Official25 托福阅读 Passage1The Evolutionary Origin of Plants文本+题目原文+答案解析【雷哥托福】2019-02-27 09:36:27 发布 来源：雷哥托福 阅读量:2835
TPO25 托福阅读 Passage1The Evolutionary Origin of Plants文本+题目原文+答案解析
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 viewpoint, 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 widespread 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 carry their 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 protect developing embryos from drying out. Protected embryos and waterless dispersal of sex cells were achieved with the origin of seed plants and the key evolutionary innovations that they introduced: pollen, seeds, and later, flowers and fruits.
TPO25托福阅读 Passage1 The Evolutionary Origin of Plants 题目
Question 1 of 14: The word “presumably” in the passage is closest in meaning to
Question 2 of 14: 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.
Question 3 of 14: The phrase “subjected to” in the passage is closest in meaning to
A. restricted by
B. distant from
C. exposed to
D. combined with
Question 4 of 14: What can be inferred from paragraph 3 about ancient green algae?
A. They lived in a generally wet environment that was sometimes dry.
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.
Question 5 of 14:The word “desolate” in the passage is closest in meaning to
D. dried out
Question 6 of 14: 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.
Question 7 of 14: 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 400 million years earlier.
D. It lacked the presence of any organisms.
Question 8 of 14: the word “posed” in the passage is closest in meaning to
Question9 of 14 ：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
Question10 of 14: 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
Question11 of 14: 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.
Question 12 of 14: Which of the following best describes the author’s presentation of the information about land plants?
A. The author provided an 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 plant groups.
D. The author resents evidence to support the hypothesis that plants first fully evolved in water before finding their way to land.
Question13 of 14: 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.
A. The environmental conditions of freshwater habitats, unlike those of ocean habitats, are highly variable.
B. 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.
C. Ancient fresh water green algae must have evolved features that enable them to withstand extremes of temperature and periods of dryness.
D. These adaptations served their descendant well as they invaded land.
Question14 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.
In moving from water to land, ancestral plants overcame many obstacles in order to survive.
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.
TPO25托福阅读Passage1The Evolutionary Origin of Plants 真题解析
Question 1 of 14
解析：enormous，巨大的，庞大的，极大的；近义词是extremely large。根据词汇所在句的上下句推断词意，下半句的an enormous geologic area上半句的the Tharsis bulge的同位语，而通过three very large volcanoes可以判断Tharsis bulge的特点是大。
Question 2 of 14
解析：第一段中，Olympus Mons和volcanoes on the Tharsis bulge的对比要定位到最后2句：Olympus Mons的高度是25千米；三个火山的高度是18千米，所以Olympus Mons比较高，C正确。
Question 3 of 14
解析：distinctive，独特的，有特色的，与众不同的；近义词是characteristic，特有的; 独特的; 表示特性的; 显示…的特征的。
Question 4 of 14
解析：A项对应第二段第2句中的volcanoes with broad, sloping slides；B项对应第一段第1句话，火山表面有太阳系里已知的最大火山(the largest known in the solar system)；C项对应第二段第3句话，All four show distinctive lava channels…similar to those found on shield volcanoes on Earth；D项说它们高度都在25千米以上，与原文信息不符，原文提到它们只有18千米，只有D错误。
Question 5 of 14
解析：roughly，大约，大致，差不多；近义词是approximately，大约。根据词汇所在句的前后逻辑关系可推断，因为40 percent that of Earth是个不确切的值，所以对应roughly 2.5 times as high也是估计值
Question 6 of 14
解析：作者将Maxwell Mons和Hawaiian shield volcanoes进行比较的句子是在第三段第4句，这个例子是为了证明第3句话的观点，The lower the gravity, the lesser the weight and the greater the height of the mountain，这句话就是在说星球表面重力和火山高度的关系。Venus和Earth两个星球重力差不多，因此火山的高度也是基本一致的，所以这个例子证明了火山高度与星球重力之间是有直接关系的。只有A项准确地对应作者举这个例子的目的。
Question 7 of 14
解析：高亮句句意：“科学家们还没有直接证据证明这些火山依旧活跃；但是如果火山在一亿年前活跃过，那么它很有可能就还是活跃的，因为按照这些火山的大小推断，休眠周期可以在一亿年”。句子前后是转折关系。C项语义完全符合原句，“如果火山和一亿年以前一样活跃，那么它们可能还是活跃的”；A项错在“科学家依旧相信这些火山在距今一亿年间前活跃过”这个信息在原句并没有出现；B项的extensive impact cratering原句没有提及； D项错在“尽管火山和一亿年以前一样活跃”在原文中只是条件而不是事实。
Question 8 of 14
Question 9 of 14
解析：题干问的是：火星上陨石坑的填充比月球上快得多，由此作者想要说明的问题是什么。根据craters fill in much faster on mars than on the moon定位到最后一句，火星的大气（Martian atmosphere）是具有腐蚀性的，风搬运尘土比陨石撞击抹掉陨石坑的速度更快。D项准确概括了作者的论点，风在火星上是强有力的腐蚀力量。 A选项的比较对象错误，原文是火星的erase比撞击快，不是火星的撞击比月亮的撞击快；B项在原文没有依据；C项的地表干燥不能解释陨石坑的填充速度差异。
Question 10 of 14
解析：对应题干内容的原文在倒数第2句中，解释few craters less than 5 kilometers in diameter的原因定位到最后一句话，大意是“火星大气有腐蚀性且风力强劲”，C项的表述是作者举例的目的。
Question 11 of 14
解析：第五段2句话讲的都是与火星表面年龄相关的内容。the extent of large impact cratering serves as an age indicator for the Martian surface：巨大陨石坑的范围作为探测火星表面年龄的提示。Age estimates ranging from four billion years for Mars’s southern highlands to a few hundred million years，推测年龄有40亿年的，也有几千万年的，据此可知火星不同表面的年龄是不一样的，故选B
Question 12 of 14
解析：题干内容出现在第3句，A comparison…demonstrates the differences，differences定位到第六段倒数第3句，However, the ejecta on Mars gives the distinct impression of a liquid that has splashed or flowed out of crater（火星上的喷出物是以液体形式从火山口溢出的），C正确。A项与倒数第2句话矛盾，不是ejecta成了permafrost layer，permafrost layer的位置是under the surface；B项表述指的是Moon’s Copernicus crater的喷出物；D项在文中没有依据。
Question 13 of 14
解析：插入句的主语是This surface feature，大意是说表面特征会导致一个关于火星表面下的推测。所以插入句的上一句应该是一个surface feature，下文应该是推测的具体内容。B处前的a liquid that has splashed or flowed out of crater代表的就是surface feature，B处后的a layer of permafrost lies just a few meters under the surface就是地质学家们推测的内容。
Question 14 of 14
解析：文章整体是在介绍火星表面的主要地理特征。B项对应第二段和第三段的大意：火星上有shield volcanoes，而且这些火山的高度与火星的低表面重力直接相关；C项对应第四段大意：原文的Martian craters get filled considerably faster than their lunar counterparts对应C项前半句，段首句对应后半句；F项对应原文最后一段大意：对于火山口喷出物的研究显示火山表面下有一层冻土。
A项与第二段的there is no plate motion on Mars表述矛盾；D项与第五段大意矛盾；E项与最后一段大意矛盾。