Although some animals exhibit a mild skin reaction to urushiol, an oil produced by plants such as poison oak and pois...

Irina on August 26, 2019

@Minerva,

The stimulus tells us that although some animals exhibit a mild skin reaction to an oil produced by plants such as poison oak/ ivy, only humans develop painful rashes. In fact, wood rats even use branches from the poison oak plant to build their nests. Therefore, this oil probably did not evolve as a chemical defense in these plants.

The question asks us which of the following facts will most strengthen the argument.

(A) Wood rats build their nests using dead, brittle branches, not live ones.

Incorrect. This fact attacks the evidence offered in support of the conclusion, and thus weakens the argument.

(B) A number of different animals use poison oak and poison ivy as food sources.

Correct. This fact provides further evidence that poison oak/ ivy is generally not harmful to animals, thus it strengthens the fact that its oil largely fails to act as a chemical defense.

(C) It is common for plants to defend themselves by producing chemical substances.

Incorrect. This fact is irrelevant. It might be common for plants in general, but the argument is only about poison oak/ ivy.

(D) In approximately 85 of human population, very small amounts of urushiol can cause a rash.

Incorrect. This fact merely restates one of the premises that humans develop rashes, it does not add anything to the argument.

(E) Poison oak and poison ivy grew particularly well in places where humans have altered natural forest ecosystems.

Incorrect. This fact merely tells us that poison oak/ ivy prefers certain ecosystems, it has nothing to do with the chemical properties of its oil.

Does it make sense?

Let me know if you have any further questions.