Q10 - In a vast ocean region

[danitay]

I was torn between A and E on this one. Is E wrong because it's too general? Since the stimulus refers to "a vast ocean region," it implies that specific ocean region, so one can't infer anything about all bodies of water (because for ex. some bodies of water may not have plankton or plankton eating bacteria in them, in which case high phosphorus may not lead to low oxygen). Am I on the right/wrong track with this?

Thanks a lot!

[dina]

Yes, I ruled out E because it is too general. The phosphorous affects oxygen only through bacteria in the stem. But in E, they're saying ANY body of water, so in bodies of water without this bacteria, there may not be such relationship.

[jackson5]

hey for inference questions, are we suppose to make assumptions based on the stimulus or are we suppose to make connections on the given information? I was really confused because in strengthen, the right answer is usually doesn't contain given information.

[kky215]

hey for inference questions, are we suppose to make assumptions based on the stimulus or are we suppose to make connections on the given information? I was really confused because in strengthen, the right answer is usually doesn't contain given information.

Inference questions belong to the "prove" family stem of questions and thus you are NEVER allowed to bring in new pieces of information that is not discussed in the original stimulus. The correct answer to any inference question MUST BE TRUE all the time given the facts in the stimulus.

[chunsunb]

I would like to propose a different explanation as to why (E) is wrong.
I think it is because of the word "proportional."
For two objects to be inversely proportional, it must be that if one is multiplied by k factor, the other must be multiplied by 1/k.
In other words, in this question, (E) suggests that doubling the oxygen in the body of water will decrease the level of phosphorus by half.

This is not supported by the passage, which merely says that the two Are negatively correlated.

To rebut your explanation of why (E) is wrong,
I think that (E) is no more "general" or "vague" as (A).

[christine.defenbaugh]

I would like to propose a different explanation as to why (E) is wrong.
I think it is because of the word "proportional."
For two objects to be inversely proportional, it must be that if one is multiplied by k factor, the other must be multiplied by 1/k.
In other words, in this question, (E) suggests that doubling the oxygen in the body of water will decrease the level of phosphorus by half.

This is not supported by the passage, which merely says that the two Are negatively correlated.

To rebut your explanation of why (E) is wrong,
I think that (E) is no more "general" or "vague" as (A).

I like the way you're thinking, chunsunb!

All we know from the stimulus is that 1) phosphorus levels doubled and 2) oxygen levels went down. That doesn't necessarily mean the decrease was proportional. And even if it had been, that doesn't necessarily mean that adding more phosphorus would have the same inversely proportional impact.

So, you are spot on that the word proportional is a big red flag!

However, I'd caution you not to dismiss the other reason for eliminating (E). Let's walk through the original question from top to bottom. Since it is an inference question, we know we're looking for an answer choice that is totally supportable, but may not be predictable.

Let's sort our information:

1) All information is about a particular ocean region
2) agricultural runoff comes from a nearby river
3) this runoff has doubled the phosphorus
4) phosphorus stimulates plankton growth
5) when plankton die, bacteria eat them - uses oxygen
6) low oxygen = few fish survive

Don't dismiss point #1! We know that phosphorous stimulates the growth of plankton in this particular ocean region. Does that happen in EVERY body of water? No idea! (E) tries to claim something is true in every body of water, and that's too bold for the information we have.

So there are two excellent reasons to dismiss (E)! The fact that it applies to all bodies of water AND the word "proportional".

Let's take a quick look at the remaining incorrect answers:
(B): Timeline problem! We know what's happening now, but that doesn't tell us what happened before the phosphorus doubled.

(C): Timeline problem! We know what's happening now, but that doesn't tell us what would happen in future without agricultural runoff.

(D): We know the phosporus levels have doubled, but that doesn't necessarily mean that the quantity of runoff itself has doubled - maybe it's just a lot more concentrated with phosphorus now!


That leaves us with (A). We know that the agricultural runoff --> doubled phosphorus. We know that phosphorus --> stimulates plankton growth. Link those two up, and we can say that this agricultural runoff contributes to plankton growth in this region. Note that (A) is not attempting to make a claim about all bodies of water, or all agricultural runoff - it's only talking about THIS agricultural runoff, THIS river, and the plankton in THIS region.

Great work everyone!

[zen]

Here's a short explanation.

So the gist of the stimulus that I got was that agricultural runoff has caused phosphorus levels to double. Consequently, more plankton grows, which leads to more oxygen because as more plankton die( if more plankton are born, more are going to die) they are eaten by bacteria who use up oxygen; now, since more oxygen is being used up, there is less for fish, so fish die.

Wrong Answers:

B) We do not know anything about the region before the phosphorus levels doubled; we only know about the current state after it doubled. It come be the case that fish had a tough time surviving before. Now it is just even harder.

C) I'm always skeptical about conditionals because they requirement the sufficient condition to be met in order to obtain. In this case, we are given no information in order to meet the sufficient assumption, and therefore, we cannot infer anything about the state of affairs that would occur if agricultural runoff stopped.

D) Tempting, but we do not know if the quantity of the agricultural runoff itself has doubled; we are only told that the phosphorus levels have doubled-- this can happen without the increase in agricultural runoff. Maybe the chemicals the farmers use have changed but the amount they use has stayed the same?

E) We are not given enough information to infer any specific relationship about oxygen in the water except that less oxygen = less fish. We don't know anything more that would allow us to infer a clean and proper ratio like this answer choice is giving us.

Correct Answer:

A) We do know that the agricultural runoff has caused the phosphorus levels in the water to double. We know this phosphorus has made more plankton, which inevitably die; when they die, bacteria eat them and use up oxygen in the water which leaves an insufficient amount for fish. I think it is very safe to say that the agricultural runoff contributes to the growth of plankton.