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]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] 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]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

OA:

PLEASE EXPLAIN ANSWERS..

thanks for the explanations kudos..

From these experiments, Fildes and Whitaker conclude that the:
1. Mutants are of genetic origin and are not induced by environmental training.
2. The concentration of tryptophan is unrelated to the appearance of these mutants in the bacteria.

Now, to confirm these results, Fildes and Whitaker used an innovative plating technique using pile fabrics, ... demonstrated that the mutants were in fact genetically present or preadapted, as the identical locations of the mutant strains of bacteria on the replica plates...


If the mutants were not already present, then the locations would be different rather than identical. This is what is stated in the last sentence of the passage.

[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 [Irrelevant]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. [Out of scope]

D) It demonstrates that no tryptophan was present in the original agar culture. [This is opposite of what is stated above]

E) It establishes that the original agar culture contained the necessary metabolites for bacterial reproduction. [No such findings in the plating method]




_________________

Want to improve your CR: http://gmatclub.com/forum/cr-methods-an-approach-to-find-the-best-answers-93146.html
Tricky Quant problems: http://gmatclub.com/forum/50-tricky-questions-92834.html
Important Grammer Fundamentals: http://gmatclub.com/forum/key-fundamentals-of-grammer-our-crucial-learnings-on-sc-93659.html

GMATNinja Sir could you please help me in such passages, they seem too much convoluted to me - also, the OA mentioned for the Primary Purpose question seems wrong to me. How to approach such passages - especially question 1?
_________________

A lot needs to be learned from all of you.

Hi,

Can you post the OE for 2 question?

Regards
_________________

Kudos if my post helps!

Long And A Fruitful Journey - V21 to V41; If I can, So Can You!!

My study resources:
1. Useful Formulae, Concepts and Tricks-Quant
2. e-GMAT's ALL SC Compilation
3. LSAT RC compilation
4. Actual LSAT CR collection by Broal
5. QOTD RC (Carcass)
6. Challange OG RC
7. GMAT Prep Challenge RC