蚂蚁。

Extrafloral nectaries at the base of each sepal attract several kinds of insects, but 96 percent of them are ants, several different species of them.

当芽还很小的时候，大概不到四分之一英寸长，萼片蜜腺就已经存在并产生花蜜。

When buds are still small, less than a quarter of an inch long, the sepal nectaries are already present and producing nectar.

随着花朵的发展和果实的成熟，它们继续这样做（生产花蜜）。

They continue to do so as the flower develops and while the fruit matures.

观察结果毫无疑问，蚂蚁保护了牵牛花和水果免受蚂蚱、毛毛虫和种子甲虫等敌对势力的联合攻击。

Observations leave little doubt that ants protect morning glory flowers and fruits from the combined enemy force of grasshoppers, caterpillars, and seed beetles.

Bentley将没有蚂蚁生长的6种植物的种子产量与被蚂蚁占据的17种植物的种子产量进行了比较。

Bentley compared the seed production of six plants that grew where there were no ants with that of seventeen plants that were occupied by ants.

未受保护的植物每株只生45粒种子，但被蚂蚁占据的植物每株可以生产211粒种子。

Unprotected plants bore only 45 seeds per plant, but plants occupied by ants bore 211 seeds per plant.

尽管蚂蚁的大小不足以杀死或严重伤害蚂蚱，但蚂蚁通过咬蚂蚱的足部来赶走它们。

Although ants are not big enough to kill or seriously injure grasshoppers, they drive them away by nipping at their feet.

种子甲虫比蝗虫小得多，因此更容易受到（蚂蚁）伤害。

Seed beetles are more vulnerable because they are much smaller than grasshoppers.

蚂蚁会捕食成年的甲虫，在雌虫将卵产在正在发育的果实上时会侵扰雌虫，并吃掉许多甲虫设法产下的卵。

The ants prey on the adult beetles, disturb females as they lay their eggs on developing fruits, and eat many of the eggs they do manage to lay.

According to paragraph 1, floral nectar and extrafloral nectar are alike in that

To say that ants are “persistent” defenders of plants means that

What can be inferred from paragraph 2 about the ants that are attracted to the extrafloral nectaries?

According to paragraph 3, what was the position of the opponents of the “protectionist” hypothesis?

The word “skeptical” 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.

According to paragraph 4, what effect does the destruction of the corolla have on plants?

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

What role does paragraph 5 play in the passage?

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

According to paragraph 5, what did Bentley’s comparative study show?

According to paragraph 5, ants defend morning glory plants from seed beetles in each of the following ways EXCEPT

Look at the four squares  that indicate where the following sentence could be added to the passage. Sometimes they capture the insects to feed their protein-hungry larvae.  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.

Protection of Plants by Insects Many plants—one or more species of at least 68 different families—can secrete nectar even when they have no blossoms, because they bear extrafloral nectaries (structures that produce nectar) on stems, leaves, leaf stems, or other structures. These plants usually occur where ants are abundant, most in the tropics but some in temperate areas. Among those of northeastern North America are various plums, cherries, roses, hawthorns, poplars, and oaks. Like floral nectar, extrafloral nectar consists mainly of water with a high content of dissolved sugars and, in some plants, small amounts of amino acids. The extrafloral nectaries of some plants are known to attract ants and other insects, but the evolutionary history of most plants with these nectaries is unknown. Nevertheless, most ecologists believe that all extrafloral nectaries attract insects that will defend the plant. Ants are probably the most frequent and certainly the most persistent defenders of plants.  Since the highly active worker ants require a great deal of energy, plants exploit this need by providing extrafloral nectar that supplies ants with abundant energy.  To return this favor, ants guard the nectaries, driving away or killing intruding insects that might compete with ants for nectar.  Many of these intruders are herbivorous and would eat the leaves of the plants.  Biologists once thought that secretion of extrafloral nectar has some purely internal physiological function, and that ants provide no benefit whatsoever to the plants that secrete it. This view and the opposing “protectionist” hypothesis that ants defend plants had been disputed for over a hundred years when, in 1910, a skeptical William Morton Wheeler commented on the controversy. He called for proof of the protectionist view: that visitations of the ants confer protection on the plants and that in the absence of the insects a much greater number would perish or fail to produce flowers or seeds than when the insects are present. That we now have an abundance of the proof that was called for was established when Barbara Bentley reviewed the relevant evidence in 1977, and since then many more observations and experiments have provided still further proof that ants benefit plants. One example shows how ants attracted to extrafloral nectaries protect morning glories against attacking insects. The principal insect enemies of the North American morning glory feed mainly on its flowers or fruits rather than its leaves. Grasshoppers feeding on flowers indirectly block pollination and the production of seeds by destroying the corolla or the stigma, which receives the pollen grains and on which the pollen germinates. Without their colorful corolla, flowers do not attract pollinators and are not fertilized. An adult grasshopper can consume a large corolla, about 2.5 inches long, in an hour. Caterpillars and seed beetles affect seed production directly. Caterpillars devour the ovaries, where the seeds are produced, and seed beetle larvae eat seeds as they burrow in developing fruits. Extrafloral nectaries at the base of each sepal attract several kinds of insects, but 96 percent of them are ants, several different species of them. When buds are still small, less than a quarter of an inch long, the sepal nectaries are already present and producing nectar. They continue to do so as the flower develops and while the fruit matures. Observations leave little doubt that ants protect morning glory flowers and fruits from the combined enemy force of grasshoppers, caterpillars, and seed beetles. Bentley compared the seed production of six plants that grew where there were no ants with that of seventeen plants that were occupied by ants. Unprotected plants bore only 45 seeds per plant, but plants occupied by ants bore 211 seeds per plant. Although ants are not big enough to kill or seriously injure grasshoppers, they drive them away by nipping at their feet. Seed beetles are more vulnerable because they are much smaller than grasshoppers. The ants prey on the adult beetles, disturb females as they lay their eggs on developing fruits, and eat many of the eggs they do manage to lay.