This thread is for students to ask and answer each other's questions for the MCAT, DAT, OAT, and PCAT subjects. All posts from the other Q & A threads that are not either students' questions or moderators' replies will be moved to this thread. Students, please post your own answers to other students' questions here in this thread--or else in the main MCAT forum--rather than in the regular Q & A threads.

If you are a pre-health (MCAT, PCAT, DAT, OAT) test prep instructor, or you have a graduate-level background in one of the MCAT subjects, or you are a senior undergrad who scored well on the MCAT, and you would like to help answer questions for one of the regular Q & A threads, please PM Shrike or QofQuimica and let them know. Again, all undergrad students who are currently studying for any of these tests should NOT post answers to other students' questions in any of the regular Q & A threads. Thanks to everyone for your cooperation..

Cool. :thumbup: I'll bet Shrike also proposed credential requirements for anyone answering questions. :laugh: ;)

Cool. :thumbup: I'll bet Shrike also proposed credential requirements for anyone answering questions. :laugh: ;)
I finally realized what your moniker is.

Yeah! Let the learning begin!

Cool. :thumbup: I'll bet Shrike also proposed credential requirements for anyone answering questions. :laugh: ;)
I did.

But... I am happy to have help from anyone whose answers are (1) correct; (2) clear; and (3) constructed to help people do better on MCAT problems. Clarity and consiseness may occasionally be necessary victims of the inherent complexity of the subject matter, but appropriatness for the MCAT, never.

I will be moderating the physics thread, or perhaps co-moderating physical sciences with Q -- this is still be discussed. Anyone wishing to post one, or one hundred, answers to physics questions, please PM me.

Two excellent users, Shrike and QofQuimica, have proposed setting up a Q&A subforum within the MCAT forum. They will make themselves available to answer questions for those studying for the MCAT.

This forum will operate differently than the standard forum. Only posts asking specific questions or providing direct answers will be allowed. Other discussions about the MCAT will be moved to the main MCAT forum.
Thank you, Lee (and everyone else who helped), for giving us this opportunity. Now we've just got to prove it was worth the trouble.

I am happy to have help from anyone whose answers are (1) correct; (2) clear; (3) concise; and (4) constructed to help people do better on MCAT problems. Celerity and conciseness may occasionally be necessary victims of the inherent complexity of the subject matter, but appropriatness for the MCAT, never.
Oh, I agree! But you must admit to being, from time to time, rather shrill on this point.

As for myself, even though I fared reasonably well on the MCAT, I would not consider myself an expert on any topic. I found it to be much less a test of knowledge and more an exercise in reading comprehension and application of basic principles.

Cool. :thumbup: I'll bet Shrike also proposed credential requirements for anyone answering questions. :laugh: ;)

I think we've agreed that this should not be a requirement, or if it is, it should be loosened from what was originally suggested. :laugh:

Oh, I agree! But you must admit to being, from time to time, rather shrill on this point.
I do so admit, though I might have chosen a different (albeit no less friendly) adjective.

Your help will be welcome. Everyone's help will be welcome, if it meets the requirements (which are really just common sense).

I think we've agreed that this should not be a requirement, or if it is, it should be loosened from what was originally suggested. :laugh:
As I've shown in the stickified thread, I believe we should pass the mantle for granting imprimaturs to the individual thread moderators. In turn, those mods will realize, as I and I'm sure you already do, that the more help we accept, the more reasonable our task will be.

I think that there will be a lot of repeat questions, so hopefully they won't get too long because a lot of people will find that their questions have already been answered. What do you (or anyone else) think?
Unfortunately, I think you may be overestimating many SDNers' willingness to look for answers themselves by reading over existing threads. One thought would be to create a solutions library of various problem types--didn't you suggest a FAQ in a previous message?--and then link the stock answer in for incoming questions.

Thank you for setting up our sub-forum, Lee. :thumbup: Shrike, I had another thought. Since we have a single sub-forum, maybe what we could do would be to organize threads by subtopics? That way, if someone is looking for help with optics, say, there would be a single optics thread for them to read through. But a magnetism question or a density question would each go to its own thread, not mixed in with the optics. The individual threads might get long and cumbersome eventually, but I think that there will be a lot of repeat questions, so hopefully they won't get too long because a lot of people will find that their questions have already been answered. What do you (or anyone else) think?
I think this is a goal at which we can aim, but we won't be hitting it for a while. Why don't we keep each subject together for now, and consider splitting the threads later?

I do think a FAQ list at the top of each thread will eventually be the most valuable contribution we make.

Now that we have our own forum (thank you again!), do you want to co-moderate Physical Sciences with me, or have your own Chemistry thread(s)?

I do so admit, though I might have chosen a different (albeit no less friendly) adjective.
Ah, but shrill was just irresistable, given your alter-ego. Listen! (http://www.percevia.com/explorer/db/birds_of_north_america_western/obj/198/target.aspx)

Ah, but shrill was just irresistable, given your alter-ego. Listen! (http://www.percevia.com/explorer/db/birds_of_north_america_western/obj/198/target.aspx)
Wow, you're good -- most people don't even know what a shrike is.

The call is rather dull, but the song is interesting. And that of the Northen Shrike, a species about which you won't find much information (and of which I couldn't fnd a decent avatar picture) is better.

I'd have PMed you about this, but that capability seems to have gotten disabled when I got moderating privileges. I'll take that trade.

Glad to see this finally came to be. I'm sure I will be using this for next April! Good luck with the forum Shrike and Q :luck:

Unfortunately, I think you may be overestimating many SDNers' willingness to look for answers themselves by reading over existing threads. One thought would be to create a solutions library of various problem types--didn't you suggest a FAQ in a previous message?--and then link the stock answer in for incoming questions.

Ok, that makes sense. We'll answer questions and have a FAQ thread for each subject, and then when the questions come up again, we can link people to the answer post in the FAQ thread. :thumbup:

Shrike, I am willing to go either way, whichever your physicness prefers. :p I guess if we go with individual FAQ threads, we should decide how we will handle questions that are interdisciplinary. Or, alternatively, we could split the difference, and do both: ex. have a gen chem FAQ, a physics FAQ, and a physical science FAQ. Ditto for BS, and then separate ones for VR, WS, and strategy? If we go this way, it's a lot of threads (9 total: 3 for BS, 3 for PS, 1 for VR, 1 for WS, and 1 for strategy), but then we could assign moderating duties to each FAQ thread. (ex. you could do physics, I could do gen chem, and we could both do physical sciences.) What do you think?

Shrike, I am willing to go either way, whichever your physicness prefers. :p I guess if we go with individual FAQ threads, we should decide how we will handle questions that are interdisciplinary. Or, alternatively, we could split the difference, and do both: ex. have a gen chem FAQ, a physics FAQ, and a physical science FAQ. Ditto for BS, and then separate ones for VR, WS, and strategy? If we go this way, it's a lot of threads (9 total: 3 for BS, 3 for PS, 1 for VR, 1 for WS, and 1 for strategy), but then we could assign moderating duties to each FAQ thread. (ex. you could do physics, I could do gen chem, and we could both do physical sciences.) What do you think?
I propose we use the six-thread model (do we need a separate thread for WS?), and we'll deal with interdisciplinary issues when and if they arise. I think that people will have an easier time finding information if we track, roughly, the subject divisions they see in the reference material (and courses) that most of them are using. Boring, but effective.

So if you agree, I'll just take physics for now; chemistry's yours. Not that I don't like the idea of co-moderating with you, you understand.

Hey y'all,
I just wanted to say thanks for this! It's a great idea :). I know I'll be back once my MCAT prep gets kicked into serious gear.

Again, much thanks :D .

I propose we use the six-thread model (do we need a separate thread for WS?), and we'll deal with interdisciplinary issues when and if they arise. I think that people will have an easier time finding information if we track, roughly, the subject divisions they see in the reference material (and courses) that most of them are using. Boring, but effective.

So if you agree, I'll just take physics for now; chemistry's yours. Not that I don't like the idea of co-moderating with you, you understand.

I don't know if we need a WS one or not. I guess people don't ask many questions about WS, but if there were a thread, maybe they would? Ok, so let's go with your six (physics, gen chem, organic, bio, VR/WS and strategy/general) for now.

I DO think that you don't want to moderate with me. :( But I guess I'll survive. :love:

Ok, everyone, feel free to ask away. :)

I DO think that you don't want to moderate with me. :( But I guess I'll survive. :love:
Hey, baby, wanna moderate together?

(See, I don't think it quite captures the mood.)

Wow, you're good -- most people don't even know what a shrike is.

The call is rather dull, but the song is interesting. And that of the Northen Shrike, a species about which you won't find much information (and of which I couldn't fnd a decent avatar picture) is better.

I'd have PMed you about this, but that capability seems to have gotten disabled when I got moderating privileges. I'll take that trade.
Fixed the PM problem! :)

Fixed the PM problem! :)
Thank you.

I just wanted to say that this is an awesome idea. This is cool because through the midst of all the other posts that flood the forums, this allows for a more organization of the posts for people needing help vs. those fooling around wasting time waiting for scores etc.

One more thing I would like to propose:

Not for MCAT, but for Preallo.......

There are several posts almost everyday on the same subject such as
1. how to fill in the EC's
2. What are my chances threads

I was thinking we could make a sticky with the threads for the 2 following things mentioned above, as well as with links for the secondary promts thread and residency match list thread that phil has in his sig.

In other words, I would like a sticky for current useful links to important threads. This might eliminate many of the over excessive threads which ask the same question every other day.

Also, sometimes doing a search doesn't help find the post you are looking for, so this would make it easier for the current applicants.

Thanks

gujuddoc
(Ekta)

Hey, baby, wanna moderate together?

(See, I don't think it quite captures the mood.)

Hey, you stick to physics! *I* get to make the chemistry. :meanie: ;)

This thread is for students to ask and answer each other's questions for the MCAT, DAT, OAT, and PCAT subjects. All posts from the other Q & A threads that are not either students' questions or moderators' replies will be moved to this thread. Students, please post your own answers to other students' questions here in this thread--or else in the main MCAT forum--rather than in the regular Q & A threads.

If you are a pre-health (MCAT, PCAT, DAT, OAT) test prep instructor, or you have a graduate-level background in one of the MCAT subjects, or you are a senior undergrad who scored well on the MCAT, and you would like to help answer questions for one of the regular Q & A threads, please PM Shrike or me and let us know. Again, all undergrad students who are currently studying for any of these tests should NOT post answers to other students' questions in any of the regular Q & A threads. Thanks to everyone for your cooperation..

In other words, I would like a sticky for current useful links to important threads. This might eliminate many of the over excessive threads which ask the same question every other day.
Ummmm... you mean like this (http://forums.studentdoctor.net/showthread.php?t=139393) stickied thread?

(sorry! :o )

Ummmm... you mean like this (http://forums.studentdoctor.net/showthread.php?t=139393) stickied thread?

(sorry! :o )


Thanks!!!! Didn't realize it was updated. I know there used to be one last summer, but it didn't have much links.

I guess EvoDevo updated it. Now if only people would look at it before posting 5 threads a day on the very same topic.

Hey, you stick to physics! *I* get to make the chemistry. :meanie: ;)


Awwwww how cute!!!!!!!!!!

Shrike,

The new MCATers will need your help creating a Verbal strategy board as well. Maybe you can give a better strategy then that dude from 1998 or 1999 that everyone's always quoting.

Sorry I was trying to edit and the server was slow. But I realized that Lorelei already has the Verbal management job offer. That leaves ya physics. :meanie: :meanie: :meanie:

Thanks!!!! Didn't realize it was updated. I know there used to be one last summer, but it didn't have much links.

I guess EvoDevo updated it. Now if only people would look at it before posting 5 threads a day on the very same topic.
You're asking way too much of people. Most can't be bothered to actually look info up before blathering on.

One more thing I would like to propose:

Not for MCAT, but for Preallo.......I would recommend bringing up PA related propositions in PA, so as not to take away from the discussion here. Q&S need to hammer out the Q&A. ;)

I would recommend bringing up PA related propositions in PA, so as not to take away from the discussion here. Q&S need to hammer out the Q&A. ;)


hahahahaha :laugh: :laugh: :laugh:

Hey, you stick to physics! *I* get to make the chemistry. :meanie: ;)
Just catalyzin', darling. Activation energy and all. Doesn't change the end result, of course.

You're asking way too much of people. Most can't be bothered to actually look info up before blathering on.

:laugh: :laugh: How true

Just catalyzin', darling. Activation energy and all. Doesn't change the end result, of course.

:laugh: :laugh:

Q&S need to hammer out the Q&A. ;)
... and then get to QC.

Thanks for your help, bananaface.

Thanks for this forum, for those that might be retaking the exam and who have done the reading that a TPR or Kaplan course might require...how do you think one should approach studying this time around?

Thanks for this forum, for those that might be retaking the exam and who have done the reading that a TPR or Kaplan course might require...how do you think one should approach studying this time around?
Go ahead and put this question in the "general questions" thread, when it appears. Perfect grist for the mill.

Shrike,

I just noticed a bio thread is not created yet. Are you going to be trying to manage creating one for that as well??? Just curious.

How do i get density of a certain gas using PV=nRT ?
PV = nRT --> n / V = P / RT
D = m/V = n*MM / V = P*MM / RT
(MM: molar mass of the gas)

Yes.

With all of this talent on the MCAT floating around here, I wonder why the various posters don't get together and create an SDN Guide to the MCAT.

With all of this talent on the MCAT floating around here, I wonder why the various posters don't get together and create an SDN Guide to the MCAT.
I think that's kind of what we're doing now.

QofQuimica: lol, we've discussed doing it. But actually, a forum is better; this will be a kind of a living, evolving SDN Guide to the MCAT.

Just wanted to thank everyone that is contributing to this forum. The explanations that are being provided are amazing. Without a doubt this will be a great asset to all those taking the mcat.

This mnemonic comes to us courtesy of Turkeyman.

So you have uncle Ben(Benzene), and he's a lazy leech.
If you lend him money to go party(electron donating), he'll love you, and want you sit across or next to him at the dinner table (ortho/para).
If you don't lend him any money, he'll hate you and want at least 1 person between you and him (meta).

One exception is that Uncle Ben respected Uncle Hal (halides) even if he didnt give Ben any electrons, because of his character. So, in effect, he would always let Uncle Hal sit across or next to him at the dinner table.

Actually, this mnemonic is from EK's Audio Osmosis

Several people have pointed out common spelling and grammar mistakes. It's always a good idea to try and correct these in your writing. However, it's important to know that the MCAT Writing Sample IS NOT a spelling or grammar test. Your score is based on how well you fulfill the three tasks and write a unified essay.



I don't know if I'd agree with that. Maybe in general it's true but I still think in my case it's not. I took the MCAT in April 05 and got an M. As far as I'm concerned I completed the 3 tasks (As per Kaplan) and also had unity.(So I was expecting at least an O. Hell, I still remember the prompt for at least one and my take on it for anybody that cares. Then again I might be breaking copyright law by revealing the prompt even if a paraphrase it.) Actually I would describe my essays as blatantly doing the tasks. The only thing that I can think of would be maybe it was my handwriting, which is so bad people kept telling me I wrote like a doctor when I was a kid. If that's why I got the grade I did I'd understand, otherwise my score is yet another WS anomaly.

Aaaarrrrggggghhhhhh! Sorry I just felt like doing that. It really is frustrating trying to get the sense of what the author is saying in the passages. I have resorted to writing key ideas for each paragraph and I got a 4 :thumbdown
I am trying to get a sense of the author's tone. I felt like I was making progress in the EK material but it is so...frustrating. :mad:

That said, here's what I personally did. I would read the passage through, reading critically but not taking a huge amount of time to figure out details I didn't understand. I did make sure that I understood the overall argument and thrust of the passage though. Then I read the questions, answered the ones I knew, and referred back to the passage for the few that I didn't.

I never skipped passages, because for me it was more trouble than it was worth to remember what I had to come back to.

Again, my strategy was what personally worked for me. I'm a fast reader (I did always finish ahead of time), I'm good at grasping arguments, and I had a double engineering/humanities major so I was somewhat used to reading humanities passages. (The art ones were the worst for me.) And I'm not used to marking up textbooks so it never really occurred to me to mark up the passages, though I did occasionally underline or star things that I knew I was coming back to.

In general, I think it's a good idea to read the passage first, because if you can get a handle on the argument (as I described upthread) you will be able to answer several of the questions very quickly, and know where things are when you need to refer back. Whether to underline or make notes is up to you - I essentially mapped the passage in my head, but I think most people do better with some actual marks on the page.

Skipping passages, again, is a personal thing, but I'd recommend only doing it if you come to a passage that's making you freak out for whatever reason. If you're going to be wasting time hyperventilating, go on to the next one, but as long as you can stay calm and tackle the passages one by one I think steaming ahead is probably the best way to go.

This is exactly how I, too, prefer to take the test. I think the retention factor is more beneficial in the long run - in terms of time - than immediatly jumping to the questions, and then scanning the passage for answers. The only downside to such an approach is that the paragraphs tend to be written with a lot of "..." interspersed between the sentences. I don't know why they do that. No med textbook is written like that. Hopefully... I'll.... get...... used.....to...... that...... way...... of....... reading. :rolleyes:

That just shows where they've removed content while editing the passages to be suitable for the MCAT. They take out stuff that's irrelevant or too difficult, but also they cut down on transitions and repetitions, making it more challenging to read.

I suppose I'm like you in that I grasp the main point of an argument fairly quickly, so I won't easily be thrown off by the condensed format. I think thats also part psychology. You kinda "feel" the author. But the use of .... slows down my reading speed more than anything else. I'm simply not used to reading that way. You know how when you're normally reading, and the ... comes up, you automatically slow down. Thats what it is here. The effect isn't that dramatic; I'm managing around a 12 on the practice tests, with a little bit of time to spare, on a fairly consistent basis. Wouldn't mind bringing it up 2 points, however. Every point counts.

Yes, it can and is, and for exactly the reason you state. Before the fat is metabolized in the Citric Acid Cycle, it must be converted to Acetyl CoA. This is done by beta oxidation, which produces FADH2 and NADH while consuming one ATP per pair, which gives another 4 ATP per pair of carbon molecules. The total then is 4 from beta oxidation plus 12 from Krebs cycle for a net of 16 ATP per two carbons, or about 8 ATP per carbon.

Hi!
I am sorry. I did not understand the question or the comments.
I think that a "fair" or more appropriate question would be about comparing the number of ATP produced during the total oxidation of a glucose molecule, and the total oxidation of a 6 carbon fatty acid, not a triglyceride or glycerol.
Oxidation of a 6 carbon fatty acid:
We spend 2 ATP for activation
Fatty acid +ATP+CoA ----------- Acyl CoA + AMP +2P

Number of acetyl CoA produced: 3 (# carbons/2 =6/2 = 3)

#of rounds to convert the fatty acid in Acetyl Co A = 2 (number of acetyl CoA -1)

( Or you can see it better:

C-C-C-C-C-C

1st. round: C-C-C-C + C-C

Yes, it can and is, and for exactly the reason you state. Before the fat is metabolized in the Citric Acid Cycle, it must be converted to Acetyl CoA. This is done by beta oxidation, which produces FADH2 and NADH while consuming one ATP per pair, which gives another 4 ATP per pair of carbon molecules. The total then is 4 from beta oxidation plus 12 from Krebs cycle for a net of 16 ATP per two carbons, or about 8 ATP per carbon.

I think that the real comparition would be glucose vs 6 carbon fatty acid:

6 carbon fatty acid yields 3 acetyl Co A in 2 rounds of beta-oxidation

3x12 = 36
Each round 5 ATP (1 NADH +1FADH2) 2x5 =10

Minus 2 ATP used for activation of the fatty acid (1 ATP ---AMP + 2P)

Total 44 ATP > 36 ATP

I think that the real comparition would be glucose vs 6 carbon fatty acid:

6 carbon fatty acid yields 3 acetyl Co A in 2 rounds of beta-oxidation

3x12 = 36
Each round 5 ATP (1 NADH +1FADH2) 2x5 =10

Minus 2 ATP used for activation of the fatty acid (1 ATP ---AMP + 2P)

Total 44 ATP > 36 ATP
The question regarded the metabolism of the fatty acid chains of trigyceride.

http://www.np.edu.sg/~dept-bio/biochemistry/aab/topics/fats/fatbreakdown.gif

The beta oxidation mentioned is the part of fatty acid metabolism that provides the additional ATP/carbon that makes fats store more energy.

The beta oxidation mentioned is the part of fatty acid metabolism that provides the additional ATP/carbon that makes fats store more energy.
It often is stated that one sequalae of type I diabetes is ketoacidosis. I'm just speculating, but it would seem like the inability of insulin to get glucuse into the cell results in the hydro. of fatty acids. This in turn results in the release of ketone bodies, which, apparently, results in lowing plasma pH below the optimal range.
If anyone can confirm or correct I'd apprecriate.
Oh, the MCAT level issue. It would seem that this discussion began squarely within the scope of the test. I don't want to break the rules of the thread, but it seems like the natural developement the discussion may now be going beyond that scope. It's your call Nutmeg.

It often is stated that one sequalae of type I diabetes is ketoacidosis. I'm just speculating, but it would seem like the inability of insulin to get glucuse into the cell results in the hydro. of fatty acids. This in turn results in the release of ketone bodies, which, apparently, results in lowing plasma pH below the optimal range.
If anyone can confirm or correct I'd apprecriate.
Oh.

Im not really sure what you are asking to confirm but yes if insulin is not doing its job either from type 1 or type 2 then beta oxidation occurs. acetyl coa and glycerol go to liver and produces keto bodies primarily for the brain. Ketones are acidic thus lower your pH, this is why some diabetics have something called keto strips. You piss on them and it detects ketones present in your urine.

The B cell mediated involves antibodies specific to an antigen. Once the antigen is bound by the antibody it is eliminated by either having a white cell destroy it by phagocytosis or by a series of reactions with blood proteins destroying it.

The T-cell doesn't involve antibodies instead a T-lymphocyte has antibody like protein on its membrane. It becomes either helper T cells, memory T cells, suppressor T cells and killer T cells. Killer T cells destroy the antigen once it matches with the protein on its membrane. Suppressor T cells wind down the immune response.

To sum it up the B cell method is the "antibody method"
T-cell is the "brute force cell destroys antigen method" Sort of like a cell eating up and destroying its prey.

Secondary response is when the antigen is remembered by the T or B memory cells from previous instrusion. Instead of going through the whole process of "trying to find the antibody from scratch that matches" it already has memory cells that "remember" the antigen hence all they need to do is "crank out from the memory cells specific to that antigen the antibodies or the killer T cellls.

The B-cell doesn't involve antibodies . . .
Wha? I love this thread. I really hope it remains a helpful high quality discussion.

Sorry my mistake. Typo. B cells make atnibodies. T cells don't. :rolleyes:
Dam this biology :mad:

Typo corrected.

T cells recognize antigen that has been processed and presented in the context of a major histocompatability complex. CD8 T cells bind Ag/MHC class I and CD4 T cells bind Ag/MHC class II. This interaction activates the T cells to respond by direct cytotoxic action (CD8) or by expression of cytokines to effect the adaptive response (CD4).

One more question guys, this one about circulation and the MCAT. In tracing the blood around the heart and to the lungs I found Kaplan's explanation to be well...krappy. The left side I think pumps the deoxygenated blood, I know there's a systole and a diastole which are the lub/dub. Blood from the lower body is from the inferior vena cava, upper superior. But I'm just having trouble piecing it all. Can someone give me a good rundown for the MCAT?


Vena cava: deoxy blood > right atrium > atrioventricular tricuspid valve > right ventricle > pulmonic valve/artery > pulmonary circuit > pulmonary vein (oxygenated blood) > left atrium > atrioventricular mitral valve > left ventricle > aortic valve > aorta to systemic circulation.

So then - the left side does not pump deoxygenated blood, just the opposite. Systole is ventricular contraction (pumping) and diastole is ventricular relaxation (filling). Check out a physiology textbook to get familiar with this as well as the electrical properties of the heart i.e., SA node AV node...

So then - the left side does not pump deoxygenated blood, just the opposite.

Yeah, thats what I would think too. The aorta is actually the largest artery. When the left ventricle contracts, it really contracts, meaning the pressure is enormous. And this is also why the left ventricle contains more cardiac muscle than the right. Of course the pressure decreases as the blood moves along. You may want to remember the relative sizes of the blood vessels as well. From largest diameter to smallest:

Artery ---> arteriole ---> capillary ---> venule ---> vein

I should've said, the pressure in the aorta is enormous. Excuse me. If I remember right, the aorta itself contracts rather passively. Which is why the walls of the aorta (and all other arteries) differ considerably, relative to tissue structure, from the other types of blood vessels (the pressure is greater in the arteries). Which implies that the proportion of intima, elastica, & adventitia differs, from blood vessel to blood vessel. I don't recall the exact proportions, unfortunately, but I think tunica elastica is greater in the aorta? Elastica = elastic = recoil.

I should've said, the pressure in the aorta is enormous. Excuse me. If I remember right, the aorta itself contracts rather passively. Which is why the walls of the aorta (and all other arteries) differ considerably, relative to tissue structure, from the other types of blood vessels (the pressure is greater in the arteries). Which implies that the proportion of intima, elastica, & adventitia differs, from blood vessel to blood vessel. I don't recall the exact proportions, unfortunately, but I think tunica elastica is greater in the aorta? Elastica = elastic = recoil.

Do we have to know about the tunica elastica?

I was reading my Examcrackers materials and I'm confused on 2 questions:

1) Compared to an electron with a principal quantum number of 1, an electron with a principal quantum number of 2 will have:

a. a lower energy
b. a higher energy
c. a negative spin
d. a positive spin

I picked b. because I thought that the further the electrons from the nucleus, the higher the energy. But their answer is a. Their explanation in the back of the book is: The principal quantum number (n) represents the energy level of the electron. The lowest energy shell is n=1. As n increases, the shells move farther from the nucleus and energy increases. So wasn't I right? Do you think this was a typo?

2) Which of the following best explains why sulfur can make more bonds than oxygen?

a. Sulfur is more electronegative than oxygen.
b. Oxygen is more electronegative than sulfur.
c. Sulfur has 3d orbitals not available to oxygen.
d. Sulfur has fewer valence electrons.

I got this question right by process of elimination, but I'm trying to understand why choice c. is the correct answer. I thought that since sulfur is in group VIA that it has 3p orbitals and that the transition elements are the only ones with d orbitals. Can you please explain why choice c. is the correct answer? The explanation in the back of the book is not clear to me. They explain that because sulfur is larger than oxygen, sulfur has 3d subshells available that allow electrons to form bonds and break the octet rule of Lewis structure.

Thanks for you help!

Rad11, I just saw ur question and wanted to let you know that it was a typo. I love Examkrackers, but their books do have a bit of typos. In case you are unsure about other questions u can go to the website, and look under the forums. Thats where i found out if the questions were typos or not. :)

Rad11, I just saw ur question and wanted to let you know that it was a typo. I love Examkrackers, but their books do have a bit of typos. In case you are unsure about other questions u can go to the website, and look under the forums. Thats where i found out if the questions were typos or not. :)

Hey frany584, thanks a lot for clarifying that for me. I was sure I had the right answer, but you never know. I still need the explanation to question # 2, though :o

Hey RAD11, there is another discussion about d orbitals and why certain atoms can/cannot have five bonds on the first page of this thread, i hope it provides some clarification:

Posted by Learfan:

1. I think that you are confusing hybridization of atoms that are bonding to other atoms with electron configurations for lone atoms. All atoms have d-orbitals, but elements that are in row 3 or greater of the periodic table have low-lying d-orbitals that are available for bonding. A phosphorus central atom with five bonds WOULD have one of its 3d orbitals included in its hybridization. In other words, when it has five bonds and trigonal bipyramidal geometry, its hybridization is sp3d. That d comes from one of the 3d orbitals in the phosphorus atom. So there are five sp3d orbitals, used to make the five bonds to the phosphorus. Keep in mind that elements in rows 1 and 2 will NEVER exceed their octets, because aren't any 1d or 2d orbitals to make sp3d or sp3d2 hybrid orbitals. So nitrogen, right above phosphorus, can never have five bonds.

Do we have to know about the tunica elastica?

no. You can save it for medical school. ;)

Okay, looks like I gave some wrong info. I studied this last yr... so pardon moi. There is indeed a tunica elastica, but it has nothing to do with blood vessel pressure. These are the three layers: tunica intima (think intimate - inside - innermost), tunica media (think middle), & adventitia (think outermost, in this case, connective tissue).

According to http://www.maexamhelp.com/id99.htm:

"Blood is pumped from the ventricles into large elastic arteries that branch repeatedly into smaller and smaller arteries until the branching results in microscopic arteries called arterioles. The arterioles play a key role in regulating the blood flow into the tissue capillaries. About 10% of the total blood volume is in the systemic arterial system at any given time."

Example: blood is pumped from the left ventricle to the aorta (which is an elastic artery). Remember that the left ventricle has to pump blood to the entire body; hence the great pressure in the aorta. The walls of the aorta will expand (contract) as a result; they need to be able to both contract (without rupturing) and recoil. The expansion and recoil is made possible by the elastic tissue of the tunica media. The adventita prevents the vessel from rupturing.

According to

http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab12b/EXAMPLES/Exmusart.htm:

"In muscular arteries such as the one shown at left, the wall is composed mainly of smooth muscle. Elastic CT is present, to be sure, but not nearly to the extent that it is in the elastic arteries.
The smooth muscle of the wall of distributing arteries makes them very extensible, and also provides for a counter force to be exerted. As the vessel expands the smooth muscle cells are stretched. Reacting to this they begin to contract. The peak of their contraction comes at about the point where systole ends and diastole begins; thus the contraction of the arterial walls dampens out the pulsations of the flow to provide a more or less steady supply of blood at normal pressure into the capillary beds."

This makes sense if you consider that muscular arteries are also the distributing arteries. If they simply pumped blood at full speed into capillaries, the capillaries (which are extremely thin and function as diffusion mechanisms - think " pulmonary alveoli" here) - would rupture. Smooth muscle contracts slowly; this allows the blood to flow into capillaries at exactly the right rate. As for capillaries, their walls consist of a simple layer of endothelium (simple squamous eptithelium). This makes sense if you consider that the red blood cells (erythrocytes) of the capillary which passes through a tissue must somehow release the oxygen they contain, and pick up CO2. This is accomplished via diffusion. Venules connect capillaries to veins; veins carry deoxygenated blood back to the right side of the heart. Veins also contain valves, to prevent the backflow of blood. The pressure in veins is low, hence the valves.

Yeah, thats what I would think too. The aorta is actually the largest artery. When the left ventricle contracts, it really contracts, meaning the pressure is enormous. And this is also why the left ventricle contains more cardiac muscle than the right. Of course the pressure decreases as the blood moves along. You may want to remember the relative sizes of the blood vessels as well. From largest diameter to smallest:

Artery ---> arteriole ---> capillary ---> venule ---> vein
Circulation goes like this : left heart --> aorta --> arteries --> arterioles ---> capillaries ---> venules --> veins --> vena cava --> right heart.

THe maximum pressure is in aorta and the lowest is in the vena cava, i think

Circulation goes like this : left heart --> aorta --> arteries --> arterioles ---> capillaries ---> venules --> veins --> vena cava --> right heart.

THe maximum pressure is in aorta and the lowest is in the vena cava, i think

You are mostly correct. Its already been mentioned in this thread... deoxygenated blood enters the right side of the heart (superiorly, from the superior vena cava, inferiorly, from the inferior vena cava, while the left side of the heart pumps oxygenated blood to the rest of the body. I think its also good to know that blood flows from the right side of the heart to the lungs before going to the left side. I don't know if the MCAT will question you about semilunar valves/mitral valves & all that. Also remember that the aorta is itself an artery (the largest one, in fact). So to somewhat modify what you wrote above:

Right atrium ---> Right ventricle ---> Pulmonary trunk ---> Pulmonary arteries (lungs) ---> Pulmonary capillaries ---> Pulmonary veins ---> Left atrium ---> Left ventricle ---> aorta (elastic artery) ---> muscular arteries ---> arteriolies ---> capillaries ---> venules ---> veins ---> vena cavae

Just remember that between "right" and "left" comes pulmonary, and that pulmonary refers to lungs; the rest will come easily. Another point the MCAT might test you on is the difference between systemic & pulmonary circulation. Systemic (think system, think body) = circulation to the rest of the body, pulmonary = circulation to the lungs. The two are not exactly independant of each other, which is why I like to remember it in one go. There is also coronary circulation, which just means there are two coronary arteries (right main & left main) which give blood to the tissues of the heart.

The maximum pressure is in the aorta, and the lowest is in the right atrium. If you want to be more exact:

"As blood leaves the aorta and flows through the systemic circulation, its pressure falls progressively as the distance from the left ventricle increases. Blood pressure decreases to about 35mmHg as blood passes from systemic arteries to systemic arterioles and into capilliaries. At the venous end of capilliaries, blood pressure has droped to about 16mmHg. Blood pressure continues to drop as blood enters systemic venules and then veins because these vessels are farthest from the left ventricle. Finally, blood pressure reaches 0mmHg as blood flows into the right ventricle."

I was wondering if Shrike's method for attacking PS passages applies to Bio-- is it a good to skim the passage at most and focus on the reactions, figures, graphs, equations, etc then dig into the questions? I could see where certain subjects (CAC, maybe certain physio passages) this would be great, but what about genetics passages? Any thoughts?

Aside to Shrike: I used your method for PS, and went from 9's and 10's to 12's on my practice exams. Thanks for making my toughest section my strongest!

What was the method that you used that made you go up so many points, will u please let me know?? physics is my weak subject too

Look here (http://forums.studentdoctor.net/showthread.php?t=207650), post 7

From Examcrackers 1001 Questions in MCAT Chemistry:

In the following reaction, which is run at 600K, 4.5 moles of nitrogen gas are mixed with 11 moles of hydrogen gas:

N2(g) + 3H2(g) --> 2NH3(g)

The reaction produces 6 moles of ammonia. What is the percent yield of ammonia?

A. 42%
B. 57%
C. 82% --> ANSWER
D. 100%

Their explanation in the back of the book: Hydrogen is the limiting reagent. Eleven moles of hydrogen should produce 11 x 2/3 = 7.3 moles of ammonia. If it actually produces 6 moles, the yield is 6/7.3, which is a lot more than half.....WHAT???!!!!! :eek: Can someone please explain this to me? How did hydrogen become the limiting reagent? :(


Does the question always have to give you the starting amount in moles or grams in order to figure out the limiting reagent and/or the percent yield?

Thanks a bunch!

From Examcrackers 1001 Questions in MCAT Chemistry:

In the following reaction, which is run at 600K, 4.5 moles of nitrogen gas are mixed with 11 moles of hydrogen gas:

N2(g) + 3H2(g) --> 2NH3(g)

The reaction produces 6 moles of ammonia. What is the percent yield of ammonia?

A. 42%
B. 57%
C. 82% --> ANSWER
D. 100%

Their explanation in the back of the book: Hydrogen is the limiting reagent. Eleven moles of hydrogen should produce 11 x 2/3 = 7.3 moles of ammonia. If it actually produces 6 moles, the yield is 6/7.3, which is a lot more than half.....WHAT???!!!!! :eek: Can someone please explain this to me? How did hydrogen become the limiting reagent? :(


Does the question always have to give you the starting amount in moles or grams in order to figure out the limiting reagent and/or the percent yield?

Thanks a bunch!

Hydrogen is the limiting reagent because in the example if you have 4.5 moles of nitrogen equals 13.5 moles of hydrogen (the ratio of nitrogen to hydrogen is 1:3). In the question stem they tell you that you use 11 moles of hydrogen, which is less than the 13.5 moles calculated above. This makes hydrogen the limiting reagent because the reaction is limited by the actual amount (11 moles) of hydrogen used. Since hydrogen is the limiting reagent you can use the ratio of hydrogen to ammonia (3:2) to figure out the number of moles of ammonia produced. 11/x=3/2 or x=(2/3) 11=7.3. Since you can't use a calculator during the mcat, you know that 6/7.3 is much greater than 50% so you can eliminate choices a and b, and d doesn't make sense because we know that the actual yeild(6) doesn't equal the theoretical(7.3). So the answer is c. I hope this helps. And more importantly I hope I'm right. :)

RAD11, i do the problem just a tad different than philchemist, but get the same answer and thought maybe seeing a different approach might help as well :) . I do it by converting the moles of reactants given, to moles of product:

4.5 moles N2 (2 moles NH3/ 1 mole N2) = 9 moles NH3
11 moles H2 (2 moles NH3/ 3 moles H2) = ~7.3 moles NH3

looking at that i can see that the amount of hydrogen given produces less product, thus it has to be the limiting reagant. Because hydrogen is the limiting reagent, it determines the maximum amount of product that can be produced (our theoretical yield). Now, my actual yield = 6 moles. So the percent yield = actual/theoretical *100. hope that helps! :D

For a second, I thought the subject was orgasmal biology... so dissapointed.

For a second, I thought the subject was orgasmal biology... so dissapointed.


Check the urology forum, they may have something up your alley ;)

Hydrogen is the limiting reagent because in the example if you have 4.5 moles of nitrogen equals 13.5 moles of hydrogen (the ratio of nitrogen to hydrogen is 1:3). In the question stem they tell you that you use 11 moles of hydrogen, which is less than the 13.5 moles calculated above. This makes hydrogen the limiting reagent because the reaction is limited by the actual amount (11 moles) of hydrogen used. Since hydrogen is the limiting reagent you can use the ratio of hydrogen to ammonia (3:2) to figure out the number of moles of ammonia produced. 11/x=3/2 or x=(2/3) 11=7.3. Since you can't use a calculator during the mcat, you know that 6/7.3 is much greater than 50% so you can eliminate choices a and b, and d doesn't make sense because we know that the actual yeild(6) doesn't equal the theoretical(7.3). So the answer is c. I hope this helps. And more importantly I hope I'm right. :)

Yes, you are. Nice job. :thumbup:

Queen of Q said it a lot better (medium pressure... never even heard of that, my knowledge must be a tad elementary!!!), but if you want a more condensed version:

The properties of an ideal gas come from the Kinetic-Molecular Theory:

(I) The molecules of the gas are spaced far apart

(II) The molecules of the gas have no interaction with each other

(III) Any collisions between the gas molecules themselves or the gas molecules & the walls of the container are elastic

On the basis of assumption (I), you can conclude that the gas is at low pressure. On the basis of (II), its clear that there are no intermolecular forces between the molecules of the ideal gas.

And of course..... the famous PV = nRT. A physical chemistry book will have the actual derivation of this. What it says is that any ideal gas can be completely described by four variables: pressure, volume, number of moles of gas, & temperature.

At low temperature & high pressure, the ideal-gas law fails because a gas begins to liquify, if I remember right.

Kaplan's Complete guide to the MCAT has a list of about 6 possible question stems and how to attack them. This may help you decide how to approach those questions. I just went to my local library and made notes on the 5 pages that cover this concept. Also Lukewhite( a kplan MCAT instuctor I believe) made some very good posts on question stems which I will post below.



Out of the few AAMC passages I've done, it seems like there is a certain taxonomy of question stems:

1. The main idea of the passage is ...
2. The author would most/least likely agree with ...
3. The word "..." as used in the passage refers to...

One more question guys, this one about circulation and the MCAT. In tracing the blood around the heart and to the lungs I found Kaplan's explanation to be well...krappy. The left side I think pumps the deoxygenated blood, I know there's a systole and a diastole which are the lub/dub. Blood from the lower body is from the inferior vena cava, upper superior. But I'm just having trouble piecing it all. Can someone give me a good rundown for the MCAT?

left side of the heart pumps oxygenated blood...remember, diff. b/w left side of body and left side of picture in book! go by what is your left on your own body.
I'm not going to bother saying the whole blood circulation, you can just look it up on any search engine and find many better explanations/pictures than I or Kaplan will give

Because Im pretty sure i wasnt supposed to ask a specific question from an aammc practice test I deleted my question.

I don't think you are allowed to put actual test questions here. But I have the tests and all their solutions. I wish you told me before you purchased it because I would have given it to you free. I have the TPR soln's for 4R and can send them to you if you send me a PM.

Edited to delete quoted portion.......

Oh and thanks Q for answering my question last night for my friend.

I don't think you are allowed to put actual test questions here. But I have the tests and all their solutions. I wish you told me before you purchased it because I would have given it to you free. I have the TPR soln's for 4R and can send them to you if you send me a PM.

Edited to delete quoted portion.......

Oh and thanks Q for answering my question last night for my friend.

I have 4R but I don't have the answers to them. Is there anyway I can get a hold of them..would you care??

Thanks

I wanted to elaborate on "myfavred" nice concise statement. Translation begins on a free floating ribosome in the cytosol. If the nascent polypetide expresses a hydrophobic SIGNAL SEQUENCE in the first 16-30 amino acids, a signal recognition particle (SRP) will carry the entire complex to the ER. The growing protein will either be inserted into the ER lumen or threaded through the membrane of the ER.
What peptides have the SIGNAL SEQUENCE, & thus will be translated at the ER?
Proteins destined to be secreted, or end up in the "secretory pathway" will have the SIGNAL SEQUENCE. These include polypeptides that will eventually be in the lumen, or membranes of the ER, Golgi, lysomes, plasma membrane, as well as all secreted proteins.

What polypeptides will be translated in the cytosol because they lack the hydrophobic signal sequence?
Pretty much all the rest, including, proteins that will "live" in the nucleus, cytolsol, & mitochondria.

I don't think we have to know "the definition of ribosome" in this concrete detail. I don't think we are responsible for knowing this. WE were thought this in cell biology if I recall but as far as mcat is concerned a ribosome, the simplest way to put it is that ribosomal subunits, also called svedberg units are made in the nucleolus and they then attach to the mRNA. They can be either found free in the cytoplasm or attached to the ER which is then called the RER. THe process of translation is taken place via the ribosome. If the ribosome wasn't there carrying the mRNA, the TrNA couldn't bring form the anticodon-codon bond to form the protein. I don't think you're responsible for the intricate details regarding the signal sequence and polypeptide recognition.

I have 4R but I don't have the answers to them. Is there anyway I can get a hold of them..would you care??

Thanks


PM Me. Please for anyone needing AAMC tests, or soln's or having questions about that, I would rather discuss through PM

Re: AAMC test 4R. For those of you who pm'd me about the solutions, I have the solutions for the unrevised version of 4R, when it was still called AAMC 4, rather then 4R(4 revised). This means that the verbal solutions will be in front rather then after the physical sciences. So the numbers will not correspond to the question number. I'll try to get the solutions for the more revised test. So that should probably answer your questions about concern to why they are not correlating with the question number. Prior to 2003, the test was in the form..... Verbal first, then physical, and then biological. Furthermore, there were 5 more questions on verbal making a total of 65 questions in verbal, rather then 60 questions. And hence, that's why the numbers are off when you compare the test to the solutions that you have.

Gotgames,

I hope that answers your questions.

To the rest of you who have that version of the solutions, if I had another more revised set of solutions, I would email you but that's all I have so bare with me and hopefully I'll find time to look through it and pm you an email where I can send an attachment to you with the correct number vs. solution number. So you know which answers correspond to which.

Thanks

guju

Queen of Q said it a lot better (medium pressure... never even heard of that, my knowledge must be a tad elementary!!!), but if you want a more condensed version:

The properties of an ideal gas come from the Kinetic-Molecular Theory:

(I) The molecules of the gas are spaced far apart

(II) The molecules of the gas have no interaction with each other

(III) Any collisions between the gas molecules themselves or the gas molecules & the walls of the container are elastic

On the basis of assumption (I), you can conclude that the gas is at low pressure. On the basis of (II), its clear that there are no intermolecular forces between the molecules of the ideal gas.

And of course..... the famous PV = nRT. A physical chemistry book will have the actual derivation of this. What it says is that any ideal gas can be completely described by four variables: pressure, volume, number of moles of gas, & temperature.

At low temperature & high pressure, the ideal-gas law fails because a gas begins to liquify, if I remember right.

So a real gas will behave ideally at high temperatures and low pressures or low pressure and high temperature??I'm so confused

So a real gas will behave ideally at high temperatures and low pressures or low pressure and high temperature??I'm so confused

You are saying the same thing twice and not realizing it! :) Gases behave ideally at LOW PRESSURE, HIGH TEMPERATURE. Think about it...at low pressure, gases are free to take up more volume, and at high temperatures, gases are less likely to condense into liquids.

as far as mcat is concerned a ribosome, the simplest way to put it is that ribosomal subunits, also called svedberg units are made in the nucleolus and they then attach to the mRNA.

Forgive me for being nitpicky, since the rest of your post is right on, Nitya2284. Ribosomal subunits are not called svedberg units. A Svedberg unit is used for describing sedimentation coefficients of macromolecules.

The 30S & 50S subunits of prokaryotic ribosomes are called as such because that's 'where they lie' when ultracentrifuged.

The 30S & 50S subunits of prokaryotic ribosomes are called as such because that's 'where they lie' when ultracentrifuged.
Good point. This is why when the 30S & 50S subunits are assembled the prok. ribosome is only 70S. Similiarly, the euk. subunits are 40S & 60S and assembly to form an 80S riboome.
The S units are derived from both the surface area & mass. Think of a feather floating downward. If one assembled two feathers together, there is no reason to assume that their descent would somehow be additive.

Forgive me for being nitpicky, since the rest of your post is right on, Nitya2284. Ribosomal subunits are not called svedberg units. A Svedberg unit is used for describing sedimentation coefficients of macromolecules.

The 30S & 50S subunits of prokaryotic ribosomes are called as such because that's 'where they lie' when ultracentrifuged.

k that was my mistake..yeah you're right. I didn't notice that I mentioned Svedberg units.

You are saying the same thing twice and not realizing it! :) Gases behave ideally at LOW PRESSURE, HIGH TEMPERATURE. Think about it...at low pressure, gases are free to take up more volume, and at high temperatures, gases are less likely to condense into liquids.

k right just making sure..thanks a bunch

So a real gas will behave ideally at high temperatures and low pressures or low pressure and high temperature??I'm so confused

Just think of a gas in a closed cylindrical container, with a movable piston (your chem book will have a picture). The lower the piston, the greater the pressure. Keep in mind that pressure is a force: P = F/A. If the force increases while the area gets smaller, then the pressure on the gas is increasing. Now imagine that the gas absorbed some heat energy. This would mean its temperature increases. Temperature is a measure of the average kinetic energy (energy of motion)... so if the temperature increases, the kinetic energy is also going to increase. So the motion of the gas molecules is going to increase... which means the gas will push upward against the cylinder. Now the pressure on the gas molecules is going to decrease, because the A in the P = F/A is increasing. To summarize, for an ideal gas, high temperature = lots of kinetic energy = greater volume = less pressure.

Just think of a gas in a closed cylindrical container, with a movable piston (your chem book will have a picture). The lower the piston, the greater the pressure. Keep in mind that pressure is a force: P = F/A. If the force increases while the area gets smaller, then the pressure on the gas is increasing. Now imagine that the gas absorbed some heat energy. This would mean its temperature increases. Temperature is a measure of the average kinetic energy (energy of motion)... so if the temperature increases, the kinetic energy is also going to increase. So the motion of the gas molecules is going to increase... which means the gas will push upward against the cylinder. Now the pressure on the gas molecules is going to decrease, because the A in the P = F/A is increasing. To summarize, for an ideal gas, high temperature = lots of kinetic energy = greater volume = less pressure.

that definitely makes sense now. Thanks!

After taking a diag, what would be some good ways to go through it?

If the topic was something we haven't covered in class, should I wait for that lecture, or go ahead read up on it and try to figure out the anwer?

Also is it worth taking the same diag again?

Thanks!!


I took the MCAT twice, and the difference between my science scores the first and the second time I took it were that I reviewed whatever I got wrong, when I took a diag.

The best way to see improvement in your scores is to constantly assess what you are doing wrong. When you take diags, don't just take them to see how you do. Go back and assess what your weak points are and constantly review them over an over until you get the idea and understand it well.

What I did......

Instead of reading the solution right away, I looked at what the right answer was and tried to figure it out first by reassessing my steps in coming to the original answer and trying see where I went wrong. If I still didn't understand it, then I went ahead and looked at the solution they gave and reviewed it until I understood it.

If the topic is something that you are weak in, try to spend a little extra time doing practice in that area. But the optimal way of increasing your score is reviewing what you got wrong and why......was it issue with that subject? Was it issue with the timing?? Etc. Then work from there and focus your energy on changing those weak points into strong points.

Other then that........

The other thing to realize is that the schedule a prep course gives, is only a guide.. However, that does not mean you should slow yourself down if you wish to go ahead of them and feel confident in doing so. Many people in my TPR used the schedule as a guide for class but went a head in their study schedule and studied for 2 months, then did a block a day of the workbook for the next month after that.

This worked for them. Others went ahead but then did the workbook 2 times through, so they would understand the material to the fullest and not forget.

Yet, others did half of a block one day and then the other half at a later date so they would still have practice problems in that area to do.

And yet others, only did problems in the area of weakness.

You just have to assess what is the best study schedule for you as an individual. One suggestion.....if you are taking a prep course, ask your teachers what they suggest for your individual situation.

The TPR books are plenty. I strongly suspect that's true of Kaplan's, EK's, and so on, also.

I have not seen a biology or chemistry book , other than TPR's Science Reviews, since before many of you were born. I scored 14, twice, in the PS section, and 12 in BS without any O-chem (even ours).


Agreed with this sentiment. The TPR review books are plenty and if you have their workbooks and in class compendium, that will give you some of the best practice out there.

My PS and BS section, this past April, was very much like a combo of what I saw in the in class compendium and workbooks.

Which section did you people find the most time consuming to get through? Organic? General chemistry? Biology? Verbal? Physics?

For me.....

Well excluding Verbal......

The Organic was the easiest to get through for a few reasons...

I had been tutoring others in organic in the recent past, that I retained that knowledge real well. Secondly, they were the shortest chapters in the TPR science review books, so that made them get through easier. There were only 5 organic chapters to get through, and 6th chapter which was actually a biochemistry chapter. Again, biochem was a subject that I was strong on, making that part of bio 1 and organic 6 very easy to get through. I had also tutored my roommate in biochem in the fall, so that made it fresh in my mind.

From the 5 orgo chapters, only the first 4 were like orgo lecture material, the 5th was more lab materials and very basic. The questions that I had on the MCAT about orgo chapter 5 was as basic at the material in that chapter too. The other orgo stuff was a bit more complex but you could reason your way through it.

The Physics and genchem took me a month to review. Many concepts in physics and genchem overlapped in some ways and had ways or interrelating to one another, so this was not to hard to review.

Bio, on the other hand, is where I spent the most time. Bio had some very very very very long and tedious chapters to get through and it was quite detailed, so this took the most of my time. The physio stuff I think is what took the longest for me.

I'm having trouble with an Examkrackers general chemistry question. Its in the EK Chemistry book (5th edition), page 43, questions 46 and 48. The two questions require a diagram so I won't bother explaining it on here. Hopefully someone with the EK books can help me out.

For question 46, correct me if I'm wrong, but the answer is D because beaker one decomposes into calcium oxide and carbon dioxide. The carbon dioxide produced in beaker one is then used to react with calcium oxide in beaker two therefore producing calcium carbonate in beaker two, because carbon dioxide is in a gas form.

As for question 48, I'm completely lost. I dont even know where to start, heh. Thanks in advance.

this is correct. It seems like you understand question 46. Answer A should require little thought and is wrong

answer B and C are opposite so require attention. both of them discuss the amount of Ca changing which is not possible because if you look at the equation Ca is never in the gas phase.


also at the EK website they will field questions on all of their books and MCAT based questions in general as well.


For question 46, correct me if I'm wrong, but the answer is D because beaker one decomposes into calcium oxide and carbon dioxide. The carbon dioxide produced in beaker one is then used to react with calcium oxide in beaker two therefore producing calcium carbonate in beaker two, because carbon dioxide is in a gas form.

when studying for the mcat, i keep falling asleep, even though i got 10 hours of sleep. how do you manage to stay awake? i got myself a caramel frap so that it might help keep me awake, but i still fell asleep. when i am focused, i read for a little while, and then have to get up and walk around. this will be my 2nd time taking the mcat

how do u stay focused/awake?


the fear of applying MSTP with a sub 30 scores keeps me awake and alert...


short of that, try tea (the buzz is mellower and more prolonged) and sometimes smelling perfume/cologne gets you pepped up for a bit. That was something that my RA freshman year (10 years ago; wow, I feel old suddenly) passed along to me and its always helped. :thumbup:

the fear of applying MSTP with a sub 30 scores keeps me awake and alert...


short of that, try tea (the buzz is mellower and more prolonged) and sometimes smelling perfume/cologne gets you pepped up for a bit. That was something that my RA freshman year (10 years ago; wow, I feel old suddenly) passed along to me and its always helped. :thumbup:


did u drink black tea or green tea? which is better?

this is correct. It seems like you understand question 46. Answer A should require little thought and is wrong

answer B and C are opposite so require attention. both of them discuss the amount of Ca changing which is not possible because if you look at the equation Ca is never in the gas phase.


also at the EK website they will field questions on all of their books and MCAT based questions in general as well.

thanks for the reply. mm, I think I get question 46 now.

As for question 48, anyone have any insight? I'm completely lost on that question. I actually did take a look at the EK website for that question and alot of people seemed to have questions about number 48 as well. Nevertheless, after looking at Dr. Calvin's explanations on the EK website, I was still confused. I don't know where partial pressure comes into play. Basically, all I understand is that the answer is 'A' because if the partial pressure equilibrium constant is less than the partial pressure of carbon dioxide , the rxn will shift left. But it cant shift left because it needs to react with CaO, which it cant because it is removed. But my question is, isnt CaO present because its being produced by the decomposition of Calcium Carbonate in beaker one? thanks again.

did u drink black tea or green tea? which is better?



I personally drink black (it's the UK I me), but green is just as good; if I recall, black is slightly more caffienated

Black tea is definitely much stronger then green tea.

As for what Q was suggesting, meditation is an art I wish I learned. Would help me to do what she's saying and sit for long times without a break. I needed to give myself a few breaks in between, otherwise my mind would start wandering.

I'm having trouble with an Examkrackers general chemistry question. Its in the EK Chemistry book (5th edition), page 43, questions 46 and 48. The two questions require a diagram so I won't bother explaining it on here. Hopefully someone with the EK books can help me out.

For question 46, correct me if I'm wrong, but the answer is D because beaker one decomposes into calcium oxide and carbon dioxide. The carbon dioxide produced in beaker one is then used to react with calcium oxide in beaker two therefore producing calcium carbonate in beaker two, because carbon dioxide is in a gas form.

As for question 48, I'm completely lost. I dont even know where to start, heh. Thanks in advance.

Sorry, I don't have a copy of the EK book, so I can't help you based on this info you've given. Do any of you other mods have a copy of EK to help this student?

I took the Kaplan MCAT #6 and did terrible. I got BS 7, VR 7, and PS 9. That being only a 3 point increase from my terrible 20 diag score and its been a month of studying since then. My goal is a 10 on each section (for verbal I would be happy with a 9 but at least a 2-3 pt increase on each section from what I have would be ideal for me). I am planning on taking the August MCAT but am also considering taking the April one instead. I only have 2 weeks till registration is due and I was wondering what some of you experienced ones would suggest. What do you think I should do, how should I put time into studying. I do plan to start studying a little more intensely as I have been taking it a little easy for the past month. I am taking the Kaplan class and mainly just do the readings they assign, not much more aside from some of the examkrackers material and audio osmosis. There are 5/6 weeks left to the big day, and do you think I can pull off a 2-3 point increase from what I have for each section? Thanks in advance for your responses.

(I did post this as a new thread in the MCAT forum but was not sure it was the right place to post so i'm posting the same message here. I'm brand new to the forum and find it an excellent place of valuable information)

I took the Kaplan MCAT #6 and did terrible. I got BS 7, VR 7, and PS 9. That being only a 3 point increase from my terrible 20 diag score and its been a month of studying since then. My goal is a 10 on each section (for verbal I would be happy with a 9 but at least a 2-3 pt increase on each section from what I have would be ideal for me). I am planning on taking the August MCAT but am also considering taking the April one instead. I only have 2 weeks till registration is due and I was wondering what some of you experienced ones would suggest. What do you think I should do, how should I put time into studying. I do plan to start studying a little more intensely as I have been taking it a little easy for the past month. I am taking the Kaplan class and mainly just do the readings they assign, not much more aside from some of the examkrackers material and audio osmosis. There are 5/6 weeks left to the big day, and do you think I can pull off a 2-3 point increase from what I have for each section? Thanks in advance for your responses.

(I did post this as a new thread in the MCAT forum but was not sure it was the right place to post so i'm posting the same message here. I'm brand new to the forum and find it an excellent place of valuable information)

I am taking the august mcat, like yourself. Although my story is slightly different, since i started with a 25 diag, and I have been studying hard for the past month, including now, so my suggestion is as follows: I actually am taking some of this from gujudoc, since he gave me good advice: if I were you, I would take the exam, but you should study as follows. Firstly, study intensely, take notes on what you don't understand or remember, and when you read, study very thoroughly, and take all the subject exams available in your books. Additionally, take a practice verbal exam every other day>>this is very important! You will lose some of the test taking skill, if you don't practice enough. You must do at least 3 passages every other day, and go over the answers carefully. If you keep that up, you'll hopefully be in the 30 range by the real thing.

Good luck, we're in the same boat here.

I am taking the august mcat, like yourself. Although my story is slightly different, since i started with a 25 diag, and I have been studying hard for the past month, including now, so my suggestion is as follows: I actually am taking some of this from gujudoc, since he gave me good advice: if I were you, I would take the exam, but you should study as follows. Firstly, study intensely, take notes on what you don't understand or remember, and when you read, study very thoroughly, and take all the subject exams available in your books. Additionally, take a practice verbal exam every other day>>this is very important! You will lose some of the test taking skill, if you don't practice enough. You must do at least 3 passages every other day, and go over the answers carefully. If you keep that up, you'll hopefully be in the 30 range by the real thing.

Good luck, we're in the same boat here.

Just wanted to point out that I'm female :D :p :)

But to the poster, that you were responding to........Listen the above quoted. Good advice.

I reviewed those topics 3 times now so I'm going to make notecards on all of those so I can get them straight once and for all!! Maybe someone was nice enough to make a neat document on it.


Howdy,

I was just reviewing over Equilibrium and Acids and Bases. It seems to me that there are a truckload of formulas to remember.

Ones for Ksp, Keq, Kb, Ka, pKa, pKb, how they relate to eachother, pH, pOH, how to find concentration of something in a buffer solution, how to find pH with strong acids/bases, and on and on. Can someone post a concise explanation of Equilibrium and acid/base stuff? I know it seems like a lot to ask... but... yeah :rolleyes:

I reviewed those topics 3 times now so I'm going to make notecards on all of those so I can get them straight once and for all!! Maybe someone was nice enough to make a neat document on it.

We will try to do this soon. In the meantime, if you haven't already, you may want to check mcatpearls.com and see if there is some info there to help you.

This thread is for students to ask and answer each other's questions for the MCAT, DAT, OAT, and PCAT subjects. All posts from the other Q & A threads that are not either students' questions or moderators' replies will be moved to this thread. Students, please post your own answers to other students' questions here in this thread--or else in the main MCAT forum--rather than in the regular Q & A threads.

If you are a pre-health (MCAT, PCAT, DAT, OAT) test prep instructor, or you have a graduate-level background in one of the MCAT subjects, or you are a senior undergrad who scored well on the MCAT, and you would like to help answer questions for one of the regular Q & A threads, please PM Shrike or me and let us know. Again, all undergrad students who are currently studying for any of these tests should NOT post answers to other students' questions in any of the regular Q & A threads. Thanks to everyone for your cooperation.

Yes. http://forums.studentdoctor.net/showpost.php?p=2711972&postcount=6


I get get through to that link :(

I get get through to that link :(

Hmm, not sure why; it works fine for me. :confused: Ok, I re-posted it in the gen chem topics with explanations thread anyway; it's the fifth post there in case this link won't work for you either: http://forums.studentdoctor.net/showpost.php?p=2773903&postcount=5

Hmm, not sure why; it works fine for me. :confused: Ok, I re-posted it in the gen chem topics with explanations thread anyway; it's the fifth post there in case this link won't work for you either: http://forums.studentdoctor.net/showpost.php?p=2773903&postcount=5


got it thank you!!!! :D

Does anyone have a quick trick to know which acids are strong and which are weak? Same for bases??

Nothing to do with your question, but I just wanted to say that I PM'd you something that I thought you may be able to use to prepare for the MCAT. Let me know if you got it.

Nothing to do with your question, but I just wanted to say that I PM'd you something that I thought you may be able to use to prepare for the MCAT. Let me know if you got it.


I just messaged you back, thank you so much! And to think, I left SDN for 5 minutes.... tsk tsk, now I know never to leave my computer! :rolleyes:

Thanks alot though Guju!!! :)

what is the best way to remember how to determine if a reaction is SN1, SN2, E1, or E2? Here's what I have from class, but where do E1 rxns fit? How do you distinguish between SN1 and E1?


Alkyl halide 1 2 3
Nucleophile

Strong SN2 E2 (mostly) E2
SN2

Weak No rxn SN1 SN1


Thanx for the help!

what is the best way to remember how to determine if a reaction is SN1, SN2, E1, or E2? Here's what I have from class, but where do E1 rxns fit? How do you distinguish between SN1 and E1?


Alkyl halide 1 2 3
Nucleophile

Strong SN2 E2 (mostly) E2
SN2

Weak No rxn SN1 SN1


Thanx for the help!
I had absolutely no idea what to make of your notes until I hit the quote button. Unfortunately, the SDN server will get rid of extra spaces, and the table formatting gets lost entirely. Anyone else trying to read this, hit the "quote" button and take a gander.

As for E1 versus Sn1: the Sn1 needs a nucleophile because you need to have an adding group that is more stable than the leaving group. By contrast, the E1 reaction requires a weak base because you need to deprotonate the carbocation to get the alkene (if the base is strong, you should expect E2, not E1).

I found this to be a pretty good chart for distinguishing.
http://ludwig.chem.selu.edu/sarah/CHEM266/SN1vsSN2vsE1vsE2.html

alright im getting overwhelmed with all these reactions some of which we didnt even talk about! Should i just memorize that this reagent does this and this does this? Like PCC ive never even heard of. Will the mcat tell you what the reagent does?

So what exactly is the secret -- if it is really a secret -- to doing well at OChem? I'm taking GenChem now, but as I walk the chemistry halls at my school, I can't help but notice the grade postings for OChem courses. A lot of Cs and Ds, a few Bs, and fewer As still.

Any advice on how to both understand OChem and go about studying the material?

So what exactly is the secret -- if it is really a secret -- to doing well at OChem? I'm taking GenChem now, but as I walk the chemistry halls at my school, I can't help but notice the grade postings for OChem courses. A lot of Cs and Ds, a few Bs, and fewer As still.

Any advice on how to both understand OChem and go about studying the material?

Dont just memorize rxns. Understand why X and Y are occuring. Also, pay attention to general trends in rxs b/c they always appear.

And start studying for your first exam during your first week of class. What i mean by this is to review a little EVERY NIGHT and then when test time comes you will have reviewed everything at least once. Then you can just do lots and lots of practice problems.

hope this helps

Hey daofu -
My forte is definitely not chem... I haven't actually found my forte... Anyway, I'm still on chapter one in the chemistry, but I pulled this off the EK site for you:

"By the same reasoning as for question 47, Kp for this reaction is the partial pressure of CO2 at equilibrium. Thus if the partial pressure of CO2 is greater than Kp the reaction will try to shift to the left...but there is no CaO in the container! So it can't shift left and equilibrium can't be reached. If the partial pressure of CO2 were less than Kp, the reaction would try to shift to the right--and succeed, because the beaker of calcium carbonate is still there. CaO would be formed in this reaction."

:sleep:
Oh, sorry, I'm awake! I'm awake! That chapter is next week.

Caboose.

O.k., now my question:

Conjugated proteins = nonproteinaceous component havin' globs

Are cytochromes just examples of these class of proteins or are there other globs that require prosthetic shtuff too?

Just wondering.


Caboose

Sorry didnt read your question before i replied.

hi everybody, i'm new to the forums,i'm medical student,alex university,egypt and i guess i'll get lots of benifit from u guys ;) :) :rolleyes:

Maybe someone can help me clarify this. Regarding the force of an electric field and a magnetic field. I had this straight a few weeks ago but I seemed to forget it again.

When a negative charge is traveling perpendicular to an electric field it feels a force in the opposite direction then the electric field force vector is pointing. However If it is a postive charge then it feels a force in the same direction. Is that correct? How about magnetic field. If a postive charge goes through a magnetic field does it feel a force in the same directions as the magnetic field force vector is pointing, and would it be oppostive if it was a negative charge?

hi everybody, i'm new to the forums,i'm medical student,alex university,egypt and i guess i'll get lots of benifit from u guys ;) :) :rolleyes:

Welcome to the forum, asmaa, and feel free to ask questions if you have any. :)

Hello, anybody out there who just took Kaplan 11R full length? Can anybody please convince me what the correct answer is to question 12 (in Physical Sciences Passage 2)? I think it's "A" and not "D". ("A" says 1.32 volts, which is what I got by adding the OXIDATION potential for copper, -.34V, with the REDUCTION potential for aluminum, 1.66V. On the other hand "D" is what we get when we add the REDUCTION pot for copper, .34V, with the REDUCTION pot for Aluminum, 1.66V). I think D is wrong and am confused at the discrepancy in Kaplan's answer key which says that "In this cell, Copper will be reduced and Aluminum will be oxidized, so reverse(??!!) the sign on
the Aluminum value from the table." In the table the only value given is the positive Al reduction value of 1.66V. I need help, anybody who has done this problem, can you help me? ThanKS!!! :)

Maybe someone can help me clarify this. Regarding the force of an electric field and a magnetic field. I had this straight a few weeks ago but I seemed to forget it again.

When a negative charge is traveling perpendicular to an electric field it feels a force in the opposite direction then the electric field force vector is pointing. However If it is a postive charge then it feels a force in the same direction. Is that correct? How about magnetic field. If a postive charge goes through a magnetic field does it feel a force in the same directions as the magnetic field force vector is pointing, and would it be oppostive if it was a negative charge?

Dear gotgame, Happily the equations are vector equations i.e. we can tell the direction of the force (+ =same direction; or - =opp. direction) by looking at the sign of the other side. Look at the equations, I've put vectors in bold.
First electric field. The equation is F = qE. You're correct, for pos. charges the force F is same direction as E and for neg. charges it is in the opp. or reverse direction, it points against the direction of the electric field.
Now for magnetic field. The equation here is F = qvBsinA. Here, F means the force felt by the charged particle, qv is the velocity vector of the particle, and B is the magnetic field vector of the magnetic field thru which the charged particle is traveling. The direction of the force is given by the Right Hand Rule, or RHR, which, if you have a right hand, is very easy. Extend your right hand forwards like you would in a handshake, but stiffen it so your fingers and thumb, joined, point straight ahead, and your palm faces to your left. Now raise up your thumb so it points vertically upwards. Now watch this. The RHR will give you the direction of the magnetic force felt by a charged particle in a magnetic field. Do it like this. Your fingers point in the direction of qv and your palm faces in the same direction as B, the magnetic field vector, and your thumb is showing you the direction of F, the force felt by the charged particle. Note that the three vectors are all perpendicular to each other. HOWEVER IF THE PARTICLE IS NEGATIVE the vector qv will point in the reverse direction. Make your hand flip towards yourself and make your palm face to the left again BECAUSE THE DIRECTION OF THE MAGNETIC FIELD HAS NOT CHANGED. Your thumb should now point DOWNWARDS and this means that the direction of the force on the negative particle is opposite to the direction of the force on the positive particle, if everything else stays the same. Hope this helps, Omar :)

Thanks a lot Omar! That really helps.

My compliments on the forum, very nice site. Does this forum have latex?

Hello, anybody out there who just took Kaplan 11R full length? Can anybody please convince me what the correct answer is to question 12 (in Physical Sciences Passage 2)? I think it's "A" and not "D". ("A" says 1.32 volts, which is what I got by adding the OXIDATION potential for copper, -.34V, with the REDUCTION potential for aluminum, 1.66V. On the other hand "D" is what we get when we add the REDUCTION pot for copper, .34V, with the REDUCTION pot for Aluminum, 1.66V). I think D is wrong and am confused at the discrepancy in Kaplan's answer key which says that "In this cell, Copper will be reduced and Aluminum will be oxidized, so reverse(??!!) the sign on
the Aluminum value from the table." In the table the only value given is the positive Al reduction value of 1.66V. I need help, anybody who has done this problem, can you help me? ThanKS!!! :)


http://forums.studentdoctor.net/showthread.php?p=2837931#post2837931

A passage about an X-ray device states that electrons are accelerated from the cathode to the anode by an electric field. One question after the passage asks : What is the direction of the electric field that accelerates the electrons? The answer is FROM THE ANODE TO THE CATHODE. Can anyone explain? Is there an error?

A passage about an X-ray device states that electrons are accelerated from the cathode to the anode by an electric field. One question after the passage asks : What is the direction of the electric field that accelerates the electrons? The answer is FROM THE ANODE TO THE CATHODE. Can anyone explain? Is there an error?


For the MCAT, know that the direction of an electric field goes from positive to negative.

In the example above, electrons are accelerated from the cathode to the anode. Since electrons are negatively charged and are in this case accelerated towards the anode by an electric field, the anode should be positively charged.

Therefore, if the anode is positively charged, the electric field goes from anode to cathode.

to determine if a molecule is aromatic it has to satisfy Huckels Rule of 4n+1

How do you determine n?

n is any positive integer. Also, isn't it 4n+2?

So, benzene qualifies as an aromatic compound because it has 6 pi electrons. For n=1, 4n+2 = 6

n is any positive integer. Also, isn't it 4n+2?

So, benzene qualifies as an aromatic compound because it has 6 pi electrons. For n=1, 4n+2 = 6


Sorry. Yes 4n+2. Up until now I have been counting the c=c and multiplying by 2 and then adding any extra electrons. I am not sure if I am doing this correctly. Please explain it to me.

Sorry. Yes 4n+2. Up until now I have been counting the c=c and multiplying by 2 and then adding any extra electrons. I am not sure if I am doing this correctly. Please explain it to me.

I believe n is the number of carbons with a pi orbital in a conjugated system. So if it looked like this: c-c=c-c=c-c that would be 6 carbons and 6 n.

Sorry if this is wrong info!

I believe n is the number of carbons with a pi orbital in a conjugated system. So if it looked like this: c-c=c-c=c-c that would be 6 carbons and 6 n.

Sorry if this is wrong info!
No, this is not correct. Please see my post above. Also, I am going to move these posts to the student group study thread. If you all would like to continue studying together, you should do it there.

No, this is not correct. Please see my post above. Also, I am going to move these posts to the student group study thread. If you all would like to continue studying together, you should do it there.

I stand corrected :) Thanks QofQuimica!

I stand corrected :) Thanks QofQuimica!
Your strategy will work in many cases, but you have to be careful because some rings have more or fewer atoms and are still aromatic. For example, furan, pyrrole, and cyclopentadiene anion are all n=1 aromatic compounds, but they only have five atoms in the ring. Likewise, cycloheptatriene cation is an n=1 aromatic with seven atoms in the ring. If you go by # of pi electrons, you won't go wrong.

P.S. Sorry but I can't draw the structures here, so if you don't know what these molecules I mentioned are, you'll have to look them up. :o

is this the right thread? Ok I have a question about testesterone. Since it inhibits FSH secretion, wouldnt it inhibit spermatogenesis? Like those body builders who took too much testesterone. But why does the TPR book and another book say it also facilitates spermatogenesis. Is there something I'm missing here?

Also the same goes for estrogen right, that it inhibits FSH, which inhibits ovary. Is that what happens in a birth control pill?

Just a bit confused.

2) The birth control pill is generally giving progesterone so that the endometrial layers that the ovum would normally implant into is sloughed off. The woman still ovulates and the ova can be fertilized, but it inhibits implantation.

1) As for testosterone...it does facilitate spermatogenesis. FSH and LH are produced in the Ant. Pituitary. It is mainly LH that stimulates testosterone production. However, the inhibition that you are reading about is probably the negative feedback the testosterone has on FSH. Increasing Testosterone will inhibit FSH production so that you get less LH production and an eventual reduction in testosterone.

I could be wrong on #2, but it sort of makes sense if you look at the back ass-wards way the body regulates itself.

QofQuimica,


What is the splitting pattern for the second most downfield carbon 1-chloro-2-methyl propane?

I am getting confused as to whether the three hydrogens on the end carbon and the 2-methyl are equivalent.

My answer was 6 because they seem equivalent, where is my thinking wrong?


Thank you,


'Rambler

Those 6 H atoms are equivalent, but they are only split by the one hydrogen on the adjacent Carbon atom, so they will produce a (doublet, 6H) resonance

To answer your original question, it actually doesn't matter whether they are equivalent or not. The second most downfield Hydrogen is the Hydrogen attached to the #2 Carbon atom. It will get split by 8 hydrogens on adjacent carbons, so it will produce a (9-tet (I don't know the official term), 1H) resonance.

I think where you might've been getting confused is:

1. What makes the resonances more downfield (in this molecule, it is the proximity to an electron-withdrawing substituent -- the Cl atom). The two protons on the #1 carbon will resonate most downfield, followed by the proton on the #2 carbon, followed by the 6 methyl protons.

2. Splitting vs. Height (Integration.) The height of the peak is proportional to the number of equivalent protons, while the splitting (in simple n+1 splitting) is the number of protons on ADJACENT carbon atoms + 1

Hope that clears things up....

Jota

Didn't see this thread at first but I have an easy question.

http://i38.photobucket.com/albums/e130/zxw493/ratedeterminingstep.jpg

Which step (1 or 2) is the rate determining step? Thanks.

Didn't see this thread at first but I have an easy question.

http://i38.photobucket.com/albums/e130/zxw493/ratedeterminingstep.jpg

Which step (1 or 2) is the rate determining step? Thanks.

2

Even though the energy of activation is greater for the first step than it is for the second?

.

No, of course you are right -- I'm not sure what I was thinking.
Trust, this why I asked I asked this question it was marked wrong on a test, I choose the first step.

this is response from the Professor:
Think about the intermediate, it could go to the left over a small hump or to the rate over large hump.

This is the Professor and it was only worth 2 points out of 110, so I just dropped it. But doesn't this response completely ignore the energy of activation of the first step?

Trust, this why I asked I asked this question it was marked wrong on a test, I choose the first step.

this is response from the Professor:
Think about the intermediate, it could go to the left over a small hump or to the rate over large hump.

This is the Professor and it was only worth 2 points out of 110, so I just dropped it. But doesn't this response completely ignore the energy of activation of the first step?

I knew, I was right the first time. The second part of the reaction has the highest energy transition state, therefore, for a given energy input, fewer molecules will be able to reach that transition state than for the first part of the reaction. That's why it is the rate-limiting step.

The activation energy for the second part of the reaction is the activation energy for the first + the activation energy for the second part, so the activation energy for the second part is not lower than that for the first part.

Make Sense?

Jota

I got another one. Why are my diabetic friends overweight? I keep thinking of all the diabetics I know and they've all been a little overweight. They have decreased insulin activity, (through whatever mechanism), which means the cells aren't able to take in all that glucose and store it. They kind of look like they are storing it though. I feel so rude. Anyway, is this because of something else gone astray?

Caboose.

I got another one. Why are my diabetic friends overweight? I keep thinking of all the diabetics I know and they've all been a little overweight. They have decreased insulin activity, (through whatever mechanism), which means the cells aren't able to take in all that glucose and store it. They kind of look like they are storing it though. I feel so rude. Anyway, is this because of something else gone astray?

Caboose.

Type II Diabetes is due to unresponsivity to insulin. That is why Type II diabetic will have higher blood sugars. They still make insulin, but there is some inability to make more when they need it so some do need daily insulin injections.

Now to the overweight question...Insulin is the major anabolic hormone of the body...meaning that it synthesizes substances instead of breaking them down (catabolism). Insulin increases the glycogenesis and increased deposition of adipose tissue.

So...insulin is ineffective at upregulating the glucose transporters that allow the glucose to be taken into the cells (resulting in high blood sugars). Increases anabolic activities that increase the deposit of fat through a different mechanism.

Type I, if you are interested, is inability to produce insulin due to pancreatic beta-cell activity.

--Hope I didn't miss anything, I am just writing from memory.

What is the source of the bouyant force? Is it electromagnetic in origin?

Also, does it do work when moving an object "up" just as gravity does in pulling it "down"?

Yes and Yes.

k you're not understanding what chirality means? have you taken the class or have you read a book? chiral means (hand) mirror image... meaning if you looked in a mirror with your right hand and pressed it against the mirror it wouldn't be your left hand in the mirror it would be your mirror image of your right hand... this also means nonsuperimposible mirror image...

making sense yet? achiral means no mirror image i.e. meso or diasteromer... which is two chiral centers of different attachments on each chiral carbon...

i have a last minute question about op/meta directors. i know most things are op, and i need to just remember which are meta (for some reason, this is the hardest thing EVER for me!)

is it safe to say carbonyl's are meta directors, or is there an exception to that? any help is appreciated.

sasha

ok, please go to your organic book... because this is something basic, but alas your book might not make it so basic... I will try to help...

ACTIVATING/DONATING are groups like NH2, OH,<<strong>> CH3 WEAK o,p directors and halides are weak deacivators/ELECTRON WITHDRAWING... o,p directors...

now, your carbonyls cooh and NO2 CF3, etc are strong electron withdrawing M directors... get it... but, REMEMBER

the trick is this... whenever there is an OP DIRECTOR meaning ACTIVATING/DONATING GROUP including halides... they are the winners when there are two groups... Roles like Steric Hinderance will play a factor on which O OR P is directed too...

hope that helped...