Q16

[lhermary]

I put C and have no clue why the answer is B? 24-26 is my evidence for C.

Thanks

[maryadkins]

Tough passage!

The lines we actually want to look to here are in the last paragraph, which is where the quoted language in the question stem appears (lines 36-38). In this paragraph, we are told that if bacteria detect chemical gradient by measuring it simultaneously at both the front and back of the cell body (line 52), then they "would not respond" to jump in concentration (line 54).

(B) says this. (They don't change their pattern of motion).

The key on this kind of inference question that references a specific portion of the text is to go back to that part of the passage for your answer.

(A) and (C) both give the opposite, that the bacteria's behavior changes.

(D) and (E) are both unsupported. These are not statements that jive with the passage's discussion of bacteria simultaneously measuring concentration of an attractant in the front and back of the cell body.

Hope this helps!

[WaltGrace1983]

I just wanted to add, and I totally had to catch myself from doing this to, is that we are concerned with what happens if the front/back measurement theory is correct. The lines you cited, while particularly helpful to understanding how all this bacteria stuff works, is NOT particularly helpful when it comes to differentiating the theories in some way - which is exactly what we want to do.

What we are given here is like an LR problem. The passage is the stimulus and we are trying to strengthen the argument.

What is the argument's conclusion? It is what is found in #16's stem. So the conclusion is that "Bacteria detect changes in the concentration of an attract by measuring its concentration in front and back of the cell body."

So now we need to use the passage's information to our benefit. What does the passage say about the front/back theory? The passage states that "IF front to back theory....they would not respond to the jump in concentration" (51-55)

(B) matches.