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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
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
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?
□ 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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- Fall '13