Conditional reasoning and Must Be True Problems. pg 136 #2

[reop6780]

This intimidating question was not only confusing with stimuli but with answers.

While the correct answer is E, the rest of the answers are exaggerated somehow.

I assume the expression of "only," and "all" in answer A and B were noticeable enough to imply exaggeration.

However, I do not understand why answer C is exaggerated while answer E is absolutely correct.

The explanation cites from the stimuli that it deals with one unusual nucleomorph, and the answer C tries to generalize this case.

Then, how about answer E?
One unusual nucleomorph is found in a chlorarachiniophyte. And is it okay to say "Chlorarachiniophytes emerged.." to state "the nucleomorph were the remains of an engulfed organism's nucleus" ?

Nucleomorph is only part of Chlorarachiniophytes. How is it not exaggerated answer?

[BethRibet]

Hi Reop,

Thanks for this question. Many test-takers do find the especially advanced scientific jargon in this question intimidating!

Regarding answer choice C, one can rule it because there is actually not enough support in the stimulus to tell us how nucleomorphs at large originate. As you note, we only have an example of a case in which a particular nucleomorph formation is linked to a particular event. This answer chance attempts to link all nucleomorph formations to that same event.

Regarding answer choice E, there is not similar overgeneralization -- the conditions in the answer choice are entirely applicable to the example of the chlorarachniophytes.

The conditional relationship that applies here is essentially this:

If not the remains of an engulfed organism's nucleus, then single version of gene
or ~REON --> SVG
The contrapositive is then ~SVG --> REON
or If not a single version of the gene, then it is the remains of an engulfed organism's nucleus

Applying the logical rule to this case: The chlorarachniophyte has two versions of the gene, i.e. it does not have a single version of the gene. By the contrapositive, then it must follow that the chlorarachniophyte has a nucleomorph that was formed by the engulfing of an organism. From the first premise, we know that when an organism engulfs another in this way, the process is called endosymbiosis.

It then follows that Chlorarachniophyes were the product of endosymbiosis, which corresponds to answer choice E.

I hope this helps!

Beth