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发表于 2011-9-15 11:05:11
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追加几个,同样是Ex11的文章:
The deep sea typically has a sparse fauna dominated by tiny worms and crustaceans, with an even sparser distribution of larger animals. However, near
Line 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.
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.
答案B,我选了C,that these large, sedentary organisms do in fact feed on bacteria
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
答案E。虽然定位很容易,可是我怎么也没看出来引出“smokers”的作用啊!这类题怎么做? |
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