AAMC CBT9 and 9R OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT9 and 9R.

Please post ONLY questions pertaining to AAMC CBT9 and 9R.
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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[dipbk]

Hey Guys,

I just did Practice Test 9, and on the biological reasoning I am a bit confused for question 38 regarding the Peptide A and Experiment 2. I dont understand how it states that OC activity can only be stimulated when Peptide A and OB are present however in the table there is no OC activity when they are present together.

Thanks!!

View attachment 182139

i too am confused about the reasoning for the solution to #38. does anyone have any insight? I thought based on the results reported in the table that "b" was correct...

 

[bleach121]

Hello, for question 103 of BS
(A semilogarithmic plot of the data used to generate Figure 1 would look like which of the following graphs?),

I don't understand how the semilogarithmic plot of the data would look like the graph in answer choice D.

At time = 10 hours the number of bacteria should be close to zero, yet the semilogarithmic plot shows that it is close to 10,000 at t=10. How can this be explained? Thank you.

 

[JMMTB]

If you look closer at the original plot, you will see that at t=10 hrs it is not quite 0. The scale on the original is 100,000 for every tick mark. So if you look super closely t=10 has it about 1/10 of the way up from 0 which is 10,000. This is the exact reason why we need the have the semilogarithmic plot to show us the actual changes. In order to solve this question you don't even have to read the passage or look at the original graph. The only answer choice that has logarithmic scaling is D.

 

[yjj8817]

For #93, it says embryonic agnathan brains have a pituitary system unlike the adult aganatans. I don't understand how from this fact, one can conclude that the answer is degenerative state. Does having a certain structure as an embryo mean something?

 

[yjj8817]

For 84 in verbal, why can't "classical tomb" be a part of answer? The third paragraph about the 2nd version of painting mentions how the tomb is changed in shape.

 

[Shirafune]

This was by far the worst test for me! It looks like I backtracked like 1 months of progress.
Anybody else feel like this?

 

[Marleywh]

For 84 in verbal, why can't "classical tomb" be a part of answer? The third paragraph about the 2nd version of painting mentions how the tomb is changed in shape.

The tomb is not classic, that's the point, it is represented by a simple shape.

Also I just took this test, got my highest score yet on verbal! PS15, VR13, BS14!

 

[Oh_Gee]

can someone explain the answer to me? i knew to eliminate A and D right off the bat but still don't get why B is the answer. i don't even understand how the machines work after re-reading the passage several times

 

[Oh_Gee]

This was by far the worst test for me! It looks like I backtracked like 1 months of progress.
Anybody else feel like this?

lol the dialysis passage had me like "f*** this i'll come back to you last". still don't understand how it works

were you able to figure it out how it works from the diagrams and passage?

 

[justadream]

can someone explain the answer to me? i knew to eliminate A and D right off the bat but still don't get why B is the answer. i don't even understand how the machines work after re-reading the passage several times

Basically the machine works by taking in your blood (filled with wastes) and putting it in the dialysate fluid (which is CLEAN). Diffusion occurs so that the wastes go to the dialysate fluid and thus when the blood is repumped back into your body, it is CLEAN.

During this filtration process, the filter lets small molecules like urea pass through. Proteins are too big to pass through so no blood proteins will go into the dialysate fluid. Think about why this is. If your blood proteins could go into the dialysate fluid, you would probably die since all your blood proteins would diffuse out of the blood.

 

[justadream]

For #93, it says embryonic agnathan brains have a pituitary system unlike the adult aganatans. I don't understand how from this fact, one can conclude that the answer is degenerative state. Does having a certain structure as an embryo mean something?

Yes, oftentimes phases you see in the embryonic stage retrace the development of that thing from its ancestors. Many of these traits are gone by adulthood (thanks to evolution, many of the traits are no longer needed).

 

[Oh_Gee]

lol the dialysis passage had me like "f*** this i'll come back to you last". still don't understand how it works

Basically the machine works by taking in your blood (filled with wastes) and putting it in the dialysate fluid (which is CLEAN). Diffusion occurs so that the wastes go to the dialysate fluid and thus when the blood is repumped back into your body, it is CLEAN.

During this filtration process, the filter lets small molecules like urea pass through. Proteins are too big to pass through so no blood proteins will go into the dialysate fluid. Think about why this is. If your blood proteins could go into the dialysate fluid, you would probably die since all your blood proteins would diffuse out of the blood.

ohh wait let me see if i get it. looking at just figure 1, the blood inflow goes through that white space where ions exchange from the white space to the darker space but the proteins don't exchange at all. they just keep going through to the blood outflow pump. is that right? also what's the point of this if there's the same amount of ions in the blood vs the dialysate. will there be exchange of ions if the concentrations are all the same?

 

[Oh_Gee]

138. i don't get it. the answer is saying the only way for the gene therapy is to get it into an embryo? i thought the gene therapy was to help babies-adults.

 

[justadream]

ohh wait let me see if i get it. looking at just figure 1, the blood inflow goes through that white space where ions exchange from the white space to the darker space but the proteins don't exchange at all. they just keep going through to the blood outflow pump. is that right? also what's the point of this if there's the same amount of ions in the blood vs the dialysate. will there be exchange of ions if the concentrations are all the same?

Yes, your understanding is generally right.

The point of having the same amount of ions is so that the dialysate fluid is isotonic. You wouldn't want to have a hypertonic dialysate solution (or else salts will flow into your blood). If you had a hypotonic dislysate solution, the salts in your blood would escape into the dialysate fluid.

 

[justadream]

138. i don't get it. the answer is saying the only way for the gene therapy is to get it into an embryo? i thought the gene therapy was to help babies-adults.

I think it can work for everyone.

Plus, the other answers are blatantly wrong so go with this one.

 

[Oh_Gee]

Yes, your understanding is generally right.

The point of having the same amount of ions is so that the dialysate fluid is isotonic. You wouldn't want to have a hypertonic dialysate solution (or else salts will flow into your blood). If you had a hypotonic dislysate solution, the salts in your blood would escape into the dialysate fluid.

so how does the waste in the patient's blood go into the dialysate if they're both isotonic to each other

 

[justadream]

so how does the waste in the patient's blood go into the dialysate if they're both isotonic to each other

The salts (e.g., NaCl) are isotonic.

The wastes (e.g., urea) are not.

 

[Oh_Gee]

The salts (e.g., NaCl) are isotonic.

The wastes (e.g., urea) are not.

so the urea, creatine are the waste products? we assume those are small enough to fit in the pores?

 

[justadream]

so the urea, creatine are the waste products? we assume those are small enough to fit in the pores?

Yes I think so. Urea isn't really that big of a molecule (compared to proteins).

http://en.wikipedia.org/wiki/Urea

 

[confuciastt]

Hey guys, I have a question on BS #129. So it says Peptide B inhibits Peptide A binding, which would reduce osteoblatin production. I reasoned that the existing concentration of osteoblatin prior to Peptide B introduction would remain the same since we have no reason to believe it's being consumed in any way. However, the answer is osteoblatin concentration decreases. Can someone please explain this to me?

I googled the question and one previous poster on SDN had the same question, but it didn't get answered

 

[justadream]

Hey guys, I have a question on BS #129. So it says Peptide B inhibits Peptide A binding, which would reduce osteoblatin production. I reasoned that the existing concentration of osteoblatin prior to Peptide B introduction would remain the same since we have no reason to believe it's being consumed in any way. However, the answer is osteoblatin concentration decreases. Can someone please explain this to me?

I googled the question and one previous poster on SDN had the same question, but it didn't get answered

Peptide A is in charge of producing osteoblatin. I believe peptide A does so by binding to receptors on plasma membranes. If you block these receptors with peptide B, then you start making less osteoblatin.

You can assume that osteoblatin (a peptide) decreases because all peptides eventually are degraded. Peptides have to constantly be regenerated and if the rate of regeneration is less than normal, the net effect is less osteoblatin.

 

[confuciastt]

Peptide A is in charge of producing osteoblatin. I believe peptide A does so by binding to receptors on plasma membranes. If you block these receptors with peptide B, then you start making less osteoblatin.

You can assume that osteoblatin (a peptide) decreases because all peptides eventually are degraded. Peptides have to constantly be regenerated and if the rate of regeneration is less than normal, the net effect is less osteoblatin.

Ahhh so they are being degraded - thank you!

 

[DrDreams]

Ok So in question 51, it says there is a block that is moving at constant speed, and the Tcos is the direction of the magnitude of frictional force.

How the heck can you have constant speed, if the force that is causing you to move the Tcos component, is canceled out by the frictional force. I maybe out of it or something that I can't see it.

 

[justadream]

Ok So in question 51, it says there is a block that is moving at constant speed, and the Tcos is the direction of the magnitude of frictional force.

How the heck can you have constant speed, if the force that is causing you to move the Tcos component, is canceled out by the frictional force. I maybe out of it or something that I can't see it.

This is like the textbook example of something at constant speed.

You can have constant speed when:
1) Not moving (V = 0)
2) Forces cancel out. Thus, the NET FORCE = 0.

For example, let's say you have a box sliding on the ground at 1 m/s. I push it to the right with a force of 5 N. You push it to the left with a force of 5N. The net force = F = ma = 5N - 5N = 0


Acceleration = 0. Speed = constant.

 

[DrDreams]

Oh man, I realize it was basic, but I just couldn't understand how something that is losing energy to friction can have a constant speed.

 

[justadream]

Oh man, I realize it was basic, but I just couldn't understand how something that is losing energy to friction can have a constant speed.

A good real life example is driving with cruise control.

 

[erythrocyte666]

Hi I had a few Questions:
BS #104:
Asks about a biological membrane and why it creates an osmotic pressure differential. Now I know the osmotic pressure experiment and all with a water permeable membrane separating two differently concentrated ionic solutions; but the term biological membrane implied to me the fluid mosaic model of the plasma membrane which says that non polar substances can dissolve in the membrane and because polar solutes can't they stay separate and a gradient develops. I guess it's not the best answer, but I'd still have picked B considering membrane channels/carriers. How would a "biological membrane" allow water to pass through? Aquaporins?

 

[erythrocyte666]

Also, BS #135:
Why can't the answer be D

 

[Gauss44]

Please Help!

Passage about Sensibility and Intelligence

Passage 4, questions 72 and 73 from AAMC9 CBT (or it's equivalent on the R version)

72 begins, "Suppose that persons of average intelligence..."

73 begins, "Which of the following passage contentions..."

Please explain YOUR reasoning about why the correct answer is more correct than any wrong answer, esp. answer C for 72 and answer D for 73. (Do NOT bother copying and pasting the answer key verbatim as it has NOT been helpful. And please don't insult me even if YOU found these questions to be easy. I've been averaging above 12 on VR.)

Thanks in advance!

 

[Gauss44]

Also see the question directly above.

Biology: In the below question, regarding the membrane with smaller pores, why don't the large particles get in the way? In other words, why aren't large particles blocking the smaller pores, or why isn't the correct answer C?

http://forums.studentdoctor.net/threads/aamc-9-174.310005/

 

[baxt1412]

hey everybody... had a question on AAMC 9 question # 13

i got the question correct, but i had a different though process and wanted to know if my thought process was another way to get to the same answer or if it was just luck.

My thought process:
The passage states that gasoline w/out additives can be inefficient. So adding in an anti-knock compound will increase efficiency. Then the passage also says that the higher the octane rating, the slower it burns and smoother the piston operates. I took smoother to be less knocking aka more efficient.

So from that I figured, high octane rating = high(er) efficiency. So when the question asked for what uses the least oxygen, I took that as what is the most efficient with oxygen? So I just paralleled them calling a fuel with a high octane rating as efficient with efficiency with oxygen. So I picked EtOH because it had the highest octane rating and thus I thought it had the highest efficiency and highest oxygen-consuming efficiency. Is this valid or just luck?




=======edit=======
also, on specifically #112 (but passage 3 of BS in general), what is the definition of filtration rate? i assumed it was the rate at which "stuff" was filtered out meaning really huge stuff would be "filtration rate"d out a lot aka filtered out a lot. but i'm trying to understand the reasoning and it seems inverse to what i was thinking.

**sorry for the seam, i had to piece together two screenshots**

 

[lazyindy]

@baxt1412
regarding question 13: haha I first solved it the same way as you did! but it was just a coincidence that EtOH had the highest octane rating and also required the least amount of oxygen to combust. The passage implies gases that burn too rapidly as inefficient so it has nothing to do with the amount of oxygen needed.

here's how I approached it while post-gaming: combustion is the conversion of hydrocarbons with general empirical formula CHO. The general equation is CxHxOx + _O2 --> _CO2 + _H20. As you can see if you increase the number of carbons on the original hydrocarbon alkane, more moles of CO2 are produced on the product side, meaning that you have to balance this out by adding more O2 molecules to the reactant side. Thus hydrocarbons with the least amount of carbons relative to the number of Oxygens will require the least amount of oxygen molecules to fully combust. EtOH has 2 carbons while the rest of the additives have more than that 2 so its the best answer.

 

[lazyindy]

and regarding question 112: no matter how large or small the pores of an excretory membrane are, smaller molecules will always be filtered (moved out) at a greater rate than larger molecules. So the filtration rate should decrease with increasing molecular size (eliminating A and B). SInce membrane 1 has larger pores, it will allow passage of larger molecules than membrane 2 but the rates of both would be the same (choice D).

 

[sps27]

So in this question, does not the -ve numbers signify like -278 > -680. OR is the -ve sign for exothermic, endothermic rxns simply a matter of showing energy release and energy absorbed and the values are still a mod of that number?

 

[ciestar]

So in this question, does not the -ve numbers signify like -278 > -680. OR is the -ve sign for exothermic, endothermic rxns simply a matter of showing energy release and energy absorbed and the values are still a mod of that number?

It's asking what releases the most energy, therefore, which is the most exothermic.

 

[sps27]

It's asking what releases the most energy, therefore, which is the most exothermic.

So the -ve sign only denotes direction of energy flow in Thermodynamics? The numbers are still treated like numerically. Is that right?

 

[ciestar]

So the -ve sign only denotes direction of energy flow in Thermodynamics? The numbers are still treated like numerically. Is that right?

In this case, I treated them more like absolute values. The biggest one indicated the largest energy change, and since it's negative, it's the most exothermic.

 

[ciestar]

Also, since it's asking about heat of formation, energy is released when a bond is formed. And the sign does indicate direction of energy flow.

 

[sps27]

Also, since it's asking about heat of formation, energy is released when a bond is formed. And the sign does indicate direction of energy flow.

Thanks bud. The sad part is I've got questions like these correct in EK 1001 practice and here I come and get all confused in an exam and goof up on simple ones...... Anyways, such is mcat life. Congratz on your 31.......you did well.

 

[blkgrnblkylw]

Question 3 asks what changes to a circuit element will increase the capacitance of the capacitor. I understand why increasing the area of the capacitor is the correct answer, because of the equation C = (A/d) k/4piK. However, I was thinking of the equation C = q/V which you could change to C = q/IR, and therefore a decrease in resistance would cause an increase in capacitance. Does this not make sense?

 

[Cawolf]

@blkgrnblkylw

It does not because the voltage is independent of resistance with a cell of voltage V. The current is dependent on the resistance, but the voltage is not.

 

[ieatshrimp24]

For #109, the question states that the if the blood inflow rate increases, then the pressure increases which can allow the filtration rate to increase.

Is this comparable to the kidney? As in, if the pressure in the glomerulus increases, then will filtration of the blood increase as well?

 

[Cawolf]

Yes - the biggest drive for increased filtration is an increase in blood pressure.

 

[sanguinee]

#32 "Which of the following statements could explain the frequently bluish color of the EQLs?" From a preivous post on this thread, I understand that UV --> Blue light is a decrease in frequency thus increase in wavelength, but how were we supposed to know it was UV light to begin with?

 

[Cawolf]

@sanguinee

You don't need to as none of the other choices make sense.

A - We are told sodium emissions are yellow.
B - Dispersion is greater for shorter wavelengths.
C - Shorter wavelengths = higher energy. This would violate the conservation of energy.
D - Sure. Some energy is lost so the fluorescence is slight lower energy (longer wavelength).

 

[sanguinee]

@Cawolf that's what I figured. Thanks!

 

[sanguinee]

#41 PS
Doesn't the place of reduction/oxidation SWITCH in an electrolytic cell? Why isn't this so in this scenario? I saw previous explanations here as well but I still don't understand why.

 

[Cawolf]

The electrode switches, but so does the designation of anode or cathode.

Anode is literally defined as the site of oxidation, and vice versa for the cathode.

 

[sanguinee]

The electrode switches, but so does the designation of anode or cathode.

So even if it does switch, what is being changed in electrolytic as compared to galvanic? I understand that one is more favorable vs the other, but I'm not understanding how the electron flow changes if the anode and cathode are still oxidation/reduction respectively.

 

[Cawolf]

If you have a galvanic cell with electrons going left to right and then add a sufficient voltage, electrons will flow right to left.