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# Amphibian population

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Intern
Joined: 03 Jun 2009
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03 Jun 2009, 07:50
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Please explain this one in more details. I am very confused for this one.

Amphibian populations are declining in numbers worldwide. Not coincidentally, the earth’s ozone layer has been continuously depleted throughout the last 50 years. Atmospheric ozone blocks UV-B, a type of ultraviolet radiation that is continuously produced by the sun, and which can damage genes. Because amphibians lack hair, hide, or feathers to shield them, they are particularly vulnerable to UV-B radiation. In addition, their gelatinous eggs lack the protection of leathery or hard shells. Thus, the primary cause of the declining amphibian population is the depletion of the ozone layer.

Each of the following, if true, would strengthen the argument EXCEPT:

(A) Of the various types of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes.

(B) Amphibian populations are declining far more rapidly than are the populations of nonamphibian species whose tissues and eggs have more natural protection from UV-B.

(C) Atmospheric ozone has been significantly depleted above all the areas of the world in which amphibian populations are declining.

(D) The natural habitat of amphibians has not become smaller over the past century.

(E) Amphibian populations have declined continuously for the last 50 years.

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Director
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03 Jun 2009, 09:43
I think the answer should be "D", which actually weakens the arguement. If we break the arguement, it would be something like this:

Evidence
50 yrs -> ozone layer decreasing -> increased UV-B rays -> amphibians lack anything to shield -> are more vulnerable to UV-B

Conclusion
Primary cause of the declining amphibian population is the depletion of the ozone layer.

Anything that stregthens the evidence or assumption will stregthen the arguement as a whole.

A. If UV-B is the only type that can damage genes, then also the conclusion looks good.
B. "Amphibian populations are declining far more rapidly" stregthens the evidence that "amphibians are more vulnerable to UV-B"
C. If Atmospheric ozone has been significantly depleted in areas where amphibian populations are declining, then this adds to the list of evidence for stregthening the conclusion.
D. Correct Answer. This weakens the arguement. If "habitat of amphibians has not become smaller" then it means that the conclusion is wrong. This means that deletion in ozone hasn't effected amphibians.
E."Amphibian populations have declined continuously over 50 yrs" is also stregthening the arguemnt, since writer has mentioned that ozone layer has also decreased in last 50 yrs.
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03 Jun 2009, 09:52
I beg to differ..

I feel that only the choice A doesnt strengthens the argument ie. it adds no value to the argument.

A) Of the various types of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes. -doesnt add any value... the argument is that depletion is causing the damage and not UV-B alone

(B) Amphibian populations are declining far more rapidly than are the populations of nonamphibian species whose tissues and eggs have more natural protection from UV-B. Clearly strengthens

(C) Atmospheric ozone has been significantly depleted above all the areas of the world in which amphibian populations are declining. clearly strengthens

(D) The natural habitat of amphibians has not become smaller over the past century. elimnates an alternate cause.. hence strengthens

(E) Amphibian populations have declined continuously for the last 50 years.strengthen .. shows that it happned during the same time\

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Director
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03 Jun 2009, 10:17
Maybe I'm wrong, but by saying "The natural habitat of amphibians has not become smaller over the past century", I would assume that population of amphibians has not decreased in past centuary. This is opposite of what has been mentioned in the arguement.
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03 Jun 2009, 14:29
imo it should be E

i think there are two conclusions here

1)Amphibian populations are declining in numbers worldwide.
2) the primary cause of the declining amphibian population is the depletion of the ozone layer.

Each one of the below choices strengthen 1) or 2) except one choice.

jaxtor wrote:
Please explain this one in more details. I am very confused for this one.

Amphibian populations are declining in numbers worldwide. Not coincidentally, the earth’s ozone layer has been continuously depleted throughout the last 50 years. Atmospheric ozone blocks UV-B, a type of ultraviolet radiation that is continuously produced by the sun, and which can damage genes. Because amphibians lack hair, hide, or feathers to shield them, they are particularly vulnerable to UV-B radiation. In addition, their gelatinous eggs lack the protection of leathery or hard shells. Thus, the primary cause of the declining amphibian population is the depletion of the ozone layer.

Each of the following, if true, would strengthen the argument EXCEPT:

(A) Of the various types of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes.
if UV-B is the only type that can damage genes , then definitely ozone layer is the cause because ozone layer blocks UV-B.---> strengthen 2

(B) Amphibian populations are declining far more rapidly than are the populations of nonamphibian species whose tissues and eggs have more natural protection from UV-B. ---> clearly strengthen 2

(C) Atmospheric ozone has been significantly depleted above all the areas of the world in which amphibian populations are declining. ---> somewhat strengthen 2

(D) The natural habitat of amphibians has not become smaller over the past century. ---> somewhat strengthen 1

(E) Amphibian populations have declined continuously for the last 50 years. ---> neither give strength to 1 nor to 2

if population have declined continuously for 50 years and ozone has depleted continuously for 50 years that does mean that population decline is due to ozone depletion.

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Senior Manager
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03 Jun 2009, 14:34
Neochronic wrote:
I beg to differ..

I feel that only the choice A doesnt strengthens the argument ie. it adds no value to the argument.

A) Of the various types of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes. -doesnt add any value... the argument is that depletion is causing the damage and not UV-B alone

(B) Amphibian populations are declining far more rapidly than are the populations of nonamphibian species whose tissues and eggs have more natural protection from UV-B. Clearly strengthens

(C) Atmospheric ozone has been significantly depleted above all the areas of the world in which amphibian populations are declining. clearly strengthens

(D) The natural habitat of amphibians has not become smaller over the past century. elimnates an alternate cause.. hence strengthens

(E) Amphibian populations have declined continuously for the last 50 years.strengthen .. shows that it happned during the same time\

I agree that (A) is the correct answer. Whether or not UV-B rays is the only type is irrelevant to the argument. The other 4 choices strengthen the argument.

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04 Jun 2009, 03:33

jaxtor

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Re: Amphibian population   [#permalink] 04 Jun 2009, 03:33
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