新GRE阅读理解36套每日讨论--19（群14106147）

普渡哥

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.

flyerwolf

d/b/ab/c/b? 做了我10多分钟。。不行啊。

普渡哥

错了一个。好猛。

josie0710

D/B/AB/C/E 用了近20分钟

zjusolo1985

第三题怎么解丫 AB的B选项

普渡哥

ｊｏｓｉｅ全对了！恭喜啊：）
天天阅读明天见！
大家加油！