The flagellum, which bacteria use to swim, requires many parts before

Question

The flagellum, which bacteria use to swim, requires many parts before it can propel a bacterium at all. Therefore, an evolutionary ancestor of bacteria that had only a few of these parts would gain no survival advantage from them.

Which one of the following is an assumption on which the argument depends?

(A) Any of bacteria’s evolutionary ancestors that had only a few of the parts of the flagellum would be at a disadvantage relative to similar organisms that had none of these parts.
(B) For parts now incorporated into the flagellum to have aided an organism’s survival, they would have had to help it swim.
(C) All parts of the flagellum are vital to each of its functions.
(D) No evolutionary ancestor of bacteria had only a few of the parts of the flagellum.
(E) Any of bacteria’s evolutionary ancestors that lacked a flagellum also lacked the capacity to swim.

dreamer954 · Answer

Answer B
It clearly acts as a link between how flagellum help in swimming and how swimming is an advantage for survival. And hence it is the right assumption the argument depends on.

Funkenflug · Answer

I think we can exclude E because there could be other ways, not just with the flagellum, in which a bacterium could gain the ability to swim.

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kitipriyanka · Answer

Given : 1. Flagellum -> requires many parts to swim -> In bacteria
Conclusion : ancestor bacteria -> few of these parts -> gain no survival advantage from them

Analysis: Fewer parts had no advantage, so chances are that additional parts (which were missing in ancestor) may have enabled swimming capabilities in bacteria and added survival advantage

(A) Any of bacteria’s evolutionary ancestors that had only a few of the parts of the flagellum would be at a disadvantage relative to similar organisms that had none of these parts. -  we are concerned about the advantages of additional parts and not whether existing parts were a disadvantage. INCORRECT 
(B) For parts now incorporated into the flagellum to have aided an organism’s survival, they would have had to help it swim. -  Aligned with our analysis. CORRECT 
(C) All parts of the flagellum are vital to each of its functions. -  May be or may not be. but we're only concerned about the function wherein it enables swimming and not other functions. INCORRECT 
(D) No evolutionary ancestor of bacteria had only a few of the parts of the flagellum. -  Its given they only had few of these parts. INCORRECT 
(E) Any of bacteria’s evolutionary ancestors that lacked a flagellum also lacked the capacity to swim -  This is an alluring choice. But what we know from the argument is flagellum was missing but we have no idea if this was the only way they could gain capabilities of swimming or there may be other capabilities. So INCORRECT

Hence B

rish2708 · Answer

I think your analysis is not correct. Actually you are saying that there could be other ways that the bacteria could use, but look at the statement again. The statement says that bacteria REQUIRES the flagellum. It's just that the flagellum must have MANY parts. So having MANY PARTS FLAGELLUM is NECESSARY for the bacteria to swim. Thus the bacteria will have to have MANY PARTS FLAGELLUM to swim. Whether it uses other things or not is not part of our discussion and should not be brought in as it would just aid to the confusion. Also, so option E does have no impact on our conclusion? Why Because we are just saying that no flagellum means no swimming. But this does not mean Bacteria will die ( see the option -> no mention of survival) . So we can't say the bacteria will die or not , whether you attach NO FLAGELLUM or FLAGELLUM WITH SOME PARTS. Our reasoning remains as is Thought to clear this fact, because this is common trap

Hope it helps!! Regards, Rishav

Funkenflug · Answer

The original statement claims that "The flagellum, which bacteria use to swim..." Please note that it does not state that a flagellum is required to swim. Option E, in contrast, does and thereby makes a strong, generalizing statement. It simply cannot be correct, and my original argument therefore holds.

On an adjacent note, bacteria swam even before flagella evolved, using a process called "chemotaxis" (and maybe others). This knowledge is not required to answer the question, but I think it serves to further my argument: Option E cannot be correct because there could/are other methods by which bacteria could swim.

rish2708 · Answer

I am sorry but I would beg to differ, but feel free to correct my understanding: The flagellum, which bacteria use to swim, requires many parts before it can propel a bacterium at all. This simply means a bacteria can propel ahead with MANY PARTS FLAGELLUM and it is REQUIRED. ( Am I wrong here?) Assuming, that I am correct with this understanding, can we say that MANY PARTS FLAGELLUM is a REQUIREMENT for propulsion/swimming of bacteria? If it is a REQUIREMENT, can we say it's a NECESSARY condition? And if it's a NECESSARY CONDITION then it's a must and we can't say that there could be OTHER METHODS apart from use of FLAGELLUM WITH MANY PARTS too right? Please help me with this reasoning and let me know where I went wrong ( If I am wrong

) Please note I am not arguing on the point that the answer is incorrect due to this reason. The answer is incorrect ( as you said in your previous post) because it does not link survival to swimming but this reasoning that it can swim with other methods does not go well with me. Hoping for a good discussion here

Regards, Rishav

Funkenflug · Answer

Hello Rishav,

I think it might help to rewrite "The flagellum, which bacteria use to swim, requires many parts before it can propel a bacterium at all." We can isolate the clause and rewrite as "The flagellum requires many parts before it can propel a bacterium at all. The flagellum is used by bacteria to swim." Consequently, the sentence does not express that the flagellum is required for bacteria to swim.

Does this make sense?

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rish2708 · Answer

Oh yes !! I get it

It's actually the flagellum requires many parts to let bacteria swim. Thanks!! I mistakenly confused between flagellum requires many parts with bacteria requires flagellum and this is not the case. Bacteria can use other things too!! Regards, Rishav

vimas · Answer

I have a slightly different explanation for why E is wrong.

The conclusion in the argument is - "Therefore,  an evolutionary ancestor of bacteria that had only a few of these parts  would gain no survival advantage from them."

Now if you look at the bold part in this choice, it talks only about ancestors which had  flagellum with fewer parts .

However option E talks about evolutionary ancestors that lacked a flagellum (Any of  bacteria’s evolutionary ancestors that lacked a flagellum  also lacked the capacity to swim). Therefore this answer choice is not relevant and can be eliminated.

Kudos if you found this helpful.

akela · Answer

Powerscore Complete Question Explanation

Assumption. The correct answer choice is (B)

This stimulus discusses the flagellum, which is used by bacteria to swim and requires many
parts before it can propel the bacteria at all. Based on this premise, the writer concludes that an
evolutionary ancestor of bacteria that had only a few flagellum parts gained no survival advantage
from those parts:

.....  Premise: The flagellum requires many parts in order to propel a bacterium.

.....  Conclusion: A bacterial ancestor that was missing some flagellum parts would gain no survival advantage from the flagellum.

We should note that there is a significant logical leap represented here, from the premise, which
concerns an inability to aid in swimming, to a conclusion about an inability to provide any survival
advantage.

The question stem asks us to identify the assumption on which the stimulus’ conclusion depends.
This is a Supporter Assumption question, and the correct answer choice should link together the two
elements discussed above to allow the author to properly draw the conclusion that an incomplete
flagellum would offer no advantages if it were unable to propel a bacterium.

Answer choice (A): If an incomplete flagellum actually served as a disadvantage, this would justify
the conclusion in the stimulus, but it is not an assumption required by the argument. That is, the
assertion in this answer choice goes beyond what is necessary for the argument to stand—we don’t
need to know that such ancestors would be at a disadvantage—only that there would be no survival
advantage associated with limited parts of the flagellum. Since the assumption provided by this
answer choice is not required by the argument, this answer choice is incorrect.

Answer choice (B): This is the correct answer choice. This answer choice provides the required
link between the survival advantage, the parts of the flagellum and the ability to swim:

..... Premise: The flagellum requires many parts in order to propel a bacterium.

..... Assumption: For the flagellum to offer any survival advantage, it would have to aid in the ability to swim (that is, it would have to be able to propel the bacterium).

..... Conclusion: Therefore, a bacterial ancestor that was missing some flagellum parts would gain no survival advantage from the flagellum.

The above assumption is required to allow the author’s conclusion to be logically drawn from the
premise provided in the stimulus.

Answer choice (C): While this assertion might lend support to the conclusion in the stimulus, it is
not required by the argument, so this answer choice cannot be correct.

To check our work, we can apply the Assumption Negation Technique to determine whether the
negated assumption would weaken the conclusion:

..... “Not all parts of the flagellum are vital to each of its functions.”

Even if some of the flagellum's parts don’t play a role in every flagellum function, this doesn’t
weaken the argument asserting the need for a full flagellum to derive any survival benefits.

Answer choice (D): The fact that no evolutionary ancestor of bacteria had been limited to a few
parts of the flagellum—if this were the case—would not play into the argument, which is phrased
in the conditional tense, asserting that if there were such an ancestor, no survival advantage would
be gained. The assertion in this answer choice is not an assumption required by the argument in the
stimulus.

Again, we can apply the assumption negation technique by determining the effects of the negated
version of the answer choice:

.....  “Some evolutionary ancestors of bacteria had only a few of the parts of the flagellum.”

Since this assertion would not weaken the argument in the stimulus, it is confirmed that this answer
choice does not supply an assumption on which the conclusion relies.

Answer choice (E): This answer choice reinforces a point already covered by the stimulus—that
bacteria use their flagella to swim. This is not, however, an assumption required by the argument,
and since there is no mention of survival advantage, this cannot be the supporter assumption that ties
together the author’s argument.

To check our work, we can apply the assumption negation technique and determine whether the
argument in the stimulus is weakened by the negated version of the answer choice:

..... “Not all of the bacteria’s flagellum-lacking evolutionary ancestors also lacked the capacity to swim.”

Again, this assertion has no effect on the argument that an incomplete flagellum provides no survival
advantage, so this answer choice is incorrect.

VerbalBot · Answer

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The flagellum, which bacteria use to swim, requires many parts before

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The flagellum, which bacteria use to swim, requires many parts before

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