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Unformatted text preview: 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° No bacteria can survive such C. 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) 60 F or the following question, consider each of the 7. Select the sentence in the passage in which the author choices separately and select all that apply implies that vents are colonized by some of the same ani mal found in other areas of the ocean floor, which 5. The passage provides information for answering might be a weakness for the bacterial chemosynthesis which of the following questions EXCEPT? model. A □ What causes warm-water vents to form? B □ What role does hydrogen sulfide play in 8. The author refers to ―smokers‖ in the third paragraph chemosynthesis? most probably in order to C □ Do bacteria live in the vent water of smokers? (A) show how thermal shock can provide food for some vent faunas by stunning sma...
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