TPO25阅读之一（托福阅读真题）

The Evolutionary Origin of Plants

The evolutionary history of plants has been marked by a series of adaptations. The ancestors of plants were

photosynthetic single-celled organisms that gave rise to plants presumably lacked true roots, stems, leaves, and complex reproductive structures such as flowers. All of these features appeared later in the evolutionary history of plants. Of today’s different groups of algae, green algae are probably the most similar to ancestral plants. This supposition stems from the close phylogenetic (natural evolutionary) relationship between the two groups. DNA comparisons have shown that green algae are plants’ closest living relatives. In addition, other lines of evidence support the hypothesis that land plants evolved from ancestral green algae used the same type of chlorophyll and accessory pigments in photosynthesis as do land plants. This would not be true of red and brown algae. Green algae store food as starch, as do land plants and have cell walls made of cellulose, similar in composition to those of land plants. Again, the good storage and cell wall molecules of red and brown algae are different.

Today green algae live mainly in freshwater, suggesting that their early evolutionary history may have occurred in freshwater habitats. If so, the green algae would have been subjected to environmental pressures that resulted in adaptations that enhanced their potential to give rise to land-dwelling or organisms.

█The environmental conditions of freshwater habitats, unlike those of ocean habitats, are highly variable. █Water temperature can fluctuate seasonally or even daily and changing level of rainfall can lead to fluctuations in the

concentration of chemical in the water or even to period in which the aquatic habitat dries up. █Ancient fresh water green algae must have evolved features that enable them to withstand extremes of temperature and periods of dryness. █These adaptations served their descendant well as they invaded land.

The terrestrial world is green now, but it did not start out that way. When plants first made the transition ashore more than 400 million years ago, the land was barren and desolate, inhospitable to life. From a plant’s evolutionary view point, however, it was also a land of opportunity, free of competitors and predators and full of carbon dioxide and sunlight (the raw materials for photosynthesis, which are present in far higher concentrations in air than in water).So once natural selection had shaped the adaptations that helped plants overcome the obstacles to terrestrial living, plants prospered and diversified.

When plants pioneered the land, they faced a range of challenges posed by terrestrial environments. On land, the

supportive buoyancy of water is missing, the plant is no longer bathed in a nutrient solution, and air tends to dry things out. These conditions favored the evolution of the structures that support the body, vessels that transport water and nutrients to all parts of plant, and structures that conserve water. The resulting adaptations to dry land include some structural features that arose early in plant evolution; now these features are common to virtually all land plant. They include roots or root like structures, a waxy cuticle that covers the surfaces of leaves and stems and limits the evaporation of water, and pores called stomata in leaves and stems that allow gas exchange but close when water is scarce, thus reducing water loss. Other adaptations occurred later in the transition to terrestrial life and now wide spread but not universal among plants. These include conducting vessels that transport water and minerals upward from the roots and that move the photosynthetic products from the leaves to the rest of the plant body and the stiffening substance lignin, which support the plant body, helping it expose maximum surface area to sunlight.

These adaptations allowed an increasing diversity of plant forms to exploit dry land. Life on land, however, also required new methods of transporting sperm to eggs. Unlike aquatic and marine forms, land plants cannot always rely on water currents to carrytheir sex cells and disperse their fertilized eggs. So the most successful groups of land plants are those that evolved methods of fertilized sex cell dispersal that are independent of water and structures that protest

developing embryos from drying out. Protected embryos and waterless dispersal of sex cells were achieved with the origin of seed plans and the key evolutionary innovations that they introduced: pollen, seeds, and later, flowers and fruits.

Paragraph 1:

1.The word “presumably” in the passage is closest in meaning to

A. originally B. supposedly C. obviously D. usually

2. According to paragraph 1, all of the following are true of ancestral plants EXCEPT A. They had cellulose-based cell walls. B. They were closely related to green algae C. They were able to store nutrients

D. They had a sophisticated multicellular structure. Paragraph 2:

3.The phrase “subjected to” in the passage is closest in A. restricted by B. distant from C. exposed to D. combined with

Paragraph 3:

4.What can be inferred from paragraph 3 about ancient green algae? A. They lived in a generally wet environment that was sometimes day

B. They adapted better to changes in water temperature than did to other changes in the environment.

C. They inhabited areas that were close to the ocean. D. They had lived primarily on land

Paragraph 4:

5. The word “desolate” in the passage is closest in meaning to A. dusty B. hardened C. deserted D. dried out

6.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.

A. Terrestrial plants had the advantages of not having rivals and having easy access to photosynthetic material B. The abundance of photosynthetic material made life on land easier for pioneering plants

C. Once plants had eliminated their competitors and their predators, their evolutionary process proceeded smoothly. D. Plant evolution eliminated competitors and made the process of photosynthesis more efficient.

7. According to paragraph 4, which of the following is true about the terrestrial world at the time it was colonized by plants?

A. it was exposed to high levels of solar radiation B. it contained a limited supply of carbon dioxide C. it had developed 400million years earlier D. it lacked the presence of any organisms

Paragraph 5:

8. the word “posed” in the passage is closest in meaning to A. shared B. presented C. strengthened

D. concealed

9. According to paragraph 5, all of the following are problems that early terrestrial plants had to overcome Except A. a tendency to become dry

B. the inability to limit surface sunlight

C. the absence of a structure to support the body of the plant D. the inability to transport water and minerals through the plant

10. What purpose does paragraph 5 serve in the larger discussion of the origins of terrestrial plants? A. To emphasize how long it took for ancestral plants to adjust to life on land

B. To disprove the argument that land plants adapted easily to their new terrestrial environment C. To explain how plant colonization changed the physical environment of the terrestrial world D. To describe how ancestral plants solved the problems they confirmed in colonizing

Paragraph 6:

11. According to Paragraph 6, The adaptation made by terrestrial plants had which of the following effect?’ A. Plants developed reproductive strategies usable in both land and water environment B. the plant diversity achieved in water environments diminished on land C. seed plants became the dominant species among plants D. a greater range of plants was able to develop

12. Which of the following best describes the author’s presentation of the information about land plants

A. the author provided and overview of the evolutionary relationships between specific species of algae and land plants B. The author discusses the transformation plants underwent in the process of changing from an aquatic to a terrestrial environment

C. the author establishes a pattern of similarity between major land and water pant groups

D. The author resents evidence to support the hypothesis that plants first fully evolved in water before finding their way to land

13. Look at the four squares [█] that indicate where the following sentence could be added to the passage.

Scientists believe that chemical changes and a thicker exterior, among other things, may have helped ancient algae overcome the conditions in their environment.

Where would the sentence best fit? Click on a square to add the sentence to the passage.

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.

In moving from water to land, ancestral plants overcame many obstacles in order to survive. Answer Choice:

A. Neither brown nor red algae are likely to be ancestors of plants because of their difference in pigmentation B. The instability of freshwater habitats caused marine algae to develop adaptations to their harsh environment. C. The colonization of land by plants was a major revolution in the history of Earth.

D. Terrestrial plants adjusted to life on land by undergoing structural changes that enabled them to support themselves, resist drying, and exchange gases.

E. To colonize new terrestrial habitats, plants needed to create a way of reproducing without water.

F. Once plants had overcome the challenges posed by terrestrial life, they prospered by becoming less diverse.

1.presumably大概，可能，所以正确答案是B的supposedly。不认识的同学想想 assume， 叫做假定或者推断，由于前缀pre只表方向或者加强，所以这个词大致意思和assume差不多，代入，植物的祖先是光合作用的单细胞生物，怎么样缺乏根茎等等，由于植物的祖先谁也不知道是啥样，所以单细胞生物形成的植物是没有根茎等等东西这个结论只是个推测，正确答案B。 2.排除法，A的cellulose based cell walls和C的store nutrients 都可以定位至倒数第二句， 两个选项都正确，不选；B 的green algae 定位至第五句，说陆生植物进化自green algae， 所以选项B正确，不选；D的

multicellular structure 与原文第二句的信息相反，错，选； 事实上，这道题根本不需要排除，因为D选项直接跟上题的信息相反。

3.subject to意思是被…或者说遭受… 所以正确答案是C，expose to最直接的意思是曝露与XXX之下，可以引申为遭到。不认识的童鞋代入原文，B和D是绝对说不通的，A被环境压力限制好像也有点儿奇怪，所以不认识的时候比较可得C更好。

4.以ancient green algae 做关键词定位至最后两句，说古代 algae 可以忍受极端温度和一段 时间的干旱，正好就是A说的 sometimes dry，所以A是答案。B比较了水温的变化和 其他因素的变化，而原文没给出任何相关信息，错；C的close to the ocean 好像没有干旱的时候吧；D的on land 是不是太干了。

5.desolate 荒芜的，被抛弃的，所以正确答案是C，desert 名词做沙漠大家都知道，与沙漠相关的动词意思是抛弃或者荒废也比较容易理解。不认识原词的想想 isolate 隔离， 也可以想出答案了。A尘土飞扬、B硬和D干旱，都未必被废弃，所以都不对。

6.去掉括号内容提取主干，主干说是一片充满机遇的陆地，没有 competitor，没有predator， 有阳光和二氧化碳。所以正确答案是A。B选项说 photosynthetic material 丰富是对的，但easier life on land原文没讲，不选；C和D的eliminate competitors原文没讲，原文说没有competitor，而不是被 eliminate掉了。 7.以terrestrial world做关键词定位至首句，说尽管现在很 green，最初不是，刚好问的是 以前什么样，所以往下看。下一句说当植物登上陆地时，陆地是荒芜和贫瘠的，于是正确答案是D，没有organism。但说实话，个人认为这个答案并不好，但最初说选的 A也有问题，原文讲的 sunlight 不能直接被solar radiation同义替换，比较而言还是D好些，B和C完全不对。

8.pose摆放，这个简单，想想照相的时候经常会讲摆pose，所以 pose名词的意思是姿势， 动词的意思是摆，答案present，注意所有选项都是动词，present 做动词讲的意思是呈现，所以答案是 B，A分享、C加强、D掩饰都不沾边儿。

9.A的become dry定位至第二句的 air tends to dry things out，A正确，不选；C的support the body和D的 transport water and minerals定位至第三句，两个答案都正确，不选；B的 sunlight在最后一句，但跟问题问的什么困难根本不是一回事儿，错。

10.问整段的目的，看开头，第一句讲当植物登上陆地以后，面临很多问题，再看最后一句， 说

these includeblabla，都是解决问题的方法。很明显，这段讲的是植物所面对的问题 和解决方法，所以正确答案是D。A的how long 和C的change the physical environment 都没讲。B有一定迷惑性，但原文从没讲过植物很容易适应环境，更别说disprove 了，B错。

11.以adaption做关键词定位至首句，说adaption 使得干燥陆地上的植物越来越多样化，正好是题目问的影响，所以正确答案是D的a greater range，more were available。A跟B的水环境原文没有有说；C的seed plants 原文也没说。

12.这道题问的很泛，问关于 land plants 作者是怎么写的，所以需要看不止一段，看各段开 头可知倒数三段是讲陆生植物的，讲了植物从水生到陆生的过程，于是正确答案是B。 这几段几乎没有讲到藻类，所以A错；也没有水生和陆生植物的比较，C错；至于D，按其说法根本就没讲陆生植物，是讲水生植物在登上陆地之前是如何 develop 的，不沾边。

13.以 ancient algae 做过渡点，找到原文倒数第二句，所以答案非C即D。倒数第二句说有feature 使它们忍受和极端温度干旱，而待插入句讲这些都是什么样的特点，也刚好与 后面的these adaption 形成很顺的过渡，正确答案是D。此外，待插入句中的among other things也是一个很好的点。

14.Neither 选项原文完全没有讲到，原文只说绿藻是ancestor。 The instability 选项对应原文整个第三段，正确。The colonization选项的major revolution原文没有讲到，请不要想当然，所以错。Terrestrial 选项对应原文整个第五段，正确。 To colonize 选项对应最后一段前半部分，正确 ，Onceplants 选项与最后一段首句相反。