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Sub 505 Level|   Long Passage|   Science|                              
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avigutman can you pls clarify the role of 'if not self regulating' in 'insect populations, if not self-regulating, MAY at least be regulated by an agent MORE intimately connected with the insect THAN are predatory birds or parasites? What does it mean exactly'? What drew the author to say it is not self regulating based on the fact that predators are not the reason? GMATNinja @jonshukruat @ronpuruwel AndrewN MartyTargetTestPrep @gmatwhizz egmat

Also not clear on Q6 wh not A? We can say that predators have been decreasing due to which they have not been able to measure the impact correctly and draw a linkage b/w predators and population cycles due to which the claim about this missing linkage is wrong. And in Q6 how do we identify that
example of habitats' is not considered as self - regulating or intimately connected when we dont really know the definition of these terms?'
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dear GMATNinjaTwo, VeritasKarishma, MartyTargetTestPrep, AndrewN,VeritasPrepBrian,GMATRockstar
KarishmaB

avigutman, AndrewN,MartyTargetTestPrep ,

I am struggled with this question,
RC00120-01.
Quote:
Which of the following, if true, would most weaken the author???s conclusion in lines 18-22?

(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
(B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
(C) Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
(D) Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
(E) Viral disease is typically observed in a large proportion of the lepidoptera population.

I haven't gotten where my mistakes are.
my reasoning is as following:
the author points out the evidence implies that the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.
what the evidence refers to ? obviously, the evidence is mentioned in the earlier part in P1,
Quote:
The common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites, has been unproductive in the case of lepidoptera. Moreover, population ecologists??? attempts to alter cycles by changing the caterpillars??? habitat and by reducing caterpillar populations have not succeeded.
in other words, predatory birds or parasites are unproductive, which leads to picked up A, A implies the birds or parasites have dropped significantly, so there are insufficient birds or parasites, so if insufficient, even the result is unproductive, it is hard to say birds or parasites are not the driving force. maybe they are the driving force, but they are so few that you cannot get the whether they are driving force or not, so we cannot rule out this potential driving forces, therefore, weaken the conclusion.

and I am also confused by C
if virus are present on birds or parasites, additional the evidence above, you can infer both virus and birds or parasites are not the driving forces.

appreciate your help.
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Dear experts,
Can you please explain the correct answer choice for Question 1?
It says, "develop an explanation for the existence of lepidoptera population cycles." What confuses me here is we already know that the mentioned population cycle exists. We are trying to find out why the cycle occurs. Is it appropriate to say, "develop an explanation for the existence of lepidoptera population cycles?"
Thank you so much.
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Question 1



idilbayar
Dear experts,

Can you please explain the correct answer choice for Question 1?

It says, "develop an explanation for the existence of lepidoptera population cycles." What confuses me here is we already know that the mentioned population cycle exists. We are trying to find out why the cycle occurs. Is it appropriate to say, "develop an explanation for the existence of lepidoptera population cycles?"

Thank you so much.
You're right that scientists are looking for why the population cycle occurs. That's exactly what (A) is getting after: "develop an explanation for the existence of lepidoptera population cycles."

While scientists know that the population cycle exists, they still can't explain why it exists. So, they investigated parasites and predatory birds to find that explanation.

(A) is the correct answer for question 1.

I hope that helps!
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Question 6


zoezhuyan
dear GMATNinjaTwo,

I am struggled with this question,

RC00120-01.
Quote:
Which of the following, if true, would most weaken the author???s conclusion in lines 18-22?

(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.

(B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.

(C) Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.

(D) Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.

(E) Viral disease is typically observed in a large proportion of the lepidoptera population.

I haven't gotten where my mistakes are.

my reasoning is as following:

the author points out the evidence implies that the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.

what the evidence refers to ? obviously, the evidence is mentioned in the earlier part in P1,

Quote:
The common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites, has been unproductive in the case of lepidoptera. Moreover, population ecologists??? attempts to alter cycles by changing the caterpillars??? habitat and by reducing caterpillar populations have not succeeded.

in other words, predatory birds or parasites are unproductive, which leads to picked up A, A implies the birds or parasites have dropped significantly, so there are insufficient birds or parasites, so if insufficient, even the result is unproductive, it is hard to say birds or parasites are not the driving force. maybe they are the driving force, but they are so few that you cannot get the whether they are driving force or not, so we cannot rule out this potential driving forces, therefore, weaken the conclusion.

and I am also confused by C

if virus are present on birds or parasites, additional the evidence above, you can infer both virus and birds or parasites are not the driving forces.

appreciate your help.
You raise good points about (A) and (C)! Before we analyze them, let's quickly reiterate the author's conclusion at the end of the first paragraph.

Quote:
In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.
As you say, the author supports this conclusion by noting that studies about potential causes (such as predatory birds or parasites) have failed to explain the changes in lepidoptera populations.

Here's (A) again:

Quote:
Which of the following, if true, would most weaken the author’s conclusion in lines 18-22?

(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
Does this cast doubt on the idea that lepidoptera are regulated by an agent other than parasites or predatory birds? The problem is, this doesn't give us very much information. So drawing that conclusion would require a number of leaps. Is it possible that the drop in the number of bird and parasite species has prevented them from regulating lepidoptera? Possibly, but that would require a pretty big assumption, so we can't safely draw that conclusion.

From another angle: even if we did make the above assumption, we don't really know when the studies were carried out. Was it before the drop? After the drop? Again, to draw any conclusions at this point would require us to make unfounded leaps.

So, since (A) doesn't give us enough information to safely draw any useful conclusions, we can eliminate it.

Let's look at (C):

Quote:
Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
Does this weaken the author's conclusion? Not really. Keep in mind that the author's conclusion in lines 18-22 is NOT that the virus is definitely regulating lepidoptera populations. Instead, the conclusion is that something "more intimately connected to the insect" is regulating lepidoptera. The fact that the virus is present "in a number of predators and parasites" doesn't weaken the idea that something aside from predators or parasites is at play.

For that reason, we can eliminate (C).

I hope that helps!
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Quote:
6. Which of the following, if true, would most weaken the author’s conclusion in lines 25- 30 (bold lines)?
This question asks us to flex our CR muscles, but let's first take a moment to nail down the structure and purpose of this passage:

  • In paragraph 1, the author explains that a small number of lepidoptera species exhibit population cycles, and states that the driving force behind these cycles is difficult to identify. The author concludes that this driving force may be intimately connected to the insect itself, rather than being connected to the insect's predators or parasites.
  • In paragraph 2, the author presents recent work, which suggests that this driving force (a.k.a. the agent regulating population cycles) may be a virus.
  • In paragraph 3, the author notes that the virus hypothesis is attractive because it seems broadly applicable across different lepidoptera species.

OK, now let's revisit the conclusion being highlighted:

Quote:
In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.
The author concludes that whatever is regulating the population cycle is closer to the insect than it is to predatory birds or parasites. Here's how the author reaches this conclusion:

  • Studying predatory birds and parasites, thought to be potential agents, has been unproductive in the case of lepidoptera.
  • Recent study of viral disease, thanks to new techniques of molecular biology, has identified nuclear polyhedrosis viruses as a more likely agent.
  • Polyhedrosis viruses follow an infectious cycle that is intimately linked to lepidoptera, in which lepidoptera ingest the virus in the form of crystals, incubate new virus particles within their bodies, and release these crystals back into the environment upon dying.

If we're looking to weaken this conclusion, we need an answer choice that either:

  • contradicts what we've read about this link between polyhedrosis viruses and lepidoptera, or
  • delivers evidence that some other regulating agent is even more likely to be the driving force of these population cycles.

Now let's use process of elimination to go through all five choices.

Quote:
(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
This choice actually strengthens the conclusion, because it adds evidence that other potential agents (predatory birds and parasites) have significantly decreased in number in recent years. This reinforces what the author stated plainly in paragraph 1. Eliminate (A).

Quote:
(B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
This choice introduces new evidence that the regulating agent we're all looking for might be intimately linked to the habitats of lepidoptera, after all. Most importantly, this choice tells us that whatever these experiments did to habitats, that action definitely resulted in the shortening of lepidoptera population cycles. We'll keep choice (B) because it provides proof that another agent--habitat--can regulate population cycles.

bpdulog
I was down to B and C but went with C since the later part of the line dismisses the relationship with predators and the driving force of the life cycle
Quote:
(C) Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
Knowing that the nuclear polyhedrosis virus is present in a number of predators and parasites doesn't change anything we've read about the nuclear polyhedrosis virus and its link to lepidoptera. The author's conclusion does not depend on this virus existing only in lepidoptera. And the language of this answer choice doesn't include any dismissal of the intimate link between polyhedrosis viruses and lepidoptera. It simply points out that the virus is also present in predators and parasites of lepidoptera.

(C) doesn't contradict the impact of nuclear polyhedrosis viruses or provide an alternative agent, so we'll eliminate (C).

gauravmarwaha
I could easily eliminate options E, C and A and chose option D over B. Can someone help?
Quote:
(D) Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
Choice (D) does identify a potential alternative agent: weather. However, the logical statement made here is quite weak. (D) tells us that it's difficult to assess the effects of weather on lepidoptera population cycles. So even if it's possible for weather to affect these population cycles, we have no way of confirming whether that effect is actually taking place.

Likewise, I could say, "It's difficult to assess the effects of the lunar cycle on lepidoptera," but this wouldn't make me jump up and say that lunar cycles are likely to be more of a driving force of lepidoptera population cycles than nuclear polyhedrosis viruses. We're not interested in hypothetical effects that are difficult to assess. We're interested in proof that an alternative agent is truly at work. That's why we eliminate (D).

Quote:
(E) Viral disease is typically observed in a large proportion of the lepidoptera population.
This choice doesn't affect the conclusion. Much like Choice (C), it tells us a little more about the presence of viral disease in lepidoptera populations, but it doesn't mention polyhedrosis viruses and doesn't provide evidence of any alternative agent regulating population cycles. Eliminate (E).

Whew! This may have taken me an entire population cycle to write. (Yes, more bad Dad jokes. I'm practicing them. There's no "negative kudos" button, so you're stuck with them.) After all of that, (B) is the only choice that presents evidence of a regulating agent that is NOT intimately linked to the insect (instead, the agent is linked to the insect's habitat). So we keep (B) and move on.

I hope this helps!

Hey GMATNinja , Author is concluding that there is some other agent that is affecting insect's population more than birds and parasite. So a possible weakener would be to show that birds and parasites are indeed on same or greater level than this other agent. Please let me know if I am right? If I am, then wouldn't option B weaken the idea behind this weakener thereby strengthening it?
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GMATNinja
Quote:
6. Which of the following, if true, would most weaken the author’s conclusion in lines 25- 30 (bold lines)?
This question asks us to flex our CR muscles, but let's first take a moment to nail down the structure and purpose of this passage:

  • In paragraph 1, the author explains that a small number of lepidoptera species exhibit population cycles, and states that the driving force behind these cycles is difficult to identify. The author concludes that this driving force may be intimately connected to the insect itself, rather than being connected to the insect's predators or parasites.
  • In paragraph 2, the author presents recent work, which suggests that this driving force (a.k.a. the agent regulating population cycles) may be a virus.
  • In paragraph 3, the author notes that the virus hypothesis is attractive because it seems broadly applicable across different lepidoptera species.

OK, now let's revisit the conclusion being highlighted:

Quote:
In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.
The author concludes that whatever is regulating the population cycle is closer to the insect than it is to predatory birds or parasites. Here's how the author reaches this conclusion:

  • Studying predatory birds and parasites, thought to be potential agents, has been unproductive in the case of lepidoptera.
  • Recent study of viral disease, thanks to new techniques of molecular biology, has identified nuclear polyhedrosis viruses as a more likely agent.
  • Polyhedrosis viruses follow an infectious cycle that is intimately linked to lepidoptera, in which lepidoptera ingest the virus in the form of crystals, incubate new virus particles within their bodies, and release these crystals back into the environment upon dying.

If we're looking to weaken this conclusion, we need an answer choice that either:

  • contradicts what we've read about this link between polyhedrosis viruses and lepidoptera, or
  • delivers evidence that some other regulating agent is even more likely to be the driving force of these population cycles.

Now let's use process of elimination to go through all five choices.

Quote:
(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
This choice actually strengthens the conclusion, because it adds evidence that other potential agents (predatory birds and parasites) have significantly decreased in number in recent years. This reinforces what the author stated plainly in paragraph 1. Eliminate (A).

Quote:
(B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
This choice introduces new evidence that the regulating agent we're all looking for might be intimately linked to the habitats of lepidoptera, after all. Most importantly, this choice tells us that whatever these experiments did to habitats, that action definitely resulted in the shortening of lepidoptera population cycles. We'll keep choice (B) because it provides proof that another agent--habitat--can regulate population cycles.

bpdulog
I was down to B and C but went with C since the later part of the line dismisses the relationship with predators and the driving force of the life cycle
Quote:
(C) Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
Knowing that the nuclear polyhedrosis virus is present in a number of predators and parasites doesn't change anything we've read about the nuclear polyhedrosis virus and its link to lepidoptera. The author's conclusion does not depend on this virus existing only in lepidoptera. And the language of this answer choice doesn't include any dismissal of the intimate link between polyhedrosis viruses and lepidoptera. It simply points out that the virus is also present in predators and parasites of lepidoptera.

(C) doesn't contradict the impact of nuclear polyhedrosis viruses or provide an alternative agent, so we'll eliminate (C).

gauravmarwaha
I could easily eliminate options E, C and A and chose option D over B. Can someone help?
Quote:
(D) Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
Choice (D) does identify a potential alternative agent: weather. However, the logical statement made here is quite weak. (D) tells us that it's difficult to assess the effects of weather on lepidoptera population cycles. So even if it's possible for weather to affect these population cycles, we have no way of confirming whether that effect is actually taking place.

Likewise, I could say, "It's difficult to assess the effects of the lunar cycle on lepidoptera," but this wouldn't make me jump up and say that lunar cycles are likely to be more of a driving force of lepidoptera population cycles than nuclear polyhedrosis viruses. We're not interested in hypothetical effects that are difficult to assess. We're interested in proof that an alternative agent is truly at work. That's why we eliminate (D).

Quote:
(E) Viral disease is typically observed in a large proportion of the lepidoptera population.
This choice doesn't affect the conclusion. Much like Choice (C), it tells us a little more about the presence of viral disease in lepidoptera populations, but it doesn't mention polyhedrosis viruses and doesn't provide evidence of any alternative agent regulating population cycles. Eliminate (E).

Whew! This may have taken me an entire population cycle to write. (Yes, more bad Dad jokes. I'm practicing them. There's no "negative kudos" button, so you're stuck with them.) After all of that, (B) is the only choice that presents evidence of a regulating agent that is NOT intimately linked to the insect (instead, the agent is linked to the insect's habitat). So we keep (B) and move on.

I hope this helps!

Thanks so much GMATNinja for providing these explanations, but I'm confused that why choice B does not strengthen the conclusion instead. The conclusion states that "In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites." It does not say that the agent is the virus. Couldn't the experiment in choice B be that agent?

Thanks so much again.
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GMATNinja
Quote:
6. Which of the following, if true, would most weaken the author’s conclusion in lines 25- 30 (bold lines)?
This question asks us to flex our CR muscles, but let's first take a moment to nail down the structure and purpose of this passage:

  • In paragraph 1, the author explains that a small number of lepidoptera species exhibit population cycles, and states that the driving force behind these cycles is difficult to identify. The author concludes that this driving force may be intimately connected to the insect itself, rather than being connected to the insect's predators or parasites.
  • In paragraph 2, the author presents recent work, which suggests that this driving force (a.k.a. the agent regulating population cycles) may be a virus.
  • In paragraph 3, the author notes that the virus hypothesis is attractive because it seems broadly applicable across different lepidoptera species.

OK, now let's revisit the conclusion being highlighted:

Quote:
In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.
The author concludes that whatever is regulating the population cycle is closer to the insect than it is to predatory birds or parasites. Here's how the author reaches this conclusion:

  • Studying predatory birds and parasites, thought to be potential agents, has been unproductive in the case of lepidoptera.
  • Recent study of viral disease, thanks to new techniques of molecular biology, has identified nuclear polyhedrosis viruses as a more likely agent.
  • Polyhedrosis viruses follow an infectious cycle that is intimately linked to lepidoptera, in which lepidoptera ingest the virus in the form of crystals, incubate new virus particles within their bodies, and release these crystals back into the environment upon dying.

If we're looking to weaken this conclusion, we need an answer choice that either:

  • contradicts what we've read about this link between polyhedrosis viruses and lepidoptera, or
  • delivers evidence that some other regulating agent is even more likely to be the driving force of these population cycles.

Now let's use process of elimination to go through all five choices.

Quote:
(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
This choice actually strengthens the conclusion, because it adds evidence that other potential agents (predatory birds and parasites) have significantly decreased in number in recent years. This reinforces what the author stated plainly in paragraph 1. Eliminate (A).

Quote:
(B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
This choice introduces new evidence that the regulating agent we're all looking for might be intimately linked to the habitats of lepidoptera, after all. Most importantly, this choice tells us that whatever these experiments did to habitats, that action definitely resulted in the shortening of lepidoptera population cycles. We'll keep choice (B) because it provides proof that another agent--habitat--can regulate population cycles.

bpdulog
I was down to B and C but went with C since the later part of the line dismisses the relationship with predators and the driving force of the life cycle
Quote:
(C) Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
Knowing that the nuclear polyhedrosis virus is present in a number of predators and parasites doesn't change anything we've read about the nuclear polyhedrosis virus and its link to lepidoptera. The author's conclusion does not depend on this virus existing only in lepidoptera. And the language of this answer choice doesn't include any dismissal of the intimate link between polyhedrosis viruses and lepidoptera. It simply points out that the virus is also present in predators and parasites of lepidoptera.

(C) doesn't contradict the impact of nuclear polyhedrosis viruses or provide an alternative agent, so we'll eliminate (C).

gauravmarwaha
I could easily eliminate options E, C and A and chose option D over B. Can someone help?
Quote:
(D) Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
Choice (D) does identify a potential alternative agent: weather. However, the logical statement made here is quite weak. (D) tells us that it's difficult to assess the effects of weather on lepidoptera population cycles. So even if it's possible for weather to affect these population cycles, we have no way of confirming whether that effect is actually taking place.

Likewise, I could say, "It's difficult to assess the effects of the lunar cycle on lepidoptera," but this wouldn't make me jump up and say that lunar cycles are likely to be more of a driving force of lepidoptera population cycles than nuclear polyhedrosis viruses. We're not interested in hypothetical effects that are difficult to assess. We're interested in proof that an alternative agent is truly at work. That's why we eliminate (D).

Quote:
(E) Viral disease is typically observed in a large proportion of the lepidoptera population.
This choice doesn't affect the conclusion. Much like Choice (C), it tells us a little more about the presence of viral disease in lepidoptera populations, but it doesn't mention polyhedrosis viruses and doesn't provide evidence of any alternative agent regulating population cycles. Eliminate (E).

Whew! This may have taken me an entire population cycle to write. (Yes, more bad Dad jokes. I'm practicing them. There's no "negative kudos" button, so you're stuck with them.) After all of that, (B) is the only choice that presents evidence of a regulating agent that is NOT intimately linked to the insect (instead, the agent is linked to the insect's habitat). So we keep (B) and move on.

I hope this helps!

Hey GMATNinja , Author is concluding that there is some other agent that is affecting insect's population more than birds and parasite. So a possible weakener would be to show that birds and parasites are indeed on same or greater level than this other agent. Please let me know if I am right? If I am, then wouldn't option B weaken the idea behind this weakener thereby strengthening it?

rickyric395 I read the same way!
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rickyric395
GMATNinja
Quote:
6. Which of the following, if true, would most weaken the author’s conclusion in lines 25- 30 (bold lines)?
This question asks us to flex our CR muscles, but let's first take a moment to nail down the structure and purpose of this passage:

    [] In paragraph 1, the author explains that a small number of lepidoptera species exhibit population cycles, and states that the driving force behind these cycles is difficult to identify. The author concludes that this driving force may be intimately connected to the insect itself, rather than being connected to the insect's predators or parasites.
    [] In paragraph 2, the author presents recent work, which suggests that this driving force (a.k.a. the agent regulating population cycles) may be a virus.
  • In paragraph 3, the author notes that the virus hypothesis is attractive because it seems broadly applicable across different lepidoptera species.

OK, now let's revisit the conclusion being highlighted:

Quote:
In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.
The author concludes that whatever is regulating the population cycle is closer to the insect than it is to predatory birds or parasites. Here's how the author reaches this conclusion:

    [] Studying predatory birds and parasites, thought to be potential agents, has been unproductive in the case of lepidoptera.
    [] Recent study of viral disease, thanks to new techniques of molecular biology, has identified nuclear polyhedrosis viruses as a more likely agent.
  • Polyhedrosis viruses follow an infectious cycle that is intimately linked to lepidoptera, in which lepidoptera ingest the virus in the form of crystals, incubate new virus particles within their bodies, and release these crystals back into the environment upon dying.

If we're looking to weaken this conclusion, we need an answer choice that either:

    []contradicts what we've read about this link between polyhedrosis viruses and lepidoptera, or
    []delivers evidence that some other regulating agent is even more likely to be the driving force of these population cycles.

Now let's use process of elimination to go through all five choices.

Quote:
New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
This choice actually strengthens the conclusion, because it adds evidence that other potential agents (predatory birds and parasites) have significantly decreased in number in recent years. This reinforces what the author stated plainly in paragraph 1. Eliminate (A).

Quote:
New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
This choice introduces new evidence that the regulating agent we're all looking for might be intimately linked to the habitats of lepidoptera, after all. Most importantly, this choice tells us that whatever these experiments did to habitats, that action definitely resulted in the shortening of lepidoptera population cycles. We'll keep choice (B) because it provides proof that another agent--habitat--can regulate population cycles.

bpdulog
I was down to B and C but went with C since the later part of the line dismisses the relationship with predators and the driving force of the life cycle
Quote:
Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
Knowing that the nuclear polyhedrosis virus is present in a number of predators and parasites doesn't change anything we've read about the nuclear polyhedrosis virus and its link to lepidoptera. The author's conclusion does not depend on this virus existing only in lepidoptera. And the language of this answer choice doesn't include any dismissal of the intimate link between polyhedrosis viruses and lepidoptera. It simply points out that the virus is also present in predators and parasites of lepidoptera.

(C) doesn't contradict the impact of nuclear polyhedrosis viruses or provide an alternative agent, so we'll eliminate (C).

gauravmarwaha
I could easily eliminate options E, C and A and chose option D over B. Can someone help?
Quote:
Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
Choice (D) does identify a potential alternative agent: weather. However, the logical statement made here is quite weak. (D) tells us that it's difficult to assess the effects of weather on lepidoptera population cycles. So even if it's possible for weather to affect these population cycles, we have no way of confirming whether that effect is actually taking place.

Likewise, I could say, "It's difficult to assess the effects of the lunar cycle on lepidoptera," but this wouldn't make me jump up and say that lunar cycles are likely to be more of a driving force of lepidoptera population cycles than nuclear polyhedrosis viruses. We're not interested in hypothetical effects that are difficult to assess. We're interested in proof that an alternative agent is truly at work. That's why we eliminate (D).

Quote:
Viral disease is typically observed in a large proportion of the lepidoptera population.
This choice doesn't affect the conclusion. Much like Choice (C), it tells us a little more about the presence of viral disease in lepidoptera populations, but it doesn't mention polyhedrosis viruses and doesn't provide evidence of any alternative agent regulating population cycles. Eliminate (E).

Whew! This may have taken me an entire population cycle to write. (Yes, more bad Dad jokes. I'm practicing them. There's no "negative kudos" button, so you're stuck with them.) After all of that, (B) is the only choice that presents evidence of a regulating agent that is NOT intimately linked to the insect (instead, the agent is linked to the insect's habitat). So we keep (B) and move on.

I hope this helps!

Hey [url=https://gmatclub.com:443/forum/memberlist.php?mode=viewprofile&un=GMATNinja%5D%5Bb%5DGMATNinja%5B/b%5D%5B/url%5D , Author is concluding that there is some other agent that is affecting insect's population more than birds and parasite. So a possible weakener would be to show that birds and parasites are indeed on same or greater level than this other agent. Please let me know if I am right? If I am, then wouldn't option B weaken the idea behind this weakener thereby strengthening it?
Be careful about altering the author's language! The author isn't just saying there's "some other agent." She's saying that the population may be regulated "by an agent more intimately connected with the insect than are predatory birds or parasites." What might be "more intimately connected"? Maybe something inside the insect's cells. Like a virus!

So you're right that (B) is introducing the possibility of there being another agent, but because this agent is introduced by altering the habitat, it doesn't sound as though this other agent is more intimately connected to the insect. In other words, it's more likely that it's the altered habit that's influencing the life cycle. Not the “intimately connected” virus.

So that "intimately connected" phrase is doing some pretty heavy lifting here. Without it, you’d be right. But it’s here, and it’s important.

I hope that clears things up!
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Question 1: It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to... (A) develop an explanation for the existence of lepidoptera population cycles.

Explanation: The passage states that the common approach of studying the causes of population cycles in lepidoptera was to measure the mortality caused by different agents such as predatory birds or parasites. This suggests that the purpose of measuring the mortality was to develop an explanation for the existence of population cycles in lepidoptera.

Question 2: The primary purpose of the passage is to... (C) present a hypothesis about the driving force behind population cycles in lepidoptera.

Explanation: The passage primarily focuses on presenting the hypothesis that nuclear polyhedrosis viruses may be the driving force behind population cycles in lepidoptera. It discusses the research conducted, the evidence supporting the hypothesis, and the applicability of the hypothesis to different species of lepidoptera. The passage aims to present this hypothesis as a possible explanation for the regular patterns of population growth and decline observed in lepidoptera.

Question 3: According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases... (D) attacked already declining caterpillar populations.

Explanation: The passage states that before the discovery of new techniques for detecting viral DNA, population ecologists usually considered viral disease to have contributed to the decline of lepidoptera populations once it was underway, rather than to have initiated it. This implies that viral diseases were believed to attack caterpillar populations that were already in decline.

Question 4: According to the passage, nuclear polyhedrosis viruses can remain virulent in the environment only when... (E) they are sheltered from direct sunlight.

Explanation: The passage mentions that nuclear polyhedrosis viruses can remain virulent for many years in the environment if protected from direct sunlight. It states that when the viruses are embedded in durable crystals of polyhedrin protein, they can remain virulent and infect other caterpillars after the insect dies and decomposes. Therefore, the viruses' ability to remain virulent depends on being sheltered from direct sunlight.

Question 5: It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus... (C) cannot infect caterpillars' cells.

Explanation: The passage mentions that once the polyhedrin protein crystals dissolve, the nuclear polyhedrosis virus is released to infect the insect's cells. This implies that while inside the crystals, the virus cannot infect caterpillars' cells.

Question 6: Which of the following, if true, would most weaken the author’s conclusion in lines 18-22? (B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.

Explanation: The author's conclusion in lines 18-22 is that the evidence implies that lepidoptera populations may be regulated by an agent more intimately connected with the insect than predatory birds or parasites. The passage suggests that this agent may be a virus. To weaken this conclusion, we need an option that presents an alternative explanation for the population cycles. If new experiments show that altering the habitats of lepidoptera in previously untried ways result in the shortening of population cycles, it suggests that factors other than a virus may be responsible for the cycles. Therefore, option (B) weakens the author's conclusion.
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Question 5, i chose D: while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus cannot be ingested by caterpillars.

It should be true that when the virus is inside the crystal, it cannot be ingested because the virus is still there even after the crystal is ingested from statement “Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect’s cells”
And this statement also shows that a caterpillar ingests only the ‘crystal’ not the ‘virus’

Could anyone please explain option D why my understanding is wrong. Thank you!

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GMATNinja
Quote:
6. Which of the following, if true, would most weaken the author’s conclusion in lines 25- 30 (bold lines)?
This question asks us to flex our CR muscles, but let's first take a moment to nail down the structure and purpose of this passage:

  • In paragraph 1, the author explains that a small number of lepidoptera species exhibit population cycles, and states that the driving force behind these cycles is difficult to identify. The author concludes that this driving force may be intimately connected to the insect itself, rather than being connected to the insect's predators or parasites.
  • In paragraph 2, the author presents recent work, which suggests that this driving force (a.k.a. the agent regulating population cycles) may be a virus.
  • In paragraph 3, the author notes that the virus hypothesis is attractive because it seems broadly applicable across different lepidoptera species.

OK, now let's revisit the conclusion being highlighted:

Quote:
In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites.
The author concludes that whatever is regulating the population cycle is closer to the insect than it is to predatory birds or parasites. Here's how the author reaches this conclusion:

  • Studying predatory birds and parasites, thought to be potential agents, has been unproductive in the case of lepidoptera.
  • Recent study of viral disease, thanks to new techniques of molecular biology, has identified nuclear polyhedrosis viruses as a more likely agent.
  • Polyhedrosis viruses follow an infectious cycle that is intimately linked to lepidoptera, in which lepidoptera ingest the virus in the form of crystals, incubate new virus particles within their bodies, and release these crystals back into the environment upon dying.

If we're looking to weaken this conclusion, we need an answer choice that either:

  • contradicts what we've read about this link between polyhedrosis viruses and lepidoptera, or
  • delivers evidence that some other regulating agent is even more likely to be the driving force of these population cycles.

Now let's use process of elimination to go through all five choices.

Quote:
(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
This choice actually strengthens the conclusion, because it adds evidence that other potential agents (predatory birds and parasites) have significantly decreased in number in recent years. This reinforces what the author stated plainly in paragraph 1. Eliminate (A).

Quote:
(B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
This choice introduces new evidence that the regulating agent we're all looking for might be intimately linked to the habitats of lepidoptera, after all. Most importantly, this choice tells us that whatever these experiments did to habitats, that action definitely resulted in the shortening of lepidoptera population cycles. We'll keep choice (B) because it provides proof that another agent--habitat--can regulate population cycles.

bpdulog
I was down to B and C but went with C since the later part of the line dismisses the relationship with predators and the driving force of the life cycle
Quote:
(C) Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
Knowing that the nuclear polyhedrosis virus is present in a number of predators and parasites doesn't change anything we've read about the nuclear polyhedrosis virus and its link to lepidoptera. The author's conclusion does not depend on this virus existing only in lepidoptera. And the language of this answer choice doesn't include any dismissal of the intimate link between polyhedrosis viruses and lepidoptera. It simply points out that the virus is also present in predators and parasites of lepidoptera.

(C) doesn't contradict the impact of nuclear polyhedrosis viruses or provide an alternative agent, so we'll eliminate (C).

gauravmarwaha
I could easily eliminate options E, C and A and chose option D over B. Can someone help?
Quote:
(D) Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
Choice (D) does identify a potential alternative agent: weather. However, the logical statement made here is quite weak. (D) tells us that it's difficult to assess the effects of weather on lepidoptera population cycles. So even if it's possible for weather to affect these population cycles, we have no way of confirming whether that effect is actually taking place.

Likewise, I could say, "It's difficult to assess the effects of the lunar cycle on lepidoptera," but this wouldn't make me jump up and say that lunar cycles are likely to be more of a driving force of lepidoptera population cycles than nuclear polyhedrosis viruses. We're not interested in hypothetical effects that are difficult to assess. We're interested in proof that an alternative agent is truly at work. That's why we eliminate (D).

Quote:
(E) Viral disease is typically observed in a large proportion of the lepidoptera population.
This choice doesn't affect the conclusion. Much like Choice (C), it tells us a little more about the presence of viral disease in lepidoptera populations, but it doesn't mention polyhedrosis viruses and doesn't provide evidence of any alternative agent regulating population cycles. Eliminate (E).

Whew! This may have taken me an entire population cycle to write. (Yes, more bad Dad jokes. I'm practicing them. There's no "negative kudos" button, so you're stuck with them.) After all of that, (B) is the only choice that presents evidence of a regulating agent that is NOT intimately linked to the insect (instead, the agent is linked to the insect's habitat). So we keep (B) and move on.

I hope this helps!


Hello GMATNinja

Really amazing explanation with so much detail. Thank you for such amazing answers which help us understand

My doubt here pertains to choice C. The author gives the highlighted conclusion at the end of the first paragraph that there might be some other agent more closely related to the insect than the predatory birds or parasites. Till this point author has not considered the possibility of the Nuclear polyhedrosis viruses so IMO while looking for points to weaken this conclusion, we need not to consider anything in particular about this virus because the same information has not been presented yet and author doesn't use this information to arrive at this conclusion, That is the reason I rejected Option C.

If there were any other option which said that the Nuclear polyhedrosis viruses don't have that much affect on the population cycle of lepidoptera, I would have rejected the same on this ground since author's conclusion is primarily concerned with some agent which is intimately connected with the insect and author till this point doesn't say that agent has to be Nuclear polyhedrosis viruses in particular. Even if an option choice said that Nuclear polyhedrosis viruses don't affect the population cycle that much there could very well be a possibility of some other agent affecting their population cycle which is intimately connected with the insect and thus such a choice won't weaken the conclusion.

So a possible weakener here should be either a statement telling us that something else not so intimately connected with the insect affects their population cycle or a statement which shows us that its impossible for any agent intimately connected with the insect to affect their population cycle.

I don't think that we should consider the information given in the subsequent passage after the conclusion has been made to weaken the conclusion.

Please tell me if my understanding is correct or not. Will wait for your reply.
Thank you
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Tanisha2819
Hello GMATNinja

Really amazing explanation with so much detail. Thank you for such amazing answers which help us understand

My doubt here pertains to choice C. The author gives the highlighted conclusion at the end of the first paragraph that there might be some other agent more closely related to the insect than the predatory birds or parasites. Till this point author has not considered the possibility of the Nuclear polyhedrosis viruses so IMO while looking for points to weaken this conclusion, we need not to consider anything in particular about this virus because the same information has not been presented yet and author doesn't use this information to arrive at this conclusion, That is the reason I rejected Option C.

If there were any other option which said that the Nuclear polyhedrosis viruses don't have that much affect on the population cycle of lepidoptera, I would have rejected the same on this ground since author's conclusion is primarily concerned with some agent which is intimately connected with the insect and author till this point doesn't say that agent has to be Nuclear polyhedrosis viruses in particular. Even if an option choice said that Nuclear polyhedrosis viruses don't affect the population cycle that much there could very well be a possibility of some other agent affecting their population cycle which is intimately connected with the insect and thus such a choice won't weaken the conclusion.

So a possible weakener here should be either a statement telling us that something else not so intimately connected with the insect affects their population cycle or a statement which shows us that its impossible for any agent intimately connected with the insect to affect their population cycle.

I don't think that we should consider the information given in the subsequent passage after the conclusion has been made to weaken the conclusion.

Please tell me if my understanding is correct or not. Will wait for your reply.

Thank you
Sorry for not getting back to you sooner!

It sounds like you have the right idea in this case, but you don't want to be too rigid about disregarding stuff from later in the passage. Who knows, maybe there's SOMETHING about nuclear polyhedrosis virus that impacts the evidence described earlier in the passage. If so, that would be a valid answer, even though the author doesn't bring up the virus until later.

In short, you can eliminate (C) because it doesn't weaken the conclusion, not just because it fails on a technicality. ;)

I hope that helps!
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Hello from the GMAT Club VerbalBot!

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