Now, let's dive into two difficult passage, explaining the inference questions. Our goal is always the same: read the entire passage FIRST, making the main idea of the passage in our mind or notepad, constructing a MOC (map of contents) so we shall be able to pinpoint where the details are located to reply to the inference question, going back and forth between the passage and the questions, without delve too much into the details themselves.



Result: it should be to reply the questions right away once we approach them after reading the passage. It is possible. And it is also possible to apply this strategy, saving time, and nailing all the questions correctly.

There is a caveat though: not all the time we shall be able to reply to a question following the exact order from top down. I.E From A to E. Instead, you should work outside in: eliminating those answer choices that are wrong. ALWAYS at least two out of five are obviously incorrect. Work from there to reach the correct one, it is much easier to pick the correct one among three, for example, that among five!


In the shorter version of the GRE, we have inference questions. However, we might say that we do have the following:

• Basic inference
  
  - according to the passage
  - word in the context of the passage , what the word means
  - et similiar
• Pure inference
  
  - the passage implies
  - the author of the passage would be most likely to agree
  - the passage implies
  - except
• Portion role
  
  - what is the function of the highlighted sentence
  - the author mentions that specific portion for what reason
  - select in the passage the sentence
• Organization as a whole or role of the paragraph in the economy of the passage

In the following passages, we explain all these different kinds of inference questions in detail.


EXPLANATION of the PASSAGE






#1 paragraph

The deep sea typically has a sparse fauna dominated by tiny worms and crustaceans, with an even sparser distribution of larger animals.

The fauna = animals that are located in the deep of the oceans, or seas are sparse. That means we do not have a high concentration of animals per square inch or miles. Large animals are even more sparse or rare, which means that the attention is even lower.

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.

However= but= here we do have a shift. Near certain specific zone such as the vents where the water is warmer than other places, we do NOT have a sparse fauna. Instead, we do have a high concentration of animals: fish, clams, and so on. whatever, just details. But the key concept is the following. we DO NOT have sparse fauna, as in general, we do have in the deep sea.


#2 paragraph


Most deep-sea faunas rely for food on particulate matter ultimately derived from photosynthesis, falling from above.

This fauna in the deep sea takes the food from microscope elements falling from above. From above means from the ocean's surface, these elements fell to the deep sea. From up to down. This is the only thing you should keep in mind and this is also important.

The food supplies necessary to sustain the large vent communities, however, must be many times the ordinary fallout.

Here we do have a pivotal concept: because the community in the vents area is huge, then the elements that come from above are not sufficient. Therefore, these animals must have another source for their food

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.

We do have two main reasons that could explain how the fauna in the vents area take the food
1) production of food by bacteria using energy
2) advection, the drifting of food materials from surrounding regions. The food comes from the surrounding areas the vents

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.

Just keep in mind that here we do have an explanation of the reason 1) above. Just keep in mind this. No need to delve into the details. If you will need of it , you will know where the chemosynthesis process is located

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.

this sentence tells us essentially one thing: if the hypothesis is true, then chemosynthesis is the main reason how the fauna take food. chemosynthesis > 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.

Hyphotesis 1) seems the most reasonable


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.

Here, we do have a significant shift: because large animals are also found in other locations suggests that the phenomenon described at point 1) is NOT the only possible source of food.


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.

Here we do have an important fact: large animals that should rely on for food in chemosynthesis, which in turn out uses bacteria, are located in the proximity of areas where the temperature is too high and the bacteria cannot survive. Therefore, these same bacteria cannot produce the food. UNLESS the same vants are located in more mild waters.

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.

A possible solution to this paradox is that these large animals feed on bacteria that reproduce in mild vents and then these bacteria reach those areas to feed the animal a bit far aways those vents areas where the bacteria create the food. Mhhhh a complicated story, though.


#3 paragraph

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.

Notice the word nonetheless in the explanation for the fact # 1). That means we do not have a definitive conclusion or understanding of this phenomenon.
Advection is a possible alternative to food production

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.

Here is just how advection works. Just an explanation of the possible process.



EXPLANATION of the QUESTIONS

Now we should be able to reply to the questions in one breath, right away thanks to our understanding of the passage.


#1 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.

In many part of the passage we do have the following

• large sedentary organisms associated with vents
• large, sedentary organisms do in fact feed on bacteria that grow in warm-water vents,

This means that the animals in the NONvent areas are smaller than those

We can also reach this question by POE

(A) They do not normally feed on particles of food in the water. Maybe the answer is YES to this but the reality is that we do not know. For the entire passage we care about those animals that feed inside the vents
(B) They are smaller than many vent faunas.
(C) They are predators. OFF. Never see this word in the entire passage
(D) They derive nutrition from a chemosynthetic food source.We do not know. We do know that the animals inside the vents have food from bacteria. Those outside we do not know
(E) They congregate around a single main food source. If they gather or not we do not know for sure. Maybe


#2 Which of the following does the author cite as a weakness in the argument that bacterial chemosynthesis provides the foundation for the food chains at deep-sea vents?

(A) Vents are colonized by some of the same animals found in other areas of the ocean floor. CORRECT
(B) Vent water does not contain sufficient quantities of hydrogen sulfide. Easy. If you take a look to your MOC you should be able to pinpoint the exactly portion in which "hydrogen sulfide was found in vent water". It mentions nothing about sufficiency. Wrong
(C) Bacteria cannot produce large quantities of food quickly enough. In the passage is mentioned that the bacteria produce food and that probably is NOT enough. Nothing is mentioned about "quickly". Wrong
(D) Large concentrations of minerals are found in vent water. No minerals were ever mentioned in the passage. Wrong
(E) Some bacteria found in the vents are incapable of chemosynthesis. Nothing is mentioned about what the bacteria are able to do or not to some extent. Wrong



#3 Which of the following is information supplied in the passage that would support the statement that the food supplies necessary to sustain vent communities must be many times that of ordinary fallout?

I. Large vent faunas move from vent to vent in search of food.
II. Vent faunas are not able to consume food produced by photosynthesis.
III. Vents are more densely populated than are other deep-sea areas.

(A) I only
(B) III only
(C) I and II only
(D) II and III only
(E) I, II, and III

Always start where one of the answers I,II, and III is more common. In this case the II: faunas in the vent is NOT able to consume the food. This is not true. We said that is not enough food and we do have TWO possible ways they can feed. NOT that the faunas is not able to eat all the food. Wrong. Therefore, C,D, and E are wrong. We left with A and B.

A says that the animals jump from one spot to another. False. At the very most we do know that animals are also present in the nearby of the vents. NOT that they migrate from one place to another. II is wrong

B must be the answer.


#4 The author refers to "smokers" 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

This is tricky. ALWAYS see some sentence before AND after where the words is located, to see if we are able to carve some useful information.

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.

Notice the last portion highlighted above. This is a clue to say that E is the answer.


#5 Which of the following can be inferred from the passage about the particulate matter that is carried down from the surface of the ocean?

(A) It is the basis of bacterial chemosynthesis in the vents.This is false because is the energy these source of bacteria NOT the particulate. Wrong
(B) It may provide an important source of nutrition for vent faunas. Thsi is true and we do know from our MOC that this source of food is NOT enough. However, it is an important source and maybe the first one to rely on. CORRECT
(C) It may cause the internal temperature of the vents to change significantly. No totally false. Wrong
(D) It is transported as large aggregates of particles. No mention how the pariculate falls from above the surface. Wrong
(E) It contains hydrogen sulfide. From the passage: hydrogen sulfide was found in vent water. Clearly E is wrong