New research by Paul Fildes and K. Whitaker challenges the theory that

Question

New research by Paul Fildes and K. Whitaker challenges the theory that strains of bacteria can be "trained" to mutate by withholding a metabolite necessary for their regular function. In particular, they consider the case of bacteria typhosum, which needs tryptophan in order to reproduce. Earlier researchers had grown the bacteria in a medium somewhat deficient in tryptophan and observed the growth of mutant strains of the bacteria which did not need tryptophan in order to reproduce.

Fildes and Whitaker argue that the withholding of tryptophan did not induce these mutant strains of bacteria. Rather, these mutants were already present in the original sample of bacteria typhosum, albeit in a concentration too small to detect. In experimenting with the bacteria grown in agar cultures, they found that by plating out huge quantities of the bacteria, one could locate mutant strains. Because of the possibility that the lack of uniformity of the agar cultures had in fact trained mutant strains, they conducted similar experiments with liquid cultures and again found that mutant strains of the bacteria were present in the original sampling. From these experiments, Fildes and Whitaker conclude that the mutants are of genetic origin and are not induced by environmental training. They asserted that the concentration of tryptophan is unrelated to the appearance of these mutants in the bacteria.

To confirm these results, Fildes and Whitaker used an innovative plating technique using pile fabrics, such as velvet or velveteen, to accurately imprint the growth found on an original agar plate to a series of replica agar plates. The process entails taking the original agar plate, inverting it onto the velvet while using light finger pressure to transfer growth, and then imprinting the fabric, with its pattern of growth, on the new agar plates. By using this replica plating method, Fildes and Whitaker demonstrated that the mutants were in fact genetically present or preadapted, as the locations of the mutant strains of bacteria on the replica plates were identical to the locations of the mutant strains on the original agar plate.   1 
 1. It can be inferred from the passage that the replica plating method is effective for which of the following reasons?

A. It allows researchers to determine the relative sizes of different populations of bacteria.
B. It shows that no new mutant strains developed after transfer from the original agar plate.
C. It eliminates the possibility that the agar culture was contaminated by a different type of bacteria. 
D. It demonstrates that no tryptophan was present in the original agar culture.
E. It establishes that the original agar culture contained the necessary metabolites for bacterial reproduction.

2 
 2. Which of the following most accurately states the purpose of the passage?

A. To defend a scientific hypothesis from attack by an innovative technique
B. To describe a process by which bacteria can be trained to mutate
C. To present the results of an experiment designed to test an established theory
D. To argue against an established protocol on the grounds that it is outdated
E. To challenge a scientific technique used to prove a questionable theory

3 
 3. According to the passage, Fildes and Whitaker conducted the experiment with liquid culture because

A. agar culture contained tryptophan
B. liquid culture allowed for easier plating
C. agar culture could not support a sufficiently large number of bacteria
D. liquid culture offered a more consistent medium
E. agar culture did not adhere well to pile fabric

TaN1213 · Answer

2. Which of the following most accurately states the purpose of the passage?

A. To defend a scientific hypothesis from attack by an innovative technique
B. To describe a process by which bacteria can be trained to mutate
C. To present the results of an experiment designed to test an established theory
D. To argue against an established protocol on the grounds that it is outdated
E. To challenge a scientific technique used to prove a questionable theory

(A) The “innovative technique” is the replica plating method discussed in the third paragraph. This technique was used to support the scientific hypothesis of Fildes and Whitaker. Thus, the passage did not need to “defend   scientific hypothesis from attack by   innovative technique.” In addition, the passage did not even defend the theory that Fildes and Whitaker were challenging.

(B) The first sentence of the passage makes it clear that the focus will be to “challenge the theory that strains of bacteria can be “trained” to mutate,”

(C) CORRECT.  The second and third paragraphs discuss the experiments performed by Fildes and Whitaker that were designed to test the established theory, mentioned in the first paragraph, that “strains of bacteria can be “trained” to mutate.” This answer choice summarizes the entire passage.

(D) Fildes and Whitaker argue against a theory, not an established protocol. There is no mention in the passage that a particular protocol is outdated.

(E) The passage does not state that either Fildes and Whitaker’s theory, or the theory they were challenging was questionable.

HimanshuW11 · Answer

1. It can be inferred from the passage that the replica plating method is effective for which of the following reasons?

A. It allows researchers to determine the relative sizes of different populations of bacteria.
B. It shows that no new mutant strains developed after transfer from the original agar plate.
C. It eliminates the possibility that the agar culture was contaminated by a different type of bacteria.
D. It demonstrates that no tryptophan was present in the original agar culture.
E. It establishes that the original agar culture contained the necessary metabolites for bacterial reproduction.

The replica plating method is discussed in the third paragraph. The first two sentences describe the process, while the third sentence explains what was learned by using this method. The correct inference about the effectiveness of the replica plating method will be a virtual rephrasing of the facts presented in the third paragraph.

(A) We cannot infer that the replica plating method allows researchers to determine the relative sizes of different populations of bacteria. The population sizes of various bacteria populations were never discussed.

(B) CORRECT.  The last sentence of the passage states that “the locations of the mutant strains of bacteria on the replica plates were identical to the locations of the mutant strains on the original agar plate,” citing this as proof that “the mutants were in fact genetically present or preadapted.” In other words, the mutant strains did not develop after transfer from the original agar plate.

(C) The only type of bacteria mentioned in the passage was bacteria typhosum, so we cannot infer that the replica plating method eliminates the possibility that the agar culture was contaminated by a different type of bacteria.

(D) The role of tryptophan is discussed in the first and second paragraphs. This answer choice goes too far by asserting that “no tryptophan was present in the original agar culture.” We do not have enough information to make that inference.

(E) According to the first paragraph, “the necessary metabolites for bacterial reproduction” are defined as the substances “necessary for their (bacteria’s) regular function.” In the case of bacteria typhosum, that substance is tryptophan. We do not have enough information to infer that the replica plating method establishes that the original agar culture contained tryptophan. If fact, the presence of mutant strains of bacteria on the replica plates would contradict this statement rather than support it.

generis · Answer

Option E is an easier call than it appears to be.
Compare options C and E.

C.  To present the results of an experiment designed to test   an established theory

E. To challenge a  scientific technique  used to prove a   questionable theory

Answer E is incorrect for a few reasons. The big problems:

1. The main thrust is not about F and W challenging a  technique . 
Their work challenges  the theory .

The results of F and K's experiments -- what they found, what they concluded --
are mentioned three times in the passage 
The main narrative is: 
THEORY exists . . . 
F and W experiment . . . 
the results of their experiments challenge the theory.
(E) fails to mention those results.

2. The theory is not questionable. The theory is established.

****

• (1) This passage is not about challenging a technique, but rather is about experimental results that challenge a theory

F and W did not challenge a technique. They challenged a theory. 
The  very first sentence  says that 
"New research by F and W  challenges  the theory   that 
strains of bacteria can be 'trained' to mutate by withholding a metabolite necessary for their regular function."

That sentence opens the passage.

We must not be distracted by mentions of "innovative technique" 
or excruciatingly detailed descriptions of experimental steps.

If a technique or an experiment is mentioned, the mention is
connected to or in the context of  results that challenge the theory. 
(See below. I discuss textual support for C.)

E's emphasis on the other scientists' technique goes too far and is too specific 
If the main purpose were to challenge to a scientific technique,
the passage would contain a lot more information
about the other scientists' technique,
probably some challenge to their method and methodology, 
and much less mention of the theory's content.

There is not much criticism.

One sentence indicates that "catching" the already-present mutants is difficult.
That statement is not an indictment of or challenge to technique, but rather, 
a matter-of-fact reason that F and W
did other experiments . . .

. . . all of whose  results are mentioned ,
and all of whose results challenge the theory, not a scientific technique.
 
"Technique" has very little to do with the main thrust of the passage.

The passage is about experimental results that challenge the theory.

References to the theory are numerous (repeating or alluding to the first sentence)
-- First sentence of Paragraph 2:
  Fildes and Whitaker argue that the withholding of tryptophan did not induce these mutant strains of bacteria.

-- Last two sentences of Paragraph 2:
Fildes and Whitaker conclude that the  mutants are of genetic origin and are not induced by environmental training . 
They asserted that  the concentration of tryptophan is unrelated to the appearance of these mutants  in the bacteria.

-- First sentence of Paragraph 3:
To confirm  these results  (that contradict the theory)
  . . .

-- One part of the last sentence of Paragraph 3:
F and W  demonstrated that the  mutants were in fact genetically present or preadapted

F and W's purpose? To test the theory. Results challenged the theory.

-- F and W figured out that the other scientists who tested this bacterium
had missed an important detail that was easy to miss. 
Two times F and W simply tested whether they could locate the easy-to-miss markers.
They did so through experiments described in paragraph two.
Then they used an innovative technique described in the last paragraph to confirm their conclusion that 
the mutation was already present, not created by environmental stress.

But the point of first finding and then confirming the prior existence of
 already -mutated genes was to challenge the theory,
not to challenge the technique that the other scientists used.

The experiments and techniques were means to an end,
means by which F and W draw this theory-challenging conclusion:

Fildes and Whitaker conclude that the mutants  are of genetic origin 
and are not induced by environmental training. 
They asserted that the concentration of tryptophan is unrelated 
to the appearance of these mutants in the bacteria. 
Those sentences challenge the theory. Not a technique.

• (2) The theory is  not  questionable. In fact, the theory is established.

First line of the passage:
New research by Fildes and Whitaker challenges    the   theory  that 
strains of bacteria can be “trained” to mutate by XYZ.

In  particular , they consider  the case    of 
bacteria typhosum that needs tryptophan in order to reproduce. 
Earlier researchers  THE  THEORY] 
had grown the bacteria in a medium somewhat deficient in tryptophan. 
Result: mutant strains grew. 
  conclusion: the mutant strains that did not need tryptophan to grow were created by withholding tryptophan.

In their own experiment, F and W proved that in this one case, 
gene mutation was not caused by "training," as per the theory.

Now the theory, as paragraph one states, is challengED.

A theory introduced with "the" that has been challenged by the results of one experiment
is not "questionable." 
Questionable implies "probably not correct."

One example that does not fit the theory 
does not make a theory questionable in that sense.

The theory has been challenged. It may need to be tweaked.
It may need to be abandoned altogether after a critical mass of experiments. We do not know.

But the verb is  challenges . 
The article is definite: THE theory.

In one case, two researches proved that a certain bacterium 
under certain conditions was not "trained" to mutate.
The bacterium already had mutated.

F and W ran experiments to determine whether
mutant genes were detectable (yes) prior to environmental stress
and whether the genes were already mutated (yes).
Those results challenge the theory.

Option (C) is correct.
Option E is too narrow, too focused, and does not agree with the very first sentence of the passage.

Hope that helps.

VerbalBot · Answer

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New research by Paul Fildes and K. Whitaker challenges the theory that

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