Many aspects of coral reefs remain puzzling to scientists. One mystery

Question

Many aspects of coral reefs remain puzzling to scientists. One mystery concerns the relationship between Scleractinia, the coral type whose colonization produces reefs, and its symbiotic partner, a unicellular alga present in the coral's endodermic tissues. It is known that both organisms play an integral part in the formation of a reef's foundation by secreting and depositing calcium carbonate, which reacts with sea salt to form a hard limestone underlay. Scientists also know that, because of algal photosynthesis, the reef environment is oxygen rich, as similarly high amounts of carbon dioxide are rapidly removed. All of this accounts for the amazing renewability of coral reefs despite the erosion caused by waves. The precise manner in which one symbiotic organism stimulates the secretion of calcium carbonate by the other, however, remains unclear.

In addition to the unanswered question above, scientists have proposed various theories to explain the transformation of "fringing reefs" (those connected above sea level to land masses), into "barrier reefs" (those separated from shorelines by lagoons), and finally into island atolls. Although Darwin's view of the transformation is considered partially correct, some scientists feel that the creation of reef formations has more to do with the rise in sea level that occurred at the end of the last Ice Age than with a gradual submergence of the volcanic islands to which fringing reefs were originally attached. However, recent drillings at one atoll have revealed a substantial underlay of volcanic rock, which suggests that Darwin's explanation may be largely correct.

The term "coral reef" is something of a misnomer. The Scleractinia themselves generally comprise only 10 percent of the total mass of life forms of an average reef community. Algae, along with foraminifera, annelid worms, and assorted mollusks, can account for up to 90 percent of the reef mass. Moreover, the conditions under which reef growth occurs are determined by the needs of the algae, not those of the coral. Reefs flourish only in shallow, highly saline waters above 70 degrees Fahrenheit, because the algae require such an environment. Non-reef-building coral, meanwhile, occur worldwide.   1 
 1. The author suggests that coral reefs are able to survive the process of erosion

(A) primarily through the activities of algae.
(B) despite the high oxygen content of the reef environment.
(C) as a result of the combined relations of coral and algae.
(D) only if they have an above-surface connection to the shoreline.
(E) because of the volcanic rock at their base.

2 
 2. It can be inferred from the passage that Darwin

(A) believed that reefs became atolls through the sinking of volcanoes.
(B) should have expanded his studies of reefs to include those found at atolls.
(C) theorized that each reef formation was formed by an entirely different process.
(D) is less persuasive on the topic of reef formation in light of recent discoveries.
(E) was more interested in algae and coral than in other organisms living at reefs.

3 
 3. The passage does NOT discuss the relationship between

(A) algal photosynthesis and high oxygen content.
(B) Darwin's views and evidence supplied by recent research.
(C) volcanic rock and the life forms found at reefs.
(D) sea salt and calcium carbonate.
(E) wave action and the renewal of reefs.

4 
 4. Which of the following questions is most completely answered by the passage?

(A) What percentage of coral worldwide is of the reef-building type?
(B) How do rises in sea level affect reef formation?
(C) What are the requisite environmental conditions for coral reef formation?
(D) How does coral stimulate the calcareous secretions of symbiotic algae?
(E) What is the principal reason for the transformation of fringing reefs into atolls?

5 
 5. It can be inferred that the author would agree with all of the following statements EXCEPT:

(A) Coral cannot produce reefs without algae.
(B) The water around a coral reef contains high levels of oxygen.
(C) Darwin's theory about the causes of reef formation is at least partly accurate.
(D) The term "coral reef" should be abandoned by scientists.
(E) Coral are more resistant to cold temperatures than the algae that live in their tissues.

Ilanchezhiyan · Answer

For Question 5, how is E incorrect? Could you please explain?

JackyJan · Answer

1) "the coral type whose colonization produces reefs, and its symbiotic partner, a unicellular alga present in the coral's endodermic tissues" -> There you have the proof the the algae live in the tissues

2) "Reefs flourish only in shallow, highly saline waters above 70 degrees Fahrenheit, because the algae require such an environment." -> and here the proof that they need higher temperature

ReetArora · Answer

In question 4, how did we select option C

daspeir · Answer

(D)  The term "coral reef" should be abandoned by scientists . - Too extreme. author says that the term is a misnomer, but doens't say it should be abandoned altogether. author wouldn't agree with this. 
 
 (E)  Coral are more resistant to cold temperatures than the algae that live in their tissues . - The author would agree this. Author mentions "Reefs flourish only in shallow, highly saline waters above 70 degrees Fahrenheit, because the algae require such an environment. Non-reef-building coral, meanwhile, occur worldwide." This means that the algae are not very resistant to cold temperatures, the temperatures need to be above some x value for them to flourish. whereas corals occur worldwide, meaning they can exist at variety of temperatures, and hence more resistant to colder temperatures.

daspeir · Answer

The passage clearly answers this question here -  " Reefs flourish only in shallow, highly saline waters above 70 degrees Fahrenheit, because the algae require such an environment"

Kartike123 · Answer

Yes, But the questions is about "Coral Reef" and not Just "reef" also i think option B is correct.

guddo · Answer

4. Which of the following questions is most completely answered by the passage?

The passage gives a clear answer to the conditions under which coral reefs grow: reefs flourish only in shallow, highly saline waters above 70 degrees Fahrenheit because the algae require such an environment.  So the passage most completely answers the question about the environmental requirements for reef formation .

(A) What percentage of coral worldwide is of the reef-building type?

This is not answered. The passage says Scleractinia make up about 10 percent of the mass of an average reef community, not what percentage of all coral worldwide is reef-building.

(B) How do rises in sea level affect reef formation?

This is only partly discussed. The passage mentions a theory involving rising sea levels after the Ice Age, but does not fully explain how sea-level rise affects reef formation.

(C) What are the requisite environmental conditions for coral reef formation?

This is correct. The passage states that reefs flourish only in shallow, highly saline waters above 70 degrees Fahrenheit.

(D) How does coral stimulate the calcareous secretions of symbiotic algae?

This is explicitly not answered. The passage says the precise manner in which one organism stimulates calcium carbonate secretion by the other remains unclear.

(E) What is the principal reason for the transformation of fringing reefs into atolls?

This is not completely answered. The passage presents competing explanations and says Darwin’s may be largely correct, but does not definitively identify the principal reason.

Answer: (C)

egmat · Answer

Hi Kartike123,

Your instinct to read the question precisely is exactly right, but the "Coral Reef" vs "reef" distinction isn't what decides Q3 here. Let me walk through the two choices you're weighing.

Q3 asks which relationship the passage does  NOT  discuss. The trick is that a choice can name two things that  both  appear in the passage, yet the passage never actually connects them. That's the situation with  C .

Why C is the answer (the relationship that's missing)

-  Volcanic rock  shows up only in paragraph 2 - the recent drillings found "a substantial underlay of volcanic rock," and this is about how reefs  form  (the foundation/underlay).
-  The life forms found at reefs  - Scleractinia, algae, foraminifera, worms, mollusks - show up only in paragraph 3, where the point is what the reef is  made of .

The passage never links these two. It never says the volcanic rock relates to the organisms living on the reef. Both topics are present, but their  relationship  is never discussed - so  C  is the correct pick for a "does NOT discuss" question.

Why B is discussed (so it can't be the answer)

You felt B was the undiscussed one, but paragraph 2 directly connects the two: recent drilling evidence "suggests that Darwin's explanation may be largely correct." That's exactly a relationship between  Darwin's views  and  evidence from recent research  - so B  is  discussed and is eliminated.

Try this quick test to lock in the move:  Suppose a passage says "The bakery opens at 7 a.m." in one paragraph and "Many customers are students" in another. Has it discussed the  relationship  between opening time and students? No - both facts appear, but no link is drawn. That's precisely the gap in C: two things mentioned, no relationship stated.

On "Coral Reef" vs "reef" - the passage uses them for the same structures, and the misnomer point in paragraph 3 is only about  composition  (coral is just ~ 10%  of the mass). It doesn't create a volcanic-rock-to-life-forms link, so it doesn't rescue C as "discussed."

Answer: C

Many aspects of coral reefs remain puzzling to scientists. One mystery

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Many aspects of coral reefs remain puzzling to scientists. One mystery

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