In humans, ingested protein is broken down into amino acids, all of wh

Question

In humans, ingested protein is broken down into amino acids, all of which must compete to enter the brain. 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, Tryptophan then slips into the brain uncontested and is transformed into the chemical serotonin, increasing the brain's serotonin level. Thus sugars can play a major role in mood elevation, helping one to feel relaxed and anxiety-free.

Which one of the following is an assumption on which the argument depends?

(A) Elevation of mood and freedom from anxiety require increasing the level of serotonin the brain.
(B) Failure to consume foods rich in sugars results in anxiety and a lowering of mood.
(C) Serotonin can be produced naturally only if tryptophan is presented in the bloodstream.
(D) Increasing the level of serotonin in the brain promotes relaxation and freedom from anxiety.
(E) The consumption of protein-rich foods results in anxiety and a lowering of mood.

Source  :  LSAT PrepTest38 Q#22

grumpyoldman · Accepted Answer

Good question, domleon. It's a basic principle that shows up in many CR questions. The principle is that "If X, then Y" does not mean the same thing as "If Y, then X". This seems obvious when expressed this way, and it is -- but the testmakers have ways of writing "If X, then Y" statements that are hard to recognize.

In this case, the evidence definitely proves that (as long as protein is ingested first), ingestion of sugar will increase the brain's serotonin level. The conclusion is that ingesting sugar will help you feel relaxed and anxiety-free. It's fairly clear what the missing assumption is: Increasing the brain's serotonin level will help you feel relaxed and anxiety-free.

What is not so obvious is that this is really an if-then statement: If the brain's serotonin level is increased, then you are more likely to feel relaxed and anxiety-free (If X, then Y). In other words, increasing the brain's serotonin level will have this effect, but it is NOT necessarily the ONLY way to have this effect.

This is NOT the same as saying "If you feel more relaxed and anxiety-free, then your serotonin level must have increased." (If Y, then X) This statement says that increasing serotonin is the ONLY way to feel more relaxed and anxiety-free.

Choice A is wrong because it says that increasing serotonin is the ONLY way to feel more relaxed and anxiety-free -- in other words, "If you feel more relaxed etc., then your serotonin level must have increased." That's "If Y, then X", where we need "If X, then Y".

Bunuel · Answer

OFFICIAL EXPLANATION

The importance of this problem is not just in answering it correctly, but also in answering it quickly. 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. At this point in your preparation, you should constantly be on the lookout for new elements that appear in the conclusion. This problem contains the new conclusion element of “a major role in mood elevation, helping one to feel relaxed and anxiety-free.” Because this element immediately follows the assertion that the brain’s serotonin level has been increased, you should attack the answer choices by looking for an answer that fits the Supporter relationship that an increase serotonin leads to an elevated mood.

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.

hellishbrain · Answer

In humans, ingested protein is broken down into amino acids, all of which must compete to enter the brain. 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. Tryptophan then slips into the brain uncontested and is transformed into the chemical serotonin, increasing the brain’s serotonin level. Thus sugars  cause  mood elevation, helping one to feel relaxed and anxiety-free.

Which one of the following is an assumption on which the argument depends?

(A) Elevation of mood and freedom from anxiety require increasing the level of serotonin the brain.
(B) Failure to consume foods rich in sugars results in anxiety and a lowering of mood.
(C) Serotonin can be produced naturally only if tryptophan is presented in the bloodstream.
(D) Increasing the level of serotonin in the brain promotes relaxation and freedom from anxiety.
(E) The consumption of protein-rich foods results in anxiety and a lowering of mood.

For this Q can all A,B & D be correct answers?
CR bible says when we have causal reasoning as in this modified Q, effect(mood elevation) occurs only when cause(sugar) occurs.
And in such Qs assumption question is similar to strengthen question for which correct answer fits  "cause doesn't occur, effect doesn't occur"  category.
I am changing B(which originally is like "no cause, OPPOSITE effect" to
 B) Mood elevation is not observed in people who consume foods not rich sugar.  
Now it is "no cause, no effect". Does that mean this is also a correct answer?

Also according to CR bible, since this causal reasoning Q, sugar is the  only reason  for mood elevation. 
That means even A should answer the Q.
What do you think?

Below is original Q with straightforwad answer  D

gmat1220 · Answer

gmat1220 · Answer

I missed "modified B". Lets take a look

B) Mood elevation is not observed in people who consume foods not  rich   sugar. ------> This can countered with statement - mood elevation is observed in people who consume "normal" levels of sugar.

So the quantity of sugar is irrelevant to the conclusion. Conclusion rests on whether "serotonin" levels help the person "become" anxiety free and relaxed.

On the other hand, A assumes exclusivity - "requires". 
 (A) Elevation of mood and freedom from anxiety  require   increasing the level of serotonin the brain. ------>
This assumption can be countered easily - If the person has genetic propensity for serotonin levels in the blood, he doesn't require an extra dose. So "require" is plain wrong.

D is the only one left.

IanStewart · Answer

I'm 100% certain the CR 'bible' does not say that. If, for example, I make the very simple argument: 'cars cause pollution', I'm certainly not saying that cars are the *only* cause of pollution. Nor am I assuming what is known in logic as the 'converse' (negate the cause, negate the effect) - that if there were no cars, there would be no pollution. In general, if an argument is sound, the converse will not necessarily be sound; sometimes it is, and sometimes it's not. The converse is never, however, a necessary *assumption* in any argument, and remember that's what the question in your post asked for: an assumption. So your hypothetical answer B is in no way an assumption in the argument, and would not be the correct answer here.

Instead we have an argument in the form 'X causes Y, therefore X causes Z'. In the language of the question, the argument says 'sugar causes increased serotonin, therefore sugar causes happiness'. For that argument to be sound, we need to assume that Y causes Z -- that is, that serotonin causes happiness. That's why the answer is D.

hellishbrain · Answer

@IanStewart
I agree with every point(personally that is what i thought but asking these questions because CR bible seems to suggest something different) of yours except may be the first sentence.
If you are 100% certain, am I reading CR bible incorrectly? I must be missing something.

All the queries I raised are based on CR bible strategy for assumption Qs.
Please go through attached doc(exactly copied from CR bible) and make me understand.
Please see an example in the doc for the 'converse'.
Isn't 'converse' really 'effect as cause and cause as effect' and not 'negate cause, negate effect'?
Irrespective of that, CR bible says showing 'reverse doesn't exist' (category D in doc) or 'no cause, no effect'(category C) can be the assumption.

Thanks.

IanStewart · Answer

Perhaps I should have said '99% sure' instead of '100%'. I won't comment on the contents of a book without seeing quotes in context, and I don't have a copy of that book handy at the moment. I stand by what I said above, however; when someone claims that a certain cause produces a certain effect, there can still be other causes which produce that effect. That's true in real life, and on the GMAT as well. If the 'bible' says otherwise, it's plainly wrong.

As for the meaning of the 'converse' in logic, there are two equivalent ways of defining it. If we say 'When A is true, B is true', then what is known in logic as the 'converse' says 'when B is true, A is true'. You can restate that in an entirely equivalent way by saying 'when A is not true, B is not true' (if you know the language of formal logic, I'm just taking the 'contrapositive', though you don't need to know that term).

Now, when an argument is true, the converse need not be true; sometimes it is, and sometimes it is not. It's perhaps easiest to take an example from mathematics. For example, 'if x = 2, then x^2 = 4' is clearly true. The converse is not, however: 'if x^2 = 4' then it is not necessarily true that x=2, since x might be equal to -2.

In any case, when you make an argument, you are never *assuming* the converse of your argument is true; it's not an assumption, nor is it equivalent to the original argument.

getgyan · Answer

+1 D

Premise - In humans, ingested protein is broken down into amino acids, all of which must compete to enter the brain. 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. Tryptophan then slips into the brain uncontested and is transformed into the chemical serotonin, increasing the brain’s serotonin level.

Conclusion - Thus sugars cause mood elevation, helping one to feel relaxed and anxiety-free.

Clearly there is a gap between the premise and the conclusion. Any option which connects these two i.e. Serotonin with relaxation and freedom from anxiety is our answer

After the preliminary check, only options A and D are left.

(A) Elevation of mood and freedom from anxiety require increasing the level of serotonin the brain (This option is poorly constructed and does not include relaxation)
(D) Increasing the level of serotonin in the brain promotes relaxation and freedom from anxiety (This is our answer as it correctly fills the hole between the premise and the assumption)

:-D

sab7a · Answer

You have to find the missing link between the premises (blah blah increasing the brain`s scrotonin level) & the conclusion (sugars can play a major role in mood elevation). The relation between scrotonin level & mood elevation.

KarishmaB · Answer

Protein breaks down into many amino acids which compete to enter brain
Subsequently sugars produce insulin which cleans up residual amino acids except tryptophan
Tryptophan enters brain without competition and produces serotonin in brain

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

Note that the argument does not talk about feeling relaxed and anxiety free but the conclusion concludes it. So the assumption should be the missing link between the premises and the conclusion. Something that tells us that serotonin leads to feeling relaxed and anxiety-free. That is how we can establish the chain of sugar -> insulin -> tryptophan absorption -> serotonin -> feeling relaxed and anxiety free

(A) Elevation of mood and freedom from anxiety require increasing the level of serotonin the brain.
Not assumed. "require" means necessary. We do not need to assume that serotonin is necessary for freedom from anxiety etc. All we need is to establish that serotonin leads to freedom from anxiety. There could be other ways leading to freedom from anxiety too. Serotonin may not be "REQUIRED" for freedom from anxiety etc.

(B) Failure to consume foods rich in sugars results in anxiety and a lowering of mood.
Again, not necessary. Consuming sugars after proteins could result in lower anxiety. That does not mean that not consuming sugars will lead to anxiety and lowering of mood.

(C) Serotonin can be produced naturally only if tryptophan is presented in the bloodstream.
The argument says that tryptophan produces serotonin but it does not assume that that is the only way of producing serotonin naturally.

(D) Increasing the level of serotonin in the brain promotes relaxation and freedom from anxiety.
Correct. This gives us the missing link between serotonin and relaxation & freedom from anxiety. Increased level of serotonin promotes relaxation & freedom from anxiety. That is how sugars can lead to relaxation & freedom from anxiety. This is the missing necessary premise that the argument assumes for its conclusion.

(E) The consumption of protein-rich foods results in anxiety and a lowering of mood.
No such assumption.

Answer (D)

ankitbarak · Answer

GOAL/CONCLUSION:    SUGER (SEROTIN LEVEL INCREASE)  ==== RESULTS IN ====>  MOOD ELEVATION  
  CONDITIONAL QUESTION

S (SUFFICIENT CONDITION)  --------->  N (NECESSARY CONDITION)

If S occur   N occur 
 If N occur   S may or may not occur

A. If N occur , S should occur ---WRONG
B. ”RICH IN SUGER” --We are not concerned about quantity of suger so   ELIMINATED  
C. “NATURALLY” –   OUT OF CONTEXT  
D.   S occur -->N occur   –   CORRECT ANSWER  
E.   (OUT OF CONTEXT)  —PROTEIN RICH FOODS

DrVanNostrand · Answer

Hi Karishma,

Does "necessary" mean "only?"
WHat do we mean by necessary in the context of this question and why is the use of "necessary" wrong?

nikitasharma8 · Answer

if we add negation test to b then b is hitting up as assumption. can't we apply that?

ManifestDreamMBA · Answer

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

(B) Failure to consume foods rich in sugars results in anxiety and a lowering of mood.
Negation of B - Failure to consume foods rich in sugars  does not result  in anxiety and a lowering of mood.
We just know what sugar does from the conclusion. We don't know what it's absence does or does not. So, the negation has no effect on the conclusion

Hope this helps!

In humans, ingested protein is broken down into amino acids, all of wh

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Critical Reasoning (CR) Questions

In humans, ingested protein is broken down into amino acids, all of wh

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards