托福TPO42阅读文本

1、托福 TPO42 阅读文本 +题目 +答案下载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 o rigin of many species is the separation

2、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 many species, t

3、he initial isolation of a population seems to have been a geographic barrier This mode of evolving new species is called allopatric speciation.jKz4rZB。Oqe9SKjMany factors can isolate a population geographically.A mountain range may emerge and gradually split a population of organisms that can inhabi

4、t 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. EThA0BA。 lU9rZiL 。How formidabl

5、e must a geographic barrier be to keep populations apart? It dependson 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 Harris ' antelope squirre

7、 l. 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.CjMcnf4。pPMCa1HGeographic

8、 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 theisolated population and its parent population.The likelihood of allopa

9、tric 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 American mainland that managed

10、 to colonize the Galapagos Islands gave rise to all the species that now in habit the isla nds.pGm60P。bpiMu2f。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 o

11、f 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 and continents. Organisms can also be carri

12、ed to islands by other organisms, such as sea birds that travel long distances with seeds clinging to their feathers.5qDlp3l 。 TCrwtyy 。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

13、 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 andChx39g0。 5AZTj8B。their beak type, which is correlated with what they eat Accumulated

14、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 population may have undergone significant changes in its gene pool and becom

15、e 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, which could later recolonize the island from which its founding population

16、emigrated.Today each Galapagos island has multiple species of finches, with as many as ten on some islands.jgeODg4 CYkUHMDparagraph 1Biologist Ernst Mayr defined a species as “an actuallyor potentially interbreedingpopulation that does not interbreed with other such populations when there is opportu

17、nity to do so.” A key event in the origin of many species is the separa tion 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 populatio

18、n 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 speciation.tiNm4iv。 G7eSSb。1. The word“key” in the passage is closest in meaning to zbkS6Jz

19、。Z1M8CYqA. early B.crucial C.noticeable D.frequent2. The word“initial ” in the passage is closest in meaning tovRNFyIn。 Bo7jeHe。A. best B.usual C.first D.actual3. According to paragraph 1. allopatric speciation is possible whenHsfq9Iz 。 dC2kwLC。A. a population contains all the different genes presen

20、t in a species at a particular time pVPyf9D。KTkjdD1。B. a populationbecomes isolated due to the presenee of a geographic barrier eLMEPweUmHnpBMC. genetic mixing begins to occur in previously separate populations of aspecies b1r84o1。 m7Zh0tq。D. a species is successful in crossing a geographic barrieri

21、Xo4FaM。 pBn0kUe。paragraph 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 the separation of a population with i

22、ts 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 initial isolation o

23、f a population seems to have been a geographic barrier This mode of evolving new speciesWvHMIi乙 KHRLP2Jis 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,

24、certain fish populations might become isolated in this way. Similarity, a creeping glacier may gradually dividebNieNCT nDEVZO。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.HGC79Iq。 9CGokx2。4. How is paragraph 2 r

25、elated to paragraph 1?A. Paragraph 2 points out a number of ways in which the phenomenon of geographicisolation mentioned in paragraph 1 can occurak1NzPb。 uobYb7T。B. Paragraph 2 identifies discoveries that led to the conclusion presented in paragraph 1 that geographic isolation has played a rote in

26、the origin of many species TvSoN6u。 BQFfHXa。C. Paragraph 2 provides evidence supporting the statement in paragraph 1 that a population can follow its own evolutionary course once its gene pool becomes isolated qZwXeEJ S3x5YII。D. Paragraph 2 explains why the term“allopatric” was adopted to describe t

27、hemethod of speciation described in paragraph 16yv7Dan 7S7efCd。paragraph 3How 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

28、 pollen is also not hindered by such barriers, 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 whil

29、e-tailed antelope squirrel from that of the closely related Harris ' antelope 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

30、 has a more limited range in deserts south of the Grand Canyon.qLtuOEL。uiHtCwg。5.In paragraph 3, the author contrasts a variety of organisms to illustrate whichof the following points?ga2VUIw mgLmxtOA. Geographic barriers are less likely to keep apart populations of plants thanpopulations of animals

31、.fr38Jrv。1WITG2BB. Geographic barriers are more likely to keep apart populations of large organismsthan populations of small organismsTad9fQd。 jFwyOuK。C. Some members of a species are able to cross geographic barriers, while othermembers of the same species are not.FImc5Me。 tq4SNBG。D. The effectiven

32、ess of geographic barriers in keeping organisms apart depends onan organism ' s ability to move across barriers.IEW7Z4I。HHoRwkG6. Paragraph 3 supports the idea that white-tailed antelope squirrels and Hams'antelope squirrels have which of the following in common?AiAR26u。 LSiREoA。A. They are

33、the two smallest rodents now found in the southwestern UnitedStates. 5zB9040。 BDKxpsq。B. They have white coloring underneath their tailsC. They cannot cross the Grand CanyonD. They cannot survive in desert conditions paragraph 4Geographic isolation creates opportunities for new species to develop, b

34、ut 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

35、 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 GalapagosIslands gave rise to all the spec

36、ies that now inhabit the islands.IQ8WF6T。 LP3ZfPp。7. The word “undergoes” in the passage is closest in meaning to0BdrV1a。 GxcbPxJ。A. experiences B.allows C.prevents D.causes8. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect

37、choices change the meaning inU7MbuF1 23oplPaimportant 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 it qcgqQ70。 1RVkHxy。B. Genetic changes

38、in a geographical isolated population do not necessarily make the population look different enough from its parent population to be considered a new species uYPvHju。 YFkV4Z2。C. Geographical isolation allows the separated populations to evolve independentlyof each other and so can lead to the formati

39、 on of new speciesX3SQ3nmSDpM9HT。D. 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 population 2KPOSrQ。 9PgwJIW。9. Accordingto paragraph 4, why does the size of a population affect the likelih

40、oodof allopatric speciation?migTMOg MWmiEtYA. Because smaller populations are more likely than larger ones to become geographically isolated reET5ld 。 l2KSUYr。B. Because the gene pool of a small isolated population is more likely to undergosubstantial change than is the gene pool of a larger populat

41、ion6A1pSBg nJrkDSi。C. Because a isolated population can become a new species with substantially lesschange to its gene pool than would be required by a larger population Gz0jNR2 z134foT。D. Because smaller populations are more likely to be made up of stray animals orplants than larger populations are

42、fuK3qPA fm7xy9v。10. The word“ man aged in the passage is closest i n mea ning toLYAcAda jyHJdCF。A.were able B.were forced C.arrived D.expandedparagraph 5When oceanic islands are far enough apart to permit populations to evolve inisolation, but XttIZle dT2nR4dclose enough to allow occasional dispersi

43、ons to occur, 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

44、 other islands and continents. Organisms can also be carried to islandsby other organisms, such as sea birds that travel long distances with seeds clinging to their feathers.gPyx6Ae。 zacEK4a。11. Paragraph 5 supports the idea that the Galapagos island chain was able to become “ one of the world's

45、 greatest showcases of evolution ” primarily because of 6k60qLs。 2zhaDBk。A. the richness of the volcanic soil of each of the islands in the chaingjq2G40。gLLqzTH。B. the distance of the individual islands from each other and from the mainland wfVrYIW。 sVsb1Td。C. the relativity long time it took for th

46、e islands to become covered by organisms f8K1BaW。 airJbdi 。D. the outdoor laboratories that scientists have built on the islands to study evolution qsYO9pS。 PCirU5U。paragraph 6The species on the Galapagos Islands today, most of which occur nowhere else, descended from organisms that floated, flew, o

47、r 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 and their beak type, which is correlated with wh

48、at 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 population may have undergone significant changes i

49、n 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, which could later recolonize the island from which

50、 its founding population emigrated. Today each Galapagos island has multiple species of finches, with as many as ten on some islands. 6Th5SNS。 jqaQSAh。12. According to paragraph 6. what is true about the thirteen species of Galapagosfin Ches? GoJjBkBo 3dWuhHNA. All thirteenspecies are now found on m

51、ost of the Galapagos Islands BrRiRya。X4B4TRpB. All thirteen species are descended from the same population of ancestral birds UmdPm8RCFJRwj乂C. All thirteen species evolved on the island that was originally colonized by finches from the mainland. P5flTxY 。 jz0nPEI 。D. All thirteen species occur only

52、in small, completely isolated populations. gfd78xK。 aNkkqTX。13. Look at the four squares that indicate where the following sentence couldbe added to the passage. INCy25S。 pIq4GaP。This process of speciation and colonization could have been repeated over and over again, gradually involving all the isl

53、ands in the chain.Sc7Xvxy。 icioEaA 。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 close

54、ly 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 ancestral birds that co

55、lonized 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 n ew species. Later, a few individuals of this new species may have been blown by storms to a neighboring island

56、. Isolated onthis secondisland, 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. 54iH62W。

57、 yhEqftK 。14. Directions：An introductory sentence for a brief summary of the passage isprovided below.Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong inthe summary because they express ideas that are not pr

58、esented in the passage or areA0y9FTD。 1St8bP0。minor ideas in the passage.The geographic isolation of a population can result in the rise of a new species. rNuH8Q0。 0tPwOFi。Answer ChoicesA. Isolation can result when a geographic barrier forms and splits a population or when a few organisms somehowget

59、 carried across an existing geographic barrier and form a new populationvxC2w4T。 BGYraJz。B. Speciation is more likely when an isolated population is small because significant genetic changes are more likely to occur in a small population than in a largeoneMjMiguX。TV0hAD9C. Because of the geographic isolation of the Galapagos Island