Critical Reasoning

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.


Please explain option A

What one is looking for in handling this question is an answer choice that does not provide any information that further supports the conclusion.

The argument is that increased UV-B radiation resulting from ozone layer depletion is causing the amphibian population decline.

Answer choice A says that of the various types of radiation, only UV-B destroys genes. This is a trap answer, because it seems to say something that supports the argument when in reality it does not.

The argument's conclusion is is not that UV-B is the only type of radiation that can harm amphibians. The conclusion is that the cause of the declining population is the depletion of the ozone layer, which depletion allows UV-B to reach amphibians and harm them.

What is said in answer choice A does not support the conclusion that the ozone layer depletion is causing the decline in amphibian populations.

Look at the other answer choices for contrast.

B supports the conclusion because it demonstrates that populations of animals that are less affected by UV-B are not declining as much as amphibian populations, supporting the idea that UV-B that is not being blocked by ozone is making the difference.

C serves to confirm that ozone depletion is present wherever the populations are declining.

D eliminates another possible cause of population declines.

E shows that the population declines correlate with the depletion of ozone.

A alone provides no additional information supporting the conclusion.

How UV-B compares with other forms of radiation is irrelevant.

Marty Murray wrote:What one is looking for in handling this question is an answer choice that does not provide any information that further supports the conclusion.

The argument is that increased UV-B radiation resulting from ozone layer depletion is causing the amphibian population decline.

Answer choice A says that of the various types of radiation, only UV-B destroys genes. This is a trap answer, because it seems to say something that supports the argument when in reality it does not.

The argument's conclusion is is not that UV-B is the only type of radiation that can harm amphibians. The conclusion is that the cause of the declining population is the depletion of the ozone layer, which depletion allows UV-B to reach amphibians and harm them.

What is said in answer choice A does not support the conclusion that the ozone layer depletion is causing the decline in amphibian populations.

Look at the other answer choices for contrast.

B supports the conclusion because it demonstrates that populations of animals that are less affected by UV-B are not declining as much as amphibian populations, supporting the idea that UV-B that is not being blocked by ozone is making the difference.

C serves to confirm that ozone depletion is present wherever the populations are declining.

D eliminates another possible cause of population declines.

E shows that the population declines correlate with the depletion of ozone.

A alone provides no additional information supporting the conclusion.

How UV-B compares with other forms of radiation is irrelevant.

Hi Marty,

I understand what you are getting at and I can also see how other statements can be eliminated but my question is doesn't A still strengthen the argument.

If Ozone B is the only type to damage genes and it is being let in by the depletion of Ozone layer then ofcourse it is causing decline of the amphibian population. Therefore, this is affecting the cause and effect but it is one step ahead of the cause.

Please suggest what do you think of my reasoning and where do you think I am going wrong with my analysis?

[email protected] wrote:Hi Marty,

I understand what you are getting at and I can also see how other statements can be eliminated but my question is doesn't A still strengthen the argument.

If Ozone B is the only type to damage genes and it is being let in by the depletion of Ozone layer then ofcourse it is causing decline of the amphibian population. Therefore, this is affecting the cause and effect but it is one step ahead of the cause.

Please suggest what do you think of my reasoning and where do you think I am going wrong with my analysis?

You are going wrong in your analysis right here.

"If Ozone B is the only type to damage genes and it is being let in by the depletion of Ozone layer then of course it is causing decline of the amphibian population."

Consider what the argument concludes.

"the primary cause of the declining amphibian population
is the depletion of the ozone layer."

The "primary cause ..."

Your line of reasoning is that since UV-B is the only type of ozone blocked radiation that destroys genes, it is the "primary cause" of the declining amphibian population.

Perhaps where you went wrong is in limiting yourself to considering ozone layer depletion related causes. What about causes not closely related to ozone layer depletion?

Birds could be eating the amphibians.

Some kind of bacteria or fungus could be harming the health of the amphibians.

Rising temperatures could be the "primary cause" of the decline in the populations of amphibians.

So to get this right you have to consider that there could be causes other than radiation.

Notice how C, for instance, addresses the possibility of the other causes.

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

Ok, if birds' eating the amphibians were the cause of the decline, then it would make sense that the amphibian populations would be declining all over, not just where the ozone has been depleted. Similarly, it is likely that bacteria would harm the amphibians all over the planet, not just where the ozone has been depleted.

So A merely narrows down HOW ozone depletion might be resulting in the decline, if ozone depletion is in fact the primary cause, but BUT DOES NOT SUPPORT THE CONCLUSION THAT OZONE DEPLETION, rather than something else, IS THE PRIMARY CAUSE.