#23 - Scientist: Some colonies of bacteria produce

[Administrator]

Complete Question Explanation

Strengthen. The correct answer choice is (A)

In this stimulus, the scientist presents a hypothesis about the role played in bacteria by phenazines,
which are antibiotic molecules. These molecules are produced by some colonies of bacteria to fend
off other bacteria. But the scientist thinks that the phenazines may also act like molecular pipelines,
allowing interior bacteria access to nutrients that are outside of and surrounding the colony.

Although the scientist may be right about this additional role played by phenazines, the argument
does not contain any evidence supporting the hypothesis other than the presence of these essential
nutrients in the environment surrounding the colony. This is a Strengthen question. Our prephrase is
that the correct answer choice will provide an additional piece of evidence supporting the hypothesis.
There are innumerable ways in which LSAC could support this conclusion, and it is not worth your
time to try to prephrase precisely how the answer choice will do it. Just keep in mind that the correct
answer will support the idea that these nutrients are passed from the outside of the colony to the
interior by phenazines.

Answer choice (A): This is the correct answer choice, because it tells us that when phenazines are
not present there is less need to provide interior bacteria access to exterior nutrients. The flip side of
this answer choice is that when phenazines are present there is a greater need to provide such access.
This is a fairly anemic strengthen answer choice. However, it makes it at least a little more likely that
the hypothesis is correct, and so it strengthens the conclusion.

Answer choice (B): This answer choice is incorrect because it focuses on the wrong role played by
the phenazines. Do not be confused into thinking that the phenazines must either protect against
foreign bacteria or provide interior bacteria access to the exterior nutrients. The hypothesis is that the
phenazines play both roles.

Answer choice (C): It is not clear what effect this answer choice has on the hypothesis, because it
does not tell us whether the interior bacteria thrive along with the colony as a whole. If the interior
bacteria do thrive even in the absence of the phenazines, then that information would attack the
hypothesis. However, we do not know that that is the case.

Answer choice (D): This answer choice supports the fact that one function of phenazines is to protect
against foreign bacteria. However, this information is irrelevant to the hypothesis.

Answer choice (E): This answer choice has no effect on the hypothesis. We cannot be certain that
the interior bacteria are more likely to die because they do not have access to the essential nutrients
surrounding the colony, so this answer choice has no effect on the conclusion. However, if we were
to assume that the reason the interior bacteria are more likely to die is lack of access to the essential
nutrients, then this answer choice would attack the hypothesis.

[Garrett K]

This question really confused me. I understood the stimulus, but I am not sure how I can answer A strengthens the argument more than answer choice D. Answer choice A says that Bacteria that does not produce phenazine form wrinkled surfaces, but how do this play into the argument in any way? I think phenazine only helps provide nutrients to the interior bacteria and fend off foreign bacteria?

Thanks,

Garrett K

[David Boyle]

This question really confused me. I understood the stimulus, but I am not sure how I can answer A strengthens the argument more than answer choice D. Answer choice A says that Bacteria that does not produce phenazine form wrinkled surfaces, but how do this play into the argument in any way? I think phenazine only helps provide nutrients to the interior bacteria and fend off foreign bacteria?

Thanks,

Garrett K

Hello Garrett K,

This does seem like a fairly difficult question. Answer D does seem tempting, though it may not *explain* about how bacteria are fended off, or how phenazines act as pipelines, etc. Answer A at least seems to answer the pipeline issue, by saying that without phenazines, it seems the colony is forced to wrinkle itself to maximize exposure to the nutrients outside. But with the "pipeline" the phenazines provide, the wrinkles aren't needed.
(Maybe the additional surface from the wrinkling, also makes the colony more exposed and thus vulnerable to outside bacteria? so that getting rid of the wrinkles helps fend off those bacteria??)

Hope this helps,
David

[Garrett K]

thanks!

[srcline@noctrl.edu]

Hello

So I am not seeing how A strengthens the argument. The conclusion in this one is that:

phenzines also serve as molecular pipelines give interior bacteria access to essential nutrients in the environment surrounding the colony.

What does wrinkled surfaces have to do with anything?

I thought D was way better at supporting the conclusion, b/c it strengthens that argument overall phenzines are better bacteria.

Thankyou
Sarah

[Adam Tyson]

Glad you asked, Sarah! First, I am going to recommend jettisoning the conditional diagram approach to this question that your question suggests you were using. This argument is not conditional - there is no "if...then" aspect to it. Instead, it's just a fact set - the scientists have a hypothesis that the phenazines provide a pipeline to draw nutrients from outside the colony into the colony interior. Think of it like an access road, or like a literal pipeline, carrying essential stuff from the outside to the middle. That's the thing we want to strengthen, that hypothesis. We aren't concerned with the claim about fending off other bacteria, because that was a premise that we are supposed to just accept as true and it is not a part of the hypothesis that the stem asked about.

Answer D gives us no help because it fails to address the pipeline hypothesis in any way. Instead, it tells us more about the premise, and that's not what the stem asked us to help.

Answer A requires some visualization. Picture the first colony as a circle, perhaps, with pipelines of phenazines like spokes of a wheel, reaching out from the middle to the edges to get at the nutrients on the outside rim. Now, take away the phenazine pipelines - the stuff in the middle is now at a disadvantage, right? Now wrinkle your circle - turn it into something more like a clover. The middle parts are now a lot closer to edges, aren't they? Less need for pipelines to get at the nutrients!

This helps strengthen the hypothesis causally. Where bacteria have phenazines to form pipelines, they don't wrinkle but stay smooth. Take away that cause (pipelines) and the effect (smoothness) goes away, replaced by wrinkles. Neat huh?

Give that some thought and see if it makes sense to you, and if not, come back and let's try again. See you soon either way!

[Leela]

I also struggled with the "wrinkled surfaces" part of A. Adam's visual explanation below was a little helpful, but I'm still confused. The visualization makes sense to me, but I feel like the crux to getting the right answer is in the understanding of the molecular pipeline hypothesis, with little help from the stimulus. Could someone please explain how we are able to get from what is explicitly stated in the stimulus to Adam's visual interpretation?

Answer A requires some visualization. Picture the first colony as a circle, perhaps, with pipelines of phenazines like spokes of a wheel, reaching out from the middle to the edges to get at the nutrients on the outside rim. Now, take away the phenazine pipelines - the stuff in the middle is now at a disadvantage, right? Now wrinkle your circle - turn it into something more like a clover. The middle parts are now a lot closer to edges, aren't they? Less need for pipelines to get at the nutrients!

[Jeremy Press]

Hi Leela!

Adam's visualization is extremely helpful in making better sense of this question, but that specific visualization is not required of you in order to get this question right.

Here's the key: if, according to the hypothesis, the purpose of phenazines is to provide access to essential nutrients in the surrounding environment, that implies a colony of bacteria would have to do something else to get all its members those essential nutrients in the absence of phenazines. After all, essential nutrients are essential, and you have to get them somehow. In other words, as Adam said, remove the cause (phenazines), and the effect (a pipeline allowing the colony to "feed" bacteria distant from the colony's border) goes away as well.

Answer choice A presents a general scenario we'd expect in the absence of phenazines: the colony structures itself in such a way as to "increas[e] the number of bacteria that are in direct contact with the surrounding environment." This, or something like it, is what we'd expect if phenazines do serve the purpose of providing access to essential nutrients: something else, direct contact, now provides colony members access to essential nutrients.

This way of looking at the question doesn't require a perfect visual interpretation. It does require an intense focus on what phenazines are doing (providing access to something essential) and what the colony will need in the absence of phenazines (something else to provide access to that essential thing).

I hope this helps!

Jeremy

[180bound]

Conceptualizing this question was difficult for me. So I am reading that a "colony" of bacteria has its own physical barrier/membrane/boundary and these phenazines exist within these borders? I ask this because it seems that I would have to know/understand this feature in order to be able to successfully conceptualize the idea of a "pipeline". Or am I all wrong here? I had a really hard time seeing all of this in my head and thus this question stumped me pretty good.

[Jeremy Press]

Hi 180bound,

I'm not sure that you necessarily need to imagine a "border" or "membrane," per se, although that would make sense. You're probably right that that's more information than I could strictly pull from the stimulus. Instead, what you need to know at bottom is that some members of the colony are probably cut off from their surrounding environment. You can get this from the language of the hypothesis, which suggests that there are "interior bacteria," naturally read as bacteria on the inside of the colony, and from the language of "pipeline," which is something that serves the function of moving something (in this case essential nutrients) from one place (in this case the surrounding environment) to somewhere else (in this case the interior of the colony, where the interior bacteria reside). Since the phenazines serve that function, at least according to the hypothesis, it's reasonable to envision the interior bacteria as being separated from their surrounding environment. No special knowledge required!

I hope this helps!