托福-5 (1)及答案解析.doc
《托福-5 (1)及答案解析.doc》由会员分享,可在线阅读,更多相关《托福-5 (1)及答案解析.doc(98页珍藏版)》请在麦多课文档分享上搜索。
1、托福-5 (1)及答案解析(总分:148.50,做题时间:90 分钟)一、READING(总题数:0,分数:0.00)二、Part 1(总题数:1,分数:6.50)Natural SelectionFirst coined by Darwin, the term natural selection refers to the process at the core of evolutionary theory. Simply put, Darwin believed that every living organism had to struggle to survive and reprod
2、uce. By random chance, some individuals in a species would have characteristics that made them better adapted to this struggle than their contemporaries. Such individuals would be more likely to reproduce and pass their characteristics on to their offspring. Over many generations, a series of small
3、differences in characteristics would accumulate, until eventually the creatures that were produced would be so different from their original ancestors that they would constitute a new species. (A) Although Darwin did not know how variations between individual members of the same species were able to
4、 arise in the first place or how such traits could then be passed on from species to species, we now know that this process occurs through genes. (B) Genes determine what characteristics an organism will possess, from its size to its skin color to its gender. (C) Sometimes these genes become damaged
5、 or altered-a process known as mutation. (D) Most mutations are either too small to have any effect, or have detrimental effects on the organism. A few, however, can be beneficial to helping an organism survive. The organisms with these beneficial mutations are the ones that .survive and reproduce,
6、passing their particular genetic mutation on to future generations.Originally, Darwin thought that two particular types of traits were naturally selected for evolution. The first type included any and all traits that helped an organism survive, either by giving it easier access to food, better prote
7、ction from predators, or superior adaptability to shifting environmental conditions. Several examples of the natural selection of such traits have been observed since Darwin first proposed his theory. The most often cited example is the coloration of moths near industrial centers. Some of them have
8、white wings and the others have black wings. Under normal conditions, the lighter-colored moths predominate since white moths are less visible against the light-colored bark of the trees in the forests where they live, which means they can more easily avoid predators. Near industrial centers, howeve
9、r, darker-colored moths predominate, as the pollution from the factory has darkened the bark of the nearby trees. Moths landing on these trees are much more difficult to see if they have black wings. This trait has now become most common in moth populations living in areas where pollutants have chan
10、ged the color of the tree bark.The second type of naturally selected traits envisioned by Darwin involved those characteristics of an organism that made it easier for that organism to find a mate. This form of natural selection, often called sexual selection, was thought to explain the existence of
11、highly developed traits in certain animals that seemed to play no particular role in their survival, and that in some cases seemed to make it even harder for them to survive. A prime example of such a trait is the peacocks elaborate, colorful tail feathers. A long, unwieldy tail that can expand into
12、 a display of bright colors that draws the attention of any predator in the vicinity seems less likely than that of other kinds of birds to help the bird survive. However, researchers discovered that peahens invariably chose to mate with those peacocks whose tail feathers produced the most artistic
13、displays. Thus, although the peacocks tail feathers have no adaptive function in terms of coping with survival pressure, the gene that controls feather color is the one that is most likely to be passed on because of its role in the mating process.Many scientists now believe that a third type of natu
14、rally selected characteristics exists, namely those that may be harmful to an individual organism but beneficial to that organisms species. This helps to explain the persistence of certain traits that were viewed under traditional evolutionary theory as not assisting in adaptation. For instance, in
15、many animal species, including humans, a small subset of the population is homosexual. Under the old view of evolution, this could not be accounted for since homosexual individuals do not normally reproduce, meaning the gene that codes for it should have long been phased out of the gene pool. Howeve
16、r, recent studies among wild sheep populations have found that the prevalence of homosexuality in the sheep population increases in times of severe food shortages, causing the sheep to form stronger bonds with sheep of the same sex than they otherwise would. As a result, instead of fighting over a p
17、articular food source, these sheep share the food they find with each other, increasing the species chance of surviving hard times. Though still controversial, the idea that traits may be naturally selected because of their benefits to the species instead of their benefits to the individual is rapid
18、ly gaining acceptance in the scientific community because of the wide array of characteristics that it can explain, including the human tendency towards altruism,(分数:6.50)(1).The word “them“ in the passage refers to(分数:0.50)A.characteristics.B.individuals.C.species.D.contemporaries.(2).According to
19、paragraph 1, what is the end result of natural selection?(分数:0.50)A.Special individuals.B.New species.C.Random traits.D.Adapted characteristics.(3).Look at the four squares in the passage that indicate where the following sentence can be added to the passage.All of the information about an organisms
20、 physiology is contained in its DNA, which is a strand of organic chemicals composed of sequences of nucleotides called genes.Where would this sentence best fit?(分数:0.50)A.()B.()C.()D.()(4).All of the following are listed as factors that might make a trait beneficial to an organism EXCEPT its abilit
21、y to help the organism(分数:0.50)A.resemble other individuals.B.avoid predators.C.find nourishment.D.survive chang(5).The word “particular“ in the passage is closest in meaning to(分数:0.50)A.exacting.B.noteworthy.C.precise.D.specifi(6).According to paragraph 2, why was dark coloration selected for moth
22、s living near industrial areas?(分数:0.50)A.It camouflaged them from enemies.B.It made them easier to see than lighter-colored moths.C.It helped male moths attract mates.B. It allowed them to find food more rapidly.(7).The word “involved“ in the passage is closest in meaning to(分数:0.50)A.engaged.B.req
23、uired.C.included.D.implie(8).Why does the author mention the peacocks tail feathers?(分数:0.50)A.To contrast the peacocks appearance with that of moths.B.To show that not all traits are naturally selected.C.To provide an example of a sexually selected trait.D.To demonstrate the power of environmental
24、pressures.(9).What do peahens look for in peacocks?(分数:0.50)A.Large wing feathers.B.Loud mating calls.C.Artistic tail displays.D.Colorful breast plumag(10).The word “prevalence“ in the passage is closest in meaning to(分数:0.50)A.dominance.B.occurrence.C.primacy.D.increas(11).Which of the following se
- 1.请仔细阅读文档,确保文档完整性,对于不预览、不比对内容而直接下载带来的问题本站不予受理。
- 2.下载的文档,不会出现我们的网址水印。
- 3、该文档所得收入(下载+内容+预览)归上传者、原创作者;如果您是本文档原作者,请点此认领!既往收益都归您。
下载文档到电脑,查找使用更方便
2000 积分 0人已下载
下载 | 加入VIP,交流精品资源 |
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 托福 51 答案 解析 DOC