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2012新gre逻辑阅读练习题2

2011-11-25 13:40| 投稿者: bjangel| 评论: 0

摘要: 2012新gre逻辑阅读练习题2  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 f ...
2012新gre逻辑阅读练习题2

  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
  5 based on observations of 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 obser-
  10 vation, of the absence of grazers in areas of high
  phytoplankton concentration, led Hardy to propose
  his principle of animal exclusion, which hypothe-
  sized that phytoplankton produced a repellent that
  excluded grazers from regions of high phytoplankton
  15 concentration. This was the first suggestion of algal
  defenses against grazing.
  Perhaps the fact that many of these first studies
  considered only algae of a size that could be collected
  in a net (net phytoplankton), a practice that over-
  20 looked 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 subse-
  quent research. Increasingly, as in the individual
  studies of Lund, Round, and Reynolds, researchers
  25 began to stress the importance of environmental
  factors such as temperature, light, and water move-
  ments in controlling algal numbers. These environ-
  mental factors were amenable to field monitoring and
  to simulation in the laboratory. Grazing was believed
  30 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
  component of models that predicted algal population
  dynamics.
  35 The potential magnitude of grazing pressure on
  freshwater phytoplankton has only recently been
  determined empirically. Studies by Hargrave and
  Geen estimated natural community grazing rates by
  measuring feeding rates of individual zooplankton
  40 species in the laboratory and then computing com-
  munity grazing rates for field conditions using the
  known population density of grazers. The high esti-
  mates of grazing pressure postulated by these
  researchers were not fully accepted, however, until the
  45 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 zooplankton grazing rates in natural
  field conditions. In the periods of peak zooplankton
  50 abundance, that is, in the late spring and in the summer,
  Haney recorded maximum daily community grazing rates,
  for nutrient-poor lakes and bog lakes, respectively, of 6.6
  percent and 114 percent of daily phytoplankton production.
  Cladocerans had higher grazing rates than
  55 copepods, usually accounting for 80 percent of the
  community grazing rate. These rates varied seasonally,
  reaching the lowest point in the winter and early spring.
  Haney‘s thorough research provides convincing field
  evidence that grazers can exert significant pressure on
  60 phytoplankton population.
  (461 words)
  1. It can be inferred from the passage that the “first theories” of
  grazer control mentioned in the first paragraph would have been
  more convincing if researchers had been able to
  (A) observe high phytoplankton numbers under
  natural lake conditions
  (B) discover negative correlations between
  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 techniques that would
  have allowed them to bypass their field
  research concerning grazer control
  2. Which of the following, if true, would call into
  question Hardy‘s principle of animal exclusion?
  (A) Zooplankton are not the only organisms
  that are affected by phytoplankton
  repellents.
  (B) Zooplankton exclusion 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 factors.
  For the following question, consider each of the choices separately and select all that apply
  3. The author would be likely to agree with
  which of the following statements regarding
  the pressure of grazers on phytoplankton
  numbers?
  □A Grazing pressure can vary according to the
  individual type of zooplankton.
  □B Grazing pressure can be lower in nutrient-poor lakes
  than in bog lakes.
  □C Grazing tends to exert about the same
  pressure as does temperature.
  4. It can be inferred from the passage that one way
  in which many of the early researchers on grazer
  control could have improved their 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 phytoplankton other than net
  phytoplankton could be collected in a net
  (E) understand the crucial significance of net
  phytoplankton in the diet of zooplankton
  5. According to the passage, Hargrave and Geen
  did which of the following in their experiments?
  (A) They compared the grazing rates of
  individual zooplankton species in 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 community grazing rates
  of zooplankton in the laboratory by using
  data concerning the natural community
  grazing rates of zooplankton.
  (D) They estimated the natural community
  grazing rates of zooplankton by using
  data concerning the known population
  density of phytoplankton.
  (E) They estimated the natural community
  grazing rates of zooplankton by using
  laboratory data concerning the grazing
  rates of individual zooplankton species.
  答案: D/B/AB/C/E
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