#22-Some types of organisms originated through endosymbiosis

[Administrator]

Complete Question Explanation

Must be true. The correct answer choice is (E)

Given that the nucleomorph is part of the chlorarachniophyte and is the
remains of an engulfed organism’s nucleus, we have strong evidence
that the chlorarachniophyte came about as the result of endosymbiosis
(the engulfing of one organism by another). This is most clearly stated in
answer choice (E), the correct answer.

Answer choice (A): This is an Exaggerated answer: the word “only” at
the beginning of the answer choice is too strong, and there is no evidence
in the stimulus to suggest that a conditional relationship exists between
endosymbiosis and nucleomorphs.

Answer choice (B): This is also an Exaggerated answer: the word “all” in
the middle of the answer choice is too strong.

Answer choice (C): The stimulus discusses one unusual nucleomorph
whereas the answer choice attempts to make a general statement about
all nucleomorphs. As such, the answer choice exaggerates the situation
and is incorrect. Note that the first three answer choices in this problem
all exaggerate some aspect of the stimulus. This is not surprising: in a
stimulus with complex terminology, the test makers wisely attempt to prey
upon that difficulty by presenting answers that have a degree of truth but
go just a bit too far. These answer choices are attractive to a test taker who
fails to lock down the facts of the stimulus.

Answer choice (D): This answer choice is similar to answer choice
(A), and is incorrect for similar reasons: no conditional relationship is
established where nucleomorphs are necessary for endosymbiosis.

Answer choice (E): As explained previously, this is the correct answer
choice.

[rameday]

Hello,

I had a tough time understanding how they got to the answer E.

I spotted the conditional relationship and I correctly drew my diagram. This is what I had.

negated REON FSVG

and my CP was

negated FSVG REON.

However from there I had no clue as to how to proceed to answering the question. My pre phrase was centred around the CP and when I saw that no asters were remotely related to that I realized how screwed I was.

A

[KelseyWoods]

Hi A!

You did a great job of diagramming and taking the contrapositive of the conditional statement in the last sentence. But you also need to remember to connect that conditional statement to the other information we have in the stimulus.

From the second sentence and the first part of the last sentence, we know that chlorararchniophytes have nucleomorphs that have two versions of the gene. Since it has 2 versions of the gene, that means you do NOT find a single version of the gene. You can diagram that as:

C negated FSVG

Combine that with your contrapositive of the last conditional statement:

C negated FSVG REON

Now, we can go back to the first sentence. The first sentence tells us that endosymbiosis is when one organism is engulfed by another. That means that if you are the remains of an engulfed organism's nucleus, then you have undergone endosymbiosis. You can diagram that like this:

REON END

Combine that with our conditional chain:

C negated FSVG REON END

Just looking at the ends of the conditional chain, you have:

C END

That gives you answer choice (E).

Hope this helps!

Best,
Kelsey

[rameday]

Ok that makes a lot of sense. So because of the complexity of linking the chain relationships together is it safe to say that the correct answer will deal with liking the first and last term together and I don't have to search for the contrapositve as the correct choice? Cause i am in the habit of doing the contrapositve for every diagram and that sometimes takes time and is unnecessary work.

Also this is a random concern I had but in parallel flaw. If the stimulus has a MR for example

x y and then it says y x

and then it asks you to match the flawed reasoning and the AC have two answers with MR, one which is

a b and then b a

and then another answer choice that is

negated a b and then b negated a

does the presence of the negation matter in this situation even though it is still a MR or is the answer the MR without the negation (identical to the stimulus)?

Lets say you get a stimulus that is x y and then it says y x and it says parallel that reasoning and the only other MR that parallels it is negated a b and then b negated a. Even though it is negated does that matter if it is still a MR?

A

[Robert Carroll]

rameday,

Even when there is a chain of conditionals, it's not always true that the correct answer choice will involve the entire chain. Further, the contrapositive of the chain (which is the same as the chain of contrapositives) could also be the correct answer choice. That's why it's important to diagram everything out and get all the contrapositives - the task of getting contrapositives is easy once you've got the original conditionals done, so it's not much extra work. Just be open to the possibility that any of the conditionals and contrapositives you inferred could be the correct answer, not necessarily the chain.

When you see a chain, it's good to look for an answer the uses the whole chain, but definitely not good to ignore answers that involve less than the entire chain - as an example, look at Lesson 2, p. 13, #6. The last conditional ("to be a sophisticated listener one must understand one's musical roots") is not used in the correct answer - it didn't have to be, and the correct answer still Must Be True. So be careful!

If you have a situation where it looks like there are two Mistaken Reversals and you need to parallel a MR in the stimulus, it is unlikely that the only difference between the two is that one has one condition negated - there's probably something else different, like an absolute vs qualified conclusion or something like that. Otherwise, a Mistaken Reversal is a Mistaken Reversal.

Robert Carroll

[rameday]

Ok that makes total sense. Thanks!

[sicm91]

Hi! So the explanation indicates that answer choice C exaggerates a claim to include all nucleomorphs, but doesn't answer choice E (which includes all chlorarachniphytes) also exaggerate? Also, wouldn't answer choice C also be wrong because it's the opposite of what the stimulus indicates--which is that the organism doing the engulfing is the chlorarachniphyte, not the nucleomorph. Thanks!

[KelseyWoods]

Hi sicm91!

Whether an answer choice is "exaggerated" or not always depends on the type os information we've been given in the stimulus. The stimulus might give us information about "All X..." and in that case, an answer choice about "All X..." would not be exaggerated. But when an answer choice tries to make a generalized statement about a topic that the stimulus doesn't give us general information about, then that answer choice is exaggerated.

In this case, the stimulus only tells us about "an unusual nucleomorph" within the chlorarachniophyte plant. The stimulus is about one specific nucleopmorph that we are told is "unusual," meaning that it is definitely not representative of all nucleomorphs. We can't use information about "an unusual nucleopmorph" to prove an answer choice about "nucleomorphs" more generally. That's why this answer choice is exaggerated. Of course, answer choices can be incorrect for more than one reason. Another problem with answer choice (C), as you point out, is that the stimulus tells us that this specific nucleomorph is inside of the chlorarachniophyte, rather than something engulfing a chlorarachniophyte. But even if this was switched around to say something like "Nucleomorphs originated when an organism was endosymbiotically engulfed by a chlorarachniophyte," it would still be incorrect because an example of one "unusual" nucleomorph can never be used to prove a statement about nucleomorphs in general.

The stimulus gives us much more general information about chlorarachniophytes. We know that chlorarachniophytes contain an unusual nucleomorph that has two versions of a gene which indicates that endosymbiosis has occurred. Because we have general information about chlorarachniophytes and not just information about one unusual chlorarachniophyte, we can prove a more general statement about chlorarachniophytes.

Hope this helps!

Best,
Kelsey

[mahmed19]

Hello!

I am still confused by why E is correct. Is it because of "the engulfing of one organism by another... so that a former becomes a part of the latter." Is it because we can infer that the unusual nucleomorph underwent endosymbiosis, that chlorarachniophytes also have to?

Thank you in advance

Maliha

[Robert Carroll]

Maliha,

The first sentence defines endosymbiosis as the engulfing of one organism by another so that a part of the former becomes a functioning part of the latter. The last sentence tells us that the chlorarachniophyte has two versions of a gene, and that we would expect only one version if that part of the chlorarachniophyte were not the remains of an engulfed organism's nucleus; i.e., according to the definition of endosymbiosis in the first sentence, if it were not the result of endosymbiosis. So the chlorarachniophyte has a property that could not be true unless it's undergone endosymbiosis, which is what answer choice (E) says.

Robert Carroll