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# Lyme disease is caused by a bacterium transmitted to humans

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09 Aug 2010, 06:36
Agree that Option B is correct, but why is Option D incorrect ?
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09 Aug 2010, 09:55
Food is the bone of contention between the ticks and the third species. We need to evaluate whether the method can limit the population of deer ticks. I hope you got B easily.

D is a scope shift. We are not here to ascertain the ultimate fate of the adolescent deer ticks. The argument here is to evaluate whether the method can limit the population of deer ticks based on the food they eat.

nikhilkatira wrote:
Agree that Option B is correct, but why is Option D incorrect ?

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09 Aug 2010, 13:45
D it is.
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09 Aug 2010, 14:07
nusmavrik wrote:
Food is the bone of contention between the ticks and the third species. We need to evaluate whether the method can limit the population of deer ticks. I hope you got B easily.

D is a scope shift. We are not here to ascertain the ultimate fate of the adolescent deer ticks. The argument here is to evaluate whether the method can limit the population of deer ticks based on the food they eat.

nikhilkatira wrote:
Agree that Option B is correct, but why is Option D incorrect ?

thanks for the explanation, but I am still getting little confused...please help me where am i getting wrong ?

The last sentence of the argument says"If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline. "

So as per option D, what if ticks acquire bacterium after they become adults ?
The overall number will increase...

nusmavrik what am I missing ?
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09 Aug 2010, 22:48
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In GMAT if any answer choice is asking you to bend backwards then probably its wrong - there will be herculean amount of thinking in 2 mins. That's not the technique used to crack.

D means many things hypothetically -
1) The infected number is going to first decrease and then at later point increase linearly causing the final number of infected ticks to remain the same
2) The infected number is going to decrease. Later time when the adults get infected the number is going to rise exponentially.
Basically D depends on lady luck and can take either sides. So D is not the answer. The most important thing is D is a shift in the focus of the argument.

nikhilkatira wrote:
nusmavrik wrote:
Food is the bone of contention between the ticks and the third species. We need to evaluate whether the method can limit the population of deer ticks. I hope you got B easily.

D is a scope shift. We are not here to ascertain the ultimate fate of the adolescent deer ticks. The argument here is to evaluate whether the method can limit the population of deer ticks based on the food they eat.

nikhilkatira wrote:
Agree that Option B is correct, but why is Option D incorrect ?

thanks for the explanation, but I am still getting little confused...please help me where am i getting wrong ?

The last sentence of the argument says"If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline. "

So as per option D, what if ticks acquire bacterium after they become adults ?
The overall number will increase...

nusmavrik what am I missing ?

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20 Aug 2010, 06:42
Quote:

Good question.

B IMO

Say the size of deer tick is limited by availability of animals, ie, if there were more animals to feed upon, their would be more deer ticks, but because there is less food, population of deer ticks is limited. Then when uninfected food (animals) increases, uninfected deer tick population will increase.

However, if the deer tick already has sufficient food (infected or uninfected) there is no guarantee that the tick will feed on the extra uninfected animals. So no guarantee that extra uninfected animals will increase uninfected tick population.

I didn't think about it that way, but your explanation makes sense though I do have a few concerns (though I know B is the right answer).

Question I have though, how will this decrease the population of the infected? If the population is effected by food source, then isn't it plausible that the same amount of larvae will continue to feed on the white-footed mice and that the growing population will feed on the other species? The result of this would not decrease the population of infected.

If the population size does correlate to food source, then we would have the same effect!
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20 Aug 2010, 09:44
I narrowed to B and E but picked E....

Can someone explain why E is incorrect here?
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20 Aug 2010, 12:19
tarn151 wrote:
Quote:

Good question.

B IMO

Say the size of deer tick is limited by availability of animals, ie, if there were more animals to feed upon, their would be more deer ticks, but because there is less food, population of deer ticks is limited. Then when uninfected food (animals) increases, uninfected deer tick population will increase.

However, if the deer tick already has sufficient food (infected or uninfected) there is no guarantee that the tick will feed on the extra uninfected animals. So no guarantee that extra uninfected animals will increase uninfected tick population.

I didn't think about it that way, but your explanation makes sense though I do have a few concerns (though I know B is the right answer).

Question I have though, how will this decrease the population of the infected? If the population is effected by food source, then isn't it plausible that the same amount of larvae will continue to feed on the white-footed mice and that the growing population will feed on the other species? The result of this would not decrease the population of infected.

If the population size does correlate to food source, then we would have the same effect!

It won't decrease the population of the infected, rather it will decrease the "proportion" of the infected larvae in the total population.
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20 Aug 2010, 14:51
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Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

Which of the following would it be most important to ascertain in evaluating the argument?

Conclusion: If the population of the other species increased, the number of ticks acquiring the bacterium would decline.

Premises: The other species do not harbor the bacterium. The ticks generally acquire the bacterium while feeding in the larval stages.

Assumption: That the ticks will feed on the the other species if given the opportunity to do so.

Prediction: The correct answer will address the assumption and strengthen or weaken the conclusion. It will show whether the ticks actually will feed on the other species.

To understand the answer choices more easily, rephrase them without the word whether.

(A) The populations of the other species on which deer tick larvae feed are found only in the areas also inhabited by white-footed mice. Doesn't help us determine whether the ticks will feed on the other species.
(B) The size of the deer tick population is not currently limited by the availability of animals for the tick's larval stage to feed on. In other words, the ticks have plenty of food; the number of ticks is not being held back by the amount of food available. Thus, more food will NOT lead to more ticks. Implication: Any larvae that eat the uninfected food will not increase the total population of ticks but will instead DECREASE the number of ticks getting infected, STRENGTHENING the conclusion that the number of infected ticks will decrease. CORRECT.
(C) The infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice. Outside the scope. The argument is not about how the population can be controlled but about whether the population would increase.
(D) The deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed. Tempting, but incorrect. The argument states that the way the ticks generally get infected is by feeding in the larval stages. This is a premise of the argument and cannot be disputed. Any answer choice that discusses other ways the ticks can get infected is irrelevant. Even if ticks can get infected as adults, this is not the way ticks generally get infected, so who cares? A word of advice: an answer choice that attacks a premise will not be correct. The correct answer will address the assumption, which in this case is that the ticks will feed on the other species.
(E) Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans. Out of scope. The argument isn't about other bacteria.

Hope this helps!

Mitch Hunt
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Last edited by GMATGuruNY on 27 Dec 2014, 08:12, edited 1 time in total.
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20 Aug 2010, 16:02
I think the word "only" in answer A is what makes it invalid. The other species do not have to only be in the white-footed mice habitat for the deer ticks to feed on them. They can be in areas where there are no white-footed mice too, and still be able to lower the probability of deer ticks feeding on white-footed mice in the mice's habitat.
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27 Aug 2010, 13:15
A?
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07 Sep 2010, 00:05
B is the only answer that is relevant to what the question is asking
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29 Mar 2011, 08:31
Crazy question.. it took me like 2 min alone to understand what's going on and who is eating whom and then.. I somehow understood that there is a link between normal food and infected mice, but could not decide between A and B...
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29 Mar 2011, 17:38
same here, this was no doubt a tough one. I got B in 2 minutes and 8 seconds.
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01 May 2011, 09:29
If the size of the deer population is currently limited by the availability of animals for the tick’s larval stage to feed on, although certain other species on which the larvae feed and that do not harbor the bacterium are introduced, the deer ticks are going to still eating white mice, so B.

Hope that helped.
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01 May 2011, 09:57
Central Argument: If populations of *other* species which deer ticks feed on in their larval stage increased, then fewer of the ticks would feed on white-footed mice, then the infection rate of the ticks would go down.

A - Helpful >> species overlap would indicate the possibility for feeding alternatives to the larvae. But the argument is about changes to the alternative species populations, not where they stand now. So I would eliminate.

B - Helpful >> this might be crucial in determining how many ticks themselves make it. If this is the bottleneck for the species' survival, then it would be the crucial time for any potential changes. So if more alternatives are present here, then fewer ticks would be infected.

C - Helpful >> a crash in the mouse population might eliminate the source of the bacteria. But the central argument is about increasing alternatives for the tick to feed on, not eliminating the main source of the Lyme disease bacterium. So while a compelling strategy, doesn't help with the argument.

D - Makes no sense to me >> the central argument is that the mice are the source

E - Irrelevant >> argument doesn't pertain to "other bacteria"

IMHO, B is the best choice -- I've explained above why. But still, this was a very hard question that took me 3 minutes to answer. Great post though!

If there's any hole in my reasoning, I welcome comments. As I can benefit from it too
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24 May 2011, 22:25
its B,stating the presumption that the tick population size may be limited by the availability of food.
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23 Jun 2011, 19:53
It should be B. Since it tells that the ticks only feed in their larval stage and if the white mice is only feed for the deer tick population, it makes sense to increase the other species. BTW, this is tough
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24 Jun 2011, 06:48
Fantastic question!!....And some good explanations given by the Kaplan expert!

B!..but only after spending a couple of minutes to diagram the argument and understand the issues!
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25 Jun 2011, 06:10
B it is.
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