A certain cultivated herb is one of a group of closely related plants

Solution
passage analysis                                                             
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.

There is a certain herb that belongs to a group of closely related plants. These plants grow abundantly in soils which have high concentrations of metals. For most other plants, this high metallic content of the soil is toxic/poisonous.

 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.

Agronomists, who are studying the growth of this herb, have discovered that it produces histidine in large amounts. Histidine is an amino acid. In test-tube experiments, histidine acts on the metals present in the soil and leaves them inactive.

 Hence, the herb's high histidine production must be the key feature that allows it to grow in metal-rich soils.

Therefore, the presence of histidine in large amounts must be the main factor that helps the herb grow in metal-rich soils.

Conclusion:
A certain herb's high histidine production must be the key feature that allows it to grow in metal-rich soils
Based on the fact that:
It produces large amounts of histidine, an amino acid that, in test-tube solutions, renders these metals chemically inert


pre-thinking                                                                 
Falsification question
In what scenario will the herb's high histidine production not be the key feature that allows it to grow in metal-rich soils?
Given that →herb that belongs to a group of closely related plants
                  →These plants thrive in soils that have high concentrations of metals.
                  →For most other plants, this high metallic content of the soil is toxic.
                  →this herb produces histidine in large amounts
                  →In test-tube experiments, histidine acts on the metals present in the soil and leaves them inactive

Thought Process
Agronomists credit the production of histidine in large quantities in the herb to be the single most important factor in the survival of the herb in soils that have high metallic content, because most other plants would not grow in such soils. But the other plants of the group to which this herb belongs also grow in the same metallic soil. Possibly then if histidine is responsible for the growth of this herb, then it must be responsible for the survival of the related plants also. But do those plants produce histidine?

Falsification condition#1
What if there were present some other chemicals in higher quantities instead of histidine in the other plants of the group of plants to which this herb belonged?
In that case, it is possible that those chemicals could be responsible for the survival of that group of related plants.

Assumption#1
The other closely related plants also have histidine in similar large amounts.

Falsification condition#2
What if the other closely related plants had evolved certain adaptations that helped them to survive the toxicity of the soil?
In that case, the survival could be attributed mostly to those adaptations (say special roots that help nullify toxicity)

Assumption#2
The group of closely related plants does not have any special adaptations that can be considered as key survival tools.

Answer Choice Analysis

A
The conclusion is that histidine is the reason the herb can grow in toxic soil. What histidine does in non-toxic soil is not of concern here.

Hence, this option is incorrect.

B
The answer to this evaluate question is in line with our pre-thinking assumption#1

Let us put it through the variance test

Yes- others of the closely related group of plants also produce histidine in large quantities
This strengthens our belief in the conclusion

No- others of the closely related group of plants do not produce histidine in large quantities
This weakens our belief in the conclusion. If the other plants of the same group do not produce histidine in large amounts and yet survive in the high metallic soil, then something other than histidine is the key factor helping them survive.

Hence, this is the correct choice.

C
Let us say because of histidine, some other amino acid is impacted in its production. But does that prove that histidine is or is not the key factor behind the growth. Do we know whether this other amino acid which when produced at unusually low levels has any connection with the growth of the herb? No.

Hence, it is not the correct answer.

D
Our goal is to evaluate the causality of growth in toxic soil. What happens to soil once the plant grows is not of importance to the conclusion.

Hence, not the correct option.

E
Say if the answer is yes. Does that answer my query as to whether histidine was in the first place, not responsible in inhibiting the toxicity of the soil and helping the herb thrive? In the growing stage, histidine was present in certain concentrations. We are concerned with that stage of the herb. And this option neither confirms nor refutes the strength of this argument

Hence, this is not the correct option.

I have one doubt.

We have to evaluate that "Hence, the herb's high histidine production must be the key feature that allows it to grow in metal-rich soils."
.

Argument clearly states that "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".

The information in option B provides that others of closely related groups produces the amino acids. How does this information impact the conclusion? if you say no, this clearly states that the other group doesn't have capability to grow in metal rich area. but it will not affect that herb's high histidine production must be the key feature that allows it to grow in metal-rich soils.

Responding to a pm:



(E) doesn't help us evaluate the argument. Even if the concentration of histidine decreases after the plants mature, histidine could certainly be that substance which helps them grow from saplings into mature plants on metal rich soil. Also, perhaps the plants need less histidine to handle the metals after they mature - we do not know. Knowing whether the histidine levels decrease as the plants mature cannot help us judge whether histidine helps them survive in metal rich soils.

Premise : X herb grows in metal-rich soil just fine. because of amino acid prodn but not other plants of the same group. why? it is assumed that they don't produce histidine.

conclusion -> high histidine production helps herb to grow in hostile enviornment.

Prethinking:

What if other plants also produce histidine. if yes, then we can definetely say its not the case. it's some other factor. if no, then ok, it might be histidine thing.

Worst case scenario, even if other plants don't produce histidine, it is some other factor which we dont know yet leads to growth of X herb in metal rich sol. some temp thing. or something else. (But here we are considering that all other factor are same for both of them)

so straghtaway B.

Hi Karishma,

Can you help me with the following confusion.

I was confused between B and C.
My confusion with C is that if histidine production is associated with low levels of production of other substances then maybe low level of other substances are providing protection against metals and not histidine. Can you please show me how to eliminate this?

We are trying to establish a connection between histidine and metals. (B) helps us in evaluating that connection as discussed in my explanation above.

C) Whether the herb's high level of histidine production is associated with an unusually low level of production of some other amino acid

Here, we are trying to connect histidine to "some other amino acid". We don't know if "some other amino acid" will have any connection with metals. Shouldn't we instead try to connect Histidine to metals directly?

Why is E incorrect?

It would be great if anyone can elaborate all the answer choices.....

Histidine production over the life cycle is not related to the conclusion. The conclusion is whether Histidine is the factor that allows these planst to survive in metal rich soils.

Option B:
Answer "yes": If other closely related plants (who grow in metal rich soils) also produce Histidine, then Histidine could be the factor for the survival of these plants in metal rich soils.
Answer "no": Histidine is not the factor that causes these plants to survive in metal rich soils - there should be some other factor.

"Yes" supports the conclusion and "no" opposes the conclusion. Therefore B is the correct choice.
(This yes / no approach is a basic technique to solve evaluate questions - if you cannot eliminate just by observation, use it for the other choices yourself. Please post again if you have doubts with a particular choice.)

How to eliminate A and C ? I am not able to find the reasons for elimination. Thanks

All right! This is a very hard CR question. But this simply tests causality then why it is still so hard? This is because the question stem is not asking you to Strengthen or Weaken, it is indeed asking you to do both i.e. EVALUATE the argument. (Persional opinion on toughness of the question).



Pattern: If two things found happening together then one causes the other.

Mapping of the Pattern with the argument:

Herb is growing in the soil with high concentration of metals AND herb is producing large amount of histidine. (these two things are happening together)
Histidine is causing herb to grow in such soil

What would you do to strengthen such causality?

You would bring a fact to show that the causality is indeed correct. You would say there is no other cause or say the reverse of the causality is not true.

What would you do to Weaken such causality? – Just the opposite of what you would do to strengthen (as stated above)

(A) Whether the herb can thrive in soil that does not have high concentrations of the toxic metals

We are not talking about other kind of soil here. We are focusing on the production of histidine and growth in METAL RICH SOIL. Because if you find out whether heb thrive in non-metal-rich soil then it does not tell you about the causality.

All right suppose herb does grow in the non-metal-rich soil. Then herb MAY/MAY NOT be able to grow in METAL-RICH soil and if it may indeed grow then you do not know the casue/factor that helps it to grow in metal-rich soil as well.

Think of the case – METAL RICHNESS OF SOIL does nothing to the growth of herb.

(B) Whether others of the closely related group of plants also produce histidine in large quantities

What this choice actually says is – If all other herbs THAT ARE CLOSELY RELATED to this herb, also produce histidine then this could indeed be the THING/THE CAUSE/THE FACTOR for them to grow.

Isn’t it true that if something is happening to everyone of a certain kind then there could be some cause. If I tell you that in a city all children are falling sick since last week then you would want to believe if I say that a virus or bad water from the city supply was the cause?

So if you knew THAT what happens to this herb happens to all other herbs that are closely related to it then Evaluation is done.

(C) Whether the herb’s high level of histidine production is associated with an unusually low level of production of some other amino acid

Again, this does not tell anything about the said causality. This is bringing up another causality to test i.e. whether histidine production itself is caused/associated with different type of amino acid. We need to closely keep our focus on what are the major things argument discusses.

(D) Whether growing the herb in soil with high concentrations of the metals will, over time, reduce their concentrations in the soil

Soil is rich of METAL with high concentration. How the reduction in this concentration is related to the given causality? This is certainly not talking about the factors that are involved. Histidine make the herb grow in metal rich soil. Whether less metal reich soil would do or not is not the focus of discussion.

(E) Whether the concentration of histidine in the growing herb declines as the plant approaches maturity

It is told that LARGE AMOUNT of histidine is produced. Now if that is the case why are we bothering to evaluate whether concentration of histidine declines or not.

Folks help me out here.

My logic on "E" - because if the histidine concentration declines as the plant approaches maturity, then maybe histidine was used to grow the plants and when growth was no longer needed (towards maturity), concentrations started declining.
My logic on "B" - if others of the closely related group of plants are also found to produce histidine in large quantities, it just says that this chemical is common in the group of closely related plants but it doesn't per se mean that its KEY in growth so I feel like its such a jump in conclusion here. Maybe Histidine is common in the group of the closely related plants because it serves other functions.

Please point me to where my logic is flawed (because clearly it is)

oasis90

I might be late for the party, but let me know if this helps.

Lets visualize the situation. Let say this herb thrive in soil with mercury in it. mercury is toxic to most plants. while finding the answer of this strange phenomenon , Scientists observed this plant produce a lot of histidine which probably react with this metal and inert it. But to be sure of this conclusion scientists have to do what ?

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. ---- yes or no either way histidine is rendering with this metal or not is not clear.
(B) Whether others of the closely related group of plants also produce histidine in large quantities. --- so if no then how that group is surviving in such kind of soil? there must be something else. if yes then these all kind of plants has one ting in common, histidine that must be playing some role for such situation. over all not very lucrative choice for yes part lets keep it for later.
(C) Whether the herb's high level of histidine production is associated with an unusually low level of production of some other amino acid --- this choice is not doing much to our cause.
(D) Whether growing the herb in soil with high concentrations of the metals will, over time, reduce their concentrations in the soil. --- This seems a lucrative choice. in case of yes, it makes a case for us. but metal that reduces from the soil, how to justify it, is plant absorbing that metal ? is histidine is reacting? situation is not very clear.
(E) whether the concentration of histidine in the growing herb declines as the plant approaches maturity --- so with herb reaching to maturity, concentration of histidine declines, again as we did in previous choice, metal that reduces from the soil, how to justify it, is plant absorbing that metal ? is histidine is reacting? situation is not very clear.

B is the best answer.

Hi GMATNinja,
I am confused between B and D and i chose D as the answer.
Can you please explain what is wrong with D?

Thanks a lot for your help.

Let's take another look at the conclusion of the argument:

From the passage, we know that a certain herb can survive in metal-rich soils. The conclusion of the passage states that this survival ability is due to the herb's histidine production. The correct answer choice to evaluate this argument should raise a question that, if answered, would shed more light on whether histidine is truly the "key feature" that allows the herb to grow in toxic soil.

Let's take a look at answer choice (D):

This answer choice is interesting -- if the herb reduces the amount of metals in the soil over time, then maybe later generations of the herb do not need any special adaptations to soil with toxic metals.

However, we know from the evidence in the passage that the herb can survive in toxic soil. Even if later generations do not have to do so, we still need to know whether the herb is able to survive because of its histidine production or some other factor.

In other words, even if the metals in the soil are gradually reduced over time, how did the first generation of the herb survive in the toxic soil? Answering the question raised in answer choice (D) would not clarify role of histidine in the herb's survival, so it does not help us evaluate the argument in the passage. Eliminate (D).

I hope that helps!

Hi GMATNinja VeritasKarishma nightblade354


Conclusion:the herb's high histidine production must be the key feature that allows it to grow in metal-rich soils.

As in Evaluate question Yes/No(Extremes) should Strengthen/Weaken the argument.
My question regarding the answer choice B is that for Yes answer the conclusion gets strengthen, But for No Conclusion does not gets weaken.

(B) Whether others of the closely related group of plants also produce histidine in large quantities.
Ans: No others of the closely related group of plants do not produce histidine in large quantities.
So what, It may be the case that the others do not have histidine as the key feature but histidine is the key feature of Herb. Others have some different Key feature.

These plants are "closely related". The soil is toxic to most other plants. It is highly likely that these plants share a common feature that makes them immune to the toxicity of the soil.

B should be correct answer.
Please pay attention to this line: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.
So if we get to know that other plants which exhibit the same behavior of thriving in soil with high concentrations of metals that are toxic also produce "large amounts of histidine," then we are good