Hi
question 16 has to deal with the main idea of the passage. Now, I strongly suggest you read my two examples of what I call "Black-Hole Strategy" or dealing with a question, tough, WITHOUT reading the passage. you can find here to examples
https://gre.myprepclub.com/forum/is-the-li ... tml#p45986https://gre.myprepclub.com/forum/some-rece ... tml#p58341Back to your question.
When you need to find the overall idea that the passage conveys you must read in brief the key elements of the passage itself. Actually, there is not a bullet-proof strategy because the answer arose from the sense and feeling you do have from it. Of course, there is a logic in answering it. However, these kinds of questions are NOT based on pure logic but rather common sense
Answer this question in 30 seconds is possible
Look at these key parts
Quote:
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 emerges from subterranean sources, live remarkable densities of huge clams, blind crabs, and fish.
two crucial elements here: however which is a shift in the argument and put you in the path that the passage talks about something else of that which is apparent and areas, which implies locations
Quote:
Most deep-sea faunas rely for food on particulate matter ultimately derived from photosynthesis, falling from above. The food supplies necessary to sustain the 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 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 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. 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.
Quote:
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 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 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 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.
Quote:
Nonetheless, advection is a more likely alternative food source. Research has demonstrated that advective 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 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 shock thereby contributing to the food supply of vents.
16. The passage provides information for answering which of the following questions?
(A) What causes warm-water vents to form?
In the above quotation NO sign of warm water is the key element but rather the vent
(B) Do vent faunas consume more than do deep-sea faunas of similar size?
the consumption is NOT the key element
(C) Do bacteria live in the vent water of smokers?
The key element is the vent which is basically a location, an area for food and blah blah blah.....
CORRECT(D) What role does hydrogen sulfide play in chemosynthesis?
Hydrogen is NOT a key element of what we are talking about. Notice how this is tricky because the passage talks about hydrothermal vents NOT hydrogen
(E) What accounts for the locations of deep-sea smokers?
The passage talks about the proximity of deep-sea animals to smokers areas which are still VENT areas.
From all above as you can see if you are able to use this strategy even the most complex passages can be addressed in 30 seconds. However, this implies that your level of standard English is pretty decent
regards
24 Feb 2019, 03:23
74% (02:38) correct
