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1、 为了帮助大家高效备考托福, 为大家带来托福 TPO42 阅读 Passage1 原文文本+题目+答案 解析,希望对大家备考有所帮助。 Geographic Isolation of Species Biologist Ernst Mayr defined a species as“ an actually or potentially interbreeding population that does not interbreed with other such populations when there is opportunity to do so.”A key event in t
2、he origin of many species is the separation of a population with its gene pool(all of the genes in a population at any one time)from other populations of the same species,thereby preventing population interbreeding With its gene pool isolated,a separate population can follow its own evolutionary cou
3、rse.In the formation of many species,the initial isolation of a population seems to have been a geographic barrier This mode of evolving new species is called allopatric speciation. Many factors can isolate a population geographically.A mountain range may emerge and gradually split a population of o
4、rganisms that can inhabit only lowland lakes,certain fish populations might become isolated in this way.Similarity,a creeping glacier may gradually divide a population,or a land bridge such as the Isthmus of Panama may form and separate the marine life in the ocean waters on either side. How formida
5、ble must a geographic barrier be to keep populations apart?It depends on the ability of the organisms to move across barriers.Birds and coyotes can easily cross mountains and rivers.The passage of wind-blown tree pollen is also not hindered by such barriers,and the seeds of many plants may be earned
6、 back and forth on animals In contrast,small rodents may find a deep canyon or a wide river an effective barrier.For example,the Grand Canyon,in the southwestern United Slates,separate the range of the while-tailed antelope squirrel from that of the closely related Harrisantelope squirrel.Smaller,wi
7、th a shorter tail that is white underneath,the white-tailed antelope squirrel inhabits deserts north of the canyon and west of the Colorado River in southern California Hamsantelope squirrel has a more limited range in deserts south of the Grand Canyon. Geographic isolation creates opportunities for
8、 new species to develop,but it does not necessarily lead to new species because speciation occurs only when the gene pool undergoes enough changes to establish reproductive barriers between the isolated population and its parent population.The likelihood of allopatric speciation increases when a pop
9、ulation is small as well as isolated,making it more likely than a large population to have its gene pool changed substantially.For example,in less than two million years,small populations of stray animals and plants from the South American mainland that managed to colonize the Galapagos Islands gave
10、 rise to all the species that now inhabit the islands. When oceanic islands are far enough apart to permit populations to evolve in isolation,but close enough to allow occasional dispersions to occur,they are effectively outdoor laboratories of evolution.The Galapagos island chain is one of the worl
11、d s greatest showcases of evolution Each island was born from underwater volcanoes and was gradually covered by organisms derived from strays that rode the ocean currents and winds from other islands and continents.Organisms can also be carried to islands by other organisms,such as sea birds that tr
12、avel long distances with seeds clinging to their feathers. The species on the Galapagos Islands today,most of which occur nowhere else,descended from organisms that floated,flew,or were blown over the sea from the South American mainland For instance,the Galapagos island chain has a total of thirtee
13、n species of closely related birds called Galapagos finches These birds have many similarities but differ in their feeding habits and their beak type,which is correlated with what they eat Accumulated evidence indicates that all thirteen finch species evolved from a single small population of ancest
14、ral birds that colonized one of the islands.Completely isolated on the island after migrating from the mainland,the founder population may have undergone significant changes in its gene pool and become a new species.Later,a few individuals of this new species may have been blown by storms to a neigh
15、boring island.Isolated on this second island,the second founder population could have evolved into a second new species,which could later recolonize the island from which its founding population emigrated.Today each Galapagos island has multiple species of finches,with as many as ten on some islands
16、. paragraph 1 Biologist Ernst Mayr defined a species as“ an actually or potentially interbreeding population that does not interbreed with other such populations when there is opportunity to do so.”A key event in the origin of many species is the separation of a population with its gene pool(all of
17、the genes in a population at any one time)from other populations of the same species,thereby preventing population interbreeding With its gene pool isolated,a separate population can follow its own evolutionary course.In the formation of many species,the initial isolation of a population seems to ha
18、ve been a geographic barrier This mode of evolving new species is called allopatric speciation. 1.The word“key”in the passage is closest in meaning to【词汇题】 A.early B.crucial C.noticeable D.frequent 答案:B 解析:key,关键的。 Early,早期的。Crucial,重要的,决定性的。Noticeable,显而易见的,值得注意的。 Frequent,频繁的。所以 B 选项正确。 2.The word
19、“initial”in the passage is closest in meaning to【词汇题】 A.best B.usual C.first D.actual 答案:C 解析:initial,最初的。 Best,最好的。Usual,通常的。First,第一,首先。Actual,真正的。所以 C 选项正确。 3.According to paragraph 1.allopatric speciation is possible when【事实信息题】 A.a population contains all the different genes present in a specie
20、s at a particular time B.a population becomes isolated due to the presence of a geographic barrier C.genetic mixing begins to occur in previously separate populations of a species D.a species is successful in crossing a geographic barrier 答案:B 解 析 : 根 据 allopatric speciation 定 位 至 原 文 the initial is
21、olation of a population seems to have been a geographic barrier.This mode of evolving new species is called allopatric speciation.其中have been a geographic barrier对应B选项中的the presence of a geographic barrier.所以 B 选项正确。 paragraph 1&2 Biologist Ernst Mayr defined a species as“ an actually or potentially
22、 interbreeding population that does not interbreed with other such populations when there is opportunity to do so.”A key event in the origin of many species is the separation of a population with its gene pool(all of the genes in a population at any one time)from other populations of the same specie
23、s,thereby preventing population interbreeding With its gene pool isolated,a separate population can follow its own evolutionary course.In the formation of many species,the initial isolation of a population seems to have been a geographic barrier This mode of evolving new species is called allopatric
24、 speciation. Many factors can isolate a population geographically.A mountain range may emerge and gradually split a population of organisms that can inhabit only lowland lakes,certain fish populations might become isolated in this way.Similarity,a creeping glacier may gradually divide a population,o
25、r a land bridge such as the Isthmus of Panama may form and separate the marine life in the ocean waters on either side. 4.How is paragraph 2 related to paragraph 1?【组织结构题】 A.Paragraph 2 points out a number of ways in which the phenomenon of geographic isolation mentioned in paragraph 1 can occur B.P
26、aragraph 2 identifies discoveries that led to the conclusion presented in paragraph 1 that geographic isolation has played a rote in the origin of many species C.Paragraph 2 provides evidence supporting the statement in paragraph 1 that a population can follow its own evolutionary course once its ge
27、ne pool becomes isolated D.Paragraph 2 explains why the term“allopatric”was adopted to describe the method of speciation described in paragraph 1 答案:A 解析:根据第二段第一句话 Many factors can isolate a population geographically.可 知接下来的整段内容都将围绕能引起异域种化的因素或途径。而后列举的 mountain range,creeping glacier,land bridge 都是进一
28、步的对其进行解释说明。所以 A 选项正确。 paragraph 3 How formidable must a geographic barrier be to keep populations apart?It depends on the ability of the organisms to move across barriers.Birds and coyotes can easily cross mountains and rivers.The passage of wind-blown tree pollen is also not hindered by such barrie
29、rs,and the seeds of many plants may be earned back and forth on animals In contrast,small rodents may find a deep canyon or a wide river an effective barrier.For example,the Grand Canyon,in the southwestern United Slates,separate the range of the while-tailed antelope squirrel from that of the close
30、ly related Harrisantelope squirrel.Smaller,with a shorter tail that is white underneath,the white-tailed antelope squirrel inhabits deserts north of the canyon and west of the Colorado River in southern California Hamsantelope squirrel has a more limited range in deserts south of the Grand Canyon. 5
31、.In paragraph 3,the author contrasts a variety of organisms to illustrate which of the following points?【事实信息题】 A.Geographic barriers are less likely to keep apart populations of plants than populations of animals. B.Geographic barriers are more likely to keep apart populations of large organisms th
32、an populations of small organisms C.Some members of a species are able to cross geographic barriers,while other members of the same species are not. D.The effectiveness of geographic barriers in keeping organisms apart depends on an organisms ability to move across barriers. 答案:D 解析:根据 organisms 定位至
33、原文 How formidable must a geographic barrier be to keep populations apart?It depends on the ability of the organisms to move across barriers.其中 How formidable must a geographic barrier be to keep populations apart 对 应 D 选项中的 The effectiveness of geographic barriers in keeping organisms apart. 所以 D 选项
34、正确。 本文是托福 tpo42 阅读答案解析:Explaining Dinosaur Extinction。 6.Paragraph 3 supports the idea that white-tailed antelope squirrels and Harrisantelope squirrels have which of the following in common?【事实信息题】 A.They are the two smallest rodents now found in the southwestern United States. B.They have white co
35、loring underneath their tails C.They cannot cross the Grand Canyon D.They cannot survive in desert conditions 答案:C 解析:根据 white-tailed antelope squirrels 定位至原文 For example,the Grand Canyon,in the southwestern United States,separate the range of the while-tailed antelope squirrel from that of the clos
36、ely related Harrisantelope squirrel.可 知,科罗拉多大峡谷将白尾巴羚羊松鼠和哈里斯羚羊松鼠隔绝开了,所以 C 选项正确,这两 种羚羊松鼠的共同特点就是无法跨越科罗拉多大峡谷。 paragraph 4 Geographic isolation creates opportunities for new species to develop,but it does not necessarily lead to new species because speciation occurs only when the gene pool undergoes enou
37、gh changes to establish reproductive barriers between the isolated population and its parent population.The likelihood of allopatric speciation increases when a population is small as well as isolated,making it more likely than a large population to have its gene pool changed substantially.For examp
38、le,in less than two million years,small populations of stray animals and plants from the South American mainland that managed to colonize the Galapagos Islands gave rise to all the species that now inhabit the islands. 7.The word“undergoes”in the passage is closest in meaning to【词汇题】 A.experiences B
39、.allows C.prevents D.causes 答案:A 解析:undergoes,经历,忍受。 Experiences,经历。Allows,允许。Prevents,阻止。Cause,引起。所以 A 选项正确。 8.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 essenti
40、al information【句子简化题】 A.Geographic isolation is sometimes but not always the reason for the creation of reproductive barriers between a parent population and the populations descended from it B.Genetic changes in a geographical isolated population do not necessarily make the population look differen
41、t enough from its parent population to be considered a new species C.Geographical isolation allows the separated populations to evolve independently of each other and so can lead to the formation of new species D.Geographic isolation can lead to new species only if the gene pool of the isolated popu
42、lation changes enough to prevent it from reproducing with the parent population 答案:D 解析 : 注意句子中的转折和因果关系,句子主干出现在转折后面,且要注意 only 后面的 内容。 句子大意为, 只有当物种被隔绝的基因库改变的足够多来防止它们和亲本种群繁殖时, 地理隔绝就会产生新的物种。所以 D 选项正确。 9.According to paragraph 4,why does the size of a population affect the likelihood of allopatric speci
43、ation?【事实信息题】 A.Because smaller populations are more likely than larger ones to become geographically isolated B.Because the gene pool of a small isolated population is more likely to undergo substantial change than is the gene pool of a larger population C.Because a isolated population can become a
44、 new species with substantially less change to its gene pool than would be required by a larger population D.Because smaller populations are more likely to be made up of stray animals or plants than larger populations are 答案:B 解析:根据 likelihood 定位至原文 The likelihood of allopatric speciation increases
45、when a population is small as well as isolated,making it more likely than a large population to have its gene pool changed substantially.注意句中的比较关系, 并 且其中 have its gene pool changed substantially 对应 B 选项中的 undergo substantial change.所以 B 选项正确。 10.The word“managed”in the passage is closest in meaning
46、to【词汇题】 A.were able B.were forced C.arrived D.expanded 答案:A 解析:managed,设法完成。 Were able,能够。 Were forced,被迫。 Arrived,到达。 Expanded,扩大。 所以 A 选项正确。 paragraph 5 When oceanic islands are far enough apart to permit populations to evolve in isolation,but close enough to allow occasional dispersions to occur,
47、they are effectively outdoor laboratories of evolution.The Galapagos island chain is one of the world s greatest showcases of evolution Each island was born from underwater volcanoes and was gradually covered by organisms derived from strays that rode the ocean currents and winds from other islands
48、and continents.Organisms can also be carried to islands by other organisms,such as sea birds that travel long distances with seeds clinging to their feathers. 11.Paragraph 5 supports the idea that the Galapagos island chain was able to become“one of the worlds greatest showcases of evolution”primari
49、ly because of 【事实信息题】 A.the richness of the volcanic soil of each of the islands in the chain B.the distance of the individual islands from each other and from the mainland C.the relativity long time it took for the islands to become covered by organisms D.the outdoor laboratories that scientists have built on the islands to study evolution 答案:B 解析:根据“one of the worlds greatest showcases of evolution”定位至原文前一句 话 When oceanic islands are far enough apart to permit populations to evolve in isolation,but close enough to allow occasional dispersions to occur,they are effectively outdoor la
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