RC Practice with Explanation

Tips on how to approach CAT Reading Comprehension passages
  • Don’t get into the minor details of the passage; just focus on what each paragraph has to say
  • As you read, create a map of the passage; you must remember what thing is located where in the passage
  • Once you read the question, come back to the part of the passage that is likely to have the answer
  • Compare the options and eliminate the incorrect choices based on the evidence that you see in the passage
  • Choose the answer once you are convinced of the right choice


There are a great many symbiotic relationships in the marine environment. A popular one, often noted for the striking beauty of the juxtaposition, is that of the sea anemone and the clown fish. The anemone has poison tentacles which—when they contact passing fish—paralyze the fish and drag the prey in for a meal. The clown fish uses the anemone’s tentacle “garden” as a safe haven while attracting prey for the anemone to capture, for it alone is immune to the sting of the anemone.

Another symbiotic relation that remains the subject of scientific puzzlement concerns the relationship between Scleractinia, the coral type whose colonization produces reefs, and their symbiotic partners the zooxanthellae, the unicellular algae present in the corals’ endodermic tissues. It is known that each symbiont plays an integral part in the formation of a reef’s protective limestone foundation. The coral polyps secrete calceous exoskeletons which cement themselves into an underlayer of rock, while the algae deposit still more calcium carbonate, which reacts with sea salt to create an even tougher limestone layer.

It is also known that, due to the algal photosynthesis, the reef environment is highly oxygen-saturated, while the similarly high amounts of carbon dioxide are carried off rapidly. All this accounts for the amazing renewability of coral reefs despite the endless erosion caused by wave activity. However, the precise manner in which one symbiont stimulates the secretion of calcium carbonate by the other remains unclear.

Scientists have also proposed various theories to explain the transformation of “fringing reefs,” those connected above sea level to land masses, into “barrier reefs” that are separated from shorelines by wide lagoons, and then into free-floating atolls. Though the theory postulated by Charles Darwin is considered at least partially correct, some scientists today argue that the creation of the reef forms has more to do with the rise of sea level that accompanied the end of the Ice Age. However, recent drillings at Enewetak atoll have uncovered a large underlay of volcanic rock, which suggests that Darwin’s explanation may have been more valid after all.

Even the name given to the reefs is something of a misnomer. The Scleractinia themselves generally comprise no more than 10 percent of the biota of the average reef community: zooxanthellae can account for up to 90 percent of the reef mass, along with foraminifera, annelid worms, and assorted mollusks. Moreover, reefs can flourish only in shallow, highly saline waters above 70°F., because the algae require such circumstances; yet non-reef-building corals occur worldwide under various environmental conditions, from the Arctic to the Mediterranean, home of the red coral prized for jewelry. The most likely reason that the term “coral reefs” persists is that the brilliant variety of coral shapes and colors makes aesthetic considerations more vivid than biological ones.

Question: According to the author, some scientists consider the term “coral reef” a misnomer because:
[A] the beautiful shapes and colors of reefs are produced by the Scleractinia rather than the zooxanthellae.
[B] the coral portion of a reef has little to do with the reef’s survival.
[C] “non-reef-building” corals are found throughout the world.
[D] the majority of a reef’s substance comprises zooxanthellae, foraminifera, annelid worms, and assorted molluscs while a small portion comprises the Scleractinia.
Option (D)


Your map will remind you that a full paragraph discusses the misnomer “coral reef.” Summarize the main reason why this is true: Reefs have lots of algae, not much coral. (D) matches the prediction.

Wrong answers:

(A): Faulty Use of Detail. The author argues at the end of 5 that this is why the term persists, but it doesn’t explain the misnomer.

(B): Distortion. While the reef’s conditions for growth depend on the algae, the coral could also play a major role in determining survival.

(C): Faulty Use of Detail. While true as described in 5, this doesn’t explain why the term “coral reef” would be misleading.

Strategy Point: When a question asks for an answer that is the focus of a whole paragraph, predict by summarizing the paragraph’s overall point.

Question: According to the passage, Darwin’s theory regarding coral reef transformation is not universally accepted today. Opponents of Darwin’s theory would NOT agree with which of the following statements?
[A] Coral reefs change from fringing reefs to barrier reefs, and then to free-floating atolls.
[B] Atolls are farther from land masses than are barrier reefs.
[C] Fringing reefs inevitably developed into barrier reefs because volcanic islands gradually sank into the ocean.
[D] As a result of the end of the Ice Age, increased expanses of water aided in the transformation of fringing reefs into barrier reefs.
Option (C)


A question with some tricky wording; be very careful in dissecting it. If an opponent with Darwin’s theory wouldn’t agree with something, who would agree with it? Darwin! The question is basically asking for something that is part of Darwin’s theory. Even armed with this information, the question isn’t easy. Darwin’s theory is mentioned in 4 in a roundabout fashion. Go back to review the details: The author implies that Darwin theorized that volcanic islands caused the transformation. (C) rewards that prediction.

Wrong answers:

(A): Faulty Use of Detail. This is a belief that scientists in general hold (5); it’s not a component of Darwin’s theory specifically.

(B): Faulty Use of Detail. As above, this is just a definition of terms rather than a component of Darwin’s theory.

(D): Opposite. This is the alternative to Darwin’s theory; opponents of Darwin would probably believe this.

Question: Based on the passage, which of the following is probably an assumption of scientists studying coral reefs?
[A] The theories of reef evolution through glacial melting and through volcanic subsidence are mutually exclusive.
[B] The three main types of coral reefs did not develop independently of one another.
[C] Zooxanthellae are always found in coral reefs.
[D] Intense calcification single-handedly protects reefs from destruction by waves and other natural causes.
Option (B)


A difficult question to predict; review the main points of the passage in your map. Remember to eliminate while looking for the correct answer, using the denial test as needed. (B) must be an assumption of the scientists since they study the different types of reefs with the intent of understanding how they transformed from to another. Denying (B) and arguing that the three types developed independently destroys the transformation theories that the author discusses.

Wrong answers:

(A): Opposite. The author argues in 4 that Darwin’s theory may be “partially true,” suggesting that the two theories can coexist to some extent.

(C): Opposite. The author mentions corals without algae in the last part of 5.

(D): Opposite. The author shows in s2 and 3 that a variety of factors influence reef renewal.

Question: The passage mentions the recent drillings at the Enewetak atoll. This reference serves to:
[A] stengthen the claims made by scientists today concerning reef transformation.
[B] weaken the claims made by scientists today concerning reef transformation.
[C] strengthen the claims made by Darwin concerning reef transformation.
[D] weaken the claims made by Darwin concerning reef transformation.
Option (C)


How does the Enewetak atoll fit into the passage? Mentioned in 4, the author argues that it supports Darwin’s theories about barrier reef formation. (C) matches the prediction exactly.

Wrong answers:

(A): Out of Scope. While it strengthens the claims of some scientists, it can’t strengthen the claims scientists in general since there are competing theories.

(B): Out of Scope. As above.

(D): Opposite. The author states explicitly that the evidence strengthens Darwin’s theory.

Question: [Regardless of what Darwin’s opponents may think,] according to the author, the theory proposed by Charles Darwin:
[A] is less persuasive on the topic of reef formation in light of recent discoveries.
[B] shows that each type of coral reef developed by separate, distinct processes.
[C] accurately described the transformation of fringing reefs into atolls.
[D] focused on the idea of submerging volcanic islands.
Option (D)


Review the main elements of Darwin’s theory as described by the author in 4: Darwin believed that barrier reef formation was caused by submerging volcanic islands, and the author states that this theory is probably partially true. Look for an answer that seizes on one of these points. Choice (D) simply summarizes the theory.

Wrong answers:

(A): Opposite. The author argues in 4 that it’s more persuasive in light of the evidence gathered at Enewetak atoll.

(B): Opposite. The theory’s point is to describe the transformation from one type of reef to another.

(C): Distortion. The author argues that Darwin’s theory is probably partially accurate, which also means that it’s probably partially inaccurate.

Question: Suppose that marine biologists discovered that the calceous exoskeletons produced by coral polyps stimulate the zooxanthellae to deposit calcium carbonate via a chemical stimulus. How would this finding be relevant to the study of reefs?
[A] It would explain how reefs maintain a high level of oxygen saturation.
[B] It would clarify the symbiotic relationship between Scleractinia and zooxanthellae during their formation of the protective limestone foundation.
[C] It would identify the chemical components of the reef’s protective layer.
[D] It would explain the intense colors and formations often seen in coral reefs.
Option (B)


Where is the stimulation of calcium production mentioned? Go back to 2, keeping in mind that the author states that this mechanism is not well-known. If it were shown that the coral stimulates the algae to deposit calcium, the mechanism would become clearer. (B) repeats this.

Wrong answers:

(A): Out of Scope. This isn’t a point of uncertainty, and has nothing to do with calcium deposits.

(C): Out of Scope. The author says that this is known also; the new evidence would have no bearing on it.

(D): Out of Scope. The author doesn’t discuss a connection between calcium deposits and coral colors.

Strategy Point: A good understanding of chains of evidence and points of uncertainty is key— it will be tested often on Natural Science passages.

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