Critical Reasoning

vishalwin wrote:A certain cultivated herb is one of a group of closely related plants that thrive in
soil with high concentrations of metals that are toxic to most other plants.
Agronomists studying the growth of this herb have discovered that it produces
large amounts of histidine, an amino acid that, in test-tube solutions, renders these
metals chemically inert. Hence, the herb's high histidine production must be the
key feature that allows it to grow in metal-rich soils.
In evaluating the argument, it would be most important to determine which of the
following?

(A) Whether the herb can thrive in soil that does not have high
concentrations of the toxic metals
(B) Whether others of the closely related group of plants also produce
histidine in large quantities
(C) Whether the herb's high level of histidine production is associated with
an unusually low level of production of some other amino acid
(D) Whether growing the herb in soil with high concentrations of the metals
will, over time, reduce their concentrations in the soil
(E) Whether the concentration of histidine in the growing herb declines as
the plant approaches maturity

GMATGuruNY wrote:

vishalwin wrote:A certain cultivated herb is one of a group of closely related plants that thrive in
soil with high concentrations of metals that are toxic to most other plants.
Agronomists studying the growth of this herb have discovered that it produces
large amounts of histidine, an amino acid that, in test-tube solutions, renders these
metals chemically inert. Hence, the herb's high histidine production must be the
key feature that allows it to grow in metal-rich soils.
In evaluating the argument, it would be most important to determine which of the
following?

(A) Whether the herb can thrive in soil that does not have high
concentrations of the toxic metals
(B) Whether others of the closely related group of plants also produce
histidine in large quantities
(C) Whether the herb's high level of histidine production is associated with
an unusually low level of production of some other amino acid
(D) Whether growing the herb in soil with high concentrations of the metals
will, over time, reduce their concentrations in the soil
(E) Whether the concentration of histidine in the growing herb declines as
the plant approaches maturity

This is a CAUSAL argument.
In a causal argument, A and B are observed together, and the CR concludes that A CAUSES B.

Premise = A and B are observed together:
A cultivated herb produces histidine and is able to grow in metal-rich soils.
Conclusion = A causes B:
Histidine CAUSES the herb to be able to grow in metal-rich soils.

The correct answer choice must help us determine whether this conclusion is valid.
Rephrase the answer choices as STATEMENTS.
Rephrased as a statement, the correct answer choice will either STRENGTHEN or WEAKEN the link between HISTIDINE and THE ABILITY TO GROW I METAL-RICH SOILS.
B, rephrased as a statement:
Others of the closely related group of plants also produce histidine in large quantities.
Here, other plants in the closely related group THAT THRIVE IN SOIL WITH HIGH CONCENTRATIONS OF METALS also produce HISTIDINE, STRENGTHENING the conclusion that histidine CAUSES a plant to be able to grow in metal-rich soils.

The correct answer is B.

Crystal W wrote: Thank you for your explanantion. Can you explain other choices, especially D?

RBBmba@2014 wrote:Hi Verbal Experts,
Got a quick question on this CAUSAL ARGUMENT.

In GMAT, when we have A causes B -- to STRENGTHEN this CAUSAL relation we need to find the option that says any of the followings:

1. There is NO OTHER REASON for B.

2. REVERSE CAUSATION doesn't hold true.

Am I correct ?

P.S: If yes, then which of the above satisfies here ?

DavidG@VeritasPrep wrote:

RBBmba@2014 wrote:Hi Verbal Experts,
Got a quick question on this CAUSAL ARGUMENT.

In GMAT, when we have A causes B -- to STRENGTHEN this CAUSAL relation we need to find the option that says any of the followings:

1. There is NO OTHER REASON for B.

2. REVERSE CAUSATION doesn't hold true.

Am I correct ?

P.S: If yes, then which of the above satisfies here ?

That's a reasonable way of thinking about causality arguments. In this case, the correct answer would address explanation 1. If the related species did not produce much histidine, and these plants were still surviving, then there must be another reason, aside from histidine production, that would have allowed them to do so.

RBBmba@2014 wrote:

DavidG@VeritasPrep wrote:

RBBmba@2014 wrote:Hi Verbal Experts,
Got a quick question on this CAUSAL ARGUMENT.

In GMAT, when we have A causes B -- to STRENGTHEN this CAUSAL relation we need to find the option that says any of the followings:

1. There is NO OTHER REASON for B.

2. REVERSE CAUSATION doesn't hold true.

Am I correct ?

P.S: If yes, then which of the above satisfies here ?

That's a reasonable way of thinking about causality arguments. In this case, the correct answer would address explanation 1. If the related species did not produce much histidine, and these plants were still surviving, then there must be another reason, aside from histidine production, that would have allowed them to do so.

Hi Dave,
Thanks for the clarification.

So, for a CAUSAL CR on GMAT, when we have A causes B -- to STRENGTHEN this CAUSAL relation we need to find the option that says any of the followings (in addition to the above mentioned TWO ways to STRENGTHEN):

3. There is NO OTHER REASON that causes BOTH A & B.

4. Another EVIDENCE that shows A ACTUALLY causes B.

5. If NOT A then NOT B.

ALL these FIVE are possible ways to STRENGTHEN the CAUSAL relation on GMAT CR, I guess. Am I correct ?

Anything else that we should consider in this aspect ?

DavidG@VeritasPrep wrote:You can think of 3 and 4 as being part of 1 and 2. (If there's nothing else that causes A and B, then clearly there's nothing else that causes A. And the evidence that A actually causes B is typically conveyed by stipulating that either there's no alternative cause or that it's not the case that B causes A.)

DavidG@VeritasPrep wrote:Be careful about 5. If condition A leads to scenario B, it's not necessarily true that the absence of A entails the avoidance of B. Think of a simple case. If I drive 120 mph then I will get into an accident, does not mean that if I don't drive 120 mph that I will not get into an accident.

I meant that for STRENGTHEN CAUSAL CR on GMAT, this rule #5 will hold true, BUT NOT for ASSUMPTION CAUSAL CR (in which MUST BE TRUE aspect comes into play). Is this wrong to consider ?

DavidG@VeritasPrep wrote:(But you're right that the correct answer must be logically true in an assumption question, whereas in a strengthen question, the correct answer will make the conclusion more likely if it's true.)

DavidG@VeritasPrep wrote: I'm not quite sure what you're asking here - can you elaborate?

RBBmba@2014 wrote:

DavidG@VeritasPrep wrote:(But you're right that the correct answer must be logically true in an assumption question, whereas in a strengthen question, the correct answer will make the conclusion more likely if it's true.)

Thanks for confirming this...

DavidG@VeritasPrep wrote: I'm not quite sure what you're asking here - can you elaborate?

Sure.
What I meant is: for STRENGTHEN CR on GMAT, in which we observe the CAUSAL ARGUMENT (such as A causes B), one way to STRENGTHEN the CONCLUSION of that CR could be If NOT A then NOT B. Isn't it ?

However, If NOT A then NOT B can't be the (logic of an) OA in an ASSUMPTION CAUSAL CR because it doesn't satisfy the MUST BE TRUE aspect of ASSUMPTION CR.

Is this understanding NOT correct ?

Option E is incorrect because:

1. If we consider that "the concentration of histidine in the growing herb declines as the plant approaches maturity", then it seems to contradict the PREMISE in the argument that says that this herb produces large amounts of histidine as it grows.

Moreover, even if histidine declines as the plant approaches maturity, the also it desn't substantiate or shed light that whether histidine production must be the key feature.

Am I correct ?

DavidG@VeritasPrep wrote:
Well, just because histidine production declined, doesn't necessarily mean that the plant isn't still producing large amounts of it. (If you make $2 billion in year one and $1.9 billion in year two, your profits have declined, but they're still pretty healthy.)

But the second point is 100% correct.

If we consider that "the concentration of histidine in the growing herb declines as the plant approaches maturity", then it seems to contradict the PREMISE in the argument that says that this herb produces large amounts of histidine as it grows