#22 - In humans, ingested protein is broken down into amino

[Administrator]

Complete Question Explanation

Assumption. The correct answer choice is (D)

The importance of this problem is not just in answering it correctly, but also in answering it quickly.
A major portion of LSAT success is speed related, and a question like this is an opportunity to gain
time. The first step is to recognize the argument structure:

     Premise: In humans, ingested protein is broken down into amino acids, all of which
     must compete to enter the brain.

     Premise: Subsequent ingestion of sugars leads to the production of insulin, a hormone
     that breaks down the sugars and also rids the bloodstream of residual amino
     acids, except for tryptophan.

     Premise: Tryptophan then slips into the brain uncontested and is transformed into the
     chemical serotonin, increasing the brain’s serotonin level.

     Conclusion: Sugars can play a major role in mood elevation, helping one to feel relaxed
     and anxiety-free.

Only answer choices (A) and (D) contain these two elements, and you should examine them first as
you seek to accelerate through this problem:

Answer choice (A): Although the author assumes that raising the level of serotonin is sufficient to
elevate mood, this answer claims that it is necessary. Hence, this answer is incorrect.

Answer choice (D): This is the correct answer. The author states that after the action of the sugars,
more serotonin enters the brain. The author then concludes that this leads to a mood elevation. Thus,
the author assumes that serotonin has an effect on the mood level.

Answer choice (B): The argument refers to what happens when sugars are ingested. No assumption
is made about what occurs when foods rich in sugars are not ingested.

Answer choice (C): Although the argument states that tryptophan is transformed into serotonin, no
assumption is made that this is the only way serotonin is produced.

Answer choice (E): The author does not assume the statement in this answer. We know from the first
sentence of the stimulus that ingested protein is broken down into amino acids which compete to
enter the brain. This competition could result in mood elevation even without the ingestion of sugars
since some amino acids will enter the brain (some could be tryptophan, for example). Thus, since
the author’s argument contains a scenario that would allow for the opposite of this answer choice to
occur, this answer is not an assumption of the argument.

[sotor26]

Hello,

I took the Logical reasoning (part II) of the October 2002 and had some questions regarding some of the answers:

22. I was debating between B and D.

Thank you so much!!!

[Steve Stein]

Hi,

It would be helpful to know your approach to the question--briefly, how did you break down the stimulus, and how did you norrow the answers choices to those two options?

Let us know--thanks!

Steve

[sotor26]

Hello Steve,

This was a really hard question for me to break down. I had a basic rephrase that stated that sugar produces insulin, which rids the bloody system of all amino acids but Tryptophan. Tryptophan then transforms into serotonin.

I know that there is a "blank space" in which the author links the increase of serotonin levels to be the cause of mood elevation and helping to be relaxed. However, what is the deciding factor between A and D?

Thank you again!

[Adam Tyson]

I'll chime in and say that it looks like what's happening here is similar to what you were doing with Q20 in the same section - your "prephrase" is really just a paraphrase, where you've restated the argument rather than provided what's needed to fill that blank space. However, you managed to narrow it down to the two answers that both contain the elements that you should be looking for - serotonin and feeling good - which tells me that you knew what you were doing and didn't just stumble into it. Good job!

Where answer A fails is in one word - "require". It's not necessary that serotonin be required for feeling good, only that the two be linked. Looked at conditionally, serotonin is sufficient for feeling good, but not necessary for feeling good. Answer A has that conditional relationship backwards, whereas D simply makes the link without bungling the conditional relationship.

Good work!

[sotor26]

Thank you!

It seems that I need to work on my prephrases!

[esther913]

Hi,
I thought (A) was wrong because the stimulus presented cause and effect reasoning instead of conditional reasoning.

Based on the language that was used, I thought the conclusion "...sugars can play a major role in mood elevation, helping one to feel relaxed and anxiety free" was describing a partial cause and effect relationship.

How can raising the level of serotonin be "sufficient for feeling good", when there weren't any conditional relationship indicators used to describe the relationship between sugar, increase in serotonin, and mood elevation?

Also, can a partial cause become the sufficient condition for something to occur?

Clarification would be greatly appreciated.
Thank you.

[Zach Foreman]

Esther,
You are thinking the right way. The simple way to describe why A is wrong is exactly as you said, it is trying for conditional answer rather than a causal. That is what I would normally tell my students in class.
However, the borders between causal reasoning, conditional reasoning and premise/conclusion reasoning are not always clear.
In this argument we see the causal chain of
Sugars insulin tryptophan to enter brain serotonin in the premise and then the conclusion is
sugars relaxation+ anxiety
Prephrasing should easily yield the missing link. We can see that sugar gets us to serotonin but not to relaxation and no anxiety, so we need to establish that link.

OK, but how can causal and conditional be related? Well, what if we looked at Newton's Third Law of Motion: "Any action causes an equal and opposite reaction." Since the language is causal, we would probably diagram it like this"
Action equal&opposite reaction.

But, it also has the word "any" at the beginning, which is conditional. So we could diagram it like this"
Action equal reaction + opposite reaction. On other words "If there is an action, there must be an equal and opposite reaction." So, we can diagram it either as causal or conditional.

Back to the question. Could we diagram it conditionally? Could we say, if sugar then insulin and if insulin then tryptophan in brain and if tryptophan in brain then serotonin? More specifically, could we say if serotonin then feel good? Well, if serotonin causes good feelings then doesn't it make sense that when serotonin is present, good feelings must also be present?

In a way, causal arguments always have conditional reasoning imbedded in them because if we accept that A causes B, we should also accept that when we have A, we must also have B. However, this usually doesn't work on the test because we use causal reasoning much looser than conditional. What if 99 times out of 100 serotonin causes good feelings but the other one time someone has used opiates and ruined their serotonin response? I think we would still be ok using causal reasoning but not conditional. We use "tend to" a lot in causal reasoning but that doesn't work in conditional. Of course, we could fudge our conditional reasoning to accommodate exceptions (if serotonin then high chance of feeling good) but that dilutes the power of conditional reasoning.

In sum, there are sometimes borderline cases but usually the division between conditional and causal reasoning is clear. Remember, the LSAT gives top scorers clues to help them accelerate through the test. One big one is the language that you picked up on to help your answer.

Finally to answer your last question. I would say no, a partial cause cannot be a sufficient condition. Say A + B together both cause C. Neither A nor B could be a sufficient condition. But, if A or B causes C, then A could be a sufficient condition. Basically, if there is an implied or explicit "always" or "every", it can be a sufficient condition. "Rain or or snow (always) causes my basement to become damp" could be diagramed conditionally as "If rain or snow, then dampness in basement".

[esther913]

Wow That was an awesome explanation!
Thank you so much for answering all of my questions.

Also, thank you for confirming that I was thinking the right way.

[leslie7]

Sugar -> Insulin -> Tryptophan -> Increased Serotonin

Conclusion Sugar -> Mood Elevation

(Missing increased Serotonin -> Mood Elevation)

Not A because Mood Elevation - > Increased Serotonin )

This is how I came up with the AC which seems to mirror the explanation in the textbook but the textbook doesn't use the arrows to show that Answer choice A is backwards and therefore incorrect.

So I'm just wondering if this was a correct way of doing it? If when we see a (cause and effect) relationship like this if we can/should also look at it as a conditional? or when we know whether a sentence like this paragraph has conditionals (since there are no indicator words)

I realize I got this correct but I want to make sure my thinking is aligned with the way the LSAT works so when I tackle future questions I'm feeling confident about what I'm doing. In this case, I'm not feeling so confident about it because I'm not sure if what I drew was correct, if what I drew was a causal relationship or conditional relationship or both based on the text of the stimulus and how should I know that for future questions ? (sorry, reiteration of above)