#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