Why is it (C)??
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- ohthatpatrick
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Atticus Finch
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Re: Q19
I can see why (E) was super tempting.
In the second paragraph, the passage says that the closer a bacterium gets to an attractant, the more the bacterium travels in straight runs (the less frequently it randomly tumbles).
Of course, this is LSAT, so "the closer a bacterium gets to an attractant" is rephrased in (C) as "the bacterium detects changes in the concentrations of an attractant".
Lines 23-26 are the most direct support for (C).
The third paragraph sought to answer "HOW does a bacterium detect changes in concentration?"
Two hypotheses were considered:
- comparing concentrations at its head vs. its feet
- comparing concentrations now vs. a second ago
They ended up picking the 2nd one, as you noted, in the last sentence of the passage.
But (E) is talking about changing 'intervals of time'. The passage wasn't saying that the bacterium takes a sample once every second, then once every five seconds, then once every eight seconds, etc.
It was saying (or at least implying) that the bacterium takes a sample at a REGULAR interval of time and notes whether the CONCENTRATION has changed.
Hope this helps.
In the second paragraph, the passage says that the closer a bacterium gets to an attractant, the more the bacterium travels in straight runs (the less frequently it randomly tumbles).
Of course, this is LSAT, so "the closer a bacterium gets to an attractant" is rephrased in (C) as "the bacterium detects changes in the concentrations of an attractant".
Lines 23-26 are the most direct support for (C).
The third paragraph sought to answer "HOW does a bacterium detect changes in concentration?"
Two hypotheses were considered:
- comparing concentrations at its head vs. its feet
- comparing concentrations now vs. a second ago
They ended up picking the 2nd one, as you noted, in the last sentence of the passage.
But (E) is talking about changing 'intervals of time'. The passage wasn't saying that the bacterium takes a sample once every second, then once every five seconds, then once every eight seconds, etc.
It was saying (or at least implying) that the bacterium takes a sample at a REGULAR interval of time and notes whether the CONCENTRATION has changed.
Hope this helps.
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- WaltGrace1983
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Atticus Finch
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Re: Q19
I thought (A) was super tempting but is it wrong because it is talking about the kinds of chemical attractants present? We don't need to differentiate one attractant from another attractant. They are both good and would, seemingly, lead to the same/similar patterns of movement. There seems to be support (lines 4-5) that bacteria also move according to the kinds of substances - i.e. harmful substances vs. attractants. If (A) would have said "kinds of substances" rather than "kinds of chemical attractants," would it be right?
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- ohthatpatrick
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Atticus Finch
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Re: Q19
Yeah, I see what you're saying.
You're correct that (A) is wrong because we're never talking about them reacting to one attractant more than (or differently from) another attractant.
Meanwhile, line 3-5 indicates they are attracted TO some things and repelled AWAY from another, so if you tweaked the wording of (A) to deal with "needed material vs. harmful substance" then you would be correctly describing a reason that a bacterium's motion would change.
However, the "PATTERN that characterizes the bacterium's motion" is the whole straight run / random tumble pattern. What causes THAT pattern to change?
Sensitivity to concentration of an attractant.
THAT's when we see longer straight runs and fewer random tumbles.
(B) is off because we don't discuss bacterium adopting different mechanisms (we're speculating at one point about WHICH mechanism is used to detect concentration, but we're not implying that the bacterium possesses BOTH methods and adopts one or the other at different times)
(D) is off because we never talk about neighboring bacteria's tumbling.
You're correct that (A) is wrong because we're never talking about them reacting to one attractant more than (or differently from) another attractant.
Meanwhile, line 3-5 indicates they are attracted TO some things and repelled AWAY from another, so if you tweaked the wording of (A) to deal with "needed material vs. harmful substance" then you would be correctly describing a reason that a bacterium's motion would change.
However, the "PATTERN that characterizes the bacterium's motion" is the whole straight run / random tumble pattern. What causes THAT pattern to change?
Sensitivity to concentration of an attractant.
THAT's when we see longer straight runs and fewer random tumbles.
(B) is off because we don't discuss bacterium adopting different mechanisms (we're speculating at one point about WHICH mechanism is used to detect concentration, but we're not implying that the bacterium possesses BOTH methods and adopts one or the other at different times)
(D) is off because we never talk about neighboring bacteria's tumbling.
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- MeenaV936
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Jackie Chiles
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Re: Q19
Would this also be a valid explanation for why E is wrong?
The PATTERN of motion changes in response to detecting concentrations of attractants, but whether or not any motion occurs at all is based on measuring the changes in interval measurement. So E is wrong because it deals with changes in interval measurement (whether motion occurs at all), not the concentration (pattern of motion).
The PATTERN of motion changes in response to detecting concentrations of attractants, but whether or not any motion occurs at all is based on measuring the changes in interval measurement. So E is wrong because it deals with changes in interval measurement (whether motion occurs at all), not the concentration (pattern of motion).
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- ohthatpatrick
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Atticus Finch
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Re: Q19
Hmmm, that doesn't sound quite right to me.
1. I don't think the passage ever deals with [whether any motion occurs at all]. I get the impression that they're always swimming with some pattern of runs and tumbles. Do you see anywhere in the passage where it discusses a bacterium that has just stopped and is waiting for an interval before it moves again?
2. At no point in the passage do they talk about the interval of time between measurements changing. (E) is saying "sometimes they wait 1 second before measuring concentration again ... sometimes they wait 5 seconds before measuring concentration again .... and their swimming pattern is affected by whether they measure once every second or once every five seconds". There's nothing like that in the passage.
You're making it sound like, "We DID talk about that, but in reference to something else",
but I think the passage never talked about changing the interval between measurements at all.
1. I don't think the passage ever deals with [whether any motion occurs at all]. I get the impression that they're always swimming with some pattern of runs and tumbles. Do you see anywhere in the passage where it discusses a bacterium that has just stopped and is waiting for an interval before it moves again?
2. At no point in the passage do they talk about the interval of time between measurements changing. (E) is saying "sometimes they wait 1 second before measuring concentration again ... sometimes they wait 5 seconds before measuring concentration again .... and their swimming pattern is affected by whether they measure once every second or once every five seconds". There's nothing like that in the passage.
You're making it sound like, "We DID talk about that, but in reference to something else",
but I think the passage never talked about changing the interval between measurements at all.
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