AAMC CBT10 only OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT10.

Please post ONLY questions pertaining to AAMC CBT10.
Out of respect for people who may not have completed the other exams, do not post questions or material from any other AAMC exam.

Please see this thread for the rules of order before you post.

Good luck on your MCAT!

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[Oh_Gee]

Yes. That would be the best answer.

but notice how the passage never mentions the projectile falling down, it only mentions peak height. question stem doesn't either. in projectile questions, should we always assume it falls down even if not mentioned?

 

[Shirafune]

but notice how the passage never mentions the projectile falling down, it only mentions peak height. question stem doesn't either. in projectile questions, should we always assume it falls down even if not mentioned?

You asked me if the best answer would be "It falls continuously" if we were only talking about from the ground to the object's max height. I am assuming you included direction in your question (the first half of the object's flight). Like I said, if you look at the Doppler Effect equation, an increase in velocity away from or toward the detector will cause an increase in the magnitude of the frequency shift. For this particular problem, you can assume that it falls because it will fall...
The object was thrown vertically, so clearly it will fall.

 

[justadream]

AAMC implies that you only need 2 equivalents of the Grignard reagent to get to this salt.

But don't you need 3?

The first grignard equivalent would react with the hydroxyl group. The final two equivalents of Grignard reagent are needed to add the two Ph groups.

 

[justadream]

How does absence of intermolcular interactions somehow "increase energy density"?

 

[simmac]

I really don't understand how we're supposed to know that "The spatial resolution of stacked multiwire proportional chambers is determined by the: A) applied voltage. B) density of the ionizing gas. C) density of particle tracks. D) spacing of the anode wires.

(explanation: Spatial resolution refers to the ability to locate an event in space. The closer the spacing of the anode wires, the better one can specify where an event took place—this is a limiting factor. Thus, D is the best answer.)

Did anyone see hints in passage to help you pick D??? Or is it when there's no info in passage to hint at an answer, we should pick answers that have "obvious" connections with question, e.g. spatial and spacing??? (fyi, i picked B thinking that density would affect resolution...)

 

[Janus_Kinase]

Man, most of the aamc bio questions I get wrong are subjective imo. Not just in this FL but previous ones too. For example #152, most bacterial cells and human cells are alike in a) ability to produce atp via atp synthase or c) chemical composition of their ribosomes.

I had first chosen A because it fits and it was the first choice I saw. Then I saw C and, specifically, made more sense. There are hundreds of millions of bacterial species, many who can produce ATP via other means than ATP synthase. However, at a chemical level our ribosomes are the same nitrogenous bases (mainly rRNA) It is not until at the molecular subunit level where they differ.

It can be interpreted different ways but only way is correct :/

 

[Gauss44]

ERROR???

131. Which of the following processes is least directly influenced by adrenergic drugs?

Why are they claiming that the answer is peristalsis, which is triggered by swallowing? Last time I checked, I could effectlvely swallow when my sympathetic nervous system was stimulated.

 

[NextStepTutor_3]

hey Gauss44, the answer to that question should be C - enzymatic breakdown of food molecules. in other words, you're totally right that peristalsis ISN'T the answer. are you taking it on the e-mcat website?

 

[ahisma]

Can anyone explain #43? I can't seem to understand what is exactly going on with that question. Kaplan says, "If the particle generates an electron cascade that is equidistant from any two anodes, the electrons will feel equal, attractive forces to both anodes. Since either anode can be considered the closest, the same electrons will be detected at both anodes, initiating two signals." How can the same electrons be detected in two places at once? Or do they mean the same amount will be detected at opposite anodes, as in half at one and half at the next? Thanks for any help!

 

[Cawolf]

Hey guys,

Hope you can help me with question 127. Just want some clarification. If a reaction has Pyridine with CH2Cl2, CH2Cl2 is just the solvent and pyridine is acting as a base right? If we have Pyridine with Chromium Oxide and CH2Cl2, then it is an oxidation reaction right? Just want to make sure I have my reagents down correctly. In this reaction the Pyridine deprotonates the alcohol which attacks the acyl chloride right?

Yup, DCM is the solvent and pyridine deprotonates the alcohol to an alkoxide which then attacks the carbonyl.

If you mean Chromium (VI) oxide then yes, that will selectively oxidize a primary alcohol to an aldehyde - it is called Collin's reagent (with pyridine in DCM) and is another source of Chromium (VI) like PCC.

 

[ahisma]

Man, most of the aamc bio questions I get wrong are subjective imo. Not just in this FL but previous ones too. For example #152, most bacterial cells and human cells are alike in a) ability to produce atp via atp synthase or c) chemical composition of their ribosomes.

I had first chosen A because it fits and it was the first choice I saw. Then I saw C and, specifically, made more sense. There are hundreds of millions of bacterial species, many who can produce ATP via other means than ATP synthase. However, at a chemical level our ribosomes are the same nitrogenous bases (mainly rRNA) It is not until at the molecular subunit level where they differ.

It can be interpreted different ways but only way is correct :/

Yes I did the same thing, thought of obligate anaerobes that do not use ATP synthase and the fact we share the same nucleic acids for our rRNA. "Chemical level" is ambiguous, can be atomic or molecular. But the question does state "Most bacterial cells" so have to watch out for keywords and be careful of overanalyzing. This is my biggest problem currently, especially as I try to go as fast as possible.

 

[Janus_Kinase]

Yes I did the same thing, thought of obligate anaerobes that do not use ATP synthase and the fact we share the same nucleic acids for our rRNA. "Chemical level" is ambiguous, can be atomic or molecular. But the question does state "Most bacterial cells" so have to watch out for keywords and be careful of overanalyzing. This is my biggest problem currently, especially as I try to go as fast as possible.

When I took the actual mcat, I kept telling myself "keep it simple stupid". Whenever in doubt go with simplest answer. They like to use the fact that we overanalyze everything as neurotic pre-meds . That strategy worked with bio, I got a 12, but I think I misused it with verbal lol.

 

[sanguinee]

#27

I'm not sure why this question isn't clicking for me - I understand the reaction is HOAc --> [H3O+] + [AcO-], and the Ka is Products/Reactants, but why is the [H3O+]=[AcO-]?

 

[Cawolf]

@sanguinee

Ka = Products/reactants = [H3O+][-OAc]/[HOAc]

We started with 1 equivalent of HOAc. For every equivalent of HOAc that dissociates you get 1 equivalent H3O+ and 1 equivalent -OAc. These values will always be equal (on paper) as they are "produced" at a 1:1 ratio by the dissociation of the weak acid.

This tells you that substituting [H3O+] for [-OAc] is valid and the best answer is choice D.

 

[ahisma]

@sanguinee you can visualize this with an ICE table too. The change and equilibrium rows will have have the same value for both products, H3O+ and the conjugate base.

 

[blkgrnblkylw]

Question 36.
It asks to determine the frequency difference when you change the wavelength. The two different frequencies are 1.5 x 10^15 and 5 x 10^14. The answer is 1 x 10^15. How is this the frequency difference? What is meant by frequency difference?

 

[Cawolf]

Question 36.
It asks to determine the frequency difference when you change the wavelength. The two different frequencies are 1.5 x 10^15 and 5 x 10^14. The answer is 1 x 10^15. How is this the frequency difference? What is meant by frequency difference?

Frequency 1 - Frequency 2.

The difference means one subtracted from the other.

1.5 x 10^15 = 15 x 10^14

15 x 10^14 - 5 x 10^14 = 10 x 10^14 = 1 x 10^15

 

[blkgrnblkylw]

Frequency 1 - Frequency 2.

The difference means one subtracted from the other.

1.5 x 10^15 = 15 x 10^14

15 x 10^14 - 5 x 10^14 = 10 x 10^14 = 1 x 10^15

ha, looks like I forgot how to add/subtract scientific notation

 

[sanguinee]

I understand sensory neurons are responsible here, but why is it depolarization vs hyperpolarization?

 

[Cawolf]

@sanguinee

Depolarization will cause a nerve to transmit an action potential (possibly) and since this is a sensory nerve, make us feel the burning, itching, and pain.

Hyperpolarization makes a nerve cell more negative, and less likely to "fire" - making us less likely for the nerve to be depolarized and the sensations to be felt.

 

[sanguinee]

@Cawolf
But doesn't transmission of an action potential entail depolarization, repolarization, and hyperpolarization?

 

[Cawolf]

@sanguinee

Those are the phases of an action potential, yes.

But if I say I am hyperpolarizing something, it means I am making it more difficult to depolarize. That is why the hyperpolarization phase of an AP is also known as the relative refractory period.

 

[sanguinee]

I thought sympathetic increased peristalsis of the esophagus and constricts blood vessels? This explanation says that peristalsis is inhibited and blood vessels dilate. I thought peristalsis would be decreased because it is a part of rest & digest, but wikipedia said otherwise which I why I'm confused.

 

[Cawolf]

@sanguinee

What is least effected by increased sympathetic activity? Choices A,B, and D will be inhibited so C is the answer.

explanation says that peristalsis is inhibited

I thought peristalsis would be decreased

You are agreeing with the explanation here?

But your first sentence says you thought peristalsis would be increased?

I can't really help unless I know which you actually think is true.

The correct way of looking at it is that peristalsis is effected by sympathetic activity.

 

[sanguinee]

@Cawolf
Sorry for being unclear - I thought peristalsis would be decreased, but wikipedia says it is increased?
" For example, the sympathetic nervous system can accelerate heart rate; widen bronchial passages; decrease motility(movement) of the large intestine; constrict blood vessels; increase peristalsis in the esophagus; cause pupillary dilation, piloerection (goose bumps) and perspiration (sweating); and raise blood pressure."

Anyway - I understand the answer, just the explanation was confusing. I was also confused about answer choice D's explanation - doesn't sympathetic response constrict blood vessels rather than dilate them?

 

[Cawolf]

@sanguinee

I am relatively confident that any GI peristalsis will decrease in response to sympathetic activation - I would not trust Wikipedia as a valid source.

See this quote I found:

"Esophagus: Peristaltic amplitude was increased in the distal smooth muscle part of the esophageal body after infusion of both the nonselective beta blocker propranolol and the beta-1 selective blocker metoprolol. After infusion of the beta-1 agonist prenalterol and the beta-2 selective agonist terbutaline, a profound decrease in esophageal peristaltic amplitude was seen."

Source: http://www.ncbi.nlm.nih.gov/pubmed/2864739

In regards to the effect on blood vessels - it depends where they are. Skeletal muscle will get more blood flow while abdominal organs will get less.

 

[Silence in ER]

does anyone understand passage 7 of physical sciences? I missed 43, 45, and 46 and I still cannot make heads or tails of it. Any help would be resoundingly appreciated, much thanks.

 

[quicheduty]

does anyone understand passage 7 of physical sciences? I missed 43, 45, and 46 and I still cannot make heads or tails of it. Any help would be resoundingly appreciated, much thanks.

I also missed 43 and don't understand it (how does preference for an anode translate to detection? wouldn't that just mean no detection?)

For 45, I thought of it like mass spec - using r=mv/qb you can discern between electrons and protons based on their radii of curvature, and thus their mass.

For 46, I thought of it like pixel resolution. If you have a frame that's x by x pixels, you'll have a certain image resolution. If you lower x, your image will become more pixelated (lower resolution). If you increase the x, you're increasing the resolution. Makes for higher quality photos/images and such. So I thought of spacing of anode wires as bigger vs smaller pixel areas.

 

[House D.O.]

I have a question for the Item 128

I dont see how for compound 2 the C(OH)Ph2 has priority of the Ph? Isnt a carbon that has a double bond better then just a regular carbon that is then bonded to other groups? Im confused in my orgo knowledge now...

 

[Cawolf]

@imran1011

No. the main thing you look at it is the "first point of difference".

It is the molar mass of the attached group that is most important. I suggest reviewing the Cahn-Ingold-Prelog rules.

In addition, both carbons are double bonded - the ester group carbon is double bonded to an oxygen and single bonded to a oxygen.

The way a double bond plays into priority rules is that is viewed as two single bonds to the two atoms. So a carbon double bonded to an oxygen is viewed as being single bonded to two oxygen atoms. The first point of difference is still how you determine substituent priority.