Q10 - Rhizobium bacteria living in the roots

[geverett]

I love science.

Sentence 1 (premise): Rhizobium bacteria grows in beans, and other plants that are characterized as legumes, producing fixed nitrogen which is an essential plant nutrient. Other crops, that are not characterized as legumes, such as wheat must have this fixed nitrogen supplied to it through nitrogen based fertilizer.

Sentence 2 (conclusion): If technology could produce a wheat crop which would naturally play host to rhizobium bacteria then the need for the artificial fertilizers would be reduced.

What is an assumption this argument depends upon?

Okay so let's find some gaps in the reasoning. First of all the author is assuming that if they created a wheat crop that could play host to rhizobium bacteria that they would not have to rely on an equal or greater amount of "artificial fertilizer" in order to introduce the bacteria into the roots of the wheat crop. The second gap I can see is that the author assumes that the production of the wheat crop which could host rhizobium bacteria would not result in the creation of some sort of unpredictable issue in which there is an additional need for a great or equal amount of artificial fertilizer. Let's take a look at the answer choices.

(A) "towards producing plants" The author is only making an argument for a specific type of plant "non-legume crops". This answer choice is too broad to qualify as a necessary assumption. Even if it narrowed it's scope to "non-legume crops such as wheat" it would still not qualify as a necessary assumption, because the author's argument states "if biotech. succeeds in producing wheat strains which can play host to rhizobium . . ." He introduces a conditional logic statement into the conclusion, and does not conclude anything about what biotechnology "must do" but rather a result (need for artificial fertilizers reduced) if biotech. succeeds in producing a wheat strain that can host rhizobium bacteria.
(B) This is tempting. However, remember the arguments conclusion focuses on "the need for artificial fertilizers will be reduced." If you negate this answer choice it reads "Fixed nitrogen is not the only soil nutrient supplied by artificial fertilizers." The negation of this statement is too ambiguous to be able to discern the impact. One can imagine 2 scenarios taking place if this answer choice were negated.
1. There is no reduction in the amount of artificial fertilizer, because artificial fertilizer is still required to supply other nutrients to the wheat crop. or 2. There is a reduction in the amount of artificial fertilizer, because wheat crops are getting their fixed nitrogen from rhizobium bacteria and so depend on a smaller amount of artificial fertilizer.
(C) "There are no naturally occurring strains of wheat . . ." The stimulus only makes the claim that "wheat normally must be supplied by applications of nitrogen based fertilizer." This leaves open the possibility that some wheat strains might be able to produce fixed nitrogen. This answer choice is unsupported and definitely not a necessary assumption. Get rid of it.
(D) ". . . the only crops that produce their own supply of fixed nitrogen. . ." This is also unsupported. We know that legumes do produce fixed nitrogen, but nowhere in the stimulus can you find any support that legumes are the only crops that naturally produced fixed nitrogen. Get rid of this.
(E) This is the correct answer choice. Remember the author conclusion is that "the need for artificial fertilizer will be reduced if wheat strains could host rhizobium bacteria which produce fixed nitrogen." If you negate the answer choice it would read "Rhizobium bacteria living in the roots of wheat would not produce fixed nitrogen." If that were the case then the authors argument would be blown out of the water, because he/she could not conclude that there can be any kind of reduction of artificial fertilizer based on the ability of wheat crops to host rhizobium bacteria as the rhizobium in the wheat crops would not be able to produce fixed nitrogen. Let me know if you need further clarification on this.