LSAT Explanation PT 28, S1, Q8: Generally speaking, if the same crop

LSAT Question Stem

Which one of the following, if true, most helps to explain the similarity described above between alfalfa and non-nitrogen-fixing plants? 

Logical Reasoning Question Type

This is a Paradox question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

The passage presents a paradox: generally, crops grow less well in later years because they deplete nitrogen in the soil. However, even though alfalfa increases the amount of nitrogen in the soil, it also grows less well in later years. The question asks us to identify the answer choice that best helps explain this similarity between alfalfa and non-nitrogen-fixing plants.

Let's analyze the answer choices:

a) This answer choice suggests that some plants grow better when grown with other types of plants. While this may be true, it does not address the specific issue of why alfalfa, a nitrogen-fixing plant, grows less well in later years like non-nitrogen-fixing plants. It doesn't provide a reason for the observed similarity, so it's not the correct answer.

b) This answer choice explains how alfalfa increases the nitrogen in the soil. However, we already know from the passage that alfalfa increases the nitrogen in the soil. What we need is an explanation for why alfalfa grows less well in later years, despite this nitrogen-fixing property. This answer choice doesn't provide that explanation, so it's not the correct answer.

c) This answer choice suggests that certain plants, including alfalfa, produce substances that accumulate in the soil and are toxic to the plants themselves. This provides a possible explanation for why alfalfa grows less well in later years, like non-nitrogen-fixing plants. If these toxic substances build up in the soil over time, they could be responsible for the observed decline in growth. This answer choice helps explain the similarity and is the correct answer.

d) This answer choice states that alfalfa increases nitrogen in the soil only if a certain type of soil bacteria is present. However, this doesn't directly explain why alfalfa grows less well in later years. It's possible that the bacteria is present, and alfalfa is still fixing nitrogen as expected, but there's another factor causing the decline in growth. We need more information about the bacteria and its presence or absence to determine if this is the reason for the observed similarity. This answer choice doesn't provide enough information to resolve the paradox, so it's not the correct answer.

e) This answer choice tells us that alfalfa is sensitive to juglone, a compound from black walnut trees. While this provides information about a specific vulnerability of alfalfa, it doesn't directly explain why alfalfa, in general, grows less well in later years like non-nitrogen-fixing plants. We don't know if black walnut trees are consistently present in alfalfa fields or if their presence is the main factor causing the decline in growth. This answer choice doesn't provide a sufficient explanation for the observed similarity, so it's not the correct answer.

In conclusion, the correct answer is C, as it provides a plausible explanation for the observed similarity between alfalfa and non-nitrogen-fixing plants: the accumulation of toxic substances in the soil over time.