AAMC CBT7 and 7R OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT7 and 7R.

Please post ONLY questions pertaining to AAMC CBT7 and 7R.
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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[TFS]

So, I think this relates to the fact the cells are grown in 2 separate conditions:

in the presence of cycloheximide (inhibits tx ==> tn): neuron + skin
in the presence of actinomycin D (inhibits DNA => RNA): neuron, skin, muscle

Since inhibiting translation preventing muscle formation, we know translation (and therefore its product, protein) is involved in the process of producing muscle as cells differentiate.

As far as how protein is present in the culture with actinomycin to allow neuron/skin/muscle differentiation - good question. My only guess: the protein present is protein translated earlier, BEFORE these two-cell embryos were incubated with the inhibitor?

i have the same question. just by elimination, protein is the only thing that it can be, but their explanation doesnt make sense to me. if protein was present prior to incubation with the inhibitor, then why would inhibiting translation affect signaling?

 

[joshto]

What question are you talking about?

Question 20 from PS

 

[Vanguard23]

Question 20 from PS

It's about deviations from ideal gas laws. B is such a deviation because it's a high PRESSURE. High pressure is about the volume occupied by the molecules. Low temperature deals with molecular interactions(like repulsions/attractions).

 

[puffylover]

this is regarding question 130:

which of the following statements explains most plausibly why host antibodies are ineffective against H. plyori

A. antibody proteins may be denatured in the harsh environment of the stomach (correct answer)
B. nvm.. i know this is wrong
C. H. pylori infection may suppress the activity of the immune system (picked this)
D. antibodies are not secreted from host tissues into extracellular spaces

so my question is: antibodies are secreted into the bloodstream or extracellular space? why is D wrong? will the antibodies be secreted into the stomach and that's why they denature?

 

[Hemichordate]

Did anyone else see a the mistake in the answer key?

The IR spectrum of Compound 8 (random compound) shows hydroxyl and carbonyl absorptions, respectively, at approximately:

A) 1700 and 2250 cm-1
B) 1700 and 3400 cm-1
C) 3400 and 2250 cm-1
D) 3400 and 1700 cm-1

The answer says B, it's supposed to be D.

 

[rls303]

Did anyone else see a the mistake in the answer key?

The IR spectrum of Compound 8 (random compound) shows hydroxyl and carbonyl absorptions, respectively, at approximately:

A) 1700 and 2250 cm-1
B) 1700 and 3400 cm-1
C) 3400 and 2250 cm-1
D) 3400 and 1700 cm-1

The answer says B, it's supposed to be D.

Thant's what I put too.

I was wondering regaring Item 17, Are there any covalent bonds in that molecule?

 

[rls303]

to the first question. D makes sense because since the OH is more polar, it will be more attracted to the polar film. therefore, it won't travel as far and will have a smaller Rf value.

for the 2nd question, you are correct the answer is D. check again to make sure your eyes didn't play a trick on you. even my AAMC test tells me D is the right one...maybe yours had a weird glitch or something? OH is broad stretch around 3400 and carbonyl is a peak around 1700

Is the silica plate always polar? The eluent could be nonpolar, coudln't it? I vaguely rememebr one where the eluent was hexane and the nonpolar compound had a lower Rf, and a greater retention time.

 

[starbaduk]

can someone please explain why tertiary alcohol is more reactive with HCL than the others ?

thanks

I also missed this question for the same reason. HCl will protonate hydroxyl group to water, a good leaving group. Then nucleophilic attack by Cl- will result in SN2 reaction. Cl- is not bulky, and a pretty good nucleophile... so Why can't B be the correct answer?

 

[WhizoMD]

Is anyone else frustrated with the rationale behind this one? In the first part of the explanation they essentially say A is correct....... If they used the word strengthen (or further supports) I would understand, but the word was support

 

[ModerateMouse]

I also missed this question for the same reason. HCl will protonate hydroxyl group to water, a good leaving group. Then nucleophilic attack by Cl- will result in SN2 reaction. Cl- is not bulky, and a pretty good nucleophile... so Why can't B be the correct answer?

Yes!! Can someone please explain this?

I was sitting there thinking: is it Sn1 or Sn2?

If it's Sn1, then of course tert-butyl alcohol will react faster. But, if it's Sn2 then methanol will be better.

Why isn't the Sn2 reaction (with a high concentration of the nucleophile, HCl) faster than the Sn1 reaction?

 

[ModerateMouse]

Is anyone else frustrated with the rationale behind this one? In the first part of the explanation they essentially say A is correct....... If they used the word strengthen (or further supports) I would understand, but the word was support

Yep, I got this wrong as well. I just chalked it up to 'verbal randomness.'

My reasoning was that since multiple countries are seeing people follow laws, then the evidence is stronger in favor of people making decisions that lead to better societal order.

And, since many people are all making these correct decisions, the argument is stronger...

However, now that I think of it this is not very good reasoning. After all, the people can be making the decision to 'go with the crowd' based on any number of things such as fear of prosecution by the police.

That must be it - the real rationale for the people's decisions is not necessarily what the author hints it might be. The rationale could be anything (i.e., fear of punishment). So, the point is kind of irrelevant to the author's main argument.

Does that make sense?

 

[Handinhand]

God this one just sucked. I went from a 13,11,11 on AAMC6 to a 11,10,12 on this. More than that, the curve was pretty damn ridiculous on this one, especially on PS. I got a 44/52, and that's an 11?

My one big grudge is on the Beer's law passage. The one that asks you to find C... for the life of me I couldn't figure it out. You know why? Because I thought the C from the Beer's law equation is what they wanted, not the, small, easy to miss exponent C. Also, the gas chromatography question? Do you we really to know how to interpret GC?

Oh, one last thing. The earthquake passage? Did they mistakingly put a VR passage in PS? That's what it seemed like to me.

Anybody that has since taken the MCAT want to weigh on the difficulty of this compared to the real deal?

 

[Rabolisk]

7 PS was easy IMHO. With the beers law prob, question tells you what c you are looking for. For GC as long as you understand how GC works I thought it was a gimme question..

 

[Handinhand]

It must have been because I was so damn hungry and took it a little later in the day, but I just felt like I got worked on this one. A 33? I'd be lying if I said I wasn't pissed about that.

You've got to admit, that curve is a little steep. 8 wrong drops you down 4 points on PS? That's a little ridiculous.

 

[rls303]

Hi guys,
I had a question with regards Item 34. Given that we know that Keq=kf/kr, would knowing the two Equilibrium Constants not help us in finding the kinetic rate values?

 

[Rabolisk]

Hi guys,
I had a question with regards Item 34. Given that we know that Keq=kf/kr, would knowing the two Equilibrium Constants not help us in finding the kinetic rate values?

What is your reasoning?

 

[rls303]

What is your reasoning?

Hi,
Well since they have given us the two Equilibria Constants and they differ by so much, isn't it also a reasonable conclusion based on Keq=kf/kr that they would also differ by that much as well?

 

[rls303]

Hi guys,
Another Bio question:

Regarding Passage 7 (Boy I thought it was hard lol)

For item 136, why can't B be a viable answer? The fate of isolated P cells does equal the fate of normal P cells, no? That's even what it says in the answer solution for A.

 

[Rabolisk]

Yes, kf/kr would differ by that much. That doesn't say anything about the rate of the reaction, though.

 

[rls303]

Yes, kf/kr would differ by that much. That doesn't say anything about the rate of the reaction, though.

Oh, I think I see what you are saying. So the ratio would differ, but we can't say that the individual kf's would differ?

 

[Rabolisk]

That's right. Just as a rule of thumb, equilibrium doesn't say anything about kinetics.

 

[2010premed]

I also missed this question....I retook the test...missed it both time with different answers. I really don't understand this, and I'm frustrated.

Any help would be greatly appreciated.

Yes, can some1 please explain how to choose between A and B?

 

[2010premed]

The Doppler shift can impact any wave. In this case, the wave is an impact wave travelling through the ground away from the rupture. The source of the wave is the rupture, and given that the rupture is moving, the wave it emits will be Doppler shifted. You can thus treat it as a source moving north emitting a wave, much like a car travelling north emitting a sound.



The explanation from the BR answer sheet is:

• The primary rupture is moving from south to north, so the Doppler effect is associated with north-south movement and not east-west movement. This eliminates choices A and B. Seismic waves propagating from this rupture are Doppler shifted by the motion of the rupture. Seismic waves emitted to the north are compressed by the motion of the rupture while seismic waves moving south are elongated by the motion of the rupture. Compression results in a shorter wavelength, so the wavelength of seismic waves moving to the north is decreased while the wavelength of seismic waves moving to the south is increased. The best answer is choice C.

How do we know that "Seismic waves emitted to the north are compressed by the motion of the rupture while seismic waves moving south are elongated by the motion of the rupture"? Can we use the equation delta wavelength/wavelength = v/c here?

 

[2010premed]

If two people were talking on their cellular phones within the same "cell" in a city, why would their transmissions NOT interfere:
A. The power transmitted from each phone is not high enough to interfere
B. The frequencies used by each phone are chosen to be different.

How would you definitely eliminate A?
In the passage it says "because the size of a cell is relatively small, it allows efficient communication with relatively low power phones."

 

[bullsfan1986]

Premed 2010,

I think the question you're talking about was more of a reading comprehension question than a science one. I think that the passage specifically says that both sender and receiver are on different frequencies, so you have to infer that they can communicate with each other over a small distance because of that very fact.

 

[bullsfan1986]

How do we know that "Seismic waves emitted to the north are compressed by the motion of the rupture while seismic waves moving south are elongated by the motion of the rupture"? Can we use the equation delta wavelength/wavelength = v/c here?

I think you can answer this by just knowing the fundamentals of the doppler effect. I reasoned this question by thinking that if an observer is standing in the direction the waves are being emitted (north) then he experiences a higher wave frequency and a smaller (compressed) wavelength. And if the wave is moving away from the observer (moving south) then the observer experiences a lower frequency and longer (elongated) wavelength.

 

[2010premed]

I think you can answer this by just knowing the fundamentals of the doppler effect. I reasoned this question by thinking that if an observer is standing in the direction the waves are being emitted (north) then he experiences a higher wave frequency and a smaller (compressed) wavelength. And if the wave is moving away from the observer (moving south) then the observer experiences a lower frequency and longer (elongated) wavelength.

ah, that makes sense, but how did you see that relationship? For example, you're saying that in the north, the person experiences a higher frequency and therefore a lower wavelength, but the answer choice says "by decreasing the wavelength of the seismic wave" ie, the actual wavelength is changing, and not the detected wavelength

 

[2010premed]

the equation v=c/n applied to light only, correct? (I'm inferring this from the q about light and sound waves)

 

[2010premed]

Right.

That makes sense but I still never would have picked the stomach answer since the passage seemed to indicate the 'eluding' was a direct result of something the bacterium contains/has the ability to do, not something that the host does. So I just picked the suppress answer not because I thought it was right but because it seemed to be the best of the choices presented.

Ah well. They should have just left that last sentence out!

I totally agree... how would you eliminate C for sure?

 

[2010premed]

Hey Guys, the last # of the BS section (#146) really confused me... the thing is, in the chart they are measuring the amount of radioactive nuclei (basically the percentage of cells whose nuclei have radioactive thymine) from the sample of cells which they extract. The reason why this confuses me, is since DNA is replicated in a semi-conservative model, and since it had incorporated radioactive thymine, then the amount of radioactive nuclei should remain constant and not decrease... I have a feeling that in this question, they should rather imply "the relative amount of radioactivity within cell nuclei" and then, it will be obvious that during DNA synthesis, the amount will be larger compared to when the cell has separated its DNA, thus separating the amount of radioactivity within it.


In an experiment on the phases of the cell cycle, cultures of actively dividing, synchronized cells were exposed to radioactively labeled 2-deoxythymidine for 30 minutes, then rinsed to remove the unabsorbed label. At various times thereafter, groups of cells were removed from the cultures and the nuclei examined to determine their content of radioactive material. Results are shown in the figure below.

Based on the figure, what process was occurring during hours 3-13 after treatment with radioactive 2-deoxythymidine? A
) Mitosis B
) Meiosis C
) DNA synthesis
This item includes a description of an experiment in which actively-dividing, synchronized cells were exposed to radioactively labeled 2-deoxythymidine (the nitrogen base incorporated into DNA, but not RNA). After 30 minutes of exposure to the radioactively labeled substance, the cells were rinsed to remove unabsorbed label. At various times thereafter, a group of cells from the culture were examined to determine the quantity of radioactive material in the nuclei. The figure shows a peak in radioactivity between 3 and 13 hours after treatment. This peak represents DNA synthesis, since 2-deoxythymidine is a component of DNA, but not RNA or protein.

D
) RNA synthesis

so I had a question about this... I picked DNA synthesis because I saw on the y acis it was dividing nuclei, and I know that DNA is in the nuclei. Was my reasoning correct? they explain it in a different way in the explanation

 

[bullsfan1986]

ah, that makes sense, but how did you see that relationship? For example, you're saying that in the north, the person experiences a higher frequency and therefore a lower wavelength, but the answer choice says "by decreasing the wavelength of the seismic wave" ie, the actual wavelength is changing, and not the detected wavelength

wavelength and frequency from a moving source is relative. The question asks you to relate the phenomena to Doppler, so you have to reason that the answer choice is going to be dealing with relative frequencies/wavelengths.

Instead of thinking of the seismic wave, just think of a something more intuitive like an ambulance moving from south to north. Say that you were standing south of the ambulance and your friend was standing north of the ambulance. As the ambulance moved further north you would detect a longer wavelength and a lower frequency since wavelength proportional to 1/f. Your friend who is north of the ambulance would experience the exact opposite of what you're experiencing. (Shorter wavelength and greater frequency.)

If I'm being redundant, sorry.

 

[bullsfan1986]

so I had a question about this... I picked DNA synthesis because I saw on the y acis it was dividing nuclei, and I know that DNA is in the nuclei. Was my reasoning correct? they explain it in a different way in the explanation

I think that's pretty good reasoning. I think something easier would be to see that the radioactive label is a pyrimidine. When you see its concentration increasing, you can be sure that the pyrimidine is being replicated and this can only mean that DNA synthesis is occuring.

 

[bullsfan1986]

the equation v=c/n applied to light only, correct? (I'm inferring this from the q about light and sound waves)

yes, because c=speed of light.

 

[2010premed]

thanks, your explanations really help

 

[2010premed]

1. Because earthquakes were triggered by what ultimately must have been comparatively minor energy transfer from the distant Landers quake, the triggered quakes probably occured where:
A. significant local stress forces in the earth's crust were already in precarious equilibrium
B. Earth's crust was subjected to reinforcing resonant effects cumulatively built up local stresses.

Why not B?? Maybe someone can better define resonance for me?

2. Is sound fastest in solids, followed by liquids, followed by air?

3. Bio passage 7
can someone explain experiment 3 and how it relates to the question: These experiments indicate that nematode cells adopt fates different from those of their neighbors during dev by:

4. The most likely explanation for the differences in skin blood flow between the fatty acid and fatty acid and vitamin E is that:
A. Products of FA oxidation reduce skin flow
B. Vitamin E alone icreases skin bllood flow more than FA alone

Why is B wrong? It is because FA don't increase skin blood flow at all?

119. An ulcer that penetrated the wall of the intestine would allow the contents of gI tract to enter:
A. Peritoneal cavity
B. lumen of intestine
C. Perineum

I'm clueless with the anatomy here, some enlightening would be appreciated and what other anatomy should I know?

 

[fizzgig]

second aamc down... only went over a couple of questions so far, but i'll go through it all tomorrow along with aamc 3.

this is one of the tests that is supposedly a pretty good indicator? i definitely didn't have as much time to check stuff as on aamc3..

for 2010:
1) they say it's 'relatively minor energy transfer', and if you had something adding energy at resonant frequency you could actually get quite a bit of energy to cause the quake... dunno if that was the reasoning to use but i think thats why i chose A. i havent looked at the answerkey.
2)sound is typically fastest in solids, then liq, then gas. high density should slow it down but it is typically more than compensated for by an increase in stiffness (bulk modulus)
3)one of the experiments showed that cells needed to be near each other to differentiate right (separated cells failed to make muscle i think). the third showed that if cells divided and you stopped transcription right then, the cell could (i guess temporarily) rely on stuff it inherited from cytoplasm in mitosis (it still had mrna floating around to translate or something)
4)that'd be my guess. this isn't a physicsy question where you go 'well a negative increase is just a lower increase than 0 increase'...
5)you should know the heart and lungs are in the thoracic cavity and your guts are in the peritoneal cavity. the lumen option you should be able to eliminate. the perineum is in the genital region and you wouldnt be expected to know that anatomy. it's to confuse you if you had a vague recollection of the word peritoneum.

 

[2010premed]

Great, thanks. How do you for sure eliminate lumen?

 

[fizzgig]

the contents of the GI tract are already in the lumen of the intestines. the lumen of something is the inside of it (vessels, intestines etc). the ulcer is not letting things get to the GI lumen; they're already there.

 

[emericana]

Question: How can I tell that it is momentum does this over magnatism?

I chose the answer that I chose because I thought.. hm electron= negative charge which is attracted to positive ion which makes it attracted to one direction or the other.

Does my reasoning make no sense at all?

 

[agill786]

See attachment for questions/answer choices.

Essentially, the question is:

Embryonic mouse cells divide every 10 hours at 37 degrees C. How many cells would be produced from an egg after three days?

My initial reaction to this question was that it was a trick question. Although embryonic mouse cells divide at the rate given, an unfertilized egg would not be an embryo and thus would not divide. Hence, i thought the answer would be that you still had "1 cell" (the egg) or "0 cells produced" after three days. So I picked A as the answer. The only other thing that I thought could be the case for the answer that is supposed to be correct is that 1) a zygote is technically a "fertilized egg" and therefore still an "egg" or 2) a mouse egg cell for some unknown reason could divide asexually (which I highly doubt).

Did anyone else not like this question or is there anyone out there that could help clarify things for me?

Thanks!

You know, that's what I thought too. So I guess we are to assume that it is in fact fertilized?

 

[boxer15213]

I know there was a question about #19 earlier but I still don't get it. Since in the final reaction there are 2 of the first half reactions I don't understand why you wouldn't multiply +0.34 V twice?

 

[fredxc]

I know there was a question about #19 earlier but I still don't get it. Since in the final reaction there are 2 of the first half reactions I don't understand why you wouldn't multiply +0.34 V twice?

I have the same question. Your way of doing it (which was also my way) gives -0.55 and only +0.55 is an answer choice...this should have been a giveaway, but I picked it figuring I must have made a sign error and moved on.

I think that because the V is a measure of the propensity of a particular redox reaction to happen (and not energy released like delta H), the number of moles involved doesn't really matter. I don't think that I'm articulating this in a very solid way, however. Perhaps someone else has a better understanding.

 

[GreenRabbit]

I have the same question. Your way of doing it (which was also my way) gives -0.55 and only +0.55 is an answer choice...this should have been a giveaway, but I picked it figuring I must have made a sign error and moved on.

I think that because the V is a measure of the propensity of a particular redox reaction to happen (and not energy released like delta H), the number of moles involved doesn't really matter. I don't think that I'm articulating this in a very solid way, however. Perhaps someone else has a better understanding.

You never multiply voltage by quantity. Batteries are an everyday example: if you use a bigger battery, say D vs AA, they're both 1.5V, you're just buying longer battery life. If you double the first half reaction, you're just doubling one fuel of the battery. It can now last twice as long, but you're not increasing the potential.

 

[movax]

Where is the 4th stereocenter? (#153 BS)

 

[SeminoleVesicle]

At the top of the cyclopentane.

 

[SeminoleVesicle]

You never multiply voltage by quantity. Batteries are an everyday example: if you use a bigger battery, say D vs AA, they're both 1.5V, you're just buying longer battery life. If you double the first half reaction, you're just doubling one fuel of the battery. It can now last twice as long, but you're not increasing the potential.

Voltage isn't a state function.

 

[movax]

At the top of the cyclopentane.

Between the 'x' and the circled Carbon with the H going out of page? That's a stereocenter? Does it have four different substituents? I see:
1. CH
2. CH
3. CH2
4. H

I've always been sliding by when it comes to ID'ing stereocenters and such, how would I go about this one?

 

[SeminoleVesicle]

The Carbon to the left is bonded to 2 other Carbons and 1 H
The Carbon to the top is bonded to 2 Carbons, 1 of which has the Nitrogen, and an H
The Carbon the right is bonded to 1 other Carbon, and one H
And the H

I'm sure someone can explain it better. It has four unique groups.

 

[samvillian]

Is anyone else frustrated with the rationale behind this one? In the first part of the explanation they essentially say A is correct....... If they used the word strengthen (or further supports) I would understand, but the word was support

I actually got this one right, but i had it narrowed down to both A and B... I originally had it at A, but changed it to B just based on the fact that I figured they were leaning more for us to get that from the passage...


it's a very dumb reasoning though.. I could have made a VERY strong argument for either one.

 

[dmplz707]

Can someone explain to me the reasoning behind the following questions/answers? I am so confused, I got four questions wrong on the Nematode passage (VII). Thanks

#138 The results from experiment 2 indicate that the signaling interaction of the two-cell stage most involves which class of molecules? I don't understand why can't it be rRNA??

Could someone please explain the reasoning for question #138? I believe no one has addressed this question even though it is old. Thanks!