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.

What if others of the closely related group of plants producing histidine in large quantities doesnt grow in metal-rich soils?

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