PrepTest 114, Section 2, Question 22
Some types of organisms originated through endosymbiosis, the(83 more words not shown)
Which one of the following(8 more words not shown)
- AOnly organisms of(7 more words not shown)
- BA nucleomorph within(12 more words not shown)
- CNucleomorphs originated when(6 more words not shown)
- DTwo organisms will(12 more words not shown)
- EChlorarachniophytes emerged as(8 more words not shown)
Reading the argument
Did one organism become part of another? Keep that simple question in view while reading the long names. The passage defines endosymbiosis for us: one organism takes another inside it, and part of the engulfed organism becomes a working part of the host. Then we learn about a DNA-containing structure inside a particular plant. That sounds like a possible example of the process, but finding a structure inside a plant doesn't by itself settle its origin.
The gene evidence is what makes the connection. Researchers found two versions of a gene where they would expect only one if the structure weren't the remains of an engulfed organism's nucleus. The observation fits the engulfing explanation better than the stated alternative expectation.
What we’re looking for
So my prediction for the supported inference is that this plant arose through endosymbiosis. We don't need outside biology knowledge or an explanation for every structure with this name. We need to connect the evidence about this plant to the process just defined.
Working the answers
- A
This makes endosymbiosis the only way any type of organism can come to contain a nucleomorph. The passage gives evidence about one plant and its unusual genetic finding. It doesn't rule out every other origin of nucleomorphs in every other kind of organism.
- B
Some genetic material from an engulfed organism isn't necessarily all of its genetic material. The passage identifies two versions of one gene in the structure. It doesn't establish that every piece of the other organism's genetic material is still present. B adds a completeness claim the evidence doesn't support.
- C
Watch what gets engulfed. C says another organism engulfed a chlorarachniophyte, and uses that to explain the origin of nucleomorphs generally. The passage instead examines a structure within the chlorarachniophyte as evidence of an earlier engulfing event involved in that plant's origin. C changes both the direction and the scope of the proposed explanation.
- D
Finding a nucleomorph associated with an engulfing event doesn't establish that an organism must already contain one before any such event can occur. D makes it a prerequisite for endosymbiosis. We haven't been given that requirement.
- ECorrect
The two gene versions provide evidence that the internal structure is a remnant of an engulfed organism's nucleus. Combined with the definition, that supports the claim that the plant emerged from two organisms having undergone endosymbiosis.
Notice the strength of the evidence: the passage tells us what we would expect without that history, and the observed result differs from that expectation. That supports this account; it doesn't prove an exhaustive rule that no other process could ever produce two gene versions. E stays focused on the origin of the plant described.
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