Deadpool3 wrote:
Hi
GMATNinja,
Skywalker18 VeritasKarishmaCould you please explain question number 5? Why option C is wrong?
To me, option B seems wrong for the below reason and both A & C seem correct.
Which one of the following best describes the organization of the third paragraph of the passage?
(A) Two approaches to a problem are discussed, a test that would determine which is more efficient is described, and a conclusion is made, based on experimental evidence.
(B) Two hypotheses are described, a way of determining which of them is more likely to be true is discussed, and
one said to be more accurate on the basis of experimental evidence.(C) Two hypotheses are described, the flaws inherent in one of them are elaborated, and experimental evidence confirming the other is cited. -->
isn't uniformity concentration example is used to discuss the flaw in one mechanism?(D) An assertion that a species has adopted two different mechanisms to solve a particular problem is made, and
evidence is then provided in support of that assertion.(E)
An assertion that one mechanism for solving a particular problem is more efficient than another is made, and evidence is then provided in support of that assertion. -->Incomplete
Question 5
Here's the first piece of the third paragraph:
"Biologists have proposed two mechanisms that bacteria might use in detecting changes in the concentration of a chemical attractant. First, a bacterium might compare the concentration of a chemical at the front and back of its cell body simultaneously. If the concentration is higher at the front of the cell, then it knows it is moving up the concentration gradient, from an area where the concentration is lower to an area where it is higher. Alternatively, it might measure the concentration at one instant and again after a brief interval, in which case the bacterium must retain a memory of the initial concentration."
Here, the author describes two mechanisms that bacteria
might use in a certain behavior. Let's see how that stacks up against our answer choices:
Quote:
(A) Two approaches to a problem are discussed...
(B) Two hypotheses are described...
(C) Two hypotheses are described...
(D) An assertion that a species has adopted two different mechanisms to solve a particular problem is made...
(E) An assertion that one mechanism for solving a particular problem is more efficient than another is made....
(B) and (C) are looking good! The biologists have two ideas that
might explain a certain behavior. This fits well with the word "hypothesis," which means a proposed explanation that requires further testing.
(D) and (E) are plain wrong. Biologists believe that bacteria use one mechanism OR the other, not BOTH mechanisms. For this reason, (D) is out. (E) misses the initial description of the two proposed mechanisms entirely, so it's not a good fit to describe the organization of the passage as a whole.
At this point, I'd say that (A) is on thin ice. The "problem" discussed in the paragraph is how bacteria detect changes in the concentration of a chemical attractant. Stating that two
approaches to this problem are discussed seems to imply that the
bacteria themselves have a couple of approaches to the problem -- which is a bit of a stretch. The alternative -- that the
biologists have two approaches to the problem -- doesn't really work either. They have proposed two different explanations, but are not fundamentally approaching the issue from two different directions.
(A) isn't looking great, but let's look at the second half of the paragraph to see whether it fits.
"Researchers reasoned that if bacteria do compare concentrations at different times, then when suddenly exposed to a uniformly high concentration of an attractant, the cells would behave as if they were swimming up a concentration gradient, with long, smooth runs and relatively few tumbles. If, on the other hand, bacteria detect a chemical gradient by measuring it simultaneously at two distinct points, front and back, on the cell body, they would not respond to the jump in concentration because the concentration of the attractant in front and back of the cells, though high, would be uniform. Experimental evidence suggests that bacteria compare concentrations at different times."
Here, the biologists come up with a test that would support one of their proposed ideas over the other, depending on the result of the experiment. In the last sentence ("Experimental evidence suggests that bacteria compare concentrations at different times"), we learn that the biologists did in fact perform the experiment, and it supported the second of the two proposed mechanisms.
Let's see how that matches up with our remaining answer choices:
Quote:
(A) Two approaches to a problem are discussed, a test that would determine which is more efficient is described, and a conclusion is made, based on experimental evidence.
The main issue with the second piece of (A) is "a test that would determine
which is more efficient is described..." The test outlined in the passage doesn't determine which mechanism is more efficient -- it just determines which one the bacteria
actually use. This is the death blow for (A), which was already not looking great.
Quote:
(B) Two hypotheses are described, a way of determining which of them is more likely to be true is discussed, and one said to be more accurate on the basis of experimental evidence.
This fits nicely! The biologists came up with a test that would help them determine which of their ideas was accurate. Then, based on evidence from that experiment, the second idea was supported over the first.
(B) is looking good.
Quote:
(C) Two hypotheses are described, the flaws inherent in one of them are elaborated, and experimental evidence confirming the other is cited.
The biggest difference between (B) and (C) is the phrase "the flaws inherent in one of [the hypotheses] are elaborated." So, does the passage elaborate on the flaws of one of the hypotheses?
Not that I can see. Up until the very last sentence, the passage is neutral toward both hypotheses. The author doesn't weigh in on one side or the other -- instead, he/she just describes the two possibilities, then lays out a test that will support one idea over the other. Because the author does not elaborate on the flaws of one hypothesis before revealing that the experiment supported the second hypothesis, we can eliminate (C).
I hope that helps!