Some one and a half or two billion years ago, when the earth was still

Question

Some one and a half or two billion years ago, when the earth was still poor in oxygen, a primitive bacterium that made a precarious living from the anaerobic fermentation of organic molecules engulfed a smaller cell that had somehow evolved the ability to respire. Respiration liberates far more energy than fermentation, and the growing abundance of oxygen in the atmosphere must have been the driving force behind a symbiotic relation that developed between the two cells, with the aerobic cell generating energy in return for shelter and nutrients from its larger host.

In time the engulfed cell and others like it were to become subcellular organelles, passed on by host cells to their progeny. Eventually the host cells themselves changed, developing other subcellular structures and internal membranes and segregating their genetic material in chromosomes within a nucleus. These cells were the ancestors of all modern eukaryotic (nucleated) cells. The present-day descendants of those ancient symbiotic respiring bacteria are the mitochondria, the power plants of the eukaryotic cell.

Mitochondria are oval organelles, about half a micrometer in diameter and from two to five micrometers long. The mitochondrion has an outer membrane and an extensively folded inner membrane that encloses a fluid matrix. The organelle is the site of oxidative phosphorylation, the primary source of cellular energy. In the fluid matrix, organic molecules derived from the breakdown of foodstuffs are oxidized in a series of chemical reactions known as the citric acid cycle. Electrons removed in the course of oxidation are passed along a chain of respiratory-enzyme complexes arrayed in the inner membrane, driving the phosphorylation of adenosine diphosphate to form adenosine triphosphate (ATP), the universal energy carrier of cells. The cytoplasm (the region outside the nucleus) of eukaryotic cells contains a few mitochondria to many hundreds, depending on the energy demands placed on the cell.  
 1  D 
 1. The author of the passage would most likely agree with which one of the following statements about the "symbiotic relation" in line 10?

(A) The new cell that developed out of the symbiotic relation between anaerobic and aerobic cells has not changed over the last one-and-a-half billion years.
(B) Neither anaerobic nor aerobic cells had a specific function to perform in the new cell.
(C) Anaerobic and aerobic cells combined to create a new cell because neither type of cell was capable of surviving for long on its own.
(D) Anaerobic and aerobic cells could not have joined to form a new cell in the absence of the proper atmospheric conditions.
(E) The chromosomes of eukaryotic cells were originally located in aerobic cells before aerobic cells combined with anaerobic cells to form a new cell.

2 
 E 
 2. The passage suggests which one of the following about "anaerobic fermentation" (line 2)?

(A) It occurs in the mitochondria located in cells' cytoplasm.
(B) It causes the breakdown of organic molecules during the citric acid cycle.
(C) It is the basis of energy production in modern eukaryotic cells.
(D) It can only be carried on by primitive bacterium in an oxygen-poor environment.
(E) It is not the most efficient way for cells to produce energy.

3 
 A 
 3. According to the passage, the energy released by a eukaryotic cell is

(A) generated by the mitochondria contained in its cytoplasm
(B) dependent on the transformation of adenosine triphosphate into adenosine diphosphate
(C) caused by chemical reactions that take place outside of the mitochondrion's inner membrane
(D) related to the number of chromosomes in the cell nucleus
(E) incorporated into the mitochondrion's genetic material

4 
 B 
 4. According to the passage, which one of the following occurs during the citric acid cycle?

(A) Organic molecules that are derived from food penetrate the mitochondrion's outer membrane
(B) Electrons help to transform adenosine diphosphate into adenosine triphosphate.
(C) Mitochondria from a eukaryotic cell's cytoplasm are transported to the cell's nucleus.
(D) Eukaryotic cells develop subcellular structures, internal membranes and nuclei.
(E) The fluid matrix enclosed by the mitochondrion's inner membrane is transformed into organic molecules that are later broken down in a series of chemical reactions.

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Gmatsaiyan · Accepted Answer

ANSWERS AND EXPLANATIONS 1.D, 2.E, 3.A, 4.В 
  1 . (D) We're asked to infer something about the symbiotic relationship mentioned in paragraph 1, and there's a bunch of material relating to that early on, so we have no idea specifically what the test makers are after here. In other words, as is common in Inference questions, prephrasing an answer is not a good option. We should go right to the answer choices, looking to confirm or negate each one based on the information in the passage. 
(A) and (B) are both flatly contradicted by the passage: the new cell did evolve quite a bit, and each partner cell in the original symbiotic relation did have a specific function. (C) Presumably, the cells managed pretty well on their own before the atmosphere became oxygen-rich, so there's no way we can infer that the combination occurred because the cells were in danger of dying out. (D) is the winner: the reasonable implication of oxygen being the "driving force" is that, absent all of that oxygen, the symbiotic relation that led to the formation of the new cell would have been difficult if not impossible. 
(E) not only distorts information in the passage—information in paragraph 2—but the information it plays on is located far from the cited line. An 800 test taker knows that the information needed to find the correct answer to questions containing a line reference usually won't be located very far from the cited line.

2 . (E) The line reference brings us right to the concept in question, so it's best to quickly review what's said about anaerobic fermentation. And it's what comes a bit later that's really the key to the question; we're told that "respiration liberates far more energy than fermentation," which is just another way of saying that anaerobic fermentation isn't the most efficient way for cells to produce energy. (E) is therefore inferable here. 
(A), (B), and (C) are all far removed from the detail in question and misrepresent matters anyway.
(D) might be tempting—after all, we're told that primitive bacterium in an oxygen-poor environment did employ anaerobic fermentation. But it's not valid to deduce from this that only primitive bacterium in an oxygen-poor environment can carry on anaerobic fermentation. Perhaps you put (D) on hold until you reached (E)—but we really have to work much harder to justify (D) than (E). An 800 test taker doesn't bend over backwards to justify an answer choice, knowing that if a choice takes that much work to rationalize, it's almost certainly wrong.

3 . (A) "According to the passage" signifies a detail question, and you have to expect at least a few of those to make your life somewhat miserable. But it's not that bad, really, as long as you find the subject in question and focus on what's said about it. The striking term that appears in this question is "eukaryotic cell," which we find in paragraphs 2 and 3. These references tell us a few major things: mitochondria are located in the cytoplasm of eukaryotic cells, and they power these cells. And that's really all we need to know to answer the question—(A) paraphrases that very closely. An 800 test taker does not overestimate the amount of "comprehension" that Reading Comprehension requires; she seeks to understand only as much as she needs to pick up points. 
(B) and (C) both contradict the passage: ADP is transformed into ATP, and the chemical reactions, according to information in paragraph 3, take place in the fluid matrix, which is enclosed by the mitochondrion's inner membrane. 
(D) and (E) distort details taken from the wrong paragraphs, (D) a detail in paragraph 2 and (E) a detail in paragraph 4. Of the two, (D) is likely to be more tempting, since paragraph 4 makes no mention of eukaryotic cells. But neither is directly related to the energy released by a eukaryotic cell.

4 . (B) The detail "citric acid cycle" is even easier to skim for than the detail from the previous question— it shows up only in the middle of paragraph 3. There we see that the citrus acid cycle is a set of chemical reactions that oxidize molecules derived from food. If we keep reading, we sees that the oxidation moves the electrons along to turn ADP into ATP, just as (B) says. (B)'s wording is no mystery and no real challenge. The challenge lies in figuring out where the answer is going to come from, and translating the relevant text once found into simpler words. An 800 test taker often asks himself, "where is the answer likely to come from?" (A), like a few choices in the previous question, gets it backwards. The citric acid cycle takes place in the fluid matrix, which is part of the mitochondrion's inner membrane (C) and (E) distort information in the passage. The citric acid cycle is a process that takes place within the mitochondrion; it has nothing to do with the movement of a mitochondrion from one part of the cell to another (C). Nor does the citric acid cycle result in the transformation of the fluid matrix (E); rather, a transformation (of organic molecules) occurs within the fluid matrix during the citric acid cycle. 
(D) plays on an irrelevant detail from paragraph 2. There's no reason why we should look at paragraph 2 in a question about the citric acid cycle.

Gmatsaiyan · Answer

It's quite a chore to simply chop through the heavy biology in the beginning to get a sense of where this author is going. In fact, it takes a good long while before the main character, mitochondria, even hits the stage. By the time that we recognize that the details in the beginning are presented to shed light on the evolution of mitochondria, the focus shifts to a complex discussion of the characteristics and function of mitochondria, laden of course with complicated terms and descriptions of heavy-duty processes.
 Now, sometimes dense complicated passages are followed by easy questions, and these really aren't as bad as they could be. However, every question plays in some way with the technical terms and complex mechanisms described in the passage. Recognizing the following key passage points will help, but you'll also have to go back to the passage at points to pick up a few of the details.
 Key Points of the Passage Purpose and Main Idea : The author's purpose is to describe the evolution of mitochondria and its function in present-day organisms. The passage is purely descriptive, and so there is no main idea, per se. It's simply about mitochondria. 
 Paragraph Structure : Paragraph 1 describes a turning point in organic evolution, the coming together of a host cell with a smaller respiring cell. The author speculates on how this may have occurred (increase in atmospheric oxygen), and describes the benefit to each of the participating cells. The passage is still pretty wide open at this point; there's no telling where it might go.
 An 800 test taker constantly interrogates the passage and the author until he's satisfied that he's nailed down both the author's main area of concern and purpose in writing the passage. 
Paragraph 2 continues the saga of "the little cells that could": the engulfed cell evolved into specialized subcellular organelles, and the host evolved other structures within a nucleus. The hosts are the forebears of modern eukaryotic cells, and the present-day version of the respiring symbiotic duo are the mitochondria.
 Is the author going to settle down to one concept here, or what? Thankfully, yes. Paragraph 3 describes mitochondria in great detail—its size, its structure, its function. The latter is the key, although you don't have to (and shouldn't!) try to take in the mess of technical details just yet; we'll return to those when necessary (and unfortunately, it does become necessary). The main thing is to see is that mitochondria supply cells with energy. How exactly it does that is not worth getting into just yet.

GittinGud · Answer

9 minutes, 4/4 correct. Be very careful while reading. Very tricky passage.

redskull1 · Answer

Somewhat on the easier side this passage.All straightforward questions.

No need to form any outline too.Just Read the question and go back to the relevant part of the passage.

varshsrinivasan · Answer

Agree with  redskull1  on this. Took me all of 6 mins and 30 seconds to get all 4/4 correct.

Posted from my mobile device

richirish · Answer

6 mins all correct, very curious to see the difficulty level, guessing 650-700.

Sajjad1994 · Answer

The difficulty levels are as follow:

Question #1: 700
Question #2: 700
Question #3: 650
Question #4: 700

Overall: 700

abhiprem · Answer

Can anyone please explain why option b is the right answer for the 4th question? Because the question is asking about what happens DURING the citric acid cycle but this option is talking about the electrons helping to transform adenosine diphosphate into adenosine triphosphate, which happens only AFTER the cycle.

Some one and a half or two billion years ago, when the earth was still

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GMAT Reading Comprehension (RC) Questions

Some one and a half or two billion years ago, when the earth was still

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