TPO3托福阅读Passage3原文文本+题目+答案解析

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　　TPO3托福阅读Passage3原文文本

　　The Long-Term Stability of Ecosystems

　　Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area. Ecologists use the term “succession” to refer to the changes that happen in plant communities and ecosystems over time. The first community in a succession is called a pioneer community, while the long-lived community at the end of succession is called a climax community. Pioneer and successional plant communities are said to change over periods from 1 to 500 years. These changes—in plant numbers and the mix of species—are cumulative. Climax communities themselves change but over periods of time greater than about 500 years.

　　An ecologist who studies a pond today may well find it relatively unchanged in a year’s time. Individual fish may be replaced, but the number of fish will tend to be the same from one year to the next. We can say that the properties of an ecosystem are more stable than the individual organisms that compose the ecosystem.

　　At one time, ecologists believed that species diversity made ecosystems stable. They believed that the greater the diversity the more stable the ecosystem. Support for this idea came from the observation that long-lasting climax communities usually have more complex food webs and more species diversity than pioneer communities. Ecologists concluded that the apparent stability of climax ecosystems depended on their complexity. To take an extreme example, farmlands dominated by a single crop are so unstable that one year of bad weather or the invasion of a single pest can destroy the entire crop. In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage from weather to pests.

　　The question of ecosystem stability is complicated, however. The first problem is that ecologists do not all agree what “stability” means. Stability can be defined as simply lack of change. In that case, the climax community would be considered the most stable, since, by definition, it changes the least over time. Alternatively, stability can be defined as the speed with which an ecosystem returns to a particular form following a major disturbance, such as a fire. This kind of stability is also called resilience. In that case, climax communities would be the most fragile and the least stable, since they can require hundreds of years to return to the climax state.

　　Even the kind of stability defined as simple lack of change is not always associated with maximum diversity. At least in temperate zones, maximum diversity is often found in mid-successional stages, not in the climax community. Once a redwood forest matures, for example, the kinds of species and the number of individuals growing on the forest floor are reduced. In general, diversity, by itself, does not ensure stability. Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability—just the opposite, in fact. A more complicated system is, in general, more likely than a simple system to break down. A fifteen-speed racing bicycle is more likely to break down than a child’s tricycle.

　　Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities. The destruction caused by the volcanic explosion of Mount St. Helens, in the northwestern United States, for example, pales in comparison to the destruction caused by humans. We need to know what aspects of a community are most important to the community’s resistance to destruction, as well as its recovery.

　　Many ecologists now think that the relative long-term stability of climax communities comes not from diversity but from the “patchiness” of the environment, an environment that varies from place to place supports more kinds of organisms than an environment that is uniform. A local population that goes extinct is quickly replaced by immigrants from an adjacent community. Even if the new population is of a different species, it can approximately fill the niche vacated by the extinct population and keep the food web intact.

　　TPO2托福阅读Passage3题目

　　Question 1 of 14

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

　　A. natural.

　　B. final.

　　C. specific.

　　D. complex.

　　Question 2 of 14

　　According to paragraph 1, which of the following is NOT true of climax communities?

　　A. They occur at the end of a succession..

　　B. They last longer than any other type of community..

　　C. The numbers of plants in them and the mix of species do not change..

　　D. They remain stable for at least 500 years at a time..

　　Question 3 of 14

　　According to paragraph 2, which of the following principles of ecosystems can be learned by studying a pond?

　　A. Ecosystem properties change more slowly than individuals in the system..

　　B. The stability of an ecosystem tends to change as individuals are replaced..

　　C. Individual organisms are stable from one year to the next..

　　D. A change in the members of an organism does not affect an ecosystem’s properties..

　　Question 4 of 14

　　According to paragraph 3, ecologists once believed that which of the following illustrated the most stable ecosystems?

　　A. Pioneer communities.

　　B. Climax communities.

　　C. Single-crop farmlands.

　　D. Successional plant communities.

　　Question 5 of 14

　　According to paragraph 4, why is the question of ecosystem stability complicated?

　　A. The reasons for ecosystem change are not always clear.

　　B. Ecologists often confuse the word “stability” with the word “resilience.”.

　　C. The exact meaning of the word “stability” is debated by ecologists..

　　D. There are many different answers to ecological questions..

　　Question 6 of 14

　　According to paragraph 4, which of the following is true of climax communities?

　　A. They are more resilient than pioneer communities..

　　B. They can be considered both the most and the least stable communities..

　　C. They are stable because they recover quickly after major disturbances..

　　D. They are the most resilient communities because they change the least over time..

　　Question 7 of 14

　　Which of the following can be inferred from paragraph 5 about redwood forests?

　　A. They become less stable as they mature..

　　B. They support many species when they reach climax..

　　C. They are found in temperate zones..

　　D. They have reduced diversity during mid-successional stages..

　　Question 8 of 14

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

　　A. increase.

　　B. ensure.

　　C. favor.

　　D. complicate.

　　Question 9 of 14

　　In paragraph 5, why does the author provide the information that “A fifteen-speed racing bicycle is more likely to break down than a child's tricycle ”?

　　A. To illustrate a general principle about the stability of systems by using an everyday example.

　　B. To demonstrate that an understanding of stability in ecosystems can be applied to help understand stability in other situations.

　　C. To make a comparison that supports the claim that, in general, stability increases with diversity.

　　D. To provide an example that contradicts mathematical models of ecosystems.

　　Question 10 of 14

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

　　A. increases proportionally.

　　B. differs.

　　C. loses significance.

　　D. is common.

　　Question 11 of 14

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

　　A. Ecologists now think that the stability of an environment is a result of diversity rather than patchiness..

　　B. Patchy environments that vary from place to place do not often have high species diversity..

　　C. Uniform environments cannot be climax communities because they do not support as many types of organisms as patchy environments..

　　D. A patchy environment is thought to increase stability because it is able to support a wide variety of organisms..

　　Question 12 of 14

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

　　A. foreign.

　　B. stable.

　　C. fluid.

　　D. neighboring.

　　Question 13 of 14

　　Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?.

　　In fact, damage to the environment by humans is often much more severe than damage by natural events and processes..

　　Question 14 of 14

　　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.The process of succession and the stability of a climax community can change over time. .

　　A.The changes that occur in an ecosystem from the pioneer to the climax community can be seen in one human generation..

　　B.A high degree of species diversity does not always result in a stable ecosystem..

　　C.Disagreements over the meaning of the term "stability" make it difficult to identify the most stable ecosystems..

　　D.Ecologists agree that climax communities are the most stable types of ecosystems..

　　E.The level of resilience in a plant community contributes to its long-term stability..

　　F.The resilience of climax communities makes them resistant to destruction caused by humans..

　　TPO3托福阅读Passage3解析

　　Question 1 of 14

　　正确答案：C

　　题目解析：C particular: 特别的，特定的。A是自然地;B是最终地;C是特定的;D是复杂的。根据词意，答案是C的specific。对应原文Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area.前文说assemble them flexibly，多变的，就是每个群落都不一样，强调特殊性。而且后半句话说了particular的结构取决于specific的历史，particular和specific呼应，因此答案很明显是C。

　　Question 2 of 14

　　正确答案：C

　　题目解析：B 以climax communities做关键词定位至原文第三句和最后一句： The first community in a succession is called a pioneer community, while the long-lived community at the end of succession is called a climax community. Climax communities themselves change but over periods of time greater than about 500 years.第三句说明A对，不选;最后一句说明D对，不选;B没直说，说其他communities变化周期在1-500年，climax最少是500年，说明climax比较长，B对，不选。而且最后一句也说了climax是变化的，C说反了，选。

　　Question 3 of 14

　　正确答案：A

　　题目解析：A, 本段非常短，迅速看完之后发现最后一句是结论： We can say that the properties of an ecosystem are more stable than the individual organisms that compose the ecosystem.说生态系统比组成生态系统的任意单一物种都稳定，A是答案。其他三个选项都未提及。

　　Question 4 of 14

　　正确答案：B

　　题目解析：B 以ecologists做关键词定位至本段第一二句，说生态学家认为生态系统中物种越多越稳定。接着在举例子的时候作者举到了climax communities： They believed that the greater the diversity the more stable the ecosystem. Support for this idea came from the observation that long-lasting climax communities usually have more complex food webs and more species diversity than pioneer communities.说明生态学家认为climax communities最稳定，答案B。

　　Question 5 of 14

　　正确答案：C

　　题目解析：C 以question of ecosystem stability为关键词定位至本段头两句： The first problem is that ecologists do not all agree what "stability" means.说生态学家对于什么是生态系统的稳定性依然存在争议，C是原文的忠实改写。

　　Question 6 of 14

　　正确答案：B

　　题目解析：B 关于climax communities原文有两个地方提到： In that case, the climax community would be considered the most stable, since, by definition, it changes the least over time. In that case, climax communities would be the most fragile and the least stable, since they can require hundreds of years to return to the climax state.因为生态学家对什么是稳定的定义存在两个观点：以不变这种观点看，climax是最稳定的;以快速恢复这种观点看，climax是最不稳定的，所以climax既稳定也不稳定。B明确说到两个方面，其它选项都只说到一个方面。

　　Question 7 of 14

　　正确答案：C

　　题目解析：C 以redwood forest做关键词定位至原文第三句，事实上这个redwood是前句的一个具体例子： At least in temperate zones, maximum diversity is often found in mid-successional stages, not in the climax community.前面句说至少在温带，mid是最稳定的，不是climax，紧接着就举了一个redwood的例子，可以推断redwood是温带植物，C是答案。A/B/D都与原文意思相反，而且B和D基本上意思一样，都不对。

　　Question 8 of 14

　　正确答案：B

　　题目解析：B guarantee: 保证，确保。A是增加;B是确保;C是赞成，喜欢;D是使…复杂。根据词意，B是正确答案。对应原文Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability—just the opposite, in fact.本句中有个likewise，说明它与前面句子构成类比，前句说diversity does not ensure stability, 后文的内容几乎和前句一模一样，除了动词被替换，因此guarantee的意思就是ensure。

　　Question 9 of 14

　　正确答案：A

　　题目解析：A 括号的作用是解释括号之前的文字： A more complicated system is, in general, more likely than a simple system to break down.前文说系统越复杂越容易坏，后面举了十五速赛车和小孩子的三轮车的例子，三轮车明显比赛车简单，所以就是支持前文，A正确，C正好说反，其他都没说。

　　Question 10 of 14

　　正确答案：C

　　题目解析：C pale: 苍白，使失色。A是成比例增长;B是不同;C是失去重要性;D是常见，普通。根据词意，C是正确答案。对应原文The destruction caused by the volcanic explosion of Mount St. Helens, in the northwestern United States, for example, pales in comparison to the destruction caused by humans.单词所在句之前说很多climax communities都被人类破坏了，也就是强调人的破话很严重。后面举了个例子，说圣海伦斯火山爆发造船的破坏还没有人类活动的破坏严重，所以C选项lose significance正确。

　　Question 11 of 14

　　正确答案：D

　　题目解析：D : 原文的结构是生态系统的长期稳定性不是因为diversity，而是因为patchiness，又对这个进行了解释，说物种多。A说反;B错，因为原文没有说patchiness和diversity是矛盾的;C错，因为原文比较的是patchiness和uniform，而C直接将patchiness和climax进行比较，偷换概念;D正确，注意原文貌似没有明显的因果关系，因此可能单看句子间关系的话会排除D，但原文后半句整个是对patchiness的一种解释，所以存在不明显的因果关系。

　　Question 12 of 14

　　正确答案：D

　　题目解析：D，adjacent: 相邻。A是外国的;B是稳定的;C是流动的;D是相邻的。根据词意，D是正确答案。对应原文A local population that goes extinct is quickly replaced by immigrants from an adjacent community.原文说本地的population灭绝的话会被哪里来的群落补充，可能的只有foreign和neighboring，这两个选项代入原文都是可以的，除知道这个单词的意思之外，还可以认为相邻的群落更有可能迅速补充，而外来的范围太大，不对。

　　Question 13 of 14

　　正确答案：B

　　题目解析：B 根据待插入句中的human判断，A/B/C是可能的，natural events and processes自然的过程，与第二句中的圣海伦斯火山爆发是同义替换，所以B/C可能正确，但按照先理论后实例的原则，正确答案是B不是C。

　　Question 14 of 14

　　正确答案：BCE

　　题目解析：B.C.E The changes选项与原文首段的最后一句意思相反，不选。A high degree选项对应原文第三段和第五段的首句，第四段的最后一句，正确。The level选项对应原文第六段首句，第四段倒数第二第三句，正确。Ecologists选项与原文第三段第四段的首句意思相反，不选。Disagreements选项对应原文第四段第二句，正确。The resilience选项原文没说，原文第六段说不知道为什么生物群落能抵抗破坏，不选。

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