新GRE阅读理解36套每日讨论--49（群178674184）

普渡哥

       The deep sea typically has a sparse fauna dominated
       by tiny worms and crustaceans, with an even sparser
       distribution of larger animals. However, near
       hydrothermal vents, areas of the ocean where warm water
5     emerges from subterranean sources, live remarkable
       densities of huge clams, blind crabs, and fish.
       Most deep-sea faunas rely for food on particulate matter,
       ultimately derived from photosynthesis, falling from
       above. The food supplies necessary to sustain the
10   large vent communities, however, must be many
       times the ordinary fallout. The first reports describing
       vent faunas proposed two possible sources of nutrition:
       bacterial chemosynthesis, production of food by bacteria
       using energy derived from chemical changes, and
15   advection, the drifting of food materials from
       surrounding regions. Later, evidence in support of the
       idea of intense local chemosynthesis was accumulated:
       hydrogen sulfide was found in vent water; many vent-site
       bacteria were found to be capable of chemosynthesis; and extremely
20   large concentrations of bacteria were found in samples
       of vent water thought to be pure. This final observation
       seemed decisive. If such astonishing concentrations of
       bacteria were typical of vent outflow, then food within
       the vent would dwarf any contribution from advection.
25   Hence, the widely quoted conclusion was reached
       that bacterial chemosynthesis provides the foundation
       for hydrothermal-vent food chains—an exciting prospect
       because no other communities on Earth are independent
       of photosynthesis.
30   There are, however, certain difficulties with this
       interpretation. For example, some of the large sedentary
       organisms associated with vents are also found at ordinary
       deep-sea temperatures many meters from the nearest
       hydrothermal sources. This suggests that bacterial
35   chemosynthesis is not a sufficient source of nutrition
       for these creatures. Another difficulty is that similarly
       dense populations of large deep-sea animals have been
       found in the proximity of “smokers” –vents where water emerges
       at temperatures up to 350°C. No bacteria can survive such
40   heat, and no bacteria were found there. Unless smokers
       are consistently located near more hospitable warm-water
       vents, chemosynthesis can account for only a fraction of the
       vent faunas. It is conceivable, however, that these large,
       sedentary organisms do in fact feed on bacteria that
45   grow in warm-water vents, rise in the vent water, and
       then rain in peripheral areas to nourish animals living
       some distance from the warm-water vents.
       Nonetheless, advection is a more likely alternative food
       source. Research has demonstrated that advective
50   flow, which originates near the surface of the ocean
       where suspended particulate matter accumulates,
       transports some of that matter and water to the vents.
       Estimates suggest that for every cubic meter of vent
       discharge, 350 milligrams of particulate organic
55   material would be advected into the vent area.
       Thus, for an average-sized vent, advection could
       provide more than 30 kilograms of potential food
       per day. In addition, it is likely that small live animals in
       the advected water might be killed or stunned by thermal and/or chemical
60   shock, thereby contributing to the food supply of vents.


(479 words)


For the following question, consider each of the choices separately and select all that apply
5. The passage provides information for answering
which of the following questions EXCEPT?
□A What causes warm-water vents to form?
□B What role does hydrogen sulfide play in
chemosynthesis?
□C Do bacteria live in the vent water of smokers?




6. The information in the passage suggests that the
majority of deep-sea faunas that live in nonvent
habitats have which of the following characteristics?
(A) They do not normally feed on particles of food
in the water.
(B) They are smaller than many vent faunas.
(C) They are predators.
(D) They derive nutrition from a chemosynthetic
food source.
(E) They congregate around a single main food
source.




7. Select the sentence in the passage in which the author
implies that vents are colonized by some of the same animal found in other areas of the ocean floor, which might be a weakness for the bacterial chemosynthesis model.




8. The author refers to ―smokers‖ in the third paragraph
most probably in order to
(A) show how thermal shock can provide food for
some vent faunas by stunning small animals
(B) prove that the habitat of most deep-sea animals is
limited to warm-water vents
(C) explain how bacteria carry out chemosynthesis
(D) demonstrate how advection compensates for the
lack of food sources on the seafloor
(E) present evidence that bacterial chemosynthesis
may be an inadequate source of food for
some vent faunas

vanessali123

5A
6ABE
7For example, some of the large sedentary
      organisms associated with vents are also found at ordinary
      deep-sea temperatures many meters from the nearest
      hydrothermal sources.
8E

普渡哥

正确答案：
5. AB 6. B 7."For example, some of the large sedentary" 8. E

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