#5 -Bacteria that benefit human beings when they are present

[Administrator]

Complete Question Explanation

Weaken. The correct answer choice is (C)

Here we learn of commensals: bacteria whose presence in the body can be beneficial. Helicobacter
pylori is a bacterium that seems to strengthen the immune system but can also cause stomach ulcers.
Less than a tenth of the people who carry H. pylori actually contract ulcers, so doctors now consider
that bacterium a commensal, or beneficial bacterium, as well.

The author, however, takes issue with this definition, concluding that it is “surely misguided.” This
conclusion is based on the fact that like H. pylori, the tuberculosis bacterium also only strikes about
10% of those who carry it with its associated disease—even so, the author points out, no one would
consider the tuberculosis bacterium a commensal.

The issue here is that the author has limited the analysis to a single data point: percentage of people
affected. Based on the fact that a tenth or less of the people who harbor the bacterium actually
experience the associated respective maladies, the author concludes that the two are similar cases,
and neither bacteria should be called a commensal. There is one glaring omission in the author’s
argument—a benefit associated with H. pylori was specifically mentioned in the stimulus—a
strengthening of the immune response. The author, you may have noticed, failed to mention any
benefits associated with tuberculosis.

The stimulus is followed by a Weaken question, so the correct answer will somehow hurt the
author’s argument, most likely by showing that the author’s analogy is not a great one.

Answer choice (A): The question of whether the two bacteria can be effectively treated with
antibiotics is not relevant to the issue of whether H. pylori should properly be labeled a commensal,
so this choice does not undermine the author’s argument.

Answer choice (B): This incorrect answer choice may have been appealing because the comparison
made here points to tuberculosis as a more lasting condition than stomach ulcers. The relative
lengths of time that one can be affected by each of the two conditions does not undermine the
author’s argument, which is based on the idea that they both are potentially harmful and therefore
neither should be considered a commensal.

Answer choice (C): This is the correct answer choice. If the tuberculosis bacterium provides
people with no benefits, that weakens the author’s comparison between the H. pylori bacterium
and the tuberculosis bacterium. People derive no benefit from the tuberculosis bacterium but they
do benefit from the H. pylori bacterium; this strengthens the scientist’s position that the H. pylori
bacterium is a beneficial commensal, and weakening the author’s argument to the contrary.

Answer choice(D): The fact that fewer people harbor the H. pylori bacterium does not weaken the
author’s point, which is based on percentages: the author’s point is that H. pylori bacteria negatively
affects 10% of carriers, so it should not be considered a beneficial commensal. Since the argument is
not weakened by this choice, this answer can be safely eliminated.

Answer choice (E): The fact that more people harbor H. pylori bacteria does not undermine the
author’s assertion that because H. pylori hurts 10 percent of its carriers, it should not be labeled a
beneficial commensal.

[ericau02]

I reviewed this for blind review and got this right as ac C, but during my PT i was torn between answer choices D and E fro some reason I assumed or thought that the percentage of both pylori and tuberculosis could be around the same 10% but what if it was a bigger group of ppl effected by it ? idk if that makes any sense, i know that this reasoning is incorrect, but I was just wondering if you may be able to help correct me on why it is and for future how to not get this confused with a numbers and percentages question.

[Jay Donnell]

Hi Erica!

Before I jump to the % vs # issues with D and E, I let's make sure that C stands out as correct for the correct reason!

This stimulus uses an argument based on comparison, and as Weaken questions present questionable arguments, the comparison on which it is founded is also definitely questionable.

We know that the percentage of people who harbor Mycobacter tuberculosis bacteria in their stomachs is comparable to the percentage of people who have Helicobacter pylori bacteria in their stomach, so in that sense these two variables on comparable.

However, in arguing against the idea that Helicobacter pylori should be considered a commensal, the author alludes to the tuberculosis causing bacteria in insinuating that since no one would consider that bacteria a commensal, then neither should we in regards to Helicobacter pylori.

That is based off of a similarity between the two bacteria, as if to say "well if its true for X, it must also be true for Y." But, what if there is a significant difference between the two variables? Bringing said difference up in the answers is a very common strategy in Weaken questions based off of comparisons, and that's exactly what happens here with answer choice C.


In regards to D and E here, they both fail to have any real power in attacking the argument since in applying either, we would essentially be committing the fallacy of # and %.

The argument in the stimulus was entirely concerned with the percentage measurements of the two bacterias discussed, so bringing up the number of individuals would then have no effect on the matter in question. That would mean that we are using numerical evidence in a matter of impacting a percentage based conclusion, which in itself is a common issue found in many Flaw questions.

I hope that answers your query but please respond with any points that need more clarification and I am here whenever you need me!