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This is the official Q&A thread for AAMC CBT4 and 4R.

Please post ONLY questions pertaining to AAMC CBT4 and 4R.
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!
 

sicboy188

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these threads are awesome.. thanks V!

so my question is on PS #18. its on specific gravity (easy topic, but i cant seem to wrap my head around how its working in the problem)

in fear of getting mod slap'd, i will not post the question (unless someone tells me i can)
 

Premed Worrier

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these threads are awesome.. thanks V!

so my question is on PS #18. its on specific gravity (easy topic, but i cant seem to wrap my head around how its working in the problem)

in fear of getting mod slap'd, i will not post the question (unless someone tells me i can)
I thought I read somewhere that you can now post exact questions?
Anyway, yeah that problem is a little tricky. The way I looked at it was that since it only 'lost' five grams out of fifteen that means the volume of benzene it displaced only weighed five grams, while the same volume of this object weighed 15 grams. this makes it three times as dense. If it is three times as dense as benzene and benzene has spec. grav. of .7 then .7 x 3 = 2.1

This is just my way of doing it, hope it helps.
 

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So #20 on the Bio CBT. Isn't the whole rave about antibiotic drug resistance that the actual treatment with the drug will cause resistance if all the bacteria are not killed and you stop giving the drug. Wouldn't this be more likely than a chance E.coli mutation before treatment??
 

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So #20 on the Bio CBT. Isn't the whole rave about antibiotic drug resistance that the actual treatment with the drug will cause resistance if all the bacteria are not killed and you stop giving the drug. Wouldn't this be more likely than a chance E.coli mutation before treatment??
Drugs do not CAUSE drug-resistant bacteria, they naturally select them. In your body you may have a 10^6:1 ratio of drug sensitive to chance mutant E. Coli. Now because the nonmutant is favorable with no drugs in the environment, there will be less mutant E.coli. However say we inject a drug that kill E. Coli in our bodies. What will survive? Those who are drug resistant that came about by chance mutation. Those will reproduce and our drugs are futile and we must then use stronger and stronger drugs. Hope this helps.
 

TypeSH07

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OKay thanks that makes alot of sense now. How come ingesting excess NaCl would not cause aldosterone release?
 

BloodySurgeon

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OKay thanks that makes alot of sense now. How come ingesting excess NaCl would not cause aldosterone release?
Because the body can only reabsorb a maximum amount of Na+ and if you have more Na+ ingested into your body it will want to excrete it out not reabsorb it through aldosterone.

Also, aldosterone is from a direct response of angiotensin/renin which is excreted when the blood pressure is low. With lots of NaCl the osmotic pressure is higher and there will be a greater blood pressure and renin will be inhibited.
 

thierryhenry

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Hi I just took this.

It was my highest exam yet 10 9 10 (PS, VR, BS)

I am very happy.

How does this measure up with the other AAMC, in terms of difficulty...
 

Deepa100

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It has been a while since I took Ochem I...
This is from a AAMC test solution:
The proton NMR spectrum of Compound B (ethanol) consisted of a quartet, a triplet, and a singlet.

Where does the singlet come from?
Thanks!
 
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This thread is being moved to the official discussion thread for practice test 4R. For future reference, please post test questions and solutions from AAMC exams only in the official thread made for each test.

This rule was made to protect members from accidentally clicking on a thread and seeing an answer to a test that they may not have already taken. I'm certain that you wouldn't like to see the answers to official practice exams you haven't taken yet, so please do your peers the same courtesy and only post these types of questions in the official thread.

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Kaustikos

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It has been a while since I took Ochem I...
This is from a AAMC test solution:
The proton NMR spectrum of Compound B (ethanol) consisted of a quartet, a triplet, and a singlet.

Where does the singlet come from?
Thanks!
It's a proton NMR. I think a lot of this confusion comes from people only thinking about H bound to carbons and not OH. But, if you look at an HNMR for this, you'll notice, as the above poster shows with the image, the singlet ALL the way to the left. That's there for a reason - the polar OH group pull it that way.

One thing I have noticed about NMR is that knowing this bit of info (polarity affecting where they are) tends to knock out A LOT of the answer choices almost immediately.
 

bluemonkey

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It has been a while since I took Ochem I...
This is from a AAMC test solution:
The proton NMR spectrum of Compound B (ethanol) consisted of a quartet, a triplet, and a singlet.

Where does the singlet come from?
Thanks!
The singlet does indeed come from the H on the OH, but as a bonus, why does it show up as a singlet instead of being split? What property of alcohols reduces coupling for the H on OH groups?
 

Kaustikos

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The singlet does indeed come from the H on the OH, but as a bonus, why does it show up as a singlet instead of being split? What property of alcohols reduces coupling for the H on OH groups?
The strength of the ionic bond/high electronegativity difference? I can't think of any other reason why H wouldn't have a split state from the O vs a C.

The shortness of the bond reduces the amount of free space needed to have the split states?
 

bluemonkey

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The strength of the ionic bond/high electronegativity difference? I can't think of any other reason why H wouldn't have a split state from the O vs a C.

The shortness of the bond reduces the amount of free space needed to have the split states?
Think of alcohols in terms of their acid/base properties...
 

Snowy

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Just took aamc 4:

PS (11): Dissapointed with my score, but happy to know that I'm getting there. I got 8 wrong, and looking back at all 8 of those, I'm absolutely amazed I got them wrong. Just dumb mistakes, reading the question wrong, or adding wrong. I thought this section wasn't bad at all. I was suprised too, because I got a 10 on aamc3 PS.

V (11): best ever! I'm so happy. Now if only I can do this again on aamc 5. I thought #85 and #86 were tough ones.

BS (10): I felt like this section was reallllly hard, although much less so now looking back on it. I got killed on the endothelial cells passage (4 out of 7 wrong), I guess I didn't understand the graphs at the time. I was so confused on #121, the neuron question, looked at it for about 5 minutes and still got it wrong.

What did other people think?
 

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ahh, i just finished the test a couple of minutes ago.

12 PS, 9 VR:(, 11 BS. I haven't looked at the answers yet so I'll let you know how i feel afterwards. What i do know is that i got straight 11's on AAMC5, and now I'm sad that my verbal dropped 2 pts. How do you guys feel AAMC4 compares to AAMC5, and how both of the tests compare to the other AAMCs? Thanks! Just one more week for me... :scared:
 

PrinceAli2786

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Can someone explain to me when we take the diprotic part of a molecule into account like for example #52 I chose 2 x 10^-6 instead of 1 x 10^-6

b/c I thought that the diprotic portion of H2SO4 would increase the H+ concentration:idea: but it doesn't...lol

can someone please explain when I should pay attention to diprotic part, such as only w/ OSMOTIC PRESSURE, TITRATIONS? etc anything else and how so if we do use it for them.

Thanks:)
 

Kaustikos

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Can someone explain to me when we take the diprotic part of a molecule into account like for example #52 I chose 2 x 10^-6 instead of 1 x 10^-6

b/c I thought that the diprotic portion of H2SO4 would increase the H+ concentration:idea: but it doesn't...lol

can someone please explain when I should pay attention to diprotic part, such as only w/ OSMOTIC PRESSURE, TITRATIONS? etc anything else and how so if we do use it for them.

Thanks:)
I think I know what you did. You misread/were confused by the question itself. The statement says that the solution consists of water and H2SO4. The acid DOES contribute to the pH, but that the change was small (pH = 6). Thus, the concentration is based off the pH it gave you, which equals 1x10^-6.

Hope that helps.
 

PrinceAli2786

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I think I know what you did. You misread/were confused by the question itself. The statement says that the solution consists of water and H2SO4. The acid DOES contribute to the pH, but that the change was small (pH = 6). Thus, the concentration is based off the pH it gave you, which equals 1x10^-6.

Hope that helps.
Hey, thanks for the help/reply. I thought too hard about the question, b/c I figured after that 6 - log 2 doesn't equal pH, but I just need help to REALLY know when I should take the di-protic portion into account for anything, any tips/ideas?

also how would the rxn look like end product is (HSO4)^- or (SO4)^2-
 

PrinceAli2786

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PS: #26 Why isn't the answer D, it's soaked in water etc.... b/c doesn't the passage say that it is placed in water?:confused:
 

Kaustikos

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Hey, thanks for the help/reply. I thought too hard about the question, b/c I figured after that 6 - log 2 doesn't equal pH, but I just need help to REALLY know when I should take the di-protic portion into account for anything, any tips/ideas?

also how would the rxn look like end product is (HSO4)^- or (SO4)^2-
For the sake of the MCAT, only understand that diprotics are highly acidic for the initial proton only. If you think about it conceptually, it makes sense, since the initial proton makes the deprotonation of the second proton less likely. Thus, the acidity of the second proton is significantly less than the initial.
If the MCAT wants you to take the second proton into consideration, it will ask you what the change in pH will be from the second proton or something along the lines of that. The idea is that if the pH were to be calculated according to the deprotonation of both H's, it would be closer to the pKa of the initial deprotonation.
Just understand how the initial proton basically makes the resulting monoprotic acid a weak acid and that it will not significantly affect the pH of hte resulting solution.
 

PrinceAli2786

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For the sake of the MCAT, only understand that diprotics are highly acidic for the initial proton only. If you think about it conceptually, it makes sense, since the initial proton makes the deprotonation of the second proton less likely. Thus, the acidity of the second proton is significantly less than the initial.
If the MCAT wants you to take the second proton into consideration, it will ask you what the change in pH will be from the second proton or something along the lines of that. The idea is that if the pH were to be calculated according to the deprotonation of both H's, it would be closer to the pKa of the initial deprotonation.
Just understand how the initial proton basically makes the resulting monoprotic acid a weak acid and that it will not significantly affect the pH of hte resulting solution.
thanks so much for the explanation!:thumbup:
 

unsung

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Hi I just took this.

It was my highest exam yet 10 9 10 (PS, VR, BS)

I am very happy.

How does this measure up with the other AAMC, in terms of difficulty...
I would like to know this as well. I just took it today. Btw, did you guys find the natural science verbal passages to be tougher? For some reason I did the best on the humanities passages, worse on natural science, and worst on social science. And the trend directly correlated with the amount of time I spent per Q- the more time I spent, the worse I did. :laugh:
 

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The solution to this rules out production of digestive enzymes by E. Coli because they can be produced elsewhere in the colon. How are we supposed to know this? Sorry, I can't copy & paste the question, the app wouldn't let me.
 

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For question 50 in the Physical Sciences section regarding circuits, how come the answer shows the voltage moving in the opposite direction? Does it normally flow out of the "bigger side" of the voltage source? Like l| --> vs. |l --> (if that makes any sense)?
 

dwc929

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The solution to this rules out production of digestive enzymes by E. Coli because they can be produced elsewhere in the colon. How are we supposed to know this? Sorry, I can't copy & paste the question, the app wouldn't let me.
Digestive enzymes are made in the pancreas and excreted in the SI.
 

dwc929

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The solution to this rules out production of digestive enzymes by E. Coli because they can be produced elsewhere in the colon. How are we supposed to know this? Sorry, I can't copy & paste the question, the app wouldn't let me.
Digestive enzymes are made in the pancreas and excreted in the SI.
 

ballofnerves

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For question 50 in the Physical Sciences section regarding circuits, how come the answer shows the voltage moving in the opposite direction? Does it normally flow out of the "bigger side" of the voltage source? Like l| --> vs. |l --> (if that makes any sense)?
Current flows out of the "bigger side". This is the positive flow of current, meaning that electrons flow out of the "smaller side".
 

dwc929

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Current flows out of the "bigger side". This is the positive flow of current, meaning that electrons flow out of the "smaller side".
Right, but the answer seems to have current flowing in the other direction...Kinda hard to explain the whole question but if anyone has the test and knows what I'm talking about, that'd help...thanks though
 

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# 42

Wont the kinetic energy get bigger as it gets closer to the oppositely charged electrode (because it acclerates)? So it should be more than just just slightly over the work function.
 

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These two questions seem ridiculous I feel like I had all the proper information and analyzed them correctly and still missed them. Considering 1-2 questions changes your score in the higher ranges I have to get these questions right.

Anyway I've only included the answer choices that matter

An organism is likely to be a bacterium rather than a virus if it:
A) reproduces by fission
B) has a rigid cell wall

The given answer is A which is ridiculous, a cell wall must my definition contain a cell which a virus doesn't have. The answer says void cell wall because viruses can have rigid capsids so the two can't be distinguished, BS if they would have had rigid coating then its easy but they said cell wall. Also a retro virus reproduces by fission when an infected cell reproduces by fission.


Next question

Would an increase in the level of plasma aldosterone be expected to follow ingestion of excessive quantities of NaCl?

A) No; aldosterone causes Na+ reabsorption by kidney tubules.
B)No; aldosterone causes Na+ secretion by kidney tubules.

The AAMC answer is A I chose B. I know aldosterone causes Na+ and therefore water to leave the kidney tubules. Reabsorption typically means by the body but in this case it says BY THE KIDENEY TUBULES. If I were to say X is secreted by Z. Then any normal person would say that X has left Z.

This is really just ventting but some of these questions are so capricious and makes me think the AAMC is far from infallible. In addition since you can't review your real test you would never now about these things.

Also while Im posting after doing 2 AAMCs vs 2 Kaplan FL it seems that AAMC is more about error prevention and Kaplan FL is difficult problem solving.
 

supafield

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Well for the last question it says (RE)absorption
The word implies that one compartment had sodium, lost it, and it getting it back.....

So the blood has it's Na filtered out.... and will reabsorb it via aldosterone's effects.
Not the other ways around.

I really think the prefix discredits the thinking of the kidney tubule taking the sodium back because it would had to have lost it in the first place.
 

JoeGator86

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Well the filtrate loses Na+ in the proximal, distal tubuals as well as the ascending loop. So it very well could be considered REabsorbing. It says by the tubules meaning they are doing the reabsorbing/secreting, if they wanted to run by convention they should have excluded the words by the tubules. The thing is I knew that the convention is reabsorbing means back into the body but they specifically placed those words to the contrary.
 

engineeredout

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11PS 10VR 11BS = 32

Not bad, at least I'm on a decent trend on these. Hell if I got 32 on the real thing I'd be estatic and run out and buy some black label.

Anyone else think that the VR for this section was kinda difficult? I mean I did okay, but that feminist passage was just wtf. I had to go back at the end and read it a second time. I just couldn't wrap my head around it or the answers.

I'm too burned out to actually look at which questions I got wrong so I'll check it out later and probably post more **** here.
 

engineeredout

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**** that, I ended up getting every question right on the feminist passage (#2) :confused::D


Oh and was the bio pretty easy on this one? I finished with almost 30 minutes to go and got an 11. Add to that I've never taken bio in my life so I'm just going to go with the whole child prodigy thing here and continue believing how awesome I am.


Yeah thats right ladies. An 11 in bio. Wanna see my sex pilus?
 
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engineeredout

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Okay question for real now.

PS: #30: How many grams KNO3 are in 100ml of the student-prepared solution of KNO3(aq)?

B. 22.41 g
C. 22.65 g

Now the table in the passage gives the following information:

Solute Concentration: 226.5 g/L
Molarity: 2.241 mol/L.

The correct answer is C. Now I'm probably going to kick myself for not seeing this, but why is it that they used the solute concentration and not the molarity? Narrowing it down to the two choices I of course picked the wrong one.
 

J ROD

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Okay question for real now.

PS: #30: How many grams KNO3 are in 100ml of the student-prepared solution of KNO3(aq)?

B. 22.41 g
C. 22.65 g

Now the table in the passage gives the following information:

Solute Concentration: 226.5 g/L
Molarity: 2.241 mol/L.

The correct answer is C. Now I'm probably going to kick myself for not seeing this, but why is it that they used the solute concentration and not the molarity? Narrowing it down to the two choices I of course picked the wrong one.

Well, I just looked at the solute being in the solution of a liter and multiplied by 0.1 to get the amount of grams in 100mL. You are looking for grams and you are given the amount of grams that can be put into a certain amount of water. You just do not have to use the mols here.
 

J ROD

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11PS 10VR 11BS = 32

Not bad, at least I'm on a decent trend on these. Hell if I got 32 on the real thing I'd be estatic and run out and buy some black label.

Anyone else think that the VR for this section was kinda difficult? I mean I did okay, but that feminist passage was just wtf. I had to go back at the end and read it a second time. I just couldn't wrap my head around it or the answers.

I'm too burned out to actually look at which questions I got wrong so I'll check it out later and probably post more **** here.
The feminist passage was the hard one on it. Still not too bad though. I actually though the verbal was easy except for that one. I thought the PS was a little harder than usual and the Bio was easy/about average.
 

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Okay question for real now.

PS: #30: How many grams KNO3 are in 100ml of the student-prepared solution of KNO3(aq)?

B. 22.41 g
C. 22.65 g

Now the table in the passage gives the following information:

Solute Concentration: 226.5 g/L
Molarity: 2.241 mol/L.

The correct answer is C. Now I'm probably going to kick myself for not seeing this, but why is it that they used the solute concentration and not the molarity? Narrowing it down to the two choices I of course picked the wrong one.
I remember that question... then there was another question for the same passage that required you to use molarity.

Those didn't really make sense to me.
 

bluemonkey

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The problem with molarity is that it gives you moles of solute per liter of solution, not moles of solute per liter of solvent. The solute contributes to the solution volume...

Okay question for real now.

PS: #30: How many grams KNO3 are in 100ml of the student-prepared solution of KNO3(aq)?

B. 22.41 g
C. 22.65 g

Now the table in the passage gives the following information:

Solute Concentration: 226.5 g/L
Molarity: 2.241 mol/L.

The correct answer is C. Now I'm probably going to kick myself for not seeing this, but why is it that they used the solute concentration and not the molarity? Narrowing it down to the two choices I of course picked the wrong one.
 

nfg05

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Item 127. Increased vasoconstriction has an important role in which of the following situations?
B) Increasing blood flow to muscles during exercise
D) Maintaining blood pressure during a hemorrhage

I picked B here. I swear I read in Kaplan somewhere that sympathetic activity kicks in during exercise and causes vasoconstriction in blood vessels outside skeletal muscle and vasodilation in blood vessels inside skeletal muscle. By A1v1 = A2v2, vasoconstriction means the blood moves faster to the muscles. "Increasing blood flow" isn't too specific but to me it seems that if blood is circulating through non-skeletal blood vessels more rapidly that can be interpreted as "increasing blood flow."

Furthermore, when you are hemorrhaging due to a leaky blood vessel won't vasoconstriction speed up blood flow (again, A1v1 = A2v2) and thus exacerbate the rate of blood loss through the hole? The body saying "Oh, I see we have a hole in our pipes here let's make sure to maintain a high pressure so a greater amount of blood flows out the hole" doesn't make much sense to me.


AND another note on just general ambiguity with the AAMC's (in my opinion)If the anti-inflammatory drug in treatment 1 interfered with DNA synthesis, in which phase of the cell cycle would the cells tend to be arrested?

I recognized that DNA synthesis was in the S phase, so I took the wording to mean that the cells would be arrested in G1, i.e. not able to move into S phase. Just frustrating because I understood what the question was trying to test, but because IMO the wording of the question is subject to interpretation I got it wrong.

Also have to agree with JoeGator that the change of terms from "cell wall" in the answer choices for item 142 to "rigid outer covering" in the answer explanation is completely ridiculous.
 
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engineeredout

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Item 127. Increased vasoconstriction has an important role in which of the following situations?
B) Increasing blood flow to muscles during exercise
D) Maintaining blood pressure during a hemorrhage

I picked B here. I swear I read in Kaplan somewhere that sympathetic activity kicks in during exercise and causes vasoconstriction in blood vessels outside skeletal muscle and vasodilation in blood vessels inside skeletal muscle. By A1v1 = A2v2, vasoconstriction means the blood moves faster to the muscles. "Increasing blood flow" isn't too specific but to me it seems that if blood is circulating through non-skeletal blood vessels more rapidly that can be interpreted as "increasing blood flow."

Furthermore, when you are hemorrhaging due to a leaky blood vessel won't vasoconstriction speed up blood flow (again, A1v1 = A2v2) and thus exacerbate the rate of blood loss through the hole? The body saying "Oh, I see we have a hole in our pipes here let's make sure to maintain a high pressure so a greater amount of blood flows out the hole" doesn't make much sense to me.
To quote from EK:

The sympathetic ANS deals with "fight or flight" responses. For instance, its action on the heart would be to increase beat rate and stroke volume; it works to constrict blood vessels around the digestive and excretory systems in order to increase blood flow around skeletal muscles.
I picked the same answer as you. I don't really get why its D either.

I guess maybe because the increased blood flow around the skeletal muscles would technically be due to vasodialation, but the vasoconstriction leads to vasodialation. Bad question.
 
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JoeGator86

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Think about a hemorrhage blood is lost because a artery burst so the Blood pressure drops. To compensate vasoconstriction occurs to raise the BP (less volume in circulatory system). Answer B should probably be worded to say constriction to the muscles but its not way off.
 

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The Bio on this test was so annoying, so damn tricky.
 

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It says to increase the electrical field, what would you do?
the formula in the answer they give is E= (V-IR)/L

The answer is (A), increase L by a factor of 2...shouldn't L be decreased by a factor of 2 to raise E?
 

czhang

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It says to increase the electrical field, what would you do?
the formula in the answer they give is E= (V-IR)/L

The answer is (A), increase L by a factor of 2...shouldn't L be decreased by a factor of 2 to raise E?
You are right about how L should be decreased in order to increase the electric field.
But, try reading the question again. Im pretty sure it says "Which of the following changes to the circuit will DECREASE the electric field..."
 

czhang

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To quote from EK:



I picked the same answer as you. I don't really get why its D either.

I guess maybe because the increased blood flow around the skeletal muscles would technically be due to vasodialation, but the vasoconstriction leads to vasodialation. Bad question.
Ya i picked B for this question as well..
I think the reason why B is wrong is because the question only said "increased vasoconstriction", but did not specify where. Very tricky question though O_O
 
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