Reading Comprehension

Cultivation of a single crop on a given tract of land leads eventually to decreased yields. One reason for this is that harmful bacterial phytopathogens, organisms parasitic on plant hosts, increase in the soil surrounding plant roots. The problem can be cured by crop rotation, denying the pathogens a suitable host for a period of time. However, even if crops are not rotated, the severity of diseases brought on by such phytopathogens often decreases after a number of years as the microbial population of the soil changes and the soil becomes "suppressive" to those diseases. While there may be many reasons for this phenomenon, it is clear that levels of certain bacteria, such as Pseudomonas fluorescens, a bacterium antagonistic to a number of harmful phytopathogens, are greater in suppressive than in nonsuppressive soil. This suggests that the presence of such bacteria suppresses phytopathogens. There is now considerable experimental support for this view. Wheat yield increases of 27 percent have been obtained in field trials by treatment of wheat seeds with fluorescent pseudomonads. Similar treatment of sugar beets, cotton, and potatoes has had similar results.
These improvements in crop yields through the application of Pseudomonas fluorescens suggest that agriculture could benefit from the use of bacteria genetically altered for specific purposes. For example, a form of phytopathogen altered to remove its harmful properties could be released into the environment in quantities favorable to its competing with and eventually excluding the harmful normal strain. Some experiments suggest that deliberately releasing altered nonpathogenic Pseudomonas syringae could crowd out the nonaltered variety that causes frost damage. Opponents of such research have objected that the deliberate and large-scale release of genetically altered bacteria might have deleterious results. Proponents, on the other hand, argue that this particular strain is altered only by the removal of the gene responsible for the strain's propensity to cause frost damage, thereby rendering it safer than the phytopathogen from which it was derived.
Some proponents have gone further and suggest that genetic alteration techniques could create organisms with totally new combinations of desirable traits not found in nature. For example, genes responsible for production of insecticidal compounds have been transposed from other bacteria into pseudomonads that colonize corn roots. Experiments of this kind are difficult and require great care: such bacteria are developed in highly artificial environments and may not compete well with natural soil bacteria. Nevertheless, proponents contend that the prospects for improved agriculture through such methods seem excellent. These prospects lead many to hope that current efforts to assess the risks of deliberate release of altered microorganisms will successfully answer the concerns of opponents and create a climate in which such research can go forward without undue impediment.


16. The author discusses naturally occurring Pseudomonas fluorescens bacteria in the first paragraph primarily in order to do which one of the following?
(A) prove that increases in the level of such bacteria in the soil are the sole cause of soil suppressivity
(B) explain why yields increased after wheat fields were sprayed with altered Pseudomonas fluorescens bacteria
(C) detail the chemical processes that such bacteria use to suppress organisms parasitic to crop plants, such as wheat, sugar beets, and potatoes
(D) provide background information to support the argument that research into the agricultural use of genetically altered bacteria would be fruitful
(E) argue that crop rotation is unnecessary, since diseases brought on by phytopathogens diminish in severity and eventually disappear on their own

[spoiler]
The OA to this question is D. However, I chose A because the passage mentions that 'This suggests that the presence of such bacteria suppresses phytopathogens' in the first paragraph.[/spoiler]


17. It can be inferred from the author's discussion of Pseudomonas fluorescens bacteria that which one of the following would be true of crops impervious to parasitical organisms?
(A) Pseudomonas fluorescens bacteria would be absent from the soil surrounding their roots.
(B) They would crowd out and eventually exclude other crop plants if their growth were not carefully regulated.
(C) Their yield would not be likely to be improved by adding Pseudomonas fluorescens bacteria to the soil.
(D) They would mature more quickly than crop plants that were susceptible to parasitical organisms.
(E) Levels of phytopathogenic bacteria in the soil surrounding their roots would be higher compared with other crop plants.

[spoiler]
Now, I understand the reasoning behind the correct answer to this question that is C. However, I faltered during the answering process because I didn't know the meaning of 'impervious'. How exactly are we supposed to answer such questions on the real exam?[/spoiler]


18. It can be inferred from the passage that crop rotation can increase yields in part because
(A) moving crop plants around makes them hardier and more resistant to disease
(B) the number of Pseudomonas fluorescens bacteria in the soil usually increases when crops are rotated
(C) the roots of many crop plants produce compounds that are antagonistic to phytopathogens harmful to other crop plants
(D) the presence of phytopathogenic bacteria is responsible for the majority of plant diseases
(E) phytopathogens typically attack some plant species but find other species to be unsuitable hosts

[spoiler]The OA to this question is E. However, I couldn't understand whats wrong with option A. Could anybody shed some light on why option A is incorrect?[/spoiler]

Regards,
Amit

gmat_for_life wrote:16. The author discusses naturally occurring Pseudomonas fluorescens bacteria in the first paragraph primarily in order to do which one of the following?
(A) prove that increases in the level of such bacteria in the soil are the sole cause of soil suppressivity
(B) explain why yields increased after wheat fields were sprayed with altered Pseudomonas fluorescens bacteria
(C) detail the chemical processes that such bacteria use to suppress organisms parasitic to crop plants, such as wheat, sugar beets, and potatoes
(D) provide background information to support the argument that research into the agricultural use of genetically altered bacteria would be fruitful
(E) argue that crop rotation is unnecessary, since diseases brought on by phytopathogens diminish in severity and eventually disappear on their own

[spoiler]
The OA to this question is D. However, I chose A because the passage mentions that 'This suggests that the presence of such bacteria suppresses phytopathogens' in the first paragraph.[/spoiler]

Yes, but the passage does not say that such bacteria are the SOLE, or only, cause. There could be other causes. You have to go beyond finding things that generally sound similar to noticing key details.

17. It can be inferred from the author's discussion of Pseudomonas fluorescens bacteria that which one of the following would be true of crops impervious to parasitical organisms?
(A) Pseudomonas fluorescens bacteria would be absent from the soil surrounding their roots.
(B) They would crowd out and eventually exclude other crop plants if their growth were not carefully regulated.
(C) Their yield would not be likely to be improved by adding Pseudomonas fluorescens bacteria to the soil.
(D) They would mature more quickly than crop plants that were susceptible to parasitical organisms.
(E) Levels of phytopathogenic bacteria in the soil surrounding their roots would be higher compared with other crop plants.

[spoiler]
Now, I understand the reasoning behind the correct answer to this question that is C. However, I faltered during the answering process because I didn't know the meaning of 'impervious'. How exactly are we supposed to answer such questions on the real exam?[/spoiler]

Often you can work around the word the meaning of which you don't know. In this case I am not sure how you could.

From what I have seen, most official RC questions do not contain arcane vocabulary and generally the non native English speakers with whom I have worked have not found vocabulary to be much of an issue.

18. It can be inferred from the passage that crop rotation can increase yields in part because
(A) moving crop plants around makes them hardier and more resistant to disease
(B) the number of Pseudomonas fluorescens bacteria in the soil usually increases when crops are rotated
(C) the roots of many crop plants produce compounds that are antagonistic to phytopathogens harmful to other crop plants
(D) the presence of phytopathogenic bacteria is responsible for the majority of plant diseases
(E) phytopathogens typically attack some plant species but find other species to be unsuitable hosts

[spoiler]The OA to this question is E. However, I couldn't understand whats wrong with option A. Could anybody shed some light on why option A is incorrect?[/spoiler]

The passage discusses crop rotation's effects on the soil, not on the plants themselves. Here again, you have to pay close attention to key details in order to get an RC question right.