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# Urban air contains more sulfur dioxide than does rural air, and plants

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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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17 Oct 2016, 12:59
1
akhileshdas wrote:
I came up with the assumption : Plant growth rate is not affected by Sulphur Dioxide at all and is affected by some other reason. Choice D gave me that reason and hence I selected it. egmat can you comment if my assumption is correct? I assume is it since I was able to select the right choice and none of the other choices are close to the assumption I came up with.

Same with me , I started doubting other factors affecting Plant growth ( One of the factors in my list was soil texture ), however I was content with option (D) putting the blame on the Heavy vehicular traffic.
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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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26 Oct 2016, 12:30
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This question uses the word 'evaluate' in the question stem, but is really a resolve the paradox question. tag should be changed, how do we do that?
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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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29 Oct 2016, 09:05
TheLordCommander wrote:
This question uses the word 'evaluate' in the question stem, but is really a resolve the paradox question. tag should be changed, how do we do that?

The tag is alright. Whether option D was taken into account while arriving at the conclusion is the point. It's not that the experiment poses a paradox and then option D explains the paradox. If option D was taken into account then the result of the experiment is correct, if option D was NOT taken into account, then the result may be faulty. Hence the question is an "evaluate argument" type question.
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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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05 Jan 2017, 16:05
I have read several explanations for this problem across various forums and am not satisfied with any of the answers. So, I decided to think this problem thoroughly and here is my explanation:
Facts:
Urban air SO2 > Rural air SO2
Urban plant growth < Rural plant growth

Is there are relation between SO2 and plant growth?

Experiment is conducted to filter out SO2. "Assuming" we have only one factor that affects the plant growth and that is SO2, then the result of the experiment of growing plants in the greenhouse (for those not from USA and don't know what a green house is: it is a sort of an enclosed garden) in urban and rural areas should be equal plant growth, i.e. a plant would grow 5 cms in urban area and 5 cms in rural area.
However, that is not the case: the plants still grow unequally!!! And this is the conclusion or result of the experiment.

So, now we need to figure out why they are not growing equally and forget the case about finding out whether SO2 affects the plant growth.

Choice A: Irrelevant. Experiments were conducted in greenhouse.
Choice B: This is the tricky one and needs some handling: Remember, previously we wanted to know whether SO2 affects the plant growth, this clearly shows that it does. If you thought that our aim still is to find the correlation, then you would immediately pick this choice. However, remember we have already proved that even after filtering SO2 there is unequal growth between urban greenhouse plant and rural greenhouse plant.
Choice C: Irrelevant.
Choice D: We are trying to evaluate the result of unequal growth between urban greenhouse plant and rural greenhouse plant which have both been filtered SO2. If the vehicular traffic reduced the light on the plants, then obviously the plants would grow slower. And this explains why the urban plant grew slower even after filtering SO2.
Choice E: The rate of filter change should not impact. This choice alludes towards the fact that the SO2 may have seeped in between the filter change. But it would be unsafe to assume that.
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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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23 Feb 2019, 08:23
AlbertNTN wrote:
Urban air contains more sulfur dioxide than does rural air, and plants in cities typically grow more slowly than do plants in rural areas. In an experiment to see how much of the difference in growth is due to sulfur dioxide, classes in an urban and a rural school grew plants in greenhouse at their schools and filtered the greenhouse air to eliminate sulfur dioxide. Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.
Which of the following, if true, would it be most important to take into account in evaluating the result?
a. The urban school was located in a part of the city in which levels of sulfur dioxide in the air were usually far lower than is typical for urban areas
b. At both schools, the plants in the greenhouses grew much more quickly than did plants planted outdoors in plots near the greenhouse
c. The urban class conducting the experiment was larger than the rural class conducting the experiment
d. Heavy vehicular traffic such as is found in cities constantly deposits grime on greenhouse windows, reducing the amount of light that reaches the plants inside
e. Because of the higher levels of sulfur dioxide in the air at the urban school, the air filters for the urban school’s greenhouse were changed more frequently than were those at the rural school

Pls add in details of how u tackle the qsn. Thks

Responding to a pm:

LEt's understand the argument first:

There are two facts given:
1. Urban air has more sulphur dioxide.
2. Urban plants grow slower.

We want to find the effect of high sulphur dioxide in the air on the slow growth. Say, urban plants grow at the rate of 2 cm per month. Rural grow at 8 cm per month.
If we remove sulphur dioxide from air, we might see that urban plants grow at 6 cm per month while rural grow at 10 cm per month. This will show us the effect of higher sulphur dioxide. But these numbers will be dependable when everything else is kept the same. Only then we can separate out the contribution of higher levels of sulphur dioxide. If the urban greenhouse is different from the rural greenhouse, the difference could account for a part of the difference in growth rate too. Option (D) tells us that urban greenhouse gets lesser light. This means we cannot measure the contribution of higher sulphur dioxide to slower growth rate. Hence we need option (D) to evaluate the result.

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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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27 Feb 2019, 17:47
I would have gone with answer choice D if it had explicitly stated that the plantation was done "inside the school". The question states "at the school" and every school has an open plantation field. If the students planted after filtering at both schools, I assumed that they must have to constantly filter the air at the city school as the city was more polluted as mentioned.

Not sure if I was clear enough to explain my interpretation and confusion but I had chosen E due to this reason.
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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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28 Feb 2019, 02:26
Hello,

Although I answered this question correctly, I still have a lingering doubt about how to disprove E. Could someone help me understand why E would be wrong?

Thank you!
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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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03 Mar 2019, 02:51
Isn't the question different from normal evaluate question, where we use variance test to find answer choice?
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Re: Urban air contains more sulfur dioxide than does rural air, and plants  [#permalink]

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28 Apr 2019, 09:20
KHow wrote:
Hello,

Although I answered this question correctly, I still have a lingering doubt about how to disprove E. Could someone help me understand why E would be wrong?

Thank you!

Quote:
(E) Because of the higher levels of sulfur dioxide in the air at the urban school, the air filters for the urban school’s greenhouse were changed more frequently than were those at the rural school.

We are told that "classes in an urban and a rural school grew plants in greenhouse at their schools and filtered the greenhouse air to eliminate sulfur dioxide."

So we given that the air was filtered to ELIMINATE the sulfur dioxide. Sure, the urban school may have changed the filters more frequently in order to do so, but the result would be the same: sulfur dioxide was eliminated from both greenhouses, regardless of how many filters were used by each school.

What matters is that sulfur dioxide content was effectively removed as a variable. The means for doing so at each school is not actually important.

I hope that helps!
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Re: Urban air contains more sulfur dioxide than does rural air, and plants   [#permalink] 28 Apr 2019, 09:20

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