Experts anticipate that global atmospheric concentrations of carbon

Question

Experts anticipate that global atmospheric
concentrations of carbon dioxide (CO2) will have
doubled by the end of the twenty-first century. It is
known that CO2 can contribute to global warming by
 (5)  trapping solar energy that is being reradiated as heat
from the Earth’s surface. However, some research has
suggested that elevated CO2 levels could enhance the
photosynthetic rates of plants, resulting in a lush world
of agricultural abundance, and that this CO2
 (10)  fertilization effect might eventually decrease the rate
of global warming. The increased vegetation in such an
environment could be counted on to draw more CO2
from the atmosphere. The level of CO2 would thus
increase at a lower rate than many experts have
 (15)  predicted.

However, while a number of recent studies confirm
that plant growth would be generally enhanced in an
atmosphere rich in CO2, they also suggest that
increased CO2 would differentially increase the growth
 (20)  rate of different species of plants, which could
eventually result in decreased agricultural yields.
Certain important crops such as corn and sugarcane
that currently have higher photosynthetic efficiencies
than other plants may lose that edge in an atmosphere
 (25)  rich in CO2. Patterson and Flint have shown that these
important crops may experience yield reductions
because of the increased performance of certain weeds.
Such differences in growth rates between plant species
could also alter ecosystem stability. Studies have
 (30)  shown that within rangeland regions, for example, a
weedy grass grows much better with plentiful CO2 than
do three other grasses. Because this weedy grass
predisposes land to burning, its potential increase may
lead to greater numbers of and more severe wildfires in
 (35)  future rangeland communities.

It is clear that the CO2 fertilization effect does not
guarantee the lush world of agricultural abundance that
once seemed likely, but what about the potential for the
increased uptake of CO2 to decrease the rate of global
 (40)  warming? Some studies suggest that the changes
accompanying global warming will not improve the
ability of terrestrial ecosystems to absorb CO2.
Billings’ simulation of global warming conditions in
wet tundra grasslands showed that the level of CO2
 (45)  actually increased. Plant growth did increase under
these conditions because of warmer temperatures and
increased CO2 levels. But as the permafrost melted,
more peat (accumulated dead plant material) began to
decompose. This process in turn liberated more CO2 to
 (50)  the atmosphere. Billings estimated that if summer
temperatures rose four degrees Celsius, the tundra
would liberate 50 percent more CO2 than it does
currently. In a warmer world, increased plant growth,
which could absorb CO2 from the atmosphere, would
 (55)  not compensate for this rapid increase in
decomposition rates. This observation is particularly
important because high-latitude habitats such as the
tundra are expected to experience the greatest
temperature increase.    1 
 1. Which one of the following best states the main point of the passage?

(A) Elevated levels of CO2 would enhance photosynthetic rates, thus increasing plant growth and agricultural yields.
(B) Recent studies have yielded contradictory findings about the benefits of increased levels of CO2 on agricultural productivity.
(C) The possible beneficial effects of increased levels of CO2 on plant growth and global warming have been overstated.
(D) Increased levels of CO2 would enhance the growth rates of certain plants, but would inhibit the growth rates of other plants.
(E) Increased levels of CO2 would increase plant growth, but the rate of global warming would ultimately increase.

2 
 2. The passage suggests that the hypothesis mentioned in the first paragraph is not entirely accurate because it fails to take into account which one of the following in predicting the effects of increased vegetation on the rate of global warming?

(A) Increased levels of CO2 will increase the photosynthetic rates of many species of plants.
(B) Increased plant growth cannot compensate for increased rates of decomposition caused by warmer temperatures.
(C) Low-latitude habitats will experience the greatest increases in temperature in an atmosphere high in CO2.
(D) Increased levels of CO2 will change patterns of plant growth and thus will alter the distribution of peat.
(E) Increases in vegetation can be counted on to draw more CO2 from the atmosphere.

3 
 3. Which one of the following best describes the function of the last paragraph of the passage?

(A) It presents research that may undermine a hypothesis presented in the first paragraph.
(B) It presents solutions for a problem discussed in the first and second paragraphs.
(C) It provides an additional explanation for a phenomenon described in the first paragraph.
(D) It provides experimental data in support of a theory described in the preceding paragraph.
(E) It raises a question that may cast doubt on information presented in the preceding paragraph.

4 
 4. The passage suggests that Patterson and Flint would be most likely to agree with which one of the following statements about increased levels of CO2 in the Earth’s atmosphere?

(A) They will not increase the growth rates of most species of plants.
(B) They will inhibit the growth of most crops, thus causing substantial decreases in agricultural yields.
(C) They are unlikely to increase the growth rates of plants with lower photosynthetic efficiencies.
(D) They will increase the growth rates of certain species of plants more than the growth rates of other species of plants.
(E) They will not affect the photosynthetic rates of plants that currently have the highest photosynthetic efficiencies.

5 
 5. The author would be most likely to agree with which one of the following statements about the conclusions drawn on the basis of the research on plant growth mentioned in the first paragraph of the passage?

(A) The conclusions are correct in suggesting that increased levels of CO2 will increase the photosynthetic rates of certain plants.
(B) The conclusions are correct in suggesting that increased levels of CO2 will guarantee abundances of certain important crops.
(C) The conclusions are correct in suggesting that increased plant growth will reverse the process of global warming.
(D) The conclusions are incorrect in suggesting that enhanced plant growth could lead to abundances of certain species of plants.
(E) The conclusions are incorrect in suggesting that vegetation can draw CO2 from the atmosphere.

6 
 6. The passage supports which one of the following statements about peat in wet tundra grasslands?

(A) More of it would decompose if temperatures rose four degrees Celsius.
(B) It could help absorb CO2 from the atmosphere if temperatures rose four degrees Celsius.
(C) It will not decompose unless temperatures rise four degrees Celsius.
(D) It decomposes more quickly than peat found in regions at lower latitudes.
(E) More of it accumulates in regions at lower latitudes.

7 
 7. Which one of the following, if true, is LEAST consistent with the hypothesis mentioned in lines 22–25 of the passage?

(A) The roots of a certain tree species grow more rapidly when the amount of CO2 in the atmosphere increases, thus permitting the trees to expand into habitats formerly dominated by grasses with high photosynthetic efficiencies.
(B) When grown in an atmosphere high in CO2, certain weeds with low photosynthetic efficiencies begin to thrive in cultivated farmlands formerly dominated by agricultural crops.
(C) When trees of a species with a high photosynthetic efficiency and grasses of a species with a low photosynthetic efficiency were placed in an atmosphere high in CO2, the trees grew more quickly than the grasses.
(D) When two different species of grass with equivalent photosynthetic efficiency were placed in an atmosphere high in CO2, one species grew much more rapidly and crowded the slower-growing species out the growing area.
(E) The number of leguminous plants decreased in an atmosphere rich in CO2, thus diminishing soil fertility and limiting the types of plant species that could thrive in certain habitats.

8 
 8. According to the passage, Billings’ research addresses which one of the following questions?

(A) Which kind of habitat will experience the greatest temperature increase in an atmosphere high in CO2?
(B) How much will summer temperatures rise if levels of CO2 double by the end of the twenty-first century?
(C) Will enhanced plant growth necessarily decrease the rate of global warming that has been predicted by experts?
(D) Would plant growth be differentially enhanced if atmospheric concentrations of CO2 were to double by the end of the twenty-first century?
(E) Does peat decompose more rapidly in wet tundra grasslands than it does in other types of habitats when atmospheric concentrations of CO2 increase?

sumitkrocks · Answer

1. Which one of the following best states the main point of the passage?

(A) Elevated levels of CO2 would enhance photosynthetic rates, thus increasing plant growth and agricultural yields.
(B) Recent studies have yielded contradictory findings about the benefits of increased levels of CO2 on agricultural productivity.
(C) The possible beneficial effects of increased levels of CO2 on plant growth and global warming have been overstated.
(D) Increased levels of CO2 would enhance the growth rates of certain plants, but would inhibit the growth rates of other plants.
(E) Increased levels of CO2 would increase plant growth, but the rate of global warming would ultimately increase.

Passage presents the view of experts on increasing levels of CO2, presents hypothesis that increased co2 would benefit plants in certain way and help in reducing greenhouse effect and ultimately proves the hypothesis wrong

C is the Answer IMO

2. The passage suggests that the hypothesis mentioned in the first paragraph is not entirely accurate because it fails to take into account which one of the following in predicting the effects of increased vegetation on the rate of global warming?

(A) Increased levels of CO2 will increase the photosynthetic rates of many species of plants.
(B) Increased plant growth cannot compensate for increased rates of decomposition caused by warmer temperatures.
(C) Low-latitude habitats will experience the greatest increases in temperature in an atmosphere high in CO2.
(D) Increased levels of CO2 will change patterns of plant growth and thus will alter the distribution of peat.
(E) Increases in vegetation can be counted on to draw more CO2 from the atmosphere.

B is the answer-In the last paragraph results of the simulation study presents the evidence for option B

3. Which one of the following best describes the function of the last paragraph of the passage?

(A) It presents research that may undermine a hypothesis presented in the first paragraph.
(B) It presents solutions for a problem discussed in the first and second paragraphs.
(C) It provides an additional explanation for a phenomenon described in the first paragraph.
(D) It provides experimental data in support of a theory described in the preceding paragraph.
(E) It raises a question that may cast doubt on information presented in the preceding paragraph.

A is the right answer

4. The passage suggests that Patterson and Flint would be most likely to agree with which one of the following statements about increased levels of CO2 in the Earth’s atmosphere?

(A) They will not increase the growth rates of most species of plants.
(B) They will inhibit the growth of most crops, thus causing substantial decreases in agricultural yields.
(C) They are unlikely to increase the growth rates of plants with lower photosynthetic efficiencies.
(D) They will increase the growth rates of certain species of plants more than the growth rates of other species of plants.
(E) They will not affect the photosynthetic rates of plants that currently have the highest photosynthetic efficiencies.

Refer Para 2 :
increased CO2 would differentially increase the growth rate of different species of plants 
 D is the answer

5. The author would be most likely to agree with which one of the following statements about the conclusions drawn on the basis of the research on plant growth mentioned in the first paragraph of the passage?

(A) The conclusions are correct in suggesting that increased levels of CO2 will increase the photosynthetic rates of certain plants.
(B) The conclusions are correct in suggesting that increased levels of CO2 will guarantee abundances of certain important crops.
(C) The conclusions are correct in suggesting that increased plant growth will reverse the process of global warming.
(D) The conclusions are incorrect in suggesting that enhanced plant growth could lead to abundances of certain species of plants.
(E) The conclusions are incorrect in suggesting that vegetation can draw CO2 from the atmosphere.

A is the answer IMO; i.e for certain weeds its correct 
 
6. The passage supports which one of the following statements about peat in wet tundra grasslands?

(A) More of it would decompose if temperatures rose four degrees Celsius.
(B) It could help absorb CO2 from the atmosphere if temperatures rose four degrees Celsius.
(C) It will not decompose unless temperatures rise four degrees Celsius.
(D) It decomposes more quickly than peat found in regions at lower latitudes.
(E) More of it accumulates in regions at lower latitudes.

A is the answer

7. Which one of the following, if true, is LEAST consistent with the hypothesis mentioned in lines 22–25 of the passage?

(A) The roots of a certain tree species grow more rapidly when the amount of CO2 in the atmosphere increases, thus permitting the trees to expand into habitats formerly dominated by grasses with high photosynthetic efficiencies.
(B) When grown in an atmosphere high in CO2, certain weeds with low photosynthetic efficiencies begin to thrive in cultivated farmlands formerly dominated by agricultural crops.
(C) When trees of a species with a high photosynthetic efficiency and grasses of a species with a low photosynthetic efficiency were placed in an atmosphere high in CO2, the trees grew more quickly than the grasses.
(D) When two different species of grass with equivalent photosynthetic efficiency were placed in an atmosphere high in CO2, one species grew much more rapidly and crowded the slower-growing species out the growing area.
(E) The number of leguminous plants decreased in an atmosphere rich in CO2, thus diminishing soil fertility and limiting the types of plant species that could thrive in certain habitats.

A is the answer IMO

8. According to the passage, Billings’ research addresses which one of the following questions?

(A) Which kind of habitat will experience the greatest temperature increase in an atmosphere high in CO2?
(B) How much will summer temperatures rise if levels of CO2 double by the end of the twenty-first century?
(C) Will enhanced plant growth necessarily decrease the rate of global warming that has been predicted by experts?
(D) Would plant growth be differentially enhanced if atmospheric concentrations of CO2 were to double by the end of the twenty-first century?
(E) Does peat decompose more rapidly in wet tundra grasslands than it does in other types of habitats when atmospheric concentrations of CO2 increase?

Refer: last para "This observation is particularly important because high-latitude habitats such as the
tundra are expected to experience the greatest temperature increase."

A is the answer IMO

Sajjad1994 · Answer

Explanation

6. The passage supports which one of the following statements about peat in wet tundra grasslands?

Explanation

Paragraph 3  is where tundra comes in, and the inference comes right out of  lines 46-53  in particular. We’re told that upon the melting of the permafrost, the decomposition of peat  “liberated more CO2,”  and that another 4°C increase in temperature  “would liberate 50% more.”  The missing link in that equation is  (A):  The author must believe that more peat would decompose. Where else, in the context of these eight lines, would the increased CO2 come from?

(B)  has it backwards—the peat decomposition frees CO2 rather than absorbing it. The peat is already decomposing, so (C)’s suggestion that decomposition won’t begin until a 4°C temperature increase makes no sense. And no comparisons to peat deposits elsewhere—their rate of decomposition  (D)  or their accumulation  (E) —play any role in the passage.

Answer: A

Sajjad1994 · Answer

Explanation

7. Which one of the following, if true, is LEAST consistent with the hypothesis mentioned in lines 22–25 of the passage?

Explanation

The four lines in question speculate that key, high-photosynthetic-efficiency crops may  “lose that edge”  after a major increase in CO2. On that basis alone,  (A)  and  (B)  can both be quickly dismissed because they are explicit examples of low-efficiency plants crushing higher-efficiency ones.

(E)  doesn’t mention efficiency explicitly, but its description of soil rendered less fertile and plants rendered fewer in number and weaker, all in the presence of high CO2, certainly is consistent with  lines 22-25.

And so is  (D) , in a different way.  “Consistent,”  remember, means  “non-contradictory,”  and for one of two grass species of equal efficiency to crowd out the other in a high CO2 environment doesn’t contradict anything the author says. But  (C)  explicitly does. In  (C) , contrary to  lines 22-25 , high-efficiency trees in the presence of high CO2 are outstripping the low-efficiency grasses.

Answer: C

8. According to the passage, Billings’ research addresses which one of the following questions?

Explanation

Not only is  (C)  the issue directly addressed by Billings’ tundra research, but it’s the question answered by the whole of  paragraph 3 , and indeed by the passage overall. Billings is the major test case presented by the author of the hypothesis that increased CO2 could in the end help to reverse global warming.

(A)  and  (E)  are both wrong for the same reason: The author never compares the conditions in specific earth habitats in order to make his case.

(B)  creates a serious distortion when it attaches the concept of  “doubling”  of CO2 levels, way back in  lines 1-3 , to Billings’ research, which in any case provides no precision as to rising temperature levels. (The 4°C figure is merely hypothetical, and merely deals with the tundra example.) (D)’s question, is answered—and in the affirmative—by  paragraph 2 , but not by Billings’ research specifically.

Answer: C

nikitathegreat · Answer

1. Which one of the following best states the main point of the passage?

(A) Elevated levels of CO2 would enhance photosynthetic rates, thus increasing plant growth and agricultural yields.

However, while a number of recent studies confirm
that plant growth would be generally enhanced in an
atmosphere rich in CO2, they also suggest that
increased CO2 would differentially increase the growth
(20) rate of different species of plants, which could
eventually result in decreased agricultural yields.

Based on the above passage, the differentials increase in growth rate eventually resulted in decrease in agricultural yields.
Hence, the last words -increased agricultural yields are incorrect.

(B) Recent studies have yielded contradictory findings about the benefits of increased levels of CO2 on agricultural productivity.

While this part seems correct but maybe this doesn't capture the entire picture of the passage? The passage also talks about Global Warming.

(C) The possible beneficial effects of increased levels of CO2 on plant growth and global warming have been overstated.
Correct ans. There's an initial hypothesis talks about benefits of increased levels of CO2 and then the later passages talk about how global warming actually increased and decreased agricultural productivity.

(D) Increased levels of CO2 would enhance the growth rates of certain plants but would inhibit the growth rates of other plants.
It doesn inhibit the growth rates of other plants. The plants may have differential growth rates but it doesn't inhibit.

(E) Increased levels of CO2 would increase plant growth, but the rate of global warming would ultimately increase.

This choice looks correct to me. Not sure why this is incorrect? Doesn't capture the purpose of the passage?

GMATNinja  - Can you please review my answer analysis for each option choice and let me know if my understanding is correct?

Thank you

GMATNinja · Answer

Question 1 
 
You pretty much nailed the reasoning for (A), (B), (C), and, (D). And for the most part, the incorrect answers address aspects of the passage without hitting the central point.

And this is also the problem with (E). While the passage certainly addresses increased plant growth and concludes that warming will continue, it mentions lots of other stuff too, right? It's not just that certain plants will benefit; it's that agricultural yields will decline, the kinds of plants that will benefit will lead to more wildfires, and the tundra will melt and release all sorts of terrifying stuff into the atmosphere.

In other words, the negative implications of increased CO2 go way beyond continued warming, so (E) is too specific. (C), which broadly states that any supposed benefits of increased CO2 have been overstated, captures the full general sweep of the passage, so it's better.

I hope that helps!

VerbalBot · Answer

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Experts anticipate that global atmospheric concentrations of carbon

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Experts anticipate that global atmospheric concentrations of carbon

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