AAMC CBT10 only OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT10.

Please post ONLY questions pertaining to AAMC CBT10.
Out of respect for people who may not have completed the other exams, do not post questions or material from any other AAMC exam.

Please see this thread for the rules of order before you post.

Good luck on your MCAT!

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[emericana]

One more thing... what?

The aamc solution says lowest freezing point highest concentration....

since when is .15 M a higher concentration than .2 ?

What is different about CaCl2 that gives it a higher concentration than NaCl?

 

[1nertia]

I saw someone else answered this earlier but I couldnt understand the explanation.

My questions:

I seriously do not understand the wording of the passage and was helping someone could explain it to me.

What side is the penny?
Is it Cu(NH3)4 2+?

If Cu(NH3)4 2+ is indeed the penny, how do you determine the oxidation state of Copper here?

So H is +1... so since there are 12 H that would make +12... and we need to get down to +2 .

How would we do this? Can someone explain this?

And then Cu 2+ on the right side would be +2?

Both the Kaplan and TPR book I have do not explain this adequately.

Just a few days before my exam so any help would be greatly greatly appreciated.

I think you are misunderstanding the equation. The Cu(NH3)4 2+ is the Waste Mixture not the Penny. It has an overall charge of +2. NH3 has a 0 charge therefore CU must have the +2. Copper naturally in a penny has not been oxidized so I assume its CU with a zero charge.

For your second question, you are forgetting to take into account van 't Hoff factors (i). You have to multiply the Molarity with i to get the molecule that would have the greatest effect.

 

[Rabolisk]

One more thing... what?

The aamc solution says lowest freezing point highest concentration....

since when is .15 M a higher concentration than .2 ?

What is different about CaCl2 that gives it a higher concentration than NaCl?

van't Hoff factor.

 

[TwoPaddles]

I saw someone else answered this earlier but I couldnt understand the explanation.

My questions:

I seriously do not understand the wording of the passage and was helping someone could explain it to me.

What side is the penny?
Is it Cu(NH3)4 2+?

If Cu(NH3)4 2+ is indeed the penny, how do you determine the oxidation state of Copper here?

So H is +1... so since there are 12 H that would make +12... and we need to get down to +2 .

How would we do this? Can someone explain this?

And then Cu 2+ on the right side would be +2?

Both the Kaplan and TPR book I have do not explain this adequately.

Just a few days before my exam so any help would be greatly greatly appreciated.

Even if you did not understand the question, copper is +2 on the right side of all of the equations. Since choice A is the only choice that has +2 on the right side, that's the only answer.
Btw, NH3 is a neutral molecule so you don't even have to calculate its formal charge.

 

[emericana]

One more question. I am having a VERY hard time getting Ksp stuff down.... probably because I took gen chem in 2005. has been a struggle for me.

The AAMC answer does not explain this well.

So the Ksp for copper is less than zinc.

Why would a Ksp being smaller make the procedure more efficient? is it because a larger Ksp makes it more likely to precipitate out of solution?

 

[diamethuel]

One more question. I am having a VERY hard time getting Ksp stuff down.... probably because I took gen chem in 2005. has been a struggle for me.

The AAMC answer does not explain this well.

So the Ksp for copper is less than zinc.

Why would a Ksp being smaller make the procedure more efficient? is it because a larger Ksp makes it more likely to precipitate out of solution?

It's actually the opposite of what you said (what I bolded above). The larger the Ksp, the more soluble it is, and the smaller the Ksp, the less soluble it is. The less soluble it is, the more likely it will precipitate out. Since the goal of the procedure is to precipitate out the metal, it will be more effective for copper because the copper sulfide has a smaller Ksp, and thus will precipitate out more effectively than the zinc sulfide.

 

[cwaranch]

Im really confused on the very first question in ps finding the oxidation state of the copper in a penny. Idk which is the penny and which is the waste product and is Cu^2+ considered to have an oxidation state of +2?

 

[cwaranch]

Also on #11 at room temp wouldnt it also deviate from STP?

 

[cwaranch]

On #25 they ask for the lowest freezing point im guessing they are using T=kfmi so they are looking for the lowest kf? So therefore you would find the highest i to correspond to the lowest kf. They also use the highest concentration but they use molarity and i thought with this equation you are supposed to use molality?

Last one on PS number 48...Do you just use K=P+.5density velocity^2+density*g*height? So since the leg is at a lower height it has a greater pressure?

 

[SmokeyJunior]

On #25 they ask for the lowest freezing point im guessing they are using T=kfmi so they are looking for the lowest kf? So therefore you would find the highest i to correspond to the lowest kf. They also use the highest concentration but they use molarity and i thought with this equation you are supposed to use molality?

Last one on PS number 48...Do you just use K=P+.5density velocity^2+density*g*height? So since the leg is at a lower height it has a greater pressure?

Yea, consider the source from the heart- the leg is much further away. Some of your questions are refereed to above, unless they weren't helpful.

 

[cwaranch]

Yea, consider the source from the heart- the leg is much further away. Some of your questions are refereed to above, unless they weren't helpful.

Hm it seems that is the heart is further from the leg then by the time blood gets to the leg after being pumped from the heart it would be at a lower pressure. And ya i read the thread and only asked questions after that. I figured out my Cu^2+ dilemma though.

 

[DoItToIt]

On #25 they ask for the lowest freezing point im guessing they are using T=kfmi so they are looking for the lowest kf? So therefore you would find the highest i to correspond to the lowest kf. They also use the highest concentration but they use molarity and i thought with this equation you are supposed to use molality?

Last one on PS number 48...Do you just use K=P+.5density velocity^2+density*g*height? So since the leg is at a lower height it has a greater pressure?

On the freezing point question, remember that freezing point depression (osmotic pressure and boiling point elevation also) is a colligative property, depending only on the AMOUNT of particles, not the type of particles. I don't remember the two different compounds, but I do remember that one of them dissolved into 3 ions in solution, while the other only formed two ions in solution. After eliminating the 2-ion compound answers, the more concentrated solution will have more of those ions present, making it the solution that has the lowest freezing point of those listed.

 

[MedChallenge]

Would someone please help me with #20? I've seen a couple of explanations from earlier in the thread, but I don't understand where that deltaf=v/c formula came from. Do we need to know that formula? I can't recall seeing that formula anywhere before.

I was thinking that since the denominator in the doppler effect formula should be v+vs, and the velocity of the source is decreasing as it goes up, the frequency observed should increase...where am I messing up?

If someone could explain the thought process in solving it a bit further, I'd greatly appreciate it!

 

[Catburr]

Would someone please help me with #20? I've seen a couple of explanations from earlier in the thread, but I don't understand where that deltaf=v/c formula came from. Do we need to know that formula? I can't recall seeing that formula anywhere before.

I was thinking that since the denominator in the doppler effect formula should be v+vs, and the velocity of the source is decreasing as it goes up, the frequency observed should increase...where am I messing up?

If someone could explain the thought process in solving it a bit further, I'd greatly appreciate it!

#20: What is the magnitude of the detected sound frequency shift from 170 Hz during the projectile flight describe in the passage?

A. Falls to zero, then increases.
B. Constant throughout flight.
C. Rises continuously.
D. Falls continuously.

Passage states that we have a ball thrown straight up, and the ball emits a sound at f=170 Hz. A microphone sits on the ground, stationary.

This probably isn't as detailed as you were looking for, but I just reasoned this out qualitatively, when I did it.

As it travels straight up, it's velocity is decreasing to zero. So the frequency shift (or the difference between actual frequency of 170Hz and perceived frequency on the ground) starts out high and drops to zero. Then the ball falls back down, and as velocity increases, frequency shift increases too.

Sounds like the part you messed up on is they want you to describe the frequency shift, not the apparent frequency itself.

Velocity; + is up, - is down to Earth: High (+) --> low (+) --> zero --> low (-) --> high (-)

Perceived freq: Much lower than actual freq --> slightly lower than actual freq --> actual freq --> slightly higher than actual freq --> much higher than actual freq

Magnitude of detected sound freq shift: High --> low --> zero --> low --> high

 

[MedChallenge]

Hey Catburr, thanks for responding. My apologies for bothering you again, but can you explain how you knew that the frequency shift is the difference btwn actual and perceived frequency? Is that something we're supposed to know or did you deduce that? It was a very good explanation because I totally get it, but I don't see how we're supposed to know what the freqency shift is!

#20: What is the magnitude of the detected sound frequency shift from 170 Hz during the projectile flight describe in the passage?

A. Falls to zero, then increases.
B. Constant throughout flight.
C. Rises continuously.
D. Falls continuously.

Passage states that we have a ball thrown straight up, and the ball emits a sound at f=170 Hz. A microphone sits on the ground, stationary.

This probably isn't as detailed as you were looking for, but I just reasoned this out qualitatively, when I did it.

As it travels straight up, it's velocity is decreasing to zero. So the frequency shift (or the difference between actual frequency of 170Hz and perceived frequency on the ground) starts out high and drops to zero. Then the ball falls back down, and as velocity increases, frequency shift increases too.

Sounds like the part you messed up on is they want you to describe the frequency shift, not the apparent frequency itself.

Velocity; + is up, - is down to Earth: High (+) --> low (+) --> zero --> low (-) --> high (-)

Perceived freq: Much lower than actual freq --> slightly lower than actual freq --> actual freq --> slightly higher than actual freq --> much higher than actual freq

Magnitude of detected sound freq shift: High --> low --> zero --> low --> high

 

[Catburr]

Hey Catburr, thanks for responding. My apologies for bothering you again, but can you explain how you knew that the frequency shift is the difference btwn actual and perceived frequency? Is that something we're supposed to know or did you deduce that? It was a very good explanation because I totally get it, but I don't see how we're supposed to know what the freqency shift is!

No problem. I just figured that's what frequency shift was, I'd never heard the term specifically.

EDIT: Not sure if this is helpful...but the way I figured out what they meant by shift, I guess, was simply by wondering what else could it possibly be. "Shift from" is a big hint, that literally means difference.

 

[movax]

#9 PS:

What bonding accounts for the expected increase in energy density for solid nitrogen vs. methanol?

A) Solid nitrogen contains covalent and ionic bonds; methanol contains only weak ionic bonds
B) Solid nitrogen contains covalent and ionic bonds; methanol has covalent bonds within each molecule and weak van der Waal's interactions between molecules
C) Solid nitrogen contains only covalent bonds; methanol contains only weak ionic bonds
D) Solid nitrogen contains only covalent bonds; methanol has covalent bonds within each molecule and weak intermolecular interaction

A and B can be eliminated very quickly, and methanol H bonds, so D is out, making it C (which is correct). But doesn't methanol have covalent bonds as well? Or is this just my brain being burned out and missing something obvious?

 

[Axon hillock]

#9 PS:

What bonding accounts for the expected increase in energy density for solid nitrogen vs. methanol?

A) Solid nitrogen contains covalent and ionic bonds; methanol contains only weak ionic bonds
B) Solid nitrogen contains covalent and ionic bonds; methanol has covalent bonds within each molecule and weak van der Waal's interactions between molecules
C) Solid nitrogen contains only covalent bonds; methanol contains only weak ionic bonds
D) Solid nitrogen contains only covalent bonds; methanol has covalent bonds within each molecule and weak intermolecular interaction

A and B can be eliminated very quickly, and methanol H bonds, so D is out, making it C (which is correct). But doesn't methanol have covalent bonds as well? Or is this just my brain being burned out and missing something obvious?

Your right. The answer is D not C. Check it again.

 

[EnergyDrink]

I majored in Microbiology... I've never got 2 micro questions wrong in a single passage before.

So for #124, I thought of the pro's and con's for each option. I selected D, despite knowing their reasoning behind it. I was torn between A and D; I decided to stop thinking and go with D. I understand their reasoning why D is wrong; I knew that when I chose it. However, the passage states that H pylori is isolated from 95% of ulcer patients, and that when treated with anti-acid, 95% of ulcer patients develop symptoms again. Which you can deduce to 100% of patients are unable to eliminate H pylori.

Now for the 2nd one (126)
The CHEMICAL composition of ribosomes are the same - nucleotides (rRNA) and amino acids. The physical/molecular composition is not the same. This is a far more reasonable choice than A in my opinion.

 

[Axon hillock]

I majored in Microbiology... I've never got 2 micro questions wrong in a single passage before.

So for #124, I thought of the pro's and con's for each option. I selected D, despite knowing their reasoning behind it. I was torn between A and D; I decided to stop thinking and go with D. I understand their reasoning why D is wrong; I knew that when I chose it. However, the passage states that H pylori is isolated from 95% of ulcer patients, and that when treated with anti-acid, 95% of ulcer patients develop symptoms again. Which you can deduce to 100% of patients are unable to eliminate H pylori.

Now for the 2nd one (126)
The CHEMICAL composition of ribosomes are the same - nucleotides (rRNA) and amino acids. The physical/molecular composition is not the same. This is a far more reasonable choice than A in my opinion.

Question 124: Answer choice D refers to all patients who have ulcers, not just the patients being discussed in the passage. You said the passage states the H pylori is isolated from 95% of ulcer patients. This implies that at least 5% of the population who have ulcers do no contain H pylori. Therefore, you can have an ulcer with H pylori. So if you test positive for H pylori it doesn't mean 100% that you have an ulcer.

Question 126: This is a much trickier question and its best approached by looking for what's the "best" answer. However, since you're a microbiology major I would think you know that prokaryotic and eukaroytic ribosomes are made up of different kinds of proteins as well as different RNA.

 

[EnergyDrink]

I agree with #124, A is the better answer, but I don't think it's clear - but I should have stuck with A.

I still think B is a better answer for #126. I know that they have extraordinary differences in their rRNA and protein sequence, but the chemical composition is the same. The argument I could fathom is that the question says "Most bacteria cells..." when in fact all bacteria cells are alike in that. From my other tests, this isn't the type of trick they normally try to get you on, so I think its unintentional.

 

[Axon hillock]

I agree with #124, A is the better answer, but I don't think it's clear - but I should have stuck with A.

I still think B is a better answer for #126. I know that they have extraordinary differences in their rRNA and protein sequence, but the chemical composition is the same. The argument I could fathom is that the question says "Most bacteria cells..." when in fact all bacteria cells are alike in that. From my other tests, this isn't the type of trick they normally try to get you on, so I think its unintentional.

I think the chemical composition is considered different because they contain a different ratio of components. Prokaryotic ribosomes are composed of 65% rRNA and 35% ribosomal protein. In eukaryotes the ratio is close to 1.

Anyway, I think this is a classic MCAT type question b/c the reason for why you got the question wrong is due to their wording and not due to your lack of knowledge. The MCAT tries to be tricky so you second guess yourself. Your reasoning for choosing B is solid but unfortunately A is the better answer.

 

[JiniInBottle]

For some reason, I can't get the answers for questions 95-100 on the explanations sheet. Can some post these answers only, please!!!!!

 

[YouNeverKnow22]

anyone have a rough time with Passage 7 on PS? I got most of the q's right but did not feel comfortable with it

 

[JiniInBottle]

anyone have a rough time with Passage 7 on PS? I got most of the q's right but did not feel comfortable with it

I got most of the questions wrong for passage it was really just too long to read, and difficult to grasp. I left it for the last. However, do you happen to have answer for the passage 1 of Biology? It'll be great help. thanks!

 

[YouNeverKnow22]

I got most of the questions wrong for passage it was really just too long to read, and difficult to grasp. I left it for the last. However, do you happen to have answer for the passage 1 of Biology? It'll be great help. thanks!

what do you mean? the answers show up if you click the solution button

 

[JiniInBottle]

Well, I bought the exams long time ago, and I just have the printed answers now, which apparently doesn't have the answers for those questions. So I would really appreciate it if you could just help me out here. Thanks!

 

[salim271]

PS: 11
VR: 11
BS: 13

Hey guys I have a question about PS number 25... it says that the freezing point is lowest for the soln that has the most ions. I picked D, .20M NaCl because it fully dissociates in aq solution while .15M CaCl2 doesnt, I knew for a fact that it was insoluble in water and had a Ksp, and I checked after the test when I found out that I got it wrong. How can .15M CaCl2 be the right answer? It does NOT have the highest concentration of particles in solution. If I got this one right I would have gotten a 12 in PS.

 

[JiniInBottle]

I'm pretty sure according to the solubility rules, CaCl2 disassociates and thus forms 3 solute particles in water, thus overall molarity of cacl2 would be actually .45M, making it have the greatest freezing point depression.

 

[TheRealAngeleno]

Hey guys for #26 on the PS section,

How would Indicator E work when the equivalence point of Titration 1 is at a pH = 7? The transition range for Indicator E is from pH = 8 - 10. Thanks guys.

 

[salim271]

Hey guys for #26 on the PS section,

How would Indicator E work when the equivalence point of Titration 1 is at a pH = 7? The transition range for Indicator E is from pH = 8 - 10. Thanks guys.

Read their explanation. The eq point is 7, but the ml's added at 7 and the ml's added at 8-10 are not very different at all, you cant even really tell the difference by looking at the graph. The indicator estimates the eq point, its not an exact thing. The pH at the end of the exponential part of the titration 1 is 12, which is well within the pka range of E.

 

[Joker88]

2 quick questions:

141. Which of the following aklky halides and base solvent pairs would produce the highest yield of the desired product?

D. 1-fluoro-1-methylcyclohexane and tert-Buo-/tert-BuOH

I think i maybe over thinking but was there a specific indication to why looked towards the 1-hexene to match the leaving groups and not the zaitsev product? Also, the 1-fluoro is used because its going to be involved directly in forming the alkene correct? 2-fluoro wouldnt be able to do the same job right?

146. If two stimulu, an electric shock and a light flash, are given to a planarian flat worm at the same time, a response develops that eventualy can be evoked when only the light flash is used. This result can be called conditioning if the response:

D. is not a response orginally evoked by the light flash alone

--So in general, classical conditions involves using a reward or punishment in collaboration with a stimulus. The stimulus continues to evoke a response even after the reward or punishment is taken away. If it worked, the stimulus after the conditioning will be different from a reaction to the stimulus if the conditioning (innate) never done? The explanation they wrote is kind of wordy so im just trying to simplify what theyre saying...

 

[Joker88]

Also

#41 if a monolayer of water molecules is formed over an organic oil, can avogadros number be calculated using the method described in experiments 1 and 2?

D. No, beucase the water molecules are not cylindrical in shape

Maybe i missed a piece of information in the passage. Does anyone know how avogadros number relates to this exactly??

#50 The intensity level in decibels is defined as 10log10 (I/Io), where Io is a reference intesntiy equal to the human threshold of hearing, 10^-12 W/m^2. what is the intensity of the threshold of pain, 120dB?

B. 10^0W/m^2

I really suck at these problems for some reason. If someone could show me how to work through this id really appreciate it. The explanation by the test is a little confusing.

 

[notbobtrustme]

Also

#41 if a monolayer of water molecules is formed over an organic oil, can avogadros number be calculated using the method described in experiments 1 and 2?

D. No, beucase the water molecules are not cylindrical in shape

Maybe i missed a piece of information in the passage. Does anyone know how avogadros number relates to this exactly??

#50 The intensity level in decibels is defined as 10log10 (I/Io), where Io is a reference intesntiy equal to the human threshold of hearing, 10^-12 W/m^2. what is the intensity of the threshold of pain, 120dB?

B. 10^0W/m^2

I really suck at these problems for some reason. If someone could show me how to work through this id really appreciate it. The explanation by the test is a little confusing.

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

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

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

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

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

 

[notbobtrustme]

Hey guys for #26 on the PS section,

How would Indicator E work when the equivalence point of Titration 1 is at a pH = 7? The transition range for Indicator E is from pH = 8 - 10. Thanks guys.

You could have done this through elimination as well. Only Indicator E is close the Eq point. Overshooting an Eq point automatically disqualifies an indicator.

 

[infid3l]

PS: 11
VR: 11
BS: 13

Hey guys I have a question about PS number 25... it says that the freezing point is lowest for the soln that has the most ions. I picked D, .20M NaCl because it fully dissociates in aq solution while .15M CaCl2 doesnt, I knew for a fact that it was insoluble in water and had a Ksp, and I checked after the test when I found out that I got it wrong. How can .15M CaCl2 be the right answer? It does NOT have the highest concentration of particles in solution. If I got this one right I would have gotten a 12 in PS.

you brought me to shame on the verbal!
I had 11 PS 6VR 11BS any tips on verbal?

 

[salim271]

you brought me to shame on the verbal!
I had 11 PS 6VR 11BS any tips on verbal?

Honestly this was my best VR score on any practice test. I probably just as easily could have gotten 11, so many answers seem that close that its just a 50/50 crapshoot. I took my real MCAT on the 6th and it felt the same way in VR, I dont know if I got 10 or 13.

Best thing to do imo is to follow the EK strategy and slowly deviate from it and morph it into your own strategy. EK's strategy works well for the 101 series because the questions were written with that strategy in mind. AAMCs are more difficult sometimes only because the passages and questions are not picked with EK's strategy in mind. They have to be approached differently. The main idea concept still flies, but AAMC usually asks for more details and less main idea. AAMC will also throw in a lot of different opinions in the passage that the author may or may not agree on, you'll get quotes from different people in the field and you'll have to understand what they're saying too.

My personal strategy:

- Mentally map each paragraph down to a few easy to remember words
- Look for key words that demonstrate the author's and others' opinions
- Get the main idea after finishing by quickly reviewing the passage in my head and by scanning the paragraphs.
- Treat every question as equally important. If a question is taking too long, skip it and come back to it last before you move on from the passage.
- You will most likely have to refer back to the passage, do so with a purpose always in mind, do your best to remove answer choices before looking back, that way you're juggling less possibilities when you're hopefully looking in the right place for the answer.

I think VR in many ways is the hardest section, its just too difficult to do great in every time.

 

[infid3l]

thanks a lot! i have been getting 9/10 on EK and i made a mistake in counting and my score on AAMC 10 is 7. I think I will try the strategy you mentioned and iron out the silly mistakes a make and hopefully get a better score. Thanks a lot!

 

[TheRealAngeleno]

Hey guys I have a question on Passage 4 #32 of the BS section.

I had it down to A and D and I ended up selecting D b/c wouldn't circular mitochondrial DNA be considered "the shape of the self replication structure that carry their DNA"?

 

[muhali3]

Q48 PS.

Wouldn't the pressure in the leg be less than the arm due to Poiseuille flow?

dP = Q8nL / pi x r^4

I was thinking the distance from the heart to the leg was greater than the heart to the arm, so the pressure drop would be greater.

Isn't blood a real fluid? Why shouldn't this equation be used?

 

[docntrainin]

Q48 PS.

Wouldn't the pressure in the leg be less than the arm due to Poiseuille flow?

dP = Q8nL / pi x r^4

I was thinking the distance from the heart to the leg was greater than the heart to the arm, so the pressure drop would be greater.

Isn't blood a real fluid? Why shouldn't this equation be used?

I think for this question, the formula you want to keep in mind is the formula for hydrostatic pressure aka P = density x g x y + Patm. The y value in this case is depth. We know that the density value, the g value, and Patm will be the same from leg to arm, but what will be different is the y value. The leg, as we know, is lower than the arm (think of the body as a big container - the leg has greater depth, thus a greater y value). Thus, we know that leg has a greater pressure.

I should add: if you are wondering about the rate of blood flow, it will be the same for both leg and arm.

Hope this helps!

 

[muhali3]

Yeah, the question also emphasized the difference in height, which indicates that you must use P = pgh.

But according to the Poiseuille formula for a real fluid, there would be a pressure drop.

...I guess this is just a test-taking mistake. A lot of times you can see a question from many perspectives but you have to know what way the MCAT wants you to see it.

 

[Maxine450]

For BS question 117, what is the difference between capillary endothelium and endothelial cells? I don't understand why A isn't correct.

Also for 121:

A stable differentiated cell that will not divide again during its lifetime is in which of the following stages of the cell cycle

A. G1
B. G2
C.S
D.M

I guessed it was B because at G2, the chromosomes have divided already in S and won't again. Why is it G1?

 

[mcloaf]

For the purposes of the question capillary endothelium = endothelial cells. However A is wrong because they haven't actually demonstrated viral replication within the cells. Experiment 3 simply shows that at least some antigenic protein from the virus is present in vivo at the capillary endothelium. It's sort of nitpicky, but C is simply a better answer than A.

As for 121, I think you misunderstand the phases of the cell cycle. G1 is basically interphase. S is DNA replication. G2 is when the cell replicates its proteins, increases the amount of cytosol, etc. so that daughter cells have adequate amounts of nutrients and building blocks to survive post-cytokinesis. M is mitosis, when the replicated DNA is separated and the cell splits into two. So at G2 the chromosomes have not yet divided, the cell is simply carrying around twice the amount of DNA it needs for everyday functioning while it waits to build up the rest of what it needs to pass the G2 checkpoint and enter mitosis.

 

[Ssina]

For the purposes of the question capillary endothelium = endothelial cells. However A is wrong because they haven't actually demonstrated viral replication within the cells. Experiment 3 simply shows that at least some antigenic protein from the virus is present in vivo at the capillary endothelium. It's sort of nitpicky, but C is simply a better answer than A.

As for 121, I think you misunderstand the phases of the cell cycle. G1 is basically interphase. S is DNA replication. G2 is when the cell replicates its proteins, increases the amount of cytosol, etc. so that daughter cells have adequate amounts of nutrients and building blocks to survive post-cytokinesis. M is mitosis, when the replicated DNA is separated and the cell splits into two. So at G2 the chromosomes have not yet divided, the cell is simply carrying around twice the amount of DNA it needs for everyday functioning while it waits to build up the rest of what it needs to pass the G2 checkpoint and enter mitosis.

I'll just add that Interphase is actually the phase preparing for mitosis/meiosis so it's G1+S+G2.

you can also look at this way, cell spent all that energy to replicate it's chromosomes and now it'll divide.... basically it won't waste all that energy if it doesn't want to divide... so it'll be stuck at G1

 

[mcloaf]

I'll just add that Interphase is actually the phase preparing for mitosis/meiosis so it's G1+S+G2.

you can also look at this way, cell spent all that energy to replicate it's chromosomes and now it'll divide.... basically it won't waste all that energy if it doesn't want to divide... so it'll be stuck at G1

Ah, true. I'm getting a little loose with terminology there. I always associate interphase with non-replicating cells, but you're right of course.

 

[Maxine450]

My main problem with these bio passages is understanding what exactly they're asking. Thanks for the answers!

 

[mcloaf]

My main problem with these bio passages is understanding what exactly they're asking. Thanks for the answers!

Yeah, you just have to be very careful about what they're asking/showing you. You can't assume anything that isn't explicitly stated (just like bio research in real life ).

 

[orangeblossom]

Passage V for the BS section.. organic chemistry mechanism involving 3 steps

What exactly is Step 2? It doesnt appear to be a regular grignard reaction... help!

 

[Jengreef]

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

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

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