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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[liz10]

Hey, so I'm using the princeton review explanations and the aamc ones for PS 19 on gravitational acceleration. Can anyone try to give me another explanation? I don't fully understand how they got to the answer. Thanks in advance!

 

[ThinkDoc]

could some explain to me why acidifying the solution makes the oleic acid lie down side by side? wouldn't the hydrocarbon chain resist the solution even more?

 

[ThinkDoc]

Hey, so I'm using the princeton review explanations and the aamc ones for PS 19 on gravitational acceleration. Can anyone try to give me another explanation? I don't fully understand how they got to the answer. Thanks in advance!

I'm not sure what the PR solution says. But my reasoning is that the gravitational force is GMm/r2 = m*g, therefore g = GM/r^2 since the masses cancel out.

From here, you're doubling M and doubling r, the new acceleration would be G(2M)/(2r)^2 or just GM/2r^2. Since we defined g as GM/r^2, that's just g/2. Makes sense?

 

[circulus vitios]

Question #141: Alanine has two pKA values: one at 2.35 and one at 9.87. At what pH would alanine exist primarily in the form shown below? (Alanine is shown with an NH2 group and a CO2- group.)

I understand what pH>pKA and pH<pKA means. I knew that pH>2.35 for the carboxylate group to be deprotonated. I wasn't sure about the NH2 group. Do we always assume that the group is by default NH3+ and then go from there, meaning it would have to be deprotonated (pH>9.87) to be an NH2 group?

 

[Postictal Raiden]

Question #141: Alanine has two pKA values: one at 2.35 and one at 9.87. At what pH would alanine exist primarily in the form shown below? (Alanine is shown with an NH2 group and a CO2- group.)

I understand what pH>pKA and pH<pKA means. I knew that pH>2.35 for the carboxylate group to be deprotonated. I wasn't sure about the NH2 group. Do we always assume that the group is by default NH3+ and then go from there, meaning it would have to be deprotonated (pH>9.87) to be an NH2 group?

Use the Zwitterion (COO- and NH3+) as your reference point. At a pH that is lower than the pKa of the carboxyl group, the abundance of H+ will protonate the COO-. Similarly at any pH above pKa of amino group, the NH3+ will lose a proton due to low H+ environment.

 

[circulus vitios]

Use the Zwitterion (COO- and NH3+) as your reference point. At a pH that is lower than the pKa of the carboxyl group, the abundance of H+ will protonate the COO-. Similarly at any pH above pKa of amino group, the NH3+ will lose a proton due to low H+ environment.

Thanks.

 

[Patassa]

lol, I got this one wrong too. But after looking it up, I found out Grignards act as nucleophiles only when there aren't any acidic protons available (ROH, SH, RCOOH), but if such protons are available, Grignards will first deprotonate them, acting as a base before acting as a nucleophile. So the OH group on the left is deprotonated.

Now after deprotonation, it will act as a nucleophile, attack the carbon-oxygen double bond on the right, with the MgBr attaching to the oxygen, forming a salt, and the R group attaching to the carbon. The acid workup is to remove the MgBr and protonate the respective oxygens. In this case, we have end up with two such hydroxy groups. One was a hydroxy group on the left of the compound, and the other is the former COOR group, which has now lost its ester oxygen and replaced with the respective R groups that is Ph for this example.

Since the question asks what the compound looks like right before the acid workup, remember that MgBr adds to the hydroxide oxygens, which we have two of. So choice C accurately shows what the compound will look like right before step 2b.

That grignard question was bogus, I've just dug through two text books and I can't find an example of the reaction or text defining the reaction going that way.

In what world is the proton on that alcohol considered acidic?

Ah, the third and final text book I was willing to open had this line "....are such strong bases that they will react immediately with any acid present in the rxn mixture, even very weak acids such as water and alcohols." And that's it, no examples, no mechanisms, no pictures. Just a one liner at the end of the section. Nice.

Did the MCAT seriously put the grand caveat exception to gringnard reactions on the test? Why yes, yes they did. How messed up is that.

 

[differentiating]

That grignard question was bogus, I've just dug through two text books and I can't find an example of the reaction or text defining the reaction going that way.

In what world is the proton on that alcohol considered acidic?

Ah, the third and final text book I was willing to open had this line "....are such strong bases that they will react immediately with any acid present in the rxn mixture, even very weak acids such as water and alcohols." And that's it, no examples, no mechanisms, no pictures. Just a one liner at the end of the section. Nice.

Did the MCAT seriously put the grand caveat exception to gringnard reactions on the test? Why yes, yes they did. How messed up is that.

Actually, this is pretty much the cardinal rule when it comes to Grignards - they do not react well with acids, or at least not without significant acid-base side reactions.

It's not so much that the alcohol is acidic as it is that the Grignard is super basic - it's basically the conjugate base of an alkane, which has a pKa of 50. That's stronger than pretty much any other organic molecule out there (at least, that I can think of), which means that it's a crazy-strong base. An alcohol, in contrast, has a pKa value of 16 - a difference of 34 pKa units, which provides a landslide motive force toward the side with the less acidic acid (alkane).

I'm not certain why a mech would be needed, anyway - it's just an acid-base reaction. I suppose the only thing that might be a little confusing is the complex between the oxygen anion and the MgBr+ ion, but logically it makes sense that those two ions would complex until the anion found something better to bind to (a proton).

It sounds like you might've just not had a very thorough teacher/book - my textbook (Solomons) has a good 2-3 pages on the restrictions of Grignards, and even mentions the exact situation involved in the question (basically, if you react one with an alcohol-contaning carbonyl compound, you have to be prepared to waste one molar eq. PhMgBr because of its reaction with the alcohol group - hence why a minimum of 3 eq. PhMgBr is necessary to provide the product in the AAMC question).

 

[Laufcra]

Hey question 20 on physical looks a bit weird, is it just me or is the answer not A at all? The passage describes an object projected to a height h, they say nothing about the object's descent. The frequency should continuously rise, choice C. ? "the flight described in the passage"

 

[maxknux]

Okay I am having trouble with Bio Passage II
Item 102
Which of the compounds in Table 1 has the highest Freezing point?
A) Butane (I choose this Answer) MP on table -138 C BP is 0 C
B)
C) 1,2 Ethanediol (Correct Answer) MP on table -13 C BP is 197 C
D)

Could someone explain this to me?

 

[Jepstein30]

Okay I am having trouble with Bio Passage II
Item 102
Which of the compounds in Table 1 has the highest Freezing point?
A) Butane (I choose this Answer) MP on table -138 C BP is 0 C
B)
C) 1,2 Ethanediol (Correct Answer) MP on table -13 C BP is 197 C
D)

Could someone explain this to me?

Freezing point = temperature where liquids become solids
Same as melting point = temperature where solids become liquids

So C has a higher MP/FP based on the table.

Boiling point is a phase change from liquid to gas.. not the same as freezing point.

 

[maxknux]

Freezing point = temperature where liquids become solids
Same as melting point = temperature where solids become liquids

So C has a higher MP/FP based on the table.

Boiling point is a phase change from liquid to gas.. not the same as freezing point.

Well I thought Butane has -138 C which is a smaller number then 1,2 Ethanediol which has -13 C.

Maybe my logic is wrong about this

 

[Jepstein30]

Well I thought Butane has -138 C which is a smaller number then 1,2 Ethanediol which has -13 C.

Maybe my logic is wrong about this

It's asking for the highest freezing point.

-13 > -138

 

[maxknux]

It's asking for the highest freezing point.

-13 > -138

Oh Dang, I missed it the word Highest

Thanks

 

[sillyome]

Did anyone think BS #95 (major functions of liver) was bull. The liver synthesizes angiotensinogen, which functions by raising blood pressure. This was one of the worst questions and the curve is stupid ridiculous too.
49/52 for PS for a 13
36/40 for VR for a 11
49/52 for BS for a 13...

 

[Melomare17]

had a question on aamc 10, BS, discretes, #17

why is there direct relationship between pressure and volume? i thought it would be inverse like P1V1 = P2V2 no? the answer choice says that if one decreases the other decreases---why????

 

[Gauss44]

#67 and #68

Can someone explain the answers to #67 and #68 in AAMC 10, VR? They are from the passage about turtles.

 

[Temperature101]

Did anyone think BS #95 (major functions of liver) was bull. The liver synthesizes angiotensinogen, which functions by raising blood pressure. This was one of the worst questions and the curve is stupid ridiculous too.
49/52 for PS for a 13
36/40 for VR for a 11
49/52 for BS for a 13...

I agree with you on that question... I had to go back and change my answer on it because I felt like they were asking for obvious functions of the liver... Ridiculous curve on that test...

45/52 PS... 11
22/40 VR.... 6
40/52 BS... 10

What should I freaking do for VR?

 

[Gauss44]

I agree with you on that question... I had to go back and change my answer on it because I felt like they were asking for obvious functions of the liver... Ridiculous curve on that test...

45/52 PS... 11
22/40 VR.... 6
40/52 BS... 10

What should I freaking do for VR?

Yes, to be honest, your VR needs work. Feel free to post questions on here, and if I have time and the answer, I will help.

 

[Gauss44]

VR Passage #3

Would anyone please post a map of the passage?

I don't like mine and think I've overlooked something. Thanks!

 

[Temperature101]

Yes, to be honest, your VR needs work. Feel free to post questions on here, and if I have time and the answer, I will help.

I know...ESL

 

[Gauss44]

#85
According to the information provided, the attitude of the king toward the founders of the Royal Society was most like that of:

A. a dog to fleas
D. a mouse to cats

Given the theme of revolutions and the times favoring the Puritans, I can't imagine how they got A as the correct answer. The answer key isn't helpful.

Would you explain your reasoning for choice A?

 

[Gauss44]

Who read the VR passage 7 about concepts and prototypes reasonably quickly and understood it?

Please tell me what you focused on, or tips about reading passages just like this one.

 

[Gauss44]

For #41, the passage explicitly states that the entire experiment is based on the assumption that oleic acid is cylindrical in shape. All the calculations derived are based on that assumption. With H2O, you can't use this method because it doesn't meet the assumption that the molecule is cylindrical.

For #50, every 10 decibel increase is an order of magnitude increase in the intensity. So we have 120 decibels, which is 12 orders of magnitude. Going from 10^-12 to 10^0 is 12 orders of magnitude. The other way you could do it is by plugging in each intensity into the equation given. It works out as follows:

10log (10^0/10^-12), which simplifies to 0 - (-12) = 12

= 10log(10^12); the log of 10^12 is 12, thus, the final equation simplifies to 10 * 12 = 120.

Easiest way to remember though is that 10 decibels = 1 order of magnitude.

Regarding #41, I think determining the volume oleic acid required both experiments 1 and 2, and not either or. The result of experiment 1 revealed the height (or length) of the molecule, then experiment 2 revealed the molecule's diameter.

What do you think?

This would explain why the same experiment wouldn't work in the scenario described in question #41: You cannot get water to position itself two different ways to take measurements. Water is arguably in sort of a bent cylindrical shape too, so that can't be the full all-inclusive answer.

 

[Gauss44]

#42
about why neutrons can't be detected


I understand why B is correct. Can you explain why D isn't correct?

 

[Gauss44]

#24:
Most bacterial cells and human sells are alike in:

Can anyone explain why B is wrong? Why D doesn't just say, "shape of dna."?

 

[Synapsis]

Anyone else nearly get tripped by 24 in PS? I first crossed out C and D, knowing that hydrogen peroxide was a common oxidizing agent. I guess I was lucky enough to check oxidation numbers to find that it actually gets oxidized. I literally checked this question twice more after doing it lol.

#42
about why neutrons can't be detected


I understand why B is correct. Can you explain why D isn't correct?

When I did this problem, I first crossed out A and C, and picked B because it was best supported by the passage. There may be a better response to this, but nothing in the passage would suggest that a neutron would have less (or more) energy.

#24:
Most bacterial cells and human sells are alike in:

Can anyone explain why B is wrong? Why D doesn't just say, "shape of dna."?

Ignoring that A is correct, it would be hard for me to find a reason to cross out B. Obviously eukaryotes and prokaryotes have different sized ribosomes, but does that mean the chemical composition is different? Eh, maybe, with respect to the ratio or amount of molecules inside. I can't think of a better answer, because both have rRNA and polypeptides.

 

[Synapsis]

Also, will someone explain PS #45? C makes total sense, but I ruled it out because I didn't think the purpose of the experiment was to determine unknown particles, so much as to study how particles decay, which is what the passage says. How could I get around this type of thinking?

 

[RC4L]

#85
According to the information provided, the attitude of the king toward the founders of the Royal Society was most like that of:

A. a dog to fleas
D. a mouse to cats

Given the theme of revolutions and the times favoring the Puritans, I can't imagine how they got A as the correct answer. The answer key isn't helpful.

Would you explain your reasoning for choice A?

The king gave the charter to the Royal Society because he supported the science but not the scientists. The king knew they would not destroy him but they were definitely pests. To say the king was a mouse among cats would mean that they posed a grave threat to him whereas to say the king was a dog among fleas means they did not necessarily put him in danger but he was not completely comfortable with their presence. This kinda falls under the "extreme answer choices" category that we are supposed to stay away from. If the question was re-worded to represent the concept without the analogy, "a mouse to cats" would translate into something like "the Royal Society would surely be his demise."

 

[RC4L]

#42
about why neutrons can't be detected


I understand why B is correct. Can you explain why D isn't correct?

The amount of energy is irrelevant in this case because the neutron is uncharged and wont cause ionization regardless of the energy it has. Without ionization, no detection.

 

[RC4L]

Also, will someone explain PS #45? C makes total sense, but I ruled it out because I didn't think the purpose of the experiment was to determine unknown particles, so much as to study how particles decay, which is what the passage says. How could I get around this type of thinking?

I think this involves a physics concept. In projectile motion, the vertical path of a projectile is velocity times the sin of the angle from launch. The mass of the object will directly affect the trajectory path so by measuring the radius of curvature you can find the mass of the particle and subsequently its identity. I'm pretty sure that is the reasoning behind that one. In addition, A cant be true because flight time is only relevant to horizontal velocity, B has no support in the passage, and neutrons cant ionize the gas so you wouldn't be able to find a neutrons path(C).

 

[RC4L]

#24:
Most bacterial cells and human sells are alike in:

Can anyone explain why B is wrong? Why D doesn't just say, "shape of dna."?

For B, bacterial cells have 70s ribosomes and eukaryotes have 80s ribosomes. For D, the answer is referring to the circular structure of prok chromosomes vs the linear structure of euk chromosomes. Notice the answer choice says "structures that CARRY DNA," not the shape of DNA by itself.

 

[RC4L]

#67 and #68

Can someone explain the answers to #67 and #68 in AAMC 10, VR? They are from the passage about turtles.

67) For B, the military has to take ecological consideration into support by virtue of the fact that they use tortoises in their natural habitat for study. I don't think "consideration" means support here I think it just means are ecological factors significant for any reason here. Answer choices C and D are bold assumptions and have no basis in the passage. Answer choice A is the only answer that does not contradict passage information.

 

[RC4L]

68) In the last paragraph, it says "the study makes clear that drawing broad conclusions about the species is impossible from a local study." The second to last paragraph says "the unclassified report gives a flavor of the data obtainable from spy technology." The first paragraph says "the study's importance lies in the use of advanced intelligence-gathering tools to examine the environment." Answer choices A-C do not address the question of what the scientists are particular interested in.

 

[Synapsis]

Anyone want to explain how we're supposed to know what a vole is? I got this question right by the FARTHEST stretch of the imagination (I just figured a vole might be a mouse because it looked like a word representing a rodent).

Where on the topics list is this? It's these types of questions in BS that really, really bother me.

 

[sakabato93]

Anyone else think that the particle accelerator passage was INSANE? Also, I thought that the verbal was a lot more difficult that I'm used to seeing.

 

[VitaminVater]

Can anyone explain #43 and #45 in PS?

For 43 how can one electron cascade affect 2 anodes, even if it's equidistant from them?

For 45, I was a little confused as to why they used a magnetic field. I thought since they were trying to see the trail of the particle they'd used to have it curve and stay longer in the chamber, to get more data. Are we to always assume a magnetic field on a moving charged particle is to get its radius of curvature and determine its mass/charge?

 

[VitaminVater]

Anyone want to explain how we're supposed to know what a vole is? I got this question right by the FARTHEST stretch of the imagination (I just figured a vole might be a mouse because it looked like a word representing a rodent).

Where on the topics list is this? It's these types of questions in BS that really, really bother me.

Dude, it's under evolution on the topics list:
"Identification of all species of rodents by name, picture or droppings size "
It's right above knowing the air speed velocity of a swallow varied by carrying load and continental origin

 

[gettheleadout]

Anyone want to explain how we're supposed to know what a vole is? I got this question right by the FARTHEST stretch of the imagination (I just figured a vole might be a mouse because it looked like a word representing a rodent).

Where on the topics list is this? It's these types of questions in BS that really, really bother me.

I knew it referred to a rodent of some sort, but I also reasoned that since the outbreak occurred in the Southwest US, it probably wasn't a fish (no bodies of water, in fact not much water at all), it wasn't humans since the doctors didn't get it, and if it were a snake there would be obvious bite marks on all patients to allow the doctors to connect the dots (and hopefully this would have been mentioned in the passage).

 

[gettheleadout]

Can anyone explain #43 and #45 in PS?

For 43 how can one electron cascade affect 2 anodes, even if it's equidistant from them?

For 45, I was a little confused as to why they used a magnetic field. I thought since they were trying to see the trail of the particle they'd used to have it curve and stay longer in the chamber, to get more data. Are we to always assume a magnetic field on a moving charged particle is to get its radius of curvature and determine its mass/charge?

For 43, the cascade is just the propagation of ionization reactions through the air by consecutive electron collisions and emissions. Imagine the particle flying through the gas equidistant from two anode wires; the cascade produced propagates out like a wave from a point source.

For 45, my thought was that the "time" answer just didn't seem as realistic as the "particle identification" answer. The particle can't curve too much before exiting the accelerator (or colliding with the wall), and it's already moving crazy fast, so the time increase for particle flight would probably be insignificant. On the other hand, knowing radius of curvature on top of speed gives us mass-to-charge ratio, which is pretty distinct for particles and also quite useful, since the passage mentioned (I think) looking at particles released from collisions.

 

[Neutral]

Hey question 20 on physical looks a bit weird, is it just me or is the answer not A at all? The passage describes an object projected to a height h, they say nothing about the object's descent. The frequency should continuously rise, choice C. ? "the flight described in the passage"

The wording to the answer is a bit weird but overall it's describing a projectile that ascends and descends like any other projectile. As it is ascending, the frequency is lower according to the doppler effect, but as it continues to decelerate from no longer having a force acting on it, that frequency shift gets lower and lower. Once the projectile reaches its max height, h, it is not longer moving, therefore there is no frequency shift. Then it begins to fall downward, accelerating, so the frequency shift starts increasing. When you take into account just the magnitude it goes from large shift to small shift to no shift to small shift to large shift.

Also is there an AAMC 11 thread?

 

[gettheleadout]

Also is there an AAMC 11 thread?

http://forums.studentdoctor.net/showthread.php?t=785299

 

[Neutral]

For #51, D is wrong because a mole of gas is 22.4 L at STP, not 25C right?

 

[gettheleadout]

For #51, D is wrong because a mole of gas is 22.4 L at STP, not 25C right?

Yep! 25 C is standard thermodynamic conditions.

 

[onedirection]

PS #9

What bonding accounts for the expected increase in energy density fo solid nitrogen as compared to methanol

The answer was C?

But how does methanol have weak ionic bonds

H-bonds aren't ionic bonds are they

 

[monkeyvokes]

PS #9

What bonding accounts for the expected increase in energy density fo solid nitrogen as compared to methanol

The answer was C?

But how does methanol have weak ionic bonds

H-bonds aren't ionic bonds are they

I saw two keys for this. One of them said C, one said D.
D seems the best answer.. for the reason you stated, methanol doesn't ionic bond

 

[onedirection]

Does anybody else think The biology ELISA Question in Passage IV is random

The ELISA is a test that is often used to detect antibodies to a particular organism. Would a positive result from such a test for H. pylori indicate that the patient had an ulcer?

Why was the answer "no, because the patietn could have been exposed to H. pylori and eliminated it"

But if he eliminated it, wouldn't that imply that he "had" an ulcer

so why is it No?

 

[Thisisthelife]

Does anybody else think The biology ELISA Question in Passage IV is random

The ELISA is a test that is often used to detect antibodies to a particular organism. Would a positive result from such a test for H. pylori indicate that the patient had an ulcer?

Why was the answer "no, because the patietn could have been exposed to H. pylori and eliminated it"

But if he eliminated it, wouldn't that imply that he "had" an ulcer

so why is it No?

No being exposed to the bacteria does not mean a patient will develop an ulcer. A person could be exposed to H.pylori and have eliminated it before an ulcer developed. All that a positive result indicates is that antibodies to a specific pathogen are present in the patients serum. It DOES NOT indicate how far the disease has progressed.

As far as ELISA is concerned, the reason its not that random is because the ELISA is a widely used antibody detection test. The theory behind it is not as complicated as its made out to be.

 

[Thisisthelife]

The king gave the charter to the Royal Society because he supported the science but not the scientists. The king knew they would not destroy him but they were definitely pests. To say the king was a mouse among cats would mean that they posed a grave threat to him whereas to say the king was a dog among fleas means they did not necessarily put him in danger but he was not completely comfortable with their presence. This kinda falls under the "extreme answer choices" category that we are supposed to stay away from. If the question was re-worded to represent the concept without the analogy, "a mouse to cats" would translate into something like "the Royal Society would surely be his demise."

Actually, if this option was "a cat to mice" it would probably have been the best option. I made the mistake of switching the answers in my head. If you read the question carefully, you'll notice that the first part of the analogy corresponds to the king and the second to the scientists NOT the other way around.

 

[bmoredoc]

can anyone explain #112 about the hantavirus being complementary to the lung gene? Are they implying here that the DNA from the virus was incorporated into the lung genome via a lysegenic cycle? I'm a bit confused