RC practice Passage with Explanation -43

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.


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: 4
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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: 3
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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: 2
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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: 3
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[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: 4
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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: 2
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