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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[Kaustikos]

I guess I dont even understand what they are asking in #141. How do you read figure 2 to answer this question.

Thanks

It was more of a discrete than passage based. Knowing that it asks for somatic, you can cross out D. Visceral basically means internal and I'm almost certain they were quizzing you on your knowledge of cell differentiation from the three cell layers (meso/endo/ecto) because muscle and neuronal all fall under ecto/mesoderm and only the gut is formed from the endoderm. Thus, gut is the correct choice.

 

[fuzzywuz]

Would you guys agree that Verbal was insane on this test?

First attempt at verbal yielded a 4. My second attempt, I got a 9...

 

[ghumkumari]

Hi,

Can anyone explain the answer of #77.

 

[gogopogo]

Would you guys agree that Verbal was insane on this test?

First attempt at verbal yielded a 4. My second attempt, I got a 9...

I found this too. WTF I took a bath all over the place, scored the lowest of any verbal I've taken, by a long shot. Any other aamcs have comparable difficulty so I can have more practice?

 

[Deepa100]

The primary rupture in the Landers quake moved from south to north as it progressed to its full 74-km length. How would the Doppler effect influence this?

A) By decreasing the wavelength of seismic waves propagating eastward and westward

B) By increasing the wavelength of seismic waves propagating eastward and westward

C) By decreasing the wavelength of seismic waves moving northward and increasing the wavelength of waves moving southward
The Doppler Effect will cause a bunching or squeezing of the waves moving with the rupture and an elongation of the waves opposing the rupture. This is answer C.


D) By increasing the wavelength of seismic waves moving northward and decreasing the wavelength of waves moving southward

I don't understand the explanation for C. Can some one shed some light?

 

[Deepa100]

The discussion suggests that the author considers the appropriate relationship of humans to other animals to be that of:

A) benefactor to recipient.

B) scientist to subject.

C) student to teacher.
The major emphasis in the passage, especially in the tone and attitude, is the author observing and learning from nature, culminating in the final paragraph with the author participating in the collective knowledge and wisdom of previous generations: “Tonight I watch the sky, thinking of the people who came before me and their knowledge of the placement of stars…. Whichever road I follow, I walk in the land of many gods. Behind me my ancestors say, ‘Be still. Watch and listen….’”

D) parent to child.

I don't know how I could've interpreted that ancestors as "animals"?

 

[Deepa100]

Does any one follow this reasoning?
The author commits somewhat of a logical fallacy by asserting that it is impossible to surrender responsibility. One could do so freely—although the author is right in saying that once you make that choice you have “enslaved your will to some else’s will.” In the case of someone with the hypothetical psychological condition referred to in the question, a person surrenders responsibility involuntarily, because that person would be incapable of making the decision whether to be responsible or abdicate responsibility; nonetheless, that person surrenders it.

The Q seems to be talking about "inability to break promises" which does not sound like a bad thing...

 

[CommSNTS]

This is what the reaction looked like:
2 Cu2+ + 2 H2O → 2 Cu(s) + O2 + 4 H+
The proper equation for determining Ecell is to ADD the potentials, not to subtract them (Ecell=Eanode+Ecathode). +0.34V represents copper being reduced while -1.23V represents water being oxidized; this is exactly what is occurring in the given formula for which we need to determine Ecell. Therefore, we only need to add the potentials: -1.23V + 0.34V = -0.89V = Ecell.


Does this help?

Going back to this question........

Why don't you multiply the Ecell of Copper by 2 because there are two moles in the equation? I'm really confused, haha.

 

[bluemonkey]

Going back to this question........

Why don't you multiply the Ecell of Copper by 2 because there are two moles in the equation? I'm really confused, haha.

You don't multiply by the number of moles when using Ecell=Ecat-Ean because moles don't show up anywhere in the units.

Only multiply by moles when moles actually show up in the equations/constants, ie the nernst equation and dG=-nFE. Always make sure that your units cancel out leaving you with whatever you are looking for. If something doesn't cancel out, you have done something wrong.

 

[travelbug73]

This is what the reaction looked like:
2 Cu2+ + 2 H2O → 2 Cu(s) + O2 + 4 H+
The proper equation for determining Ecell is to ADD the potentials, not to subtract them (Ecell=Eanode+Ecathode). +0.34V represents copper being reduced while -1.23V represents water being oxidized; this is exactly what is occurring in the given formula for which we need to determine Ecell. Therefore, we only need to add the potentials: -1.23V + 0.34V = -0.89V = Ecell.


Does this help?

I have to go back to this post too. I do not agree with the bolded part. You don't add two reduction potentials. You either add oxidation and reduction potentials or you subtract the reduction potential of the anode from that of the cathode. Mathematically, this is how they look:

1) Ecell = Eoxd + Ered (-1.23 + 0.34 = -0.89V)

OR

2) Ecell = Ecathode - Eanode (0.34 - (+1.23) = -0.89V)

I used the second equation but obviously incorrectly. I had not realized that the oxidation potential was given. I should have flipped the potential and I did not. The most important lesson to be learned is determining whether the given potentials are oxidation or reduction potentials.

 

[bluemonkey]

I have to go back to this post too. I do not agree with the bolded part. You don't add two reduction potentials. You either add oxidation and reduction potentials or you subtract the reduction potential of the anode from that of the cathode. Mathematically, this is how they look:

1) Ecell = Eoxd + Ered (-1.23 + 0.34 = -0.89V)

OR

2) Ecell = Ecathode - Eanode (0.34 - (+1.23) = -0.89V)

I used the second equation but obviously incorrectly. I had not realized that the oxidation potential was given. I should have flipped the potential and I did not. The most important lesson to be learned is determining whether the given potentials are oxidation or reduction potentials.

You make a REALLY important point. The different Ecell equations are not the same because of the sign conventions and whether reduction or oxidation potentials are used. Folks should pick one that they feel comfortable with and stick to it. I prefer the Ecell=Ean-Ecat because both are written as reduction potentials in this equation. There is also the voltaic vs. electrolytic factor to take into account. Be careful about your electrode designations!

 

[CommSNTS]

You don't multiply by the number of moles when using Ecell=Ecat-Ean because moles don't show up anywhere in the units.

Only multiply by moles when moles actually show up in the equations/constants, ie the nernst equation and dG=-nFE. Always make sure that your units cancel out leaving you with whatever you are looking for. If something doesn't cancel out, you have done something wrong.

Awesome, thanks! So, even if the reduction potential is given for 1 mole, but the equation shows like 100 moles being reduced, you use the same reduction potential? Weird, it must've slipped my mind. Thanks again bluemonkey.

 

[auroraboy]

I found this too. WTF I took a bath all over the place, scored the lowest of any verbal I've taken, by a long shot. Any other aamcs have comparable difficulty so I can have more practice?

OMG, I've been depressed since I finished this practice test, I scored PS 12 BS 12 VR 7
A freking 7...I've never scored below 8 or 9 and thought my verbal skills were improving.. apparently not

oh yea, I was also pissed off at earthquake passage in physics...seemed more verbal than science to me

 

[bluemonkey]

Awesome, thanks! So, even if the reduction potential is given for 1 mole, but the equation shows like 100 moles being reduced, you use the same reduction potential? Weird, it must've slipped my mind. Thanks again bluemonkey.

As long as you are dealing with standard conditions no, you do not multiply by the number of moles. If you are dealing with non-standard conditions, however, then you will need to use the Nernst equation.

 

[CommSNTS]

As long as you are dealing with standard conditions no, you do not multiply by the number of moles. If you are dealing with non-standard conditions, however, then you will need to use the Nernst equation.

Makes sense, thanks again, my man.

 

[ballofnerves]

I was wondering if somebody would be able to explain the last question of the BS section. It is #216 on the FL, involving cells dividing in the presence of a radioactive nucleotide. I don't see why mitosis can be ruled out as a possible answer.

 

[whoknows2008]

I was wondering if somebody would be able to explain the last question of the BS section. It is #216 on the FL, involving cells dividing in the presence of a radioactive nucleotide. I don't see why mitosis can be ruled out as a possible answer.

Hey there! Someone actually replied to it before: This is what they said:
If it is a linear shape, it would be mitosis, curvelinear meiosis...

Now, assuming I'm correct (and I don't have access to the graph) why would I assume that?

Because exponential functions don't graph linearly, ruling out Mitosis.
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Does that make sense? If not, I can explain further ....

 

[ballofnerves]

Hey there! Someone actually replied to it before: This is what they said:
If it is a linear shape, it would be mitosis, curvelinear meiosis...

Now, assuming I'm correct (and I don't have access to the graph) why would I assume that?

Because exponential functions don't graph linearly, ruling out Mitosis.
----
Does that make sense? If not, I can explain further ....

Thanks, I don't know how I missed that earlier reply.

I guess the thing that confuses me is that the graph goes up then goes down. I understand why it would go up (the radioactive substance is being incorporated into the new DNA), but why is there the subsequent drop?

 

[unsung]

The discussion suggests that the author considers the appropriate relationship of humans to other animals to be that of:

A) benefactor to recipient.

B) scientist to subject.

C) student to teacher.
The major emphasis in the passage, especially in the tone and attitude, is the author observing and learning from nature, culminating in the final paragraph with the author participating in the collective knowledge and wisdom of previous generations: “Tonight I watch the sky, thinking of the people who came before me and their knowledge of the placement of stars…. Whichever road I follow, I walk in the land of many gods. Behind me my ancestors say, ‘Be still. Watch and listen….’”

D) parent to child.

I don't know how I could've interpreted that ancestors as "animals"?

I think what they're trying to say is that even our ancestors had this awe and respect for nature. The thing about "Watch and listen" is also saying that we should be like students of nature and observe it, pay attention to it. It's got so much beauty and many secrets for us to learn, etc. etc. blah blah blah. The whole thing about student/teacher has to do with the author's sense of wonder/respect/awe at nature's beauty. You get the idea .

 

[Vihsadas]

The primary rupture in the Landers quake moved from south to north as it progressed to its full 74-km length. How would the Doppler effect influence this?

A) By decreasing the wavelength of seismic waves propagating eastward and westward

B) By increasing the wavelength of seismic waves propagating eastward and westward

C) By decreasing the wavelength of seismic waves moving northward and increasing the wavelength of waves moving southward
The Doppler Effect will cause a bunching or squeezing of the waves moving with the rupture and an elongation of the waves opposing the rupture. This is answer C.


D) By increasing the wavelength of seismic waves moving northward and decreasing the wavelength of waves moving southward

I don't understand the explanation for C. Can some one shed some light?

Let's say your earthquake waves (or any waves for that matter) originate from a point that is itself moving from south to north. Now, if the source is moving northward, then the waves will be "scrunched" together because the motion of the source is in the same direction of the waves. But on the south side the waves will be "stretched" because the source is moving the opposite direction of the waves.

 

[chreesteene]

Hey guys,
I just took this test and I have a question on number 171 (from Passage V in the BS section).
It asks for IR peaks for a hydroxyl group and a carbonyl group, respectively, and the choices are:

b. 1700 and 3400
d. 3400 and 1700

I picked d, but the answer key says (b) and unfortunately, I have no idea how the explanation is even related to the question. It says in the solutions for this question:

"Step 4 involves the addition of an acetyl group to compound 4, which is an acetylation reaction."

Please help! Thanks!

 

[niranjan162]

Hey guys,
I just took this test and I have a question on number 171 (from Passage V in the BS section).
It asks for IR peaks for a hydroxyl group and a carbonyl group, respectively, and the choices are:

b. 1700 and 3400
d. 3400 and 1700

I picked d, but the answer key says (b) and unfortunately, I have no idea how the explanation is even related to the question. It says in the solutions for this question:

"Step 4 involves the addition of an acetyl group to compound 4, which is an acetylation reaction."

Please help! Thanks!

D is right, it shows up as passage 2 in my test. The explanation is right sounds like you have some sorta problem or are confusing two different questions. Or I am getting confused as to which question you are asking

 

[chreesteene]

D is right, it shows up as passage 2 in my test. The explanation is right sounds like you have some sorta problem or are confusing two different questions. Or I am getting confused as to which question you are asking

Thanks for your help!

Uh, I think it's the same question but I think the passages are in a different order? I don't know, the explanation in the solutions manual made no sense because it wasn't even answering the question. IDK what the hell is going on.

 

[heronumber1one1]

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!

 

[paniwani]

i think they meant us to assume that "egg" here meant fertilized egg. just blame the MCAT for getting less points for putting more thought into a problem. (don't overthink next time)

 

[engineeredout]

So what is the consensus as to the difficulty of this exam compared to others?

I just took it (CBT) and got 10PS/12VR/10BS. Happy about my VR score, thought I did higher in PS. Oh well, I'd still be thrilled to get this on the real thing.

And there will be less orgo on the real thing than on here right? The orgo is definitely what killed me. I know I have to do some focusing on it before the real thing but still it seemed like a lot.

 

[Adnama]

So what is the consensus as to the difficulty of this exam compared to others?

I just took it (CBT) and got 10PS/12VR/10BS. Happy about my VR score, thought I did higher in PS. Oh well, I'd still be thrilled to get this on the real thing.

And there will be less orgo on the real thing than on here right? The orgo is definitely what killed me. I know I have to do some focusing on it before the real thing but still it seemed like a lot.

The recent trend has been a LOT less orgo.

 

[nfg05]

I've read what's already been written in this thread regarding Item 100, but I'm not sure I get BloodySurgeon's explanation that a hydroxyl group is more polar than a carbonyl because it participates in hydrogen bonding.

In comparing -OH to =O, I just remembered the partial positive charge on the carbon being particularly large in the carbonyl (more so than it would be on the carbon bearing the -OH ). So I guess the OH dipole is the relevant one, not comparing the CO dipole between the two molecules?

 

[nfg05]

For item 130.

Which of the following statements explains most plausibly why host antibodies are ineffective against H. pylori?
A. antibody proteins may be denatured in the harsh environment of the stomach.
C. H. pylori infection may suppress the activity of the immune system.

Could someone explain why they knew C was wrong? There are some bacteria (i.e. the species responsible for TB and leprosy) that suppress immune system activity, and I wouldn't think the AAMC expects us to have detailed knowledge of whether or not H. pylori is one of those bacterial species. It is not impossible, however, for bacteria to display such a capability.

When looking at A, the implication is that the body is basically helpless against any bacterial infection in the stomach (provided the bacteria can survive in low pH environments). Also, many proteins make it through the stomach and aren't digested until the small intestine so I was unsure whether the antibody proteins would be denatured or not. So, are all proteins DENATURED (secondary and up structure broken) in the low pH stomach and then those not digested (primary structure broken) in the stomach are digested in the small intestine?

 

[nfg05]

Item 133.
Most people infected with H. pylori do not develop gastric cancer because they:
A. do not incorporate bacterial genes into their chromosomes
B. have robust immune systems that defeat early cancers
C. eradicate the infection before any tumors develop
D. tolerate the infection without developing tumors

I ended up picking D and getting it right, only because I couldn't see a compelling reason to pick any other answer based on the passage. However, did anyone else feel like this said nothing about WHY most people don't develop gastric cancer? The answer was basically a reaffirmation of the question stem, no? My EK training was screaming in the back of my head, "Don't pick that, it doesn't address the question!" but thankfully I ignored it.

 

[JoeGator86]

Number 100 is bull C=O is more polar than an OH group. Secondly the carbonyl is resonance stabalized to have the oxygen bear a negative charge, the OH group can't do this. The question asked with is more polar and C=O that is resonance stabalized so the alcohol gets deprotonated the carbonyl wins.

 

[JoeGator86]

Which of the following alkyl halides is most readily prepared by a reaction between the corresponding alcohol and concentrated hydrochloric acid? A
) Isopropyl chloride B
) Methyl chloride C
) sec-Butyl chloride
D) t-butyl Chloride ANSWER

I got this right but I guessed between Methyl Chloride and t-butyl. T-butyl alcohol reacts SN1 and methyl chloride reacts SN2. They choose two extremes for answers and I feel both are correct is there some information about the reactivity of protonated alcohols I don't know about? The solution just said t-butyl reacts much more readily, any help on this would be much appricated.

Is it because the extra alkyl groups make t-butyl alcohol a more stable product?

 

[tmntdonjuan]

Which of the following alkyl halides is most readily prepared by a reaction between the corresponding alcohol and concentrated hydrochloric acid? A
) Isopropyl chloride B
) Methyl chloride C
) sec-Butyl chloride
D) t-butyl Chloride ANSWER

I got this right but I guessed between Methyl Chloride and t-butyl. T-butyl alcohol reacts SN1 and methyl chloride reacts SN2. They choose two extremes for answers and I feel both are correct is there some information about the reactivity of protonated alcohols I don't know about? The solution just said t-butyl reacts much more readily, any help on this would be much appricated.

Is it because the extra alkyl groups make t-butyl alcohol a more stable product?

Yes. When you start with the alcohol with the t-butyl group, you protonate the -OH with the HCl to make it a good leaving group (-OH are horrible leaving groups) making it -H2O+. This also leaves Cl- as your base (it's a really weak base). H2O will exit the alcohol leaving you with the alkyl+ ion. The main factor that makes this reaction SN1 is that you have a carbocation intermediate and you want the most stable alkyl ion possible which comes from the most substituted alkyl group (t-butyl). The fact that it is more substituted makes it better able to re-distribute the positive charge and make a more stable intermediate. Also the fact that Cl- is a base (a REALLY REALLY weak base) influences the reaction as SN1 even more since SN2 is favored by reactions with strong bases (they are better able to completely displace the leaving group without having to have a carbocation intermediate). Hope that helps.

 

[tmntdonjuan]

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!

An embryonic egg starts out with 1 cell. This is like the reverse of a half-life question. So you know the number doubles every 10 hours. 3 days gives you 72 hours. That means the initial embryo (1 cell) gets 7 division periods. You can basically formulate the equation 2^ to solve. 1->2->4->8->16->32->64->128 is the number you end up with. 50 to 500 is the only range where 128 will fit. Hope that helps.

 

[tmntdonjuan]

Number 100 is bull C=O is more polar than an OH group. Secondly the carbonyl is resonance stabalized to have the oxygen bear a negative charge, the OH group can't do this. The question asked with is more polar and C=O that is resonance stabalized so the alcohol gets deprotonated the carbonyl wins.

I think it goes by oxidation/reduction. If you look at a chart starting from oxidation->reduction C=O is more oxidized than C-OH, no? Meaning C-OH is more reduced than C=O. Reduction is basically the gain of electrons. If C-OH is more reduced than C=O then it has accepted electrons more. While the O in C=O has the octet just like C-OH, more of its electrons are tied up in the double bond than the O in C-OH. All of this points to the O in C-OH having greater negative charge. Not 100% sure of my explanation. I got this question wrong on AAMC 7 and this is the answer I came up with when I tried to rationalize it.

 

[futuredoctor10]

130. Which of the following statements explains most plausibly why host antibodies are ineffective against H. pylori?
A. antibody proteins may be denatured in the harsh environment of the stomach.
C. H. pylori infection may suppress the activity of the immune system.

Could someone explain why they knew C was wrong? There are some bacteria (i.e. the species responsible for TB and leprosy) that suppress immune system activity, and I wouldn't think the AAMC expects us to have detailed knowledge of whether or not H. pylori is one of those bacterial species.

When looking at A, the implication is that the body is basically helpless against any bacterial infection in the stomach (provided the bacteria can survive in low pH environments).

nfg05- I picked answer choice C as well. I don't understand why C is wrong.
I did not think A was correct because as you stated above its implication is that the body is basically helpless against any bacterial infection in the stomach.

 

[futuredoctor10]

So what is the consensus as to the difficulty of this exam compared to others?

I want to know what people thought. Were your scores comparable to AAMC6? I had a 4 point drop from AAMC 6 to 7 and took them within a week, under similar circumstances (sleep/simulated conditions).

I didn't finish 5 questions (randomly guessed on all of them, and missed all of them) on AAMC6 PS but I think that might have only made a 1-2 point difference, not 4 !!!

 

[amar21]

PS #36

I don't understand how I should be tackling these with multiple reaction sequences. I mean, I get that the slow step = the rds = blah blah. But when I'm tackling a question I always tend to find the NET reaction and then try to solve answers (and always get it wrong).

When finding the NET RXN, the 2 reactants that were correct won't even be a part of the net reaction (Bubbling SO3(g) through H218O).


Can anyone recommend a better approach to multi-step rate reactions?... Like, I dont even get how that makes sense not to use the net reaction? In a sense, I seem to use the net rxn and le chateliers principle instead of individual reaction steps

 

[futuredoctor10]

PS #36

I don't understand how I should be tackling these with multiple reaction sequences. I mean, I get that the slow step = the rds = blah blah. But when I'm tackling a question I always tend to find the NET reaction and then try to solve answers (and always get it wrong).

When finding the NET RXN, the 2 reactants that were correct won't even be a part of the net reaction (Bubbling SO3(g) through H218O).

Yeah for this question you do not need to find the net reaction. Since the question asks which method will produce the most SO3(18)O2-, if you look at the correct answer choice it lists reactants of that third reaction step. Using those reactants produces the most of the desired product (we don't need to do steps 1-2, since the question assumes you have both reactants of the 3rd step present for use).

Can anyone recommend a better approach to multi-step rate reactions?... Like, I dont even get how that makes sense not to use the net reaction? In a sense, I seem to use the net rxn and le chateliers principle instead of individual reaction steps

I'd say it depends on the question. If you are given a problem where you assume you start with reactants of step 1, then you need to look at the net reaction. (whereas this question is only asking how to make the most product of 1 individual reaction)
Does that help?

 

[futuredoctor10]

The discussion suggests that the author considers the appropriate relationship of humans to other animals to be that of:

A) benefactor to recipient.
B) scientist to subject.
C) student to teacher.
The major emphasis in the passage, especially in the tone and attitude, is the author observing and learning from nature, culminating in the final paragraph with the author participating in the collective knowledge and wisdom of previous generations: "Tonight I watch the sky, thinking of the people who came before me and their knowledge of the placement of stars…. Whichever road I follow, I walk in the land of many gods. Behind me my ancestors say, ‘Be still. Watch and listen….'"
D) parent to child.

I don't know how I could've interpreted that ancestors as "animals"?

I agree. I don't know why/how we are supposed to know the "ancestors" can also refer to the "animals".

The passage even goes on about how humans don't completely understand the animals, so I assumed it was not a student/teacher relationship. For example, the passage states: "I never learned the sunflower's golden language". Parent/child seemed like a better choice considering the affection the author has towards nature!

 

[futuredoctor10]

Quote:
Originally Posted by Deepa100
46 (PS):
The primary rupture in the Landers quake moved from south to north as it progressed to its full 74-km length. How would the Doppler effect influence this?

Let's say your earthquake waves (or any waves for that matter) originate from a point that is itself moving from south to north. Now, if the source is moving northward, then the waves will be "scrunched" together because the motion of the source is in the same direction of the waves. But on the south side the waves will be "stretched" because the source is moving the opposite direction of the waves.

The way I thought about this question: the rupture moves south to North.
Let's say there is a seismic wave is also moving North. When 2 waves move in the same direction, observed frequency increases. If the observed frequency increases, the observed wavelength decreases.

Likewise if a seismic wave moved South, then it would be moving in the opposite direction to the rupture, causing a decreased observed frequency. If the observed frequency decreases, observed wavelength increases.

So the correct answer is "by decreasing wavelength of seismic waves moving northward and increasing wavelength of seismic waves moving southward"

 

[hulkster]

Number 138.

Apparently their explanation entails that an inhibitor of transcription still permits protein synthesis, despite the fact that without transcription you have no mRNA? AM I seeing this wrong? Thanks for any help.

 

[futuredoctor10]

Number 138.

Apparently their explanation entails that an inhibitor of transcription still permits protein synthesis, despite the fact that without transcription you have no mRNA? AM I seeing this wrong? Thanks for any help.

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?

 

[futuredoctor10]

146.
If you look at the graph: % of the dividing nuclei with radioactive label increases dramatically from 3-13 hours.

For the % of dividing nuclei with radioactive label to increase, more nuclei are dividing, which means more mitosis must be occurring.

How is mitosis a wrong answer choice? I understand the deoxythymidine DNA is INCORPORATED into the DNA during synthesis. But once this happens, for you to notice an increase in the percentage of dividing nuclei - mitosis must be occurring right?

 

[osuguy]

bio #115

It was hypothesized that the decrease in blood flow to the skin resulted from a change in activity of the sympathetic nerves to the skin. which observation would support the hypothesis?

a change in norepinephrine content of blood draining from the skin

This explanation sucked so I was wondering if im on the right track with this. If there is less norepinephrine, there would be less stimulation by the sympathetic so that would result in less blood flow because of less dilation of the blood vessels in the skin. Was i wrong in just thinking that sympathetic nerves release norepinephrine at the synapse and that the amount flowing in the blood didnt really have much to do with it? Does norepinephrine usually get sent out in the bloodstream to activate the sympathetic system?

Thanks!

 

[nfg05]

146.
If you look at the graph: % of the dividing nuclei with radioactive label increases dramatically from 3-13 hours.

For the % of dividing nuclei with radioactive label to increase, more nuclei are dividing, which means more mitosis must be occurring.

How is mitosis a wrong answer choice? I understand the deoxythymidine DNA is INCORPORATED into the DNA during synthesis. But once this happens, for you to notice an increase in the percentage of dividing nuclei - mitosis must be occurring right?

When looking at the phrase "% of dividing nuclei with radioactive label", you should be focusing more on "with radioactive label" than "dividing." I see where you're coming from, the word "dividing" is misleading since it makes you think of mitosis and should probably have been left out altogether.

Remember the cells are synchronized as stated in the question. If they all underwent mitosis during the time frame you were talking about, the PERCENTAGE of radioactive nuclei would not change. If before mitosis there were x% radioactive and y% non-radioactive then after mitosis there will be twice as many radioactive and twice as many non radioactive as before, but those x and y percentages would still be the same. Since there is no DNA synthesis going on nuclei that were non-radioactive before cannot suddenly become radioactive during mitosis.

DNA synthesis is the better answer it CAN account for a percentage increase in the number of radioactive nuclei, since DNA synthesis converts formerly non-radioactive nuclei into radioactive nuclei, thus increasing the percentage of radioactive ones.

 

[hulkster]

bio #115

It was hypothesized that the decrease in blood flow to the skin resulted from a change in activity of the sympathetic nerves to the skin. which observation would support the hypothesis?

a change in norepinephrine content of blood draining from the skin

This explanation sucked so I was wondering if im on the right track with this. If there is less norepinephrine, there would be less stimulation by the sympathetic so that would result in less blood flow because of less dilation of the blood vessels in the skin. Was i wrong in just thinking that sympathetic nerves release norepinephrine at the synapse and that the amount flowing in the blood didnt really have much to do with it? Does norepinephrine usually get sent out in the bloodstream to activate the sympathetic system?

Thanks!

Exactly what I thought, why would neurotransmitters be in the blood, unless they also doubled as hormones, which NE does not (I dont think)

 

[nfg05]

Exactly what I thought, why would neurotransmitters be in the blood, unless they also doubled as hormones, which NE does not (I dont think)

Just as an FYI, epinephrine and norepinephrine are synthesized and secreted as hormones by the adrenal medulla. Not sure that it has much bearing on this question, but it is a fact. For the question, I was just like don't overcomplicate it MCAT is simple so sympathetic effect = norepinephrine end of story.

 

[futuredoctor10]

Remember the cells are synchronized as stated in the question. If they all underwent mitosis during the time frame you were talking about, the PERCENTAGE of radioactive nuclei would not change. If before mitosis there were x% radioactive and y% non-radioactive then after mitosis there will be twice as many radioactive and twice as many non radioactive as before, but those x and y percentages would still be the same. Since there is no DNA synthesis going on nuclei that were non-radioactive before cannot suddenly become radioactive during mitosis.

DNA synthesis is the better answer it CAN account for a percentage increase in the number of radioactive nuclei, since DNA synthesis converts formerly non-radioactive nuclei into radioactive nuclei, thus increasing the percentage of radioactive ones.

nfg05- thanks so much! Your explanation clarifies this question so much. I didn't think about it but you are right that % of x and y radioactive/nonradioactive before and after mitosis will be the same.

AAMC explanations seriously lack in some departments and your explanation is far superior for this one

 

[klm0101]

Hi. Can someone please explain #24 in the PS please. The question is :

What is the value of c in Equation 2 as determined from the data in Table 1?
A) 1
The passage states that the reaction is zero order with respect to bromine, therefore bromine can be removed from Equation 2. A comparison of the results for Experiments 2, 4 and 6 (all with acetone concentrations of 0.80 M) shows that after dividing the rates of the reactions by the rate constants, the values obtained are directly proportional to the H+ concentration indicating the reaction is first order in H+.

B
) 2 C
) 3 D
) 4

i usually understand rate questions, but i must be missing something b/c i do not get how that got that to be first order