Q23 - Zoologist: Plants preferentially absorb heavy nitrogen

[mshinners]

Question Type:
Strengthen

Stimulus Breakdown:
Some confusing stuff about nitrogen is stated. Then, we learn that bone samples from old bears have the same nitrogen levels and blood samples from new bears. The author concludes that old bears eat meat, just like the new bears.

Answer Anticipation:
This argument is based around a comparison. To strengthen that, we generally look to find a relevant similarity between the groups being compared. Here, we shifted between bone and blood samples, so I'm expecting the answer to say that these two types of samples are relevantly similar.

Correct answer:
(D)

Answer choice analysis:
(A) Out of scope. Since the conclusion is about the bears that eat things that eat the plants, the argument only cares what happens to the nitrogen once it's in the plants, not how it gets there.

(B) Out of scope. The argument only cares about the levels of nitrogen in the bears, not the rate that it got there.

(C) Irrelevant/too weak. The number of samples is unimportant, as long as it was sufficiently large in both cases. Even if you spotted that as a potential flaw, this answer only tells us they were equivalent, not that they were sufficiently large.

(D) Bingo. While this answer choice only talks about new bears, it sets blood- and bone-nitrogen levels as equivalent. This answer strengthens our comparison between old bear bones and new bear blood.

(E) Very tempting! Inverted, however. The argument uses nitrogen levels to conclude something about diet. This answer choice tells us that we can use diet to infer something about nitrogen levels. Also, this answer talks about new bear bones, whereas the argument brings up new bear blood.

Takeaway/Pattern: Comparative arguments are strengthened by relevant similarities (and weakened by relevant differences). Many times, you can figure out over what metric the answer will assert a similarity based on a shift in the comparison in the stimulus.

#officialexplanation

[ChrisB741]

I understand why D is the correct answer, because it is strengthening the blood/bones comparison between the bears.

But, i do not understand why E is incorrect. If the level of heavy nitrogen of any bear fed a meat enriched diet is the same as that in the bones of any other meat eating bear, then this seems to strengthen the comparison between the bears as well. I know that we don't know the level of nitrogen in the bones of the meat-enriched bear, but does it matter? If its the same as any other bear, than it seems to strengthen just as well as as D does.

[NoahY841]

I understand why D is the correct answer, because it is strengthening the blood/bones comparison between the bears.

But, i do not understand why E is incorrect. If the level of heavy nitrogen of any bear fed a meat enriched diet is the same as that in the bones of any other meat eating bear, then this seems to strengthen the comparison between the bears as well. I know that we don't know the level of nitrogen in the bones of the meat-enriched bear, but does it matter? If its the same as any other bear, than it seems to strengthen just as well as as D does.

I thought the same thing. However the level of nitrogen in the bones of any bear fed a meat enriched diet doesn't have to the same as any other meat eating bear. The conclusion states that the prehistoric bears were not exclusively herbivores, it doesn't state that they were necessarily omnivores. Any bear that shows heightened levels of nitrogen indicating a meat-enriched diet would be enough to prove that the population wasn't made up of entirely herbivores. E isn't relevant to the conclusion.

[EmilyL849]

Hi, Gurus

So I have a question on answer choice (E).

I think the reason (E) is wrong is because the comparison used to conclude that old bears were not exclusively herbivores is between bone samples vs. blood samples. So, (E) would support that the level of N in bone samples of bears used in the study are representative of all other meat-eating bears today. However, since the bone samples of today's bears are not used to conclude anything in the stimulus, this would be irrelevant.

What if (E) said the level of heavy N in the BLOOD samples of any bears fed a meat-enriched diet is the same as that in the BLOOD samples of any other meat-eating bears? Another thing that bothers me with this study is the word "meat-enriched". What about the bears eating less meat? What if the level of N in blood samples of those bears is higher, despite eating less meat?" That could mean that the level of N might not be a relevant gauge to determine diet of bears... Or am I stretching too far?
I think a bette way to strengthen, we need to compare the blood samples of meat eating bears to those of herbivore bears today. Because we know that in the old days, herbivores had less N in their tissues than meat-eating animals, we do not know whether that holds true now. If today's herbivores or herbivore bears have the same level of N in their blood, this would definitely weaken the argument.

I am not sure if I am going too far analyzing this.. ugh..

Thank you!

[ohthatpatrick]

I love how you’ve chosen this motif of “Dear Gurus ....”
I’m not sure what the appropriate reciprocation is:
“Dear Person Who is Thirsting for the Truth ... ”?

Anyhoo, I agreed with all of that meticulous analysis.

Since the statement is an equality, it works both ways. So I don’t think it’s “inverted structure” is a concern.

I think you’re right that without knowing whether a meat-enriched diet is a decent comparison for a bear’s natural omnivorous diet, it’s hard to know whether learning from (E) that the bone-nitrogen is the same in both cases is a good or bad thing for the argument.

A far more valuable comparison would be between strictly herbivorous and meat-eating bears.

But the objection that might occur farthest upstream is your initial thought: we don’t so far know anything about nitrogen in the BONES of modern bears. The only thing we’ve heard about is N in the BLOOD, so a useful answer would almost certainly have to take us from that premise to somewhere useful.