#22-Some types of organisms originated through endosymbiosis

[mahmed19]

That makes more sense, thank you!

[SGD2021]

Hello, if it is easier for us to solve a question like this without conditional reasoning, is it okay to just not use the diagramming method and approach it as if it were a normal (non conditional reasoning) problem?

Also, is it always the case that if the necessary condition does not occur, then we automatically know we can use that information and put it into contrapositive form to draw a new conclusion? (so if the necessary condition does not occur, the contrapositive is ALWAYS enacted, and we know the sufficient condition cannot occur)

Finally, the sufficient condition always comes after "If" in the “if, then” construction and necessary always comes after the "then," correct?

[Adam Tyson]

Correct on all counts, SGD2021! While a conditional analysis is called for here and would be a great way to simplify this otherwise complex set of statements, you aren't required to do that if you have another approach that works for you, such as a solid intuitive grasp of the information.

Whenever a Necessary Condition does not occur it must logically trigger the contrapositive such that the Sufficient Condition cannot occur, but beware of conditional relationships in which there are multiple Necessary Conditions joined with an "or." In those cases, the contrapositive is not triggered by just one Necessary Condition failing to occur; it is triggered only when ALL Necessary Conditions fail to occur (because that OR becomes an AND when you do the contrapositive.)

And yes, "if" introduces a Sufficient Condition while "then" introduces a Necessary Condition. There are many other indicator words and phrases and you should study and perhaps even memorize all of the common ones. Be especially careful of phrases that include the word "only," as in "only if" and "only when," because despite including the words "if" and "when" (which indicate Sufficient Conditions when they are by themselves), the addition of "only" converts them into Necessary Condition indicators.

Also, be careful about the special indicators "Unless," "Except," Until," and "Without," all of which indicate Necessary Conditions and which trigger what we call the "Unless Equation." That means the other condition in the relationship must be negated to become Sufficient! You can read more about that in our course books and the LR Bible, among other sources.

[lsatquestions]

I see now why E is correct, but do you mind giving a more thorough explanation of why B is incorrect. The specific nucleomorph originated through endosymbiosis, where one organism got fully engulfed by another, so it made sense to me that it held all the genetic material of the other organism. I had E as a contender but I thought the stimulus was just referring to an usual nucleomorph that was discovered and not necessarily in every chlorarachinophyte.

Is B incorrect because genetic materials are not really discussed? Or that the genetic materials are not necessarily preserved after endosymbiosis?

[katehos]

Hi lsatquestions!

The second reason you posed as to why (B) is incorrect is almost spot on! As a few others have mentioned, answer choice (B) is an Exaggerated Answer because it says "holds all of the genetic material of some other organism." When we look to the stimulus itself, we do not have evidence that proves all of the genetic material of the engulfed organism remains after endosymbiosis. In fact, we have evidence to the contrary!

If we look closely at the beginning of the stimulus, we see that the definition of endosymbiosis is "the engulfing of one organism by another so that a part of the former becomes a functioning part of the latter." The word part here is of particular importance because we don't know exactly which part remains! Sure, it seems like that part will likely include genetic material, but how much? Does it have to be all of it? Could it just be a single gene? We don't know! So, this is an Exaggerated Answer and we can eliminate it.

I hope this helps!
Kate

[sxzhao]

I'm still having trouble understanding (E)

From the stimulus, we know that the plant chlora... contained nucleomorth which is a result of the enguling process, but how can we say the plant is a result of the process?

It's like: I can tell you that I found a worm poking a whole in my apple, a known fruit; but how can I say apple the fruit is a result of the worm poking a whole?

[Jeff Wren]

Hi sxzhao,

Let's carefully examine each of the relevant facts in the stimulus.

The first sentence states that "some types of organisms resulted through endosymbiosis" (my emphasis). Notice that it is the entire organism that results from this process, not part of the organism. The stimulus then defines the process of endosymbiosis as "the engulfing of one organism by another so that a part of the former becomes a functioning part of the latter."

In other words, if you find evidence that endosymbiosis has occurred (such as finding part of another organism's DNA within a functioning part of an organism), then the entire "new" organism originated as a result of endosymbiosis, not just the part that was absorbed.

Here, since the nucleomorph within the chlorarachniophyte plant contains two different versions of a gene, which is evidence of endosymbiosis (based on the final conditional sentence in the stimulus), then the chlorarachniophyte plant originated through endosymbiosis.

Here, some unknown plant (let's call it Plant A) engulfed some other plant (Plant B) through endosymbiosis, and the resulting plant is what we call chlorarachniophyte.