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 thatdoes not interbreed with other such populations when there is opportunity to do so.”A keythe origin of many species is the separation of a population w

2、ith its gene pool (all of the genes in apopulation at any one time) from other populations of the same species, thereby preventingpopulation interbreeding With its gene pool isolated, a separate population can follow its ownevolutionary course. In the formation of many species, the initial isolation

3、 of a population seemsto have been a geographic barrier This mode of evolving new species is called allopatricspeciation.Many factors can isolate a population geographically.A mountain range may emerge andgradually split a population of organisms that can inhabit only lowland lakes, certain fishpopu

4、lations 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 marinelife in the ocean waters on either side.How formidable must a geographic barrier be to keep populations apart? It

5、 depends on the abilityof 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 ofmany plants may be earned back and forth on animals In contrast, small rodents may find

6、 a deepcanyon or a wide river an effective barrier. For example, the Grand Canyon, in the southwesternUnited Slates, separate the range of the while-tailed antelope squirrel from that of the closelyrelated Harris antelope squirrel. Smaller, with a shorterthattailis white underneath, thewhite-tailed

7、antelope squirrel inhabits deserts north of the canyon and west of the Colorado Riverin southern California Hams' antelope squirrel has a more limited range in deserts south of theGrand Canyon.Geographic isolation creates opportunities for new species to develop, but it does not necessarilylead

8、to new species because speciation occurs only when the gene pool undergoes enough changesto establish reproductive barriers between the isolated population and its parent population.Thelikelihood of allopatric speciation increases when a population is small as well as isolated, makingit more likely

9、than a large population to have its gene pool changed substantially. For example,inless than two million years, small populations of stray animals and plants from the SouthAmerican mainland that managed to colonize the Galapagos Islands gave rise to all thespecies that now inhabit the islands.When o

10、ceanic islands are far enough apart to permit populations to evolve in isolation, but closeenough to allow occasional dispersions to occur, they are effectively outdoor laboratories ofevolution.The Galapagos island chain is one of the world s greatest showcases of evolution Eachisland was born from

11、underwater volcanoes and was gradually covered by organisms derived fromstrays that rode the ocean currents and winds from other islands and continents. Organisms canalso be carried to islands by other organisms, such as sea birds that travel long distances withseeds clinging to their feathers.The s

12、pecies on the Galapagos Islands today, most of which occur nowhere else, descendedfrom organisms that floated, flew, or were blown over the sea from the South American mainlandFor instance, the Galapagos island chain has a total of thirteen species of closely related birdscalled Galapagos finches Th

13、ese birds have many similarities but differ in their feeding habits andtheir beak type, which is correlated with what they eat Accumulated evidence indicates that allthirteen finch species evolved from a single small population of ancestral birds that colonized oneof the islands.Completely isolated

14、on the island after migrating from the mainland, the founderpopulation 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 neighboringisland. Isolated on this second island, the second founde

15、r population could have evolved into asecond new species, which could later recolonize the island from which its founding populationemigrated.Today each Galapagos island has multiple species of finches, with as many as ten onsome islands.paragraph 1Biologist Ernst Mayr defined a species as“an actual

16、ly or potentially interbreedingthatpopulationdoes not interbreed with other such populations when there is opportunity to do so.” A keyin the origin of many species is the separation of a population with its gene pool (all of the genesin a population at any one time) from other populations of the sa

17、me species, thereby preventingpopulation interbreeding With its gene pool isolated, a separate population can follow its ownevolutionary course. In the formation of many species, the initial isolation of a population seemsto have been a geographic barrier This mode of evolving new species is called

18、allopatricspeciation.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 paragraph 1. allopatric speciation is possible whenA. a population contains all

19、 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 species is successful in crossing a geographic barrierparagraph 1&2Biolo

20、gist Ernst Mayr defined a species as“an actually or potentially interbreeding population thatdoes not interbreed with other such populations when there is opportunity to do so.the origin of many species is the separation of a population with its gene pool (all of the genes ina population at any one

21、time) from other populations of the same species, thereby preventing”A keypopulation interbreeding With its gene pool isolated, a separate population can follow its ownevolutionary course. In the formation of many species, the initial isolation of a population seems tohave been a geographic barrier

22、This mode of evolving new species is called allopatric speciation.Many factors can isolate a population geographically. A mountain range may emerge andgradually split a population of organisms that can inhabit only lowland lakes, certain fishpopulations might become isolated in this way. Similarity,

23、 a creeping glacier may gradually dividea population, or a land bridge such as the Isthmus of Panama may form and separate themarine life in the ocean waters on either side.4.How is paragraph 2 related to paragraph 1?A. Paragraph 2 points out a number of ways in which the phenomenon of geographiciso

24、lation mentioned in paragraph 1 can occurB. Paragraph 2 identifies discoveries that led to the conclusion presented in paragraph 1that geographic isolation has played a rote in the origin of many speciesC. Paragraph 2 provides evidence supporting the statement in paragraph 1 that a populationcan fol

25、low its own evolutionary course once its gene pool becomes isolatedD. Paragraph 2 explains why the term“allopatric” was adopted to describe the method ofspeciation described in paragraph 1paragraph 3How formidable must a geographic barrier be to keep populations apart? It depends on the abilityof th

26、e 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 ofmany plants may be earned back and forth on animals In contrast, small rodents may find a deepcanyon or a wide riv

27、er an effective barrier. For example, the Grand Canyon, in the southwesternUnited Slates, separate the range of the while-tailed antelope squirrel from that of the closelyrelated Harrisantelope squirrel. Smaller, with a shorter tail that is white underneath, the white-tailed antelope squirrel inhabi

28、ts deserts north of the canyon and west of the Colorado River insouthern California Hams' antelope squirrel has a more limited range in deserts south of theGrand Canyon.5.In paragraph 3, the author contrasts a variety of organisms to illustrate which of thefollowing points?A. Geographic barriers

29、 are less likely to keep apart populations of plants than populationsof animals.B. Geographic barriers are more likely to keep apart populations of large organismsthan populations of small organismsC. Some members of a species are able to cross geographic barriers, while other members of thesame spe

30、cies are not.D. The effectiveness of geographic barriers in keeping organisms apart depends on anorganism ability to move across barriers.6.Paragraph 3 supports the idea that white-tailed antelope squirrels and Hams' antelopesquirrels have which of the following in common?A. They are the two sma

31、llest 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 conditionsparagraph 4Geographic isolation creates opportunities for new species to develop, but it does not necessarilylea

32、d to new species because speciation occurs only when the gene pool undergoes enough changesto establish reproductive barriers between the isolated population and its parent population. Thelikelihood of allopatric speciation increases when a population is small as well as isolated, makingit more like

33、ly than a large population to have its gene pool changed substantially. For example, inless than two million years, small populations of stray animals and plants from the SouthAmerican mainland that managed to colonize the Galapagos Islands gave rise to all the speciesthat now inhabit the islands.7.

34、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 the highlightedsentence in the passage? Incorrect choices change the meaning in important ways or leaveout essential informat

35、ionA. Geographic isolation is sometimes but not always the reason for the creation ofreproductive barriers between a parent population and the populations descended from itB. Genetic changes in a geographical isolated population do not necessarily make the populationlook different enough from its pa

36、rent population to be considered a new speciesC. Geographical isolation allows the separated populations to evolve independently of each otherand so can lead to the formation of new speciesD. Geographic isolation can lead to new species only if the gene pool of the isolated populationchanges enough

37、to prevent it from reproducing with the parent population9.According to paragraph 4, why does the size of a population affect the likelihood of allopatricspeciation?A. Because smaller populations are more likely than larger ones to becomegeographically isolatedB. Because the gene pool of a small iso

38、lated population is more likely to undergosubstantial change than is the gene pool of a larger populationC. Because a isolated population can become a new species with substantially less change toits gene pool than would be required by a larger populationD. Because smaller populations are more likel

39、y to be made up of stray animals or plants thanlarger populations are10.The word“managed ”in the passage is closest in meaning toA.were able B.were forced C.arrived D.expandedparagraph 5When oceanic islands are far enough apart to permit populations to evolve in isolation, butclose enough to allow o

40、ccasional dispersions to occur, they are effectively outdoor laboratories ofevolution. The Galapagos island chain is one of the world s greatest showcases of evolution Eachisland was born from underwater volcanoes and was gradually covered by organisms derived fromstrays that rode the ocean currents

41、 and winds from other islands and continents. Organisms canalso be carried to islands by other organisms, such as sea birds that travel long distances withseeds clinging to their feathers.11.Paragraph 5 supports the idea that the Galapagos island chain was able to become“oneworld's greatest show

42、cases of evolution”primarily because ofA. the richness of the volcanic soil of each of the islands in the chainB. the distance of the individual islands from each other and from the mainlandC. the relativity long time it took for the islands to become covered by organismsD. the outdoor laboratories

43、that scientists have built on the islands to study evolutionparagraph 6The species on the Galapagos Islands today, most of which occur nowhere else, descendedfrom organisms that floated, flew, or were blown over the sea from the South American mainlandFor instance, the Galapagos island chain has a t

44、otal of thirteen species of closely related birdscalled 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 allthirteen finch species evolved from a single small populat

45、ion of ancestral birds that colonized oneof the islands. Completely isolated on the island after migrating from the mainland, the founderpopulation 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 sto

46、rms to a neighboringisland. Isolated on this second island, the second founder population could have evolved into asecond new species, which could later recolonize the island from which its founding populationemigrated. Today each Galapagos island has multiple species of finches, with as many as ten

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

48、nd that was originally colonized by finches from themainland.D. All thirteen species occur only in small, completely isolated populations.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 r

49、epeated over and over again,gradually involving all the islands in the chain.The species on the Galapagos Islands today, most of which occur nowhere else, descendedfrom organisms that floated, flew, or were blown over the sea from the South American mainlandFor instance, the Galapagos island chain h

50、as a total of thirteen species of closely related birdscalled 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 allthirteen finch species evolved from a single small p

51、opulation of ancestral birds that colonized oneof the islands.Completely isolated on the island after migrating from the mainland, the founderpopulation 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

52、by storms to a neighboringisland. 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 man

53、y as ten onsome islands. 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.The geographic isolatio