AAMC CBT9 and 9R OFFICIAL Q&A

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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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If you take into account the molecule size, then it would make sense that boiling point of the other compounds would be higher. Increasing molecular size raises BP because of increased interaction among the molecules.
 
Hi everyone,

I think these questions may have been asked before but I didn't see an explanation for them posted. Thanks for your help in advance.

AAMC 9

PS
20. What is the best explanation for the fact that a solution of NaNO2(aq) is basic?
A) NO2– is hydrolyzed with the formation of OH –(aq) ions.
The NO2- reacts with water, forming OH- ions. Thus, A is the best answer.
B) Na+ is hydrolyzed with the formation of OH –(aq) ions.
C) NaNO2(aq) decreases the Ka of HNO2(aq).
D) NaNO2(aq) increases the Ka of HNO2(aq)

I have seen this type of question before with NaCO3 being dissolved in water; I thought the Na+ would dissolve in solution and form OH- ions, but the CO3 actually gets hydrolyzed and forms OH ions in solution (thus making solution basic). That one made a little more sense: CO3 + H20 -> H2CO3 + OH-. However, I don't understand why Na isn't getting hydrolyzed in water to form OH- ions (as seen in B in this question). NaNO2 + H2O -> Na+ + OH-?

Is there a non-arbitrary way of knowing which ion gets hydrolyzed in water to produce hydroxide ions (thus making a solution basic)?

BS

111. Which of the following changes in flow rate or in solute concentrations would NOT occur if the blood inflow rate were increased, increasing the pressure in the dialysis chamber?

A) The blood volume reaching the outflow tube per unit time would increase.
B) The osmotic concentration of proteins in the dialysate fluid would increase
C) The osmotic concentration of proteins in the blood outflow would increase or remain unchanged.
D) The filtration rate across the dialysis membrane would increase.

This one was a little confusing...I get that proteins don't go through the membrane from the passage, but the wording of one of the answers (C) threw me off. The osmotic concentration of proteins in blood should NOT increase if the protein isn't going through the membrane right? I'm ok with the unchanged part, but not the 'would increase' part. The right answer makes sense in relation to the protein not filtering through the membrane (so you wouldn't see it in the dialysate fluid) but the other choice...

Just bad wording or am I missing something?
 
Hi everyone,

I think these questions may have been asked before but I didn't see an explanation for them posted. Thanks for your help in advance.

AAMC 9

PS
20. What is the best explanation for the fact that a solution of NaNO2(aq) is basic?
A) NO2– is hydrolyzed with the formation of OH –(aq) ions.
The NO2- reacts with water, forming OH- ions. Thus, A is the best answer.
B) Na+ is hydrolyzed with the formation of OH –(aq) ions.
C) NaNO2(aq) decreases the Ka of HNO2(aq).
D) NaNO2(aq) increases the Ka of HNO2(aq)

I have seen this type of question before with NaCO3 being dissolved in water; I thought the Na+ would dissolve in solution and form OH- ions, but the CO3 actually gets hydrolyzed and forms OH ions in solution (thus making solution basic). That one made a little more sense: CO3 + H20 -> H2CO3 + OH-. However, I don't understand why Na isn't getting hydrolyzed in water to form OH- ions (as seen in B in this question). NaNO2 + H2O -> Na+ + OH-?

Is there a non-arbitrary way of knowing which ion gets hydrolyzed in water to produce hydroxide ions (thus making a solution basic)?

BS

111. Which of the following changes in flow rate or in solute concentrations would NOT occur if the blood inflow rate were increased, increasing the pressure in the dialysis chamber?

A) The blood volume reaching the outflow tube per unit time would increase.
B) The osmotic concentration of proteins in the dialysate fluid would increase
C) The osmotic concentration of proteins in the blood outflow would increase or remain unchanged.
D) The filtration rate across the dialysis membrane would increase.

This one was a little confusing...I get that proteins don't go through the membrane from the passage, but the wording of one of the answers (C) threw me off. The osmotic concentration of proteins in blood should NOT increase if the protein isn't going through the membrane right? I'm ok with the unchanged part, but not the 'would increase' part. The right answer makes sense in relation to the protein not filtering through the membrane (so you wouldn't see it in the dialysate fluid) but the other choice...

Just bad wording or am I missing something?

As for the first question, you should know that HNO2 is a weak acid, hence its conjugate base,N02-, is going to be a weak base. According to Bronsted-Lowry definition, a base accepts a H+ from the acid. In this case the base would be NO2- and the acid, water. NO2- takes away the H+ from water, leaving behind OH- ions, which are basic. The Na+ ion is the conjugate acid of a strong base, NaOH, hence has no acidic properties in water. the equation you gave holds true but Na+ are spectator ions.

For #2 think of it this way. You understand that since the flow rate is higher, the proteins are not going to filter through the membrane and the conc. of proteins in the dialsylate is going to decrease. Now since the proteins are not filtering through, where are they gonna go? they will remain in blood. this could increase the conc of proteins in the blood.
 
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For #2 think of it this way. You understand that since the flow rate is higher, the proteins are not going to filter through the membrane and the conc. of proteins in the dialsylate is going to decrease. Now since the proteins are not filtering through, where are they gonna go? they will remain in blood. this could increase the conc of proteins in the blood.

Thanks for answering the first question, that makes more sense now due to NO2 (or CO3) being the base taking a proton from H20 and forming OH ions.

Hm..I think seeing the diagram would help explain what I meant. Basically you have the blood inflow from the patient (with proteins and whatnot) connected to the filter (NO proteins) connected to the outflow (back to patient). So if the proteins are not filtering through the membrane, there shouldn't be any net protein increase in the outflow...they should stay in the blood inflow. However the blood (solvent) has a larger net volume due to higher flow rate -> concentration of proteins in dialysate definitely goes down not up. Concentration of proteins in outflow should decrease, if anything, if the blood volume has increased not remain same/increase.

If you have access to the AAMC 9CBT, you can see the passage diagram I'm talking about. Hopefully that clarifies my question.
 
PS Item 27. Which action involves more work? Lifting a weight from A to B or lowering the weight from B to A?

I just used common sense here (bad idea on physics), and obviously lifting a weight requires more energy than lowering one. It made sense to me somehow that gravity was working with you when you lower it meaning you have to do less work.

I mean obviously you could just let go of the pulley and let it fall from B to A without doing any work at all right? Are they assuming that you are exerting some force on the pulley that makes the weight want to go upward (against the pull of gravity) when you're lowering the weight?
 
PS Item 46.
If a very bright light source shines on a mirror, the mirror may become warm because:
A) all of the light is reflected, and, by momentum conservation, the molecules in the mirror move, producing heat energy.
B) some of the light passes through the mirror, and, by energy conservation, potential energy is produced.
C) some of the light is absorbed by the mirror, and, by energy conservation, thermal energy is produced
D) none of the light is reflected, and, by energy conservation, mass is converted to energy.

Explanation: C. In general some of the light energy will be absorbed by the mirror, causing some heating to take place (although the amount will be small for a high-quality optical mirror). Thus, C is the best answer.



Anyone care to explain how they narrowed it down to C instead of A? The AAMC explanation just says that the mirror will absorb some light. OK... but how are you supposed to know that? It's not discussed in any Physics text or review material that I've ever seen. Is there some reason A can't happen and therefore must be wrong?
 
I have a question about #12 on the Physical Sciences.

I understand their explanation that ETOH would evaporate the fastest b/c it has the highest vapor pressure. But what I DON'T understand is how it has the highest vapor pressure??

If you look back at #7, ETOH is the molecule that can undergo hydrogen bonding...which should increase its boiling point....so shouldn't it be reasonable to conclude that ETOH would boil off last??

I thought about this too and realized it was kinda self contradictory, but was just like well the table says the vapor pressure is higher plain as day so just go with it. The only thing I can think of is that EtOH has a lower molecular weight than the others which when considered separately would tend to increase its vapor pressure compared to the others.

Granted, however, if placed in a situation where I had to decide which has a bigger impact on vapor pressure: MW or H-bonds? I'd go with H-bonds every time.
 
PS Item 46.
If a very bright light source shines on a mirror, the mirror may become warm because:
A) all of the light is reflected, and, by momentum conservation, the molecules in the mirror move, producing heat energy.
B) some of the light passes through the mirror, and, by energy conservation, potential energy is produced.
C) some of the light is absorbed by the mirror, and, by energy conservation, thermal energy is produced
D) none of the light is reflected, and, by energy conservation, mass is converted to energy.

Explanation: C. In general some of the light energy will be absorbed by the mirror, causing some heating to take place (although the amount will be small for a high-quality optical mirror). Thus, C is the best answer.



Anyone care to explain how they narrowed it down to C instead of A? The AAMC explanation just says that the mirror will absorb some light. OK... but how are you supposed to know that? It's not discussed in any Physics text or review material that I've ever seen. Is there some reason A can't happen and therefore must be wrong?


I got it by conversation of energy if the mirror heated up something must be lost from the light, which is not consistent with answer A. Also conservation of momentum is based on equal and opposite forces. Reflected light doesn't collide with the surface and there is no force accelerating it in the other direction, thus no change in momentum of the mirror. If I am wrong someone feel free to correct me.
 
PS Item 46.
If a very bright light source shines on a mirror, the mirror may become warm because:
A) all of the light is reflected, and, by momentum conservation, the molecules in the mirror move, producing heat energy.
B) some of the light passes through the mirror, and, by energy conservation, potential energy is produced.
C) some of the light is absorbed by the mirror, and, by energy conservation, thermal energy is produced
D) none of the light is reflected, and, by energy conservation, mass is converted to energy.

Explanation: C. In general some of the light energy will be absorbed by the mirror, causing some heating to take place (although the amount will be small for a high-quality optical mirror). Thus, C is the best answer.


Anyone care to explain how they narrowed it down to C instead of A? The AAMC explanation just says that the mirror will absorb some light. OK... but how are you supposed to know that? It's not discussed in any Physics text or review material that I've ever seen. Is there some reason A can't happen and therefore must be wrong?


Momentum (p) = m*v. Photons don't have mass, therefore they don't have momentum. Thats why A can't work.
 
Momentum (p) = m*v. Photons don't have mass, therefore they don't have momentum. Thats why A can't work.

To add to that, if all of the light is reflected, then none of the energy is transferred to the atoms. Therefore the temperature could not rise in the mirror.
 
can somebody explain #75 on verbal to me? I just don't understand B is right ,as the passage itself says that people who became blind developed the synesthesia. or is this just semantics??

and can somebody explain 77 to me? i chose foods since knowing the color/shape of food is important for whether you can eat it or not (ie can't just be round, but has to be red = apple not diseased apple).
 
#123 in the bio section : i get that is it an oxidation reduction, but why isn't it an isomerization as well?

Also this question from the bio section:

Capillaries in the kidney and elsewhere in the body maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following is the initial effect of a blood clot forming on the venous side of a capillary bed?


A
)
Net fluid flow in the direction of interstitial spaces will increase.
After introducing the idea of fluid homeostasis, which is obtained by balancing hydrostatic and osmotic pressures, the question asks the examinee to predict the consequences of a blood clot on the venous side of a capillary bed. To answer this, it is necessary to know that blood flows from arteries to capillaries and then to veins. If flow is blocked at the venous side, blood would accumulate in the capillaries. Thus, hydrostatic pressure would build up in the capillaries, causing a net increase in fluid flow into the interstitial spaces. A is therefore correct. B is incorrect because there will be an increase in net fluid flow into the interstitial spaces, not a decrease. C is not the best answer because the increase in osmotic pressure in the capillaries would be an indirect result of the fluid flow out of the capillaries. D is incorrect because the flow of fluid out of the capillaries would slightly increase, not decrease, the osmotic pressure. Thus, A is the best answer.
B
)
Net fluid flow in the direction of interstitial spaces will decrease.
C
)
Capillary osmotic pressure will increase.
D
)
Capillary osmotic pressure will decrease.


can someone explain what hydrostatic pressure in capallaries means? I don't understand their explanation
 
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PS Item 27. Which action involves more work? Lifting a weight from A to B or lowering the weight from B to A?

I just used common sense here (bad idea on physics), and obviously lifting a weight requires more energy than lowering one. It made sense to me somehow that gravity was working with you when you lower it meaning you have to do less work.

I mean obviously you could just let go of the pulley and let it fall from B to A without doing any work at all right?
Yeah I missed this one too, for exactly the same reason you did - using common intuition that it requires a lot more work/energy to lift a weight than lower a weight.

BUT apparently in the question they meant any type of work. So I think you exert a force to lift the weight. When you lower the weight, you exert NO force and do NO work, but gravity exerts the force to lower it and does all the work. These forces are equal and therefore, exerted over the same distance [between A/B], the work will be equivalent. W=Fxd

I think the question should have been more specific to indicate "any type of work in the system" because I assumed they meant WORK DONE BY THE PERSON. Then again it never said "by the person" so I perhaps made the wrong assumption. Very tricky of AAMC.

Are they assuming that you are exerting some force on the pulley that makes the weight want to go upward (against the pull of gravity) when you're lowering the weight?
No. I think it is that you exert no force when the weight falls downward. Gravity exerts the force (which is why you feel it is easier to lower the weight than lift it).
 
can somebody explain #75 on verbal to me? I just don't understand B is right ,as the passage itself says that people who became blind developed the synesthesia. or is this just semantics??

and can somebody explain 77 to me? i chose foods since knowing the color/shape of food is important for whether you can eat it or not (ie can't just be round, but has to be red = apple not diseased apple).

75. A & C do not undermine passage arguments. D does not "undermine" the passage (passage states a patient had brain damage and lost synesthetic ability; D says "damage to visual cortex seldom results in synesthesia". These statements are not the same but similar.) B is the most critical argument that would OVERTURN something the author states is "not present at birth" and "ONLY begins to develop when a child is learning to write."

77. I think the explanation you gave above is an example of going beyond the passage/text. "Appropriate foods by combination of any characteristics" includes characteristics like smell, taste of food which is NOT part of visual synesthesia. Additionally, the question stem states that the cells "evolved because they increased processing speed in the identification of:" You would need to process faster on (A) - dangerous predators. You don't need to process how different foods look/smell/taste rapidly- you could spend all the time in the world and still be okay.
 
how bout these..

1) Assume that a pan of “dry water” is momentarily disturbed. Which of the following concepts best explains why the resulting sloshing oscillations persist for a fairly long time?
I dont really get thir explaination/the question, even. I interperted "sloshing" as the water hitting the side of the container, then being pushed back down, and hitting the other side of the container. So i thought that was representative of newton's 3rd law...the wave hits the side of the container, and the container hits the waves right back pushing it to the other side...but whats with "fairly long time" business?

2- Wouldnt a chloride ion (-1 charge) have an electron configuration of ....3p^4?? a nonharged cl is 3p^5,and when you absorb an electron (as in electron capture) dont you go back one number on the table (one less atomic number)??

3-If oligonucleotides such as mRNA were not degraded rapidly by intracellular agents, which of the following processes would be most affected?...yeah, so not really sure where to start with this one :/ I thought oligonucleotides were just nucleotides/bases, so if they were easily degraded then that would pretty much suck for DNA/ tRNA, no?

any help is mucho appreciated :love:
 
can anybody explain why the answer is A..cause 90 is way below the boling point of cyclohexanol..I chose C
 
the answer is A - to prevent unreacted cyclohexanol from distilling

since in a distillation you are trying to seperate two things, you need the boiling point to be higher than one and lower than the other

choice B makes no sense because that is what we are trying to distill
choice C/D are also false

Usually in a distillation any modification w. the temp is to get the purest product, so the temp needed to be lower than 161C [BP of cyclohexanol]

the fact that it is lower than 90 - i don't know why they chose that temperature but 90 is lower than 161.. so answer choice A is correct
 
the answer is A - to prevent unreacted cyclohexanol from distilling

since in a distillation you are trying to seperate two things, you need the boiling point to be higher than one and lower than the other

choice B makes no sense because that is what we are trying to distill
choice C/D are also false

Usually in a distillation any modification w. the temp is to get the purest product, so the temp needed to be lower than 161C [BP of cyclohexanol]

the fact that it is lower than 90 - i don't know why they chose that temperature but 90 is lower than 161.. so answer choice A is correct

I know what you saying but 90C is below 160 the boiling point of cyclohexanol. at 90 cyclohexanol is not even boiling so it cant interfere with the process. However, it is reasonable to assume that the product could decompose( why would say it can't). Maybe they reason that mixing the two compounds lowers the boiling point of cyclohexanol.
 
Can somebody please explain that whole dyalysis passage to me?? its passage #3 in the bio section. Okay so, from what i get is that because the kidneys dont work in a patient, blood passes through this chamber which acts like the glomerulus and fliters out proteins and other large substances that remain in the blood. From here, i am very confused on what the diasylate fluid is for. It says that it bathes the blood in the chamber, but why? What is it comparable to in a functioning kidney? If someone could sum up in simple terms what is going on with this filter and what is being reabsorbed, filtered etc, and compare it to a regular kidney, that would really help me out a lot.

Also from that same passage...

#110- what would be the initial outcome if a clot was on the venous side of a capillary bed?

A) Net fluid flow in the direction of interstital spaces.
This is the answer, and i see why it happens....because since the hydrostatic pressure continues and water is being moved out at the arteriole end, the clot is prevent water from being reabsorbed at the venular end. Becuase of this, the extra water will flow out into the interstital space causing edema. Correct me if im wrong...i have a hard time understanding GFR. What i DONT get is, wouldn't osmotic pressure in the capillary increase because that extra water isn't being reabsorbed at the venular end? I guess i am not really sure how this works.

#111- Which of the following changes in flow rate would NOT occur if the blood inflow rate were increased, increasing the pressure in the dialysis chamber?

I went about this question by basically thinking that an increase in pressure would lead to an increased GFR. From that, i crossed out D since it says filtration rate increases, and i crossed out A because blood volume outflow rate would increase as well. But i was stuck between B and C and couldnt really get to the right answer. The right answer is:
B) The osmotic concentration of proteins in the dialysate fluid would increase. I guess since i didnt know the reason for the dialysate fluid in the first place i couldnt get to the right answer. Can someone help explain this one as well??

Thanks a lot!
 
I need some help for #47 in PS:

47) Visible light travels more slowly through an optically dense medium than through a vaccuum. A possible explanation for this could be that the light:

A) is absorbed and re-emitted by the atomic structure of the optically dense medium
B) is absorbed and re-emitted by the nucleus of the material in the optically dense medium
C) bounces around randomly inside of the optically dense medium before merging
D) loses amplitued as it passes through the optically dense medium

The answer was A, but i picked D. AAMC explanation says that D is a correct statment but does not answer the question. Nothing in the passage answers this question...are we just supposed to know this? I had no idea, and D just seemed to make sense. Can anyone acutally explain why A is correct compared to the other answers? thanks!
 
I have no idea about the basis of the answer as well, but we could use reasoning here. The question states that "visible light travels more slowly thru....", so we should pick a logical choice that answers the question.

If the light loses amplitude, as stated in D), the frequency and wavelength can still be the same, so it doesnt really answer the question. So A is the BEST choice.


but how do we know that its reabsorbed and re-emitted by the atomic structure and not the nucleus?
 
but how do we know that its reabsorbed and re-emitted by the atomic structure and not the nucleus?

light is made up of photons. remember if a photon hits an electron with enough energy, it goes to the next level. conversely, if an electron goes from a higher subshell to a lower subshell closer to the nucleus, a photon is released (conservation of energy)

the way i thought about this question was, this excitation/de-excitation is happening a bunch of times as the light wave/photons pass through the medium. the electrons are part of that atomic structure.
 
If the speed of the charged particle described in the passage is increased by a factor of 2, the electrical force on the particle will:
A) decrease by a factor of 2.
B) remain the same.

Electrical force depends on the particle’s charge and the strength of the electric field experienced by the particle, not on the particle’s speed. Thus, B is the best answer.

C) increase by a factor of 2.
D) increase by a factor of 4.
============
I thought the answer would be D. From energy conservation, can't we equate electrical potential energy to kinetic energy and come up with a relation between the Force and velocity?
 
If the speed of the charged particle described in the passage is increased by a factor of 2, the electrical force on the particle will:
A) decrease by a factor of 2.
B) remain the same.

Electrical force depends on the particle’s charge and the strength of the electric field experienced by the particle, not on the particle’s speed. Thus, B is the best answer.

C) increase by a factor of 2.
D) increase by a factor of 4.
============
I thought the answer would be D. From energy conservation, can't we equate electrical potential energy to kinetic energy and come up with a relation between the Force and velocity?

think about the electric field like the field of gravity. pretend there is a ball in the air. what is the force of gravity on the ball if you drop it from rest? mg. what is the force of gravity on the ball if you throw it with all your might? mg.
 
what do people think of aamc cbt9 as compared to the real thing?!?

just got my highest score of any practice test on it, with a little more than a week to go.

i agree that the oligonucleotide question is (141) crap!
 
how bout these..

2- Wouldnt a chloride ion (-1 charge) have an electron configuration of ....3p^4?? a nonharged cl is 3p^5,and when you absorb an electron (as in electron capture) dont you go back one number on the table (one less atomic number)??

any help is mucho appreciated :love:

this is not electron capture, rather, in the ionic bond between sodium and chlorine, Chlorine hogs the electron, so instead of s2p5, it is s2p6. Electrons don't change atomic mass (# of protons + neutrons) or atomic number (# of protons)
 
Quick question about PS #7. I figured MTBE is an ether, and thought that ethers CAN have Hydrogen bonding with water because of its free electrons. I know it can't hydrogen bond with itself, but thought it could interact with the Hydrogens from water. Any thoughts?
 
Had a question about #116 -

Which of these cycloalkanes will undergo free radical bromination most rapidly?
A) cyclohexane
B) methylcyclohexane
C) 1-dimethyl cyclohexane
D) 1, 2-tetramethyl cyclohexane

Please correct me if the naming's wrong :p
I answered D but the correct answer is B. I thought the additional Hydrogens would make it more likely for D to be brominated first...is it because of Br's selectivity and its tendency to choose tertiaries over methyls that the answer's B?

Thanks in advance!

EDIT
nvm i'm an idiot...i was treating cyclohexane like benzene
 
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Hi guys,

My answer key doesn't have the answers to #165, 185, 208, and 210. Could you guys give me just the letter answers (i.e. a, b ,c,or d)?

Thanks a lot.
 
For #2 think of it this way. You understand that since the flow rate is higher, the proteins are not going to filter through the membrane and the conc. of proteins in the dialsylate is going to decrease. Now since the proteins are not filtering through, where are they gonna go? they will remain in blood. this could increase the conc of proteins in the blood.


I'm having serious issues with this question because of this directly copied and pasted from the passage associated with the Q:

Protein molecules are too large to diffuse through the membrane.




WTF?
 
I'm having some trouble with PS item 1. The questions asks "Which of the following graphs best illustrates how charge accumulates on the capacitor after the switch is closed?" You can ignore the switch. Four graphs of charge versus time are presented. I was able to limit it to either a linear graph of charge increasing with time, or one of charge increasing with the rate of increase decreasing (leveling off) over time.

The leveling off graph is correct, and the solution says that "the charging of a capacitor is an exponentially decreasing process that must reach a constant value after a long time." Will someone explain why this is the case?
 
I don't understand why the answer is not four haploid sperm that simply have a DNA content twice that of normal haploid sperm. If replication occurs twice before the start of meiosis, wouldn't that just produce chromosomes with four sister chromatids (not sure if that's actually possible, but based on the hypothetical situation posed in the question, that's what i'm assuming happens)? If that's the case, then it would still line up as homologous chromosomes and split in meiosis I so that the chromosome number would be N after the reduction division, just with each chromosome having 4 chromatids. Meiosis II would cause the chromosomes to split at the centromere with each sperm ending up with N chromosomes but double the normal DNA content as each chromosome would still have a pair of chromatids. Since I understand ploidy to be a reflection of chromosome # rather than DNA content, the only way I can see diploid cells resulting from meiosis is if the second round of replication prior to the start somehow doubled the number of chromosomes in the cell rather than just doubled its DNA content...

Anyone got any ideas on this?
 
This question confused me also. The concentrations of sodium in the dialysate are comparable to that in the blood, yes, but doesn't that just make the solutions isotonic with respect to sodium and not mean that the isotonicity of the dialysate solution is the same as blood when you consider all of the solute molecules present? I chose answer A through some complicated logic which I'm not sure made sense, but I don't understand answer C. If the dialysate solution were isotonic to the blood because of the Na+ concentration, then wouldn't there be no movement of fluid across the membrane--i.e. - wouldn't the dialysis machine fail to remove "excess fluid" as the passage indicates?

In general, when you say that a fluid is "isotonic" or "hypertonic" or "hypotonic", doesn't that refer to the entire solute composition rather than a single solute molecule as tonicity is a colligative property where the number of particles and not the identity matters??

Any response on these questions would be really appreciated...I take the test on Friday and want to make sure I don't head into it with the wrong understanding of these concepts. Thanks!!
 
I'm having some trouble with PS item 1. The questions asks "Which of the following graphs best illustrates how charge accumulates on the capacitor after the switch is closed?" You can ignore the switch. Four graphs of charge versus time are presented. I was able to limit it to either a linear graph of charge increasing with time, or one of charge increasing with the rate of increase decreasing (leveling off) over time.

The leveling off graph is correct, and the solution says that "the charging of a capacitor is an exponentially decreasing process that must reach a constant value after a long time." Will someone explain why this is the case?

I got this one wrong, too. :( And it's upsetting because the answer is quite logical. The capicator cannot hold an infinite amount of charge, so the graph must level off at some point.
 
I'm having some trouble with PS item 1. The questions asks "Which of the following graphs best illustrates how charge accumulates on the capacitor after the switch is closed?" You can ignore the switch. Four graphs of charge versus time are presented. I was able to limit it to either a linear graph of charge increasing with time, or one of charge increasing with the rate of increase decreasing (leveling off) over time.

The leveling off graph is correct, and the solution says that "the charging of a capacitor is an exponentially decreasing process that must reach a constant value after a long time." Will someone explain why this is the case?

in addition to what ksmi said, a capacitor is just a set of parallel metal plates with a space in between. Because the plates are both conducting, when you apply a voltage across them, conduction electrons in the plate directly connected to the positive side of the battery/voltage source are attracted towards the voltage source, and thus that plate starts to build a positive charge. Similarly, the negative end of the voltage source repels conduction electrons and thus a negative charge builds on the capacitor plate directly connected to it. At some point, the potential difference between the two plates in the capacitor (which arises because of the charge difference between the plates) becomes equal to the potential difference of the voltage source. So initially (at t=0), a capacitor circuit acts like a short circuit (a circuit where there's just a battery and a wire connecting the two terminals of the battery) because the capacitor has no potential difference across it. As charge builds, the capacitor beings to develop a potential difference, and so the rate at which the charge builds starts to slow down. As the potential difference across the capacitor reaches the potential difference across the voltage source, electrons are no longer able to flow through the circuit, so it behaves like an open circuit. Thus, no more charge is being built up in the capacitor plates. So initially current flows extremely rapidly, so charge builds quickly. At t--->infinity, current doesn't flow at all, so charge stops building. The result is an exponential function.
 
in addition to what ksmi said, a capacitor is just a set of parallel metal plates with a space in between. Because the plates are both conducting, when you apply a voltage across them, conduction electrons in the plate directly connected to the positive side of the battery/voltage source are attracted towards the voltage source, and thus that plate starts to build a positive charge. Similarly, the negative end of the voltage source repels conduction electrons and thus a negative charge builds on the capacitor plate directly connected to it. At some point, the potential difference between the two plates in the capacitor (which arises because of the charge difference between the plates) becomes equal to the potential difference of the voltage source. So initially (at t=0), a capacitor circuit acts like a short circuit (a circuit where there's just a battery and a wire connecting the two terminals of the battery) because the capacitor has no potential difference across it. As charge builds, the capacitor beings to develop a potential difference, and so the rate at which the charge builds starts to slow down. As the potential difference across the capacitor reaches the potential difference across the voltage source, electrons are no longer able to flow through the circuit, so it behaves like an open circuit. Thus, no more charge is being built up in the capacitor plates. So initially current flows extremely rapidly, so charge builds quickly. At t--->infinity, current doesn't flow at all, so charge stops building. The result is an exponential function.

yeah, what he said :D
 
I don't understand why the answer is not four haploid sperm that simply have a DNA content twice that of normal haploid sperm. If replication occurs twice before the start of meiosis, wouldn't that just produce chromosomes with four sister chromatids (not sure if that's actually possible, but based on the hypothetical situation posed in the question, that's what i'm assuming happens)? If that's the case, then it would still line up as homologous chromosomes and split in meiosis I so that the chromosome number would be N after the reduction division, just with each chromosome having 4 chromatids. Meiosis II would cause the chromosomes to split at the centromere with each sperm ending up with N chromosomes but double the normal DNA content as each chromosome would still have a pair of chromatids. Since I understand ploidy to be a reflection of chromosome # rather than DNA content, the only way I can see diploid cells resulting from meiosis is if the second round of replication prior to the start somehow doubled the number of chromosomes in the cell rather than just doubled its DNA content...

Anyone got any ideas on this?

I guess I should post the question, that would probably help.

144. If chromosomal duplication before tetrad formation occurred twice during spermatogenesis, while the other steps of meiosis proceeded normally, which of the following would result from a single spermatocyte?

The Answer is B. Four Diploid Sperm. I put C. Four Haploid Sperm.

And I still can't make sense of how two rounds of duplication prior to the start of meiosis could lead to Four Diploid Sperm. The explanation AAMC gives is:"Because replication occurred twice instead of once prior to tetrad formation, each sperm would have twice the normal amount of DNA. As a result, four diploid sperm would be produced instead of four haploid sperm."

But I see a difference between having twice the normal amount of DNA to start and having twice the number of chromosomes.

And ignore my question about 113., I figured that one out with a little research. Good luck to everyone taking the test this weekend!
 
I've got a question about #20 in the physical sciences. It's the one that asks, "What is the best explanation for the fact that a solution of NaNO2 is basic?" I answered correctly, thankfully, but I was very confused while taking the test. The correct answer choice says "NO2- is hydrolyzed with the formation of hydroxy ions." Is it really hydrolyzed? Doesn't hydrolysis means to break up? Water "breaks up," yes, but not NO2-. Is it just bad wording on their part?
 
I've got a question about #20 in the physical sciences. It's the one that asks, "What is the best explanation for the fact that a solution of NaNO2 is basic?" I answered correctly, thankfully, but I was very confused while taking the test. The correct answer choice says "NO2- is hydrolyzed with the formation of hydroxy ions." Is it really hydrolyzed? Doesn't hydrolysis means to break up? Water "breaks up," yes, but not NO2-. Is it just bad wording on their part?

I was definitely thrown off by that wording also when I took the test. But I think technically it's right because hydrolysis technically is any reaction where water breaks up and the NO2- causes that to happen. To say that the "NO2- is hydrolyzed" sounds strange obviously because it's not broken up, so I think the wording was a little off, but technically correct...I guess that's a situation where your knowledge of what actually happens has to dominate even if the wording is questionable (if you're really sure that you're right)
 
(Example essay for an upcoming guide on how to approach the writing sample)
The goal of business should be to generate profits.

When a group of lionesses venture out in to the Savannah to hunt, they do so in the same fashion as a business focused on generating profits. Collectively, the lionesses ensure that variable factors are working in their favor to increase the total yield of gazelle kills; the sun must be in the right place, the herd of Gazelle must be running in the right direction, and the lionesses must be perfectly hidden behind rocks or in trees in order to precisely coordinate their attack. If conditions are not optimal, then the lionesses will bring home less food and the pack itself will suffer. Consequently, if the lion pack becomes too weak, it may itself become prey to other lion families. In business, as in the African Savannah, a company must produce sufficient monetary return in order to grow and flourish. In a report summarizing the views of twenty great CEOs of the modern age, the 'Economist' stated, "the major factor in a competitive business is its ability to secure and manage market share. This allows the corporation to maintain steady revenue while simultaneously controlling competition." If the company does not attempt to maximize the pertinent conditions necessary to ensure profit, it will flounder and eventually be out-competed by rival entities. Thus, without the primary goal of profit, a business cannot be ultimately successful in today’s highly competitive marketplace.

While profit is the main focus of business in the modern day, there are conditions in which it is not the driving force. In 1989, a son of a millionaire, Seth Mullin, founded a company called 'Solargen' with an overriding social goal in my mind: "to find an affordable and efficient way to utilize solar power for widespread disseminated use". As Seth indicates, the primary goal of the company is not to generate profits, but rather to make solar power affordable and efficient. In contrast to the selfish quality of profit generating businesses, Solargen's goal is altruistic in nature. The company now manufactures solar powered houses, individual solar lighting, and power systems for satellites. In addition, a report from “Science Daily” revealed over 180 peer-reviewed original research innovations were produced in Solargen's laboratories. These projects, while not borne from a profit motivated attitude, are still sufficient to sustain the company’s monetary interests. As a result of the altruistic mantra of Solargen, in 2001, Seth's company was recognized as the major impetus behind the fundamental improvement of the solar power landscape since 1989. It has been suggested by Nobel Prize-winning economist, Paul Krugman, that because “Solargen is like a cactus in the otherwise barren desert of the solar power market,” it does not have to worry about out-competing other companies—there is no other proverbial 'lion pack' to steal gazelles from Solargen. Hence, the vast majority of the market share is under Solargen's control, and Solargen does not have to focus its efforts on competition. Krugman further states, “If Solargen were to fail, it would be due to its own demerits, rather than by the external pressure of companies that generated more profit.” Indeed, Solargen has yet to fail.

In a highly competitive marketplace, a business is forced to compete for market share with rivals. In this competitive paradigm, generating profits is the only way to achieve sustainability, and hence, must be the company's primary goal. If a company cannot continue to grow monetarily, then its competitors will eventually overtake and engulf it. In contrast, as evidence by the history of Solargen, if the market is fully controlled by a single company, then the business would be free of the competition that normally cages other corporations, and can devote resources to goals not directly related to profits.
 
For those that have taken the AAMC practice test #9, this is the question about water sloshing back and forth (seiches and "dry water"). Dry water here just means a model of water that doesn't take into account viscosity.

"Assume that a pan of “dry water” is momentarily disturbed. Which of the following concepts best explains why the resulting sloshing oscillations persist for a fairly long time?"
A) Energy conservation
B) Momentum conservation
C) Newton's 3rd law
D) Archimedes' principle

I was eyeballing A and B, and put B. The answer was A. The rationale given is:

"Although some friction (energy loss) will take place, energy will be very nearly conserved over each oscillation period. As a result, the amplitude of the seiches will decay very slowly as mechanical energy is turned into heat. The other options do not pertain to the sloshing oscillations. Thus, A is the best answer."

Can someone give me a more detailed analysis for why momentum conservation doesn't apply here? I accept that energy conservation is going on, but isn't momentum conservation also going on?

Thanks!
 
Plain and simple from exam krackers:

Conservation of Momentum comes into play with collusions, the two seen on the MCAT are completely inelastic and completely elastic.

You should recognize this problem as being "simple harmonic motion." This type of problem deals with energy. Kinetic and potential. Thing of it as a pendulum to visualize it better. At the top of a swing (or slosh in this case) all energy is converted to gravitational potential. at the bottom where the pendulum is perpendicular to the ground (or the water is level) all energy is in its kinetic form.

Therefore, any kind, as in ANY KIND of "simple harmonic motion" as denoted by "Ocillations" will always be answered by "consevation of energy".

PS, this problem should be a given answer and take no longer than 10 seconds to read and instantly answer.




PS, its not momemtum becuase momentum takes into account mass and direction, this problem does not.
 
Why couldn't you consider the waves reflecting off the end of the pan as completely elastic collisions?
 
isn't momentum also only conserved when there is no external force such as the force of gravity acting upon it?
 
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