Q7 - Scientists removed all viruses

[bnuvincent]

I found D tempting, in the stimulus it states that the population actually got smaller, and D match this, and C seems unable to account for this part. Could you please explain?

[ManhattanPrepLSAT1]

Good question. I just spent a minute looking at it a few times trying to see it clearly, so this one's not easy.

Notice the subject of every other answer choice - plankton. Notice that plankton are conspicuously absent from answer choice (D). The fact that these bacteria sometimes damage other organisms is not strong enough to imply that they're likely to be damaging to plankton.

The question in a nutshell.

Scientists remove viruses in a sample of seawater and expect the population of plankton to rise - but it doesn't. The question is why?

(A) makes the situation even more puzzling. If viruses maintain lower levels of plankton, then the population of plankton should have increased when the viruses were removed.
(B) same issue as answer choice (A). If they compete for food, then an absence of viruses should have lead to an increase in the population of plankton.
(C) explains the findings of the experiment. The plankton would then need the viruses for their food supply, and so an absence of viruses would explain the drop in the plankton population.
(D) fails to discuss plankton at all.
(E) is irrelevant. Being infected by viruses does not necessarily tell us anything about population fluctuations.


Does this help clear things up?

[bnuvincent]

Yeah, so it's a little to general and doesn't specifically talk about plankton is the crux. It helps a lot. Thx.

[yusangmin]

if i have a beef with this question its that C..

ok so it says plankton utilize the nutrients released by death of organisms...but does it say they NEED to utilize them?

so its like saying..i utilize the vitamin gummy bears that my mom buys from costco sometime s...but if i dont eat them will that make me deteriorate in health necessarily?
i feel like theres a certain part of me that thinks too much sometimes for hte LSAT? please tell me where im going wrong with this.

also...doesnt E correlate with what the stim looks for? because they imply that the population is somehow connected with the population, since they believed taking away viruses would make the population go up. Implying that the viruses have some kind of effect on the plankton. *edit* oops so i just read it again..wondering does the "at any given time" do anything for this?

thanks

[linzru86]

I thought that when I first looked at C too. I think that C doesnt need to say that the plankton "need" to utilize the nutrients because the simple fact that plankton generally utilize the nutrients is enough. I see it as kind of a strengthen question where the missing piece doesn't have to definitively prove the conclusion just "help" it as here it says "most helps explain". The fact that the plankton utilize the nutrients helps explain why perhaps if that utilization ceases to take place, this could result in the death of even just some of the plankton which would mean the population got smaller just as the evidence says happened.

Like with the gummy bears, maybe the fact that your body utilizes the nutrients isn't necessary because you get those vital nutrients from other sources as well. However if there were no more gummy bears your health could deteriorate because one source of those vital nutrients were gone AND something else happened like all the other potential sources of those nutrients were no longer available as well. If you had those gummy bears still, your health may be improved again. They at least HELP although may not be necessary. Hope I make sense.

[kmewmewblue]

I don't understand (A)'s phrase "that the resources in the water will support"....

support what?

Any help will be appreciated.
Thanks

[timmydoeslsat]

I don't understand (A)'s phrase "that the resources in the water will support"....

support what?

Any help will be appreciated.
Thanks

It is telling us that viruses in seawater keep plankton from reaching a certain number that the seawater could actually support.

Example:

Seawater has enough resources to support (keep alive) 50 plankton.

However, with viruses in the picture, the plankton can only ever reach 35.

So, the viruses are keeping the plankton from ever reaching its highest possible point that the seawater can support.

[jimmy902o]

I still have a question about A. My support for this is the case of the reindeer brought onto st. matthews island back in the 40s. Basically what happened was that the initial reindeer population rose from 29 in 1944 to 6000 in 1963 due to lack of predators and favorable living conditions. However, just like the plankton in this question, the population outgrew the resources and by the 1980s the population on the island died out entirely with the main issue being overpopulation.

So with this in mind, my question is couldn't this be a valid explanation for a similar occurrence in answer choice A. Granted it took the reindeer 40+ years to die out, but the stimulus does not mention time, and the principle still holds...

[schmid215]

I still have a question about A. My support for this is the case of the reindeer brought onto st. matthews island back in the 40s. Basically what happened was that the initial reindeer population rose from 29 in 1944 to 6000 in 1963 due to lack of predators and favorable living conditions. However, just like the plankton in this question, the population outgrew the resources and by the 1980s the population on the island died out entirely with the main issue being overpopulation.

So with this in mind, my question is couldn't this be a valid explanation for a similar occurrence in answer choice A. Granted it took the reindeer 40+ years to die out, but the stimulus does not mention time, and the principle still holds...

Same thing occurred to me after initially reading (A). Absolutely a good reason to consider it, and I'm not sure why that has not been acknowledged yet in this thread. I almost picked it and moved on, but I decided to read the other choices, and (C) seemed very strong and almost certain to be the answer, so I went back to (A). I could find only two flaws, both pretty finicky. First, it does not imply necessity. Being of assistance in a given endeavor does not guarantee that absence will make the endeavor impossible. Seems to me like whatever else helped keep the population below resource straining levels could adapt in such a way as to compensate for the disappearance of viruses, or something else could step in to take its place. Second, even if the presence of viruses is necessary to keep plankton population below resource-straining levels, it is logically possible that its absence could simply lead to the plankton population being right at the maximum level.

[joseph.m.kirby]

The problems with (D) include:
-The absence of viruses "can" facilitate (perhaps in this case it doesn't)
-If the absence of viruses, in this case, did facilitate the flourishing of bacteria (assumption 1), and these bacteria sometimes damage organisms (in this case, let's assume that they did "damage" the plankton, assumption 2), then we would also have to assume (assumption 3) that the damage would cause a reduction in the population. However, perhaps the damage just relates to a deformity that doesn't necessarily affect plankton bumping-and-grinding. Overall, (D) requires a lot of assumptions, which makes this answer not as attractive as (C).

[nflamel69]

Can any geek help to explain why C and not D? I can understand that other organisms in D doesn't necessarily include planktons. By the same reasoning, I can argue that just because they utilize the the nutrients released by those organisms doesn't mean that without viruses, they have less nutrients. They could have other ways to get those nutrients as well. And how do we know that the organisms mentioned in D doesn't include planktons themselves? It could very well be the case that the amount of the planktons that are killed outweigh the planktons that benefit from the nutrients. this question is driving me nuts.

[theanswer21324]

Hi Matt,

I'm a bit unclear about how you so readily dismissed (A). The answer choice sounds like the virus was doing an effective job at keeping the plankton level stable, and once the virus was removed, the plankton could grow beyond the "maximum level that the resource in the water will support." This would mean that the population suffered some sort of collapse due to exhaustion of resources, explaining why the population got smaller.

(C) is tempting since it talks about how viruses are good, but I didn't pick it due to how weak the answer choice sounded. We have no idea if the nutrients are necessary for plankton (it just says "utlize"), so how can we infer that the population would get smaller? Maybe they could have gotten the nutrients elsewhere, or maybe the nutrients weren't even that important to begin with. It does not sound like enough to resolve the problem.

Thanks

[alex.cheng.2012]

I had narrowed this down to answers C and D. To be honest, all the answers seemed bad, but C and D were the best answers.

I must echo linzru's comments. C says that plankton utilized the nutrients that come from dead organisms killed by viruses. But no where does it implicate that these are its sole source of food, or that these are its primary source of food. Plankton could very likely survive off of other food sources fine without the nutrients coming from organisms killed by viruses.

D was a weak answer, and in my opinion, weaker than C. I should have chosen C just based on this fact. The irony is that I recognized D was a weaker answer, and still decided to choose it over C. Like previously stated, the biggest problem with this answer is that it doesn't explicitly refer to plankton. For all we know, these flourishing bacteria are harmful to organisms other than plankton.

I started to write about why I thought C was a bad answer, but you know what, we're supposed to choose the answer that would "most help." There is inherent wiggle room.

As previously stated. Answer C and D seem like the most likely winners. Answer D is weaker than answer C and seems less likely to explain the paradox than C. Therefore, C is the "best" answer.

[jasonleb1]

Hi Matt,

I'm a bit unclear about how you so readily dismissed (A). The answer choice sounds like the virus was doing an effective job at keeping the plankton level stable, and once the virus was removed, the plankton could grow beyond the "maximum level that the resource in the water will support." This would mean that the population suffered some sort of collapse due to exhaustion of resources, explaining why the population got smaller.

(C) is tempting since it talks about how viruses are good, but I didn't pick it due to how weak the answer choice sounded. We have no idea if the nutrients are necessary for plankton (it just says "utlize"), so how can we infer that the population would get smaller? Maybe they could have gotten the nutrients elsewhere, or maybe the nutrients weren't even that important to begin with. It does not sound like enough to resolve the problem.

Thanks

I had this same issue so if anyone could clear it up, I'd appreciate it. Both A and C seem to require extra inferences: A in that the population will then decrease/collapse after growing past the point its environment can support and C in that the utilization of the nutrients is necessary to the maintenance of their population size.

Thanks

[maryadkins]

I definitely see (A) as requiring an extra (and I think, dubious) inference, as you say, to reach the logic that once the plankton reach their maximum level they will then decrease? I don't actually see the reasoning of that. Why wouldn't they just stay at their maximum level?

(C) at least explains why the plankton needed the viruses.

Tricky one overall, though, agreed!

[rfrahman]

I'm a bit confused with this one. I still feel that A and C requires an equal number of assumptions for it to be correct. I got C when I took the test, but after careful blind review, I thought the answer was definitely A. Even though we would need to draw an assumption that the plankton grew past the maximum level it could support, C requires the assumption that these nutrients were necessary for the plankton's survival. They both require assumptions. How are we to judge the relative merits of these two assumptions?

However, I thought of another reason that may explain why A is wrong. The stimulus says that they expected the rate to increase dramatically, but instead they decreased. In A, could it also be wrong because in order for it to decrease, the population would need to increase first and reach the maximum level? The stimulus indicates that the population grew smaller and that there was no increase in the first place. Does that make sense or does the stimulus leave open the possibility for the population to have increased before decreasing to maintain the claim that the population actually got smaller?

[tuesdayninja]

I'm a bit confused with this one. I still feel that A and C requires an equal number of assumptions for it to be correct. I got C when I took the test, but after careful blind review, I thought the answer was definitely A. Even though we would need to draw an assumption that the plankton grew past the maximum level it could support, C requires the assumption that these nutrients were necessary for the plankton's survival. They both require assumptions. How are we to judge the relative merits of these two assumptions?

However, I thought of another reason that may explain why A is wrong. The stimulus says that they expected the rate to increase dramatically, but instead they decreased. In A, could it also be wrong because in order for it to decrease, the population would need to increase first and reach the maximum level? The stimulus indicates that the population grew smaller and that there was no increase in the first place. Does that make sense or does the stimulus leave open the possibility for the population to have increased before decreasing to maintain the claim that the population actually got smaller?

I agree with your reason on why A was wrong. I interpreted the stimulus to say that virus was removed ---> the plankton population decreased. Therefore the assumption that A requires, that the population got out of control and collapsed, is not valid.

[vstoever]

I think that C is the best answer because if Plankton utilize the nutrient released by the death of organisms killed by viruses, even if they get nutrients from other sources too, on average, all the Plankton will now have fewer food sources to get their nutrients from without viruses. This means more competition for nutrients between the Plankton which will mean at least the population will decrease a little without viruses (if not a lot).

[mswang7]

If D had said "The absence of viruses can facilitate the flourishing of bacteria that damage plankton (instead of other organisms). Notice I also removed sometimes to make the answer a bit stronger. Would it overtake C as the best answer?

[smiller]

If D had said "The absence of viruses can facilitate the flourishing of bacteria that damage plankton (instead of other organisms). Notice I also removed sometimes to make the answer a bit stronger. Would it overtake C as the best answer?

The change you made to choice (D) definitely makes it a better answer, and one that could easily be the correct answer if (C) wasn't included. I think that's a good way to look at it. Rewriting a tempting incorrect answer to make it correct is a great way to understand exactly why the original answer is not correct.

Your revised version of choice (D) might even be better than (C). It's hard to say, though. I definitely don't think that LSAC would include both choice (C) and your revised choice (D) as possible answers for this question. It would be too difficult to choose between them, even by LSAT standards!

Good work, though!