LSAT 4 | Section 1 | Logical Reasoning: Q10

LR Question 10 Explanation

QUESTION TEXT: Rhizoblum bacteria living in the roots of bean plants…

QUESTION TYPE: Necessary Assumption

CONCLUSION: If we can get Rhizobium bacteria to grow on the roots of wheat plants, the need for artificial fertilizers will be reduced.

REASONING: Rhizobium bacteria on the roots of soybeans plants can fix nitrogen. Nitrogen can also be provided by fertilizer.

ANALYSIS: We know what Rhizobium do when they are on soybean plants. Will they act the same on wheat plants? Nature is complicated.

It is important to notice that the conclusion says that the need for fertilizer will be reduced, not eliminated. That is why answer choice B is wrong.

___________

1. This has switched to talking about what we “should” do. The stimulus discusses what will or will not happen.
2. Since the need for fertilizer will only be “reduced,” this isn’t a necessary assumption. Presumably we will still use fertilizer on wheat plants, just less of it.
3. If there were a type of non-wheat grass that did have Rhizobium would the argument be ruined? (No) So this isn’t a necessary assumption.
4. Legumes were just an example. The main thing is that commercial wheat doesn’t produce nitrogen.
5. CORRECT. If Rhizobium don’t produce nitrogen when they are on the roots of wheat then we will still need just as much fertilizer.

Recap: The question begins with “Rhizoblum bacteria living in the roots of bean plants”. It is a Necessary Assumption question. Learn more about LSAT Necessary questions in our guide to LSAT Logical Reasoning question types.