#8 - Generally speaking, if the same crop is sown in a field

[srcline@noctrl.edu]

Hello ,

So I was in between answer choices C and D for this and I chose D. Correct answer was C.

So the question stem states that "which one of the following, if true, most helps to explain the similarity described above between alfalfa and non-nitrogen fixing plants? So, this is resolve the discrepancy question correct?

Conclusion: Alfalfa is nitrogen fixing plant, and thus increases the amount of nitrogen in the soil, and if planted in the same field year after year, grows less well in the later years that it does in the earlier years.

Do is wrong b/c the stimulus already tells us that alfalfa is a nitrogen fixing fixing plant. But the second half of D is throwing me off. So it says "alfalfa increases nitrogen in the soil in which it grows only if a certain type of soil bacteria is present in the soil. Wouldn't this explain why if the alfalfa is planted in the same field it grows less well in the later years b/c there is a certain bacteria that is present in the soil?

Thankyou
Sarah

[David Boyle]

Hello ,

So I was in between answer choices C and D for this and I chose D. Correct answer was C.

So the question stem states that "which one of the following, if true, most helps to explain the similarity described above between alfalfa and non-nitrogen fixing plants? So, this is resolve the discrepancy question correct?

Conclusion: Alfalfa is nitrogen fixing plant, and thus increases the amount of nitrogen in the soil, and if planted in the same field year after year, grows less well in the later years that it does in the earlier years.

Do is wrong b/c the stimulus already tells us that alfalfa is a nitrogen fixing fixing plant. But the second half of D is throwing me off. So it says "alfalfa increases nitrogen in the soil in which it grows only if a certain type of soil bacteria is present in the soil. Wouldn't this explain why if the alfalfa is planted in the same field it grows less well in the later years b/c there is a certain bacteria that is present in the soil?

Thankyou
Sarah

Hello Sarah,

Yes, it is a Resolve the Paradox question.
I think you mean, if that bacteria isn't present. What if that bacteria is present, though? Maybe it is. Do you know?

Hope this helps,
David

[srcline@noctrl.edu]

Hello David

So the problem with D is that you would need to know more about the bacteria?

Thankyou
Sarah

[Robert Carroll]

Sarah,

Answer choice (D) says that that alfalfa will increase nitrogen only if a certain type of bacteria is present. Nothing in the stimulus or answer choice (D) says that that type of bacteria is or is not present. Thus, it's possible the type of bacteria is present, in which case alfalfa would appear to fix nitrogen as normal. It's possible it's not present, in which case alfalfa won't increase nitrogen. Because no information tells us whether the type of bacteria is present or not, this answer choice fails to clear up the paradox.

Essentially, answer choice (D) is saying that, under certain conditions, something about alfalfa is different. We don't know whether those conditions exist or not, so this does not resolve the paradox.

Robert Carroll

[maximbasu]

Hi,

Would you please explain to me why answer choice A is wrong? It seems plausible.

I understand why C is correct; I just think its a stretch to assume that if the toxic substance is in the soil, the original plant will grow. Thus, if the toxic substance is produced anyway, the original plant wouldn't grow productively with or without similar plants in the soil.

Rgs and thanks,
Maxim

[Adam Tyson]

Let me turn this one around on you, Maxim - how does A resolve this paradox? In what way does it help to explain why alfalfa grows less well in later years than it does in earlier years in the same soil? We know that happens with some plants that deplete nitrogen, but alfalfa doesn't deplete nitrogen, so there has to be some other reason (alternate cause) why alfalfa acts that way. Does A give you an alternate cause?

C does do that - if alfalfa produces some poison that negatively affects the alfalfa, there's your alternate cause. Instead of nitrogen depletion, the problem is self-poisoning.

You raise the issue of the plausibility of the two answer choices, and I want to caution you against doing so. It doesn't matter if the answer is plausible or not. You are asked not whether the answer seems possible, but what effect that answer would have if it was true. How about this answer to that question - "long ago, powerful magical beings cast a spell on alfalfa that would prevent it from growing well in the same soil in later years." Plausible? No. If it was true, would it resolve the paradox by giving us a reason for alfalfa failing to grow well in later years? Absolutely! Don't question the truthfulness of the answer choice if the stem tells you to just accept them as true. Instead, just treat them as absolute truth and focus only on what impact those answer choices have.

[slynnnnn]

Hi PowerScore Staff,

I have exactly the same thinking process as the first person in the thread. I narrowed down to (C) and (D).

I do take notice that in (D), the mention of bacteria seems to lack certainty. However, the answer (C) seems to suggest that both alfalfa and some regular plants grower poorer in the succeeding years because of the existence of this "substances", which is contrary, or at least irrelevant, to the conclusion, which is that the poorer growth is contributed to the depleted nitrogen.

Is this a legitimate concern? Or it can actually be interpreted as add-on information?

Thanks,
Lynn

[Adam Tyson]

The stimulus here sets up a fact pattern, not an argument, Lynn, so there really is no conclusion. All we have are some facts, which I will paraphrase here:

1. Most crops do worse over time because they deplete nitrogen
2. Alfalfa does worse over time even though it doesn't deplete nitrogen

We have to pick the answer that explains why alfalfa, like other plants, does worse over time even though it cannot be for the same reason. So we need a different reason for alfalfa doing worse, which C gives us by introducing a toxic substance that alfalfa exudes.

Answer D doesn't give us a reason for alfalfa doing worse over time. All it does is tell us that in order for alfalfa to increase nitrogen, it needs something else. Okay, but why is alfalfa - and this means ALL alfalfa - doing worse over time? What is the alternate cause for alfalfa doing worse? Don't say "it's doing worse because the bacteria is never present and so it's actually depleting the nitrogen," because answer D says none of that and we should not be helping the answers by adding more info to them! The correct answer needs to resolve the paradox all by itself, with no additional information provided by us. Answer D falls short on that account.

[slynnnnn]

The stimulus here sets up a fact pattern, not an argument, Lynn, so there really is no conclusion. All we have are some facts, which I will paraphrase here:

1. Most crops do worse over time because they deplete nitrogen
2. Alfalfa does worse over time even though it doesn't deplete nitrogen

We have to pick the answer that explains why alfalfa, like other plants, does worse over time even though it cannot be for the same reason. So we need a different reason for alfalfa doing worse, which C gives us by introducing a toxic substance that alfalfa exudes.

Answer D doesn't give us a reason for alfalfa doing worse over time. All it does is tell us that in order for alfalfa to increase nitrogen, it needs something else. Okay, but why is alfalfa - and this means ALL alfalfa - doing worse over time? What is the alternate cause for alfalfa doing worse? Don't say "it's doing worse because the bacteria is never present and so it's actually depleting the nitrogen," because answer D says none of that and we should not be helping the answers by adding more info to them! The correct answer needs to resolve the paradox all by itself, with no additional information provided by us. Answer D falls short on that account.

Adam,

Thank you so much for this explanation!

Lynn