ps考试题目模拟试题及答案新GRE阅读考试模拟试题及答案.docx

1、ps考试题目模拟试题及答案新GRE阅读考试模拟试题及答案ps考试题目模拟试题及答案【2018年新GRE阅读考试模拟试题及答案】 Many theories have been formulated to explain the role of grazers such as zooplankton in controlling the amount of planktonic algae (phytoplankton)in lakes. The first theories of such grazer control were merely based on observations of

2、negative correlations between algal and zooplankton numbers. A low number of algal cells in the presence of a high number of grazers suggested, but did not prove, that the grazers had removed most of the algae. The converse observation, of the absence of grazers in areas of high phytoplankton concen

3、tration, led Hardy to propose his principle of animal exclusion, which hypothesized that phytoplankton produced a repellent that excluded grazers from regions of high phytoplankton concentration. This was the first suggestion of algal defenses against grazing. Perhaps the fact that many of these fir

4、st studies considered only algae of a size that could be collected in a ( phytoplankton), a practice that overlooked the smaller phytoplankton (nannoplankton)that we now know grazers are most likely to feed on, led to a de-emphasis of the role of grazers in subsequent research. Increasingly, as in t

5、he individual studies of Lund, Round, and Reynolds, researchers began to stress the importance of environmental factors such as temperature, light, and water movements in controlling algal numbers. These environmental factors were amenable to field monitoring and to simulation in the laboratory. Gra

6、zing was believed to have some effect on algal numbers, especially after phytoplankton growth rates declined at the end of bloom periods, but grazing was considered a minor ponent of models that predicted algal population dynamics. The potential magnitude of grazing pressure on freshwater phytoplank

7、ton has only recently been determined empirically. Studies by Hargrave and Geen estimated natural munity grazing rates by measuring feeding rates of individual zooplankton species in the laboratory and then puting munity grazing rates for field conditions using the known population density of grazer

8、s. The high estimates of grazing pressure postulated by these researchers were not fully aepted, however, until the grazing rates of zooplankton were determined directly in the field, by means of new experimental techniques. Using a specially prepared feeding chamber, Haney was able to record zoopla

9、nkton grazing rates in natural field conditions. In the periods of peak zooplankton abundance, that is, in the late spring and in the summer, Haney recorded maximum daily munity grazing rates, for nutrient-poor lakes and bog lakes, respectively, of 6.6 percent and 114 percent of daily phytoplankton

10、production. Cladocerans had higher grazing rates than copepods, usually aounting for 80 percent of the munity grazing rate. These rates varied seasonally, reaching the lowest point in the winter and early spring. Haneys thorough research provides convincing field evidence that grazers can exert sign

11、ificant pressure on phytoplankton population. 20. The author most likely mentions Hardys principle of animal exclusion in order to (A)give an example of one theory about the interaction of grazers and phytoplankton (B)defend the first theory of algal defenses against grazing (C)support the contentio

12、n that phytoplankton numbers are controlled primarily by environmental factors (D)demonstrate the superiority of laboratory studies of zooplankton feeding rates to other kinds of studies of such rates (E)refute researchers who believed that low numbers of phytoplankton indicated the grazing effect o

13、f low numbers of zooplankton 21. It can be inferred from the passage that the “first theories” of grazer control mentioned in line 4 would have been more convincing if researchers had been able to (A)observe high phytoplankton numbers under natural lake conditions (B)discover negative correlations b

14、etween algae and zooplankton numbers from their field research (C)understand the central importance of environmental factors in controlling the growth rates of phytoplankton (D)make verifiable correlations of cause and effect between zooplankton and phytoplankton numbers (E)invent laboratory techniq

15、ues that would have allowed them to bypass their field research concerning grazer control 22. Which of the following, if true, would call into question Hardys principle of animal exclusion? (A)Zooplankton are not the only organisms that are affected by phytoplankton repellents. (B)Zooplankton exclus

16、ion is unrelated to phytoplankton population density. (C)Zooplankton population density is higher during some parts of the year than during others. (D)Net phytoplankton are more likely to exclude zooplankton than are nannoplankton. (E)Phytoplankton numbers can be strongly affected by environmental f

17、actors. 23. The author would be likely to aGREe with which of the following statements regarding the pressure of grazers on phytoplankton numbers? I. Grazing pressure can vary aording to the individual type of zooplankton. II. Grazing pressure can be lower in nutrient-poor lakes than in bog lakes. I

18、II. Grazing tends to exert about the same pressure as does temperature. (A)I only (B)III only (C)I and II only (D)II and III only (E)I, II, and III 24. The passage supplies information to indicate that Hargrave and Geens conclusion regarding the grazing pressure exerted by zooplankton on phytoplankt

19、on numbers was most similar to the conclusion regarding grazing pressure reached by which of the following researchers? (A)Hardy (B)Lund (C)Round (D)Reynolds (E)Haney 25. It can be inferred from the passage that one way in which many of the early researchers on grazer control could have improved the

20、ir data would have been to (A)emphasize the effects of temperature, rather than of light, on phytoplankton (B)disregard nannoplankton in their analysis of phytoplankton numbers (C)collect phytoplankton of all sizes before analyzing the extent of phytoplankton concentration (D)recognize that phytopla

21、nkton other than phytoplankton could be collected in a (E)understand the crucial significance of phytoplankton in the diet of zooplankton 26. Aording to the passage, Hargrave and Geen did which of the following in their experiments? (A)They pared the grazing rates of individual zooplankton species i

22、n the laboratory with the natural grazing rates of these species. (B)The hypothesized about the population density of grazers in natural habitats by using data concerning the population density of grazers in the laboratory. (C)They estimated the munity grazing rates of zooplankton in the laboratory

23、by using data concerning the natural munity grazing rates of zooplankton. (D)They estimated the natural munity grazing rates of zooplankton by using data concerning the known population density of phytoplankton. (E)They estimated the natural munity grazing rates of zooplankton by using laboratory da

24、ta concerning the grazing rates of individual zooplankton species. 27. Which of the following is a true statement about the zooplankton numbers and zooplankton grazing rates observed in Haneys experiments? (A)While zooplankton numbers began to decline in August, zooplankton grazing rates began to in

25、crease. (B)Although zooplankton numbers were high in May, grazing rates did not bee high until January. (C)Both zooplankton numbers and grazing rates were higher in December than in November. (D)Both zooplankton numbers and grazing rates were lower in March than in June. (E)Both zooplankton numbers and grazing rates were highest in February. 答案 A D B C E C E D 内容仅供参考