New research by Paul Fildes and K. Whitaker challenges

[ShashankB122]

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.

Which of the following most accurately states the
purpose of the passage?
< To defend a scientific hypothesis from attack by an
innovative technique
< To describe a process by which bacteria can be trained
to mutate
< To present the results of an experiment designed to
test an established theory
< To argue against an established protocol on the
grounds that it is outdated
< To challenge a scientific technique used to prove a
questionable theory

OA:- C.

I clicked E. Reason:- Passage opens saying that new research challenges the theory.

Feedback please.

[tim]

Passage opens saying that new research challenges the theory.

Exactly. The new research challenges the theory. The author of the passage just reported on that. The author isn't the one challenging the theory, as E purports.

[ShashankB122]

Passage opens saying that new research challenges the theory.

Exactly. The new research challenges the theory. The author of the passage just reported on that. The author isn't the one challenging the theory, as E purports.

Thanks Tim.
I agree that passage is describing an experiment and author is reporting that experiment.
But main purpose "To present the results of an experiment designed to test an established theory" is still confusing to me. Especially when i read this line " They asserted that the concentration of tryptophan is unrelated to the appearance of these mutants in the bacteria." New experiment is challenging the earlier procedure and author is reporting new experiment in contrast to earlier theory/procedure.

[RonPurewal]

if you're doing an experiment that could potentially support a theory, then you're "testing" the theory.

if you're doing an experiment that could potentially refute a theory, then you're ALSO "testing" the theory.

[RonPurewal]

if this isn't clear, just think about "testing someone's knowledge". that could refer to asking questions in the hope that the person will get them correct ... but it could just as well refer to asking questions in the hope that the person will get them wrong!

[ShashankB122]

Thanks Ron for awesome analogies!!
Such analogies are really helpful to me.

[RonPurewal]

Thanks Ron for awesome analogies!!
Such analogies are really helpful to me.

analogies are how we're wired to learn stuff; our brains do not operate on the basis of "rules". so, yes, you should find them useful--and you should make your own analogies as part of the learning process.