托福TPO42閱讀文本

1、托福TPO42閱讀文本+題目+答案下載Geographic Isolation of SpeciesBiologist 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 p

2、opulation 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 course. In the formation of many species, the ini

3、tial 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 organisms that can inhabit only lowland lakes,

4、 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 formidable must a geographic barrier be to keep p

5、opulations 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 back and forth on animals In contrast,

6、 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 Harris antelope squirrel. Smaller, with a shorter tail that is white

7、 underneath, the white-tailed antelope squirrel inhabits deserts north of the canyon and west of the Colorado River in southern California Hams' antelope squirrel has a more limited range in deserts south of the Grand Canyon.Geographic isolation creates opportunities for new species to develop,

8、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 population is small as well

9、 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 rise to all the spec

10、ies 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 world s greatest showcas

11、es 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 travel long distance

12、s 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 thirteen species of c

13、losely related birds called Galapagos finches These birds have many similarities but differ in their feeding habits andtheir beak type, which is correlated with what they eat Accumulated evidence indicates that all thirteen finch species evolved from a single small population of ancestral birds that

14、 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 neighboring isla

15、nd. 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.paragr

16、aph 1Biologist 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 the gen

17、es 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 have

18、 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 toA.early B.crucial C.noticeable D.frequent2.The word “initial” in the passage is closest in meaning toA.best B.usual C.first D.actual3.According to para

19、graph 1. allopatric speciation is possible whenA. a population contains all the different genes present in a species at a particular timeB. a population becomes isolated due to the presence of a geographic barrierC. genetic mixing begins to occur in previously separate populations of a speciesD. a s

20、pecies is successful in crossing a geographic barrierparagraph 1&2Biologist 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 t

21、he 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 course. In the formation of m

22、any 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 organisms that can inhabi

23、t only lowland lakes, certain fish populations might become isolated in this way. Similarity, a creeping glacier may gradually dividea 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.4.How is paragraph 2 related to p

24、aragraph 1?A. Paragraph 2 points out a number of ways in which the phenomenon of geographic isolation mentioned in paragraph 1 can occurB. Paragraph 2 identifies discoveries that led to the conclusion presented in paragraph 1 that geographic isolation has played a rote in the origin of many speciesC

25、. Paragraph 2 provides evidence supporting the statement in paragraph 1 that a population can follow its own evolutionary course once its gene pool becomes isolatedD. Paragraph 2 explains why the term “allopatric” was adopted to describe the method of speciation described in paragraph 1paragraph 3Ho

26、w 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 barriers, and the seeds of many plants

27、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 closely related Harris antelope

28、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 Hams' antelope squirrel has a more limited range in deserts south of the Grand Canyon.5.In paragraph 3, t

29、he author contrasts a variety of organisms to illustrate which of the following points?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 than populations of small

30、organismsC. 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.6.Paragraph 3 supports the idea that white-taile

31、d antelope squirrels and Hams' antelope squirrels have which of the following in common?A. They are the two smallest rodents now found in the southwestern United States.B. They have white coloring underneath their tailsC. They cannot cross the Grand CanyonD. They cannot survive in desert conditi

32、onsparagraph 4Geographic 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 enough changes to establish reproductive barriers between the isolated population and its parent population

33、. 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 example, in less than two million years, small populations of stray animals and plants from the South Ame

34、rican 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 toA.experiences B.allows C.prevents D.causes8.Which of the sentences below best expresses the essential information in t

35、he highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential informationA. Geographic isolation is sometimes but not always the reason for the creation of reproductive barriers between a parent population and the populations descended from itB

36、. Genetic changes in a geographical isolated population do not necessarily make the population look different enough from its parent population to be considered a new speciesC. Geographical isolation allows the separated populations to evolve independently of each other and so can lead to the format

37、ion of new speciesD. Geographic isolation can lead to new species only if the gene pool of the isolated population changes enough to prevent it from reproducing with the parent population9.According to paragraph 4, why does the size of a population affect the likelihood of allopatric speciation?A. B

38、ecause smaller populations are more likely than larger ones to become geographically isolatedB. Because the gene pool of a small isolated population is more likely to undergo substantial change than is the gene pool of a larger populationC. Because a isolated population can become a new species with

39、 substantially less change to its gene pool than would be required by a larger populationD. Because smaller populations are more likely to be made up of stray animals or plants than larger populations are10.The word “managed” in the passage is closest in meaning toA.were able B.were forced C.arrived

40、 D.expandedparagraph 5When oceanic islands are far enough apart to permit populations to evolve in isolation, butclose enough to allow occasional dispersions to occur, they are effectively outdoor laboratories of evolution. The Galapagos island chain is one of the world s greatest showcases of evolu

41、tion 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 travel long distances with seed

42、s clinging to their feathers.11.Paragraph 5 supports the idea that the Galapagos island chain was able to become “one of the world's greatest showcases of evolution” primarily because ofA. the richness of the volcanic soil of each of the islands in the chainB. the distance of the individual isla

43、nds from each other and from the mainlandC. the relativity long time it took for the islands to become covered by organismsD. the outdoor laboratories that scientists have built on the islands to study evolutionparagraph 6The species on the Galapagos Islands today, most of which occur nowhere else,

44、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 thirteen species of closely related birds called Galapagos finches These birds have many similarities but differ in their feeding habits an

45、d 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 ancestral birds that colonized one of the islands. Completely isolated on the island after migrating from the mainland, the founder popul

46、ation 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 neighboring island. Isolated on this second island, the second founder population could have evolved into a second new species, whic

47、h 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.12.According to paragraph 6. what is true about the thirteen species of Galapagos finches?A. All thirteen species are now

48、 found on most of the Galapagos IslandsB. All thirteen species are descended from the same population of ancestral birdsC. All thirteen species evolved on the island that was originally colonized by finches from the mainland.D. All thirteen species occur only in small, completely isolated population

49、s.13.Look at the four squares that indicate where the following sentence could be added to the passage.This process of speciation and colonization could have been repeated over and over again, gradually involving all the islands in the chain.The species on the Galapagos Islands today, most of which

50、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 thirteen species of closely related birds called Galapagos finches These birds have many similarities but differ in the

51、ir 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 ancestral birds that colonized one of the islands.Completely isolated on the island after migrating from the mainland

52、, 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 neighboring island. Isolated on this second island, the second founder population could have evolved into a secon

53、d 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.14.Directions：An introductory sentence for a brief summary of the passage is provided below.Complete th

54、e 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.The geographic isolation of a population can result in

55、the rise of a new species.Answer ChoicesA.Isolation can result when a geographic barrier forms and splits a population or when a few organisms somehow get carried across an existing geographic barrier and form a new populationB.Speciation is more likely when an isolated population is small because s

56、ignificant genetic changes are more likely to occur in a small population than in a large oneC.Because of the geographic isolation of the Galapagos Islands, the species that now inhabit them have gene pools that have not changed very much since the islands were first populated.D.Fish populations are

57、 more easily isolated by geographic barriers than are populations of most other organisms because fish cannot move across areas where there is no water.E.The Galapagos Islands are well situated for speciation because they provide opportunities for population isolation while also making occasional di

58、spersions between islands possible.F.Evidence indicates that the first organisms to reach the Galapagos Islands were probably a small population of finches that,in less than two million years of isolation,evolved into thirteen species. Explaining Dinosaur ExtinctionDinosaurs rapidly became exti

59、nct about 65 million years ago as part of a mass extinction known as the K-T event, because it is associated with a geological signature known as the K-T boundary, usually a thin band of sedimentation found in various parts of the world (K is the traditional abbreviation for the Cretaceous, derived from the German name Kreidezeit). Many explanations have been proposed for why dinosaurs became extinct. For example, some have blamed dinosaur ex