FL 7 Questions

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z3lan
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FL 7 Questions

Post by z3lan » Wed May 15, 2019 12:51 am

CP 39. How do we know that Ca(OH)2 reacts with CO2 to produce a white precipitate (or that water could react with silica gel for that matter as the answer key suggests?)
CP 46. Isn't 0.04 J the work done by the strong wind? I'm having difficulty wrapping my head around how gravity does work in this situation, since the force it exerts is going in the opposite direction of the direction of motion. If the work done by gravity is 0.04 J, then what is the work done by the wind?
CP 51: I thought that anion stability is achieved by delocalized pi electrons. What does "delocalized p orbitals" mean? Isn't it the electrons that are delocalized, not the orbitals, which would stay affiliated with their respective atoms? Or are delocalized p orbitals and delocalized pi electrons used as synonyms? What exactly is going on?

CARS 6: Isn't choice A supported by the following: "the Islamic Revolution in Iran was accompanied by violence against all those accused of being connected with the former Shah's regime, thus marking the beginning of a major exodus of Iranian exiles?" Who were these exiles if not the people in the first half of the sentence connected with the Shah's regime?
CARS 10: "Today we British have, in our turn, become the invaders, albeit full of peace and good-will; "
^Isn't the bolded part sarcastic? Also for answer choice C, how do we know that the smoky steamers are representative of all modern vessels? Isn't suggesting he believes the beauty is absent in modern vessels extreme?
NS_Tutor_Will
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Re: FL 7 Questions

Post by NS_Tutor_Will » Wed May 15, 2019 8:30 am

Thanks for the questions!

Q39: For this one, you just have to know about the possible reactions that could occur and then choose whichever seems most likely. Don't shy away from using context clues ("hmm... I see that option A and B are multiples of 100, I wonder if there's a species that has a molar weight of 100 g... Oh, CaCO3!). One clue is also in the "white precipitate" which, perhaps, is chalk: CaCO3! But there's no real passage info or anything, it's one of those either figure out the precipitate's identity or not type questions.

Q46: So the work done by gravity could technically be -0.04 J or 0.04 J depending on how you set you're positive and negative directions. Work is force x distance or you can think of it as a change in energy (i.e. lifting an object gives it potential energy). Seeing it as negative work will probably clear up your confusion, it's just that we set the negative direction as positive in this case. In this scheme, the work done by the wind is -0.04 J.

Q51: Yes, it's more standard to see it as delocalized pi electrons in p-orbitals that are overlapping. I'll let the content team know that we may want to clarify this.

Q6: Yes, A is clearly stated in the passage but there is no evidence or example given to defend that claim. If there were specific examples or data given to back up that claim, then A would have specific examples/evidence, but as currently formulated, it's just stated and then not defended.

Q10: I don't think it's sarcastic, though I can see why you might think so given Britain's long history of colonial subjugation. I think the author is drawing a distinction between the wars that were fought over Norway long ago and the British desire for trade and industry. I think the "extreme" heuristic is more useful when there is extreme language in the answer choice (i.e. if the answer stated "the author despises modern ships because they are ugly" that would be a bit strong). Given that the author says the ships that are on the oceans now are "ugly, smoky steamers" I think it's fair to say that the author would agree that modern ships aren't as beautiful as the Viking ships.

I hope this is helpful!
z3lan
Posts: 101
Joined: Thu Feb 28, 2019 5:24 pm

Re: FL 7 Questions

Post by z3lan » Wed May 15, 2019 2:17 pm

Yep, that's helpful! I'm still confused about the leaf though. If gravity is doing -0.04 J of work, and the wind is doing 0.04 J of work, then how is the leaf moving?
z3lan
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Joined: Thu Feb 28, 2019 5:24 pm

Re: FL 7 Questions

Post by z3lan » Wed May 15, 2019 5:00 pm

I have a few more questions.

Bio/Biochem

#20: Don't cancer cells tend to like glycolysis as a source of energy as opposed to oxidative phosphorylation due to the danger of messing with cytochrome c, a mediator of apoptosis? Therefore wouldn't we expect oncogenic proteins to inhibit the ETC?
#37: What do the asterisks mean on Figure 1? I had interpreted them as meaning the control was significantly different from the mild and deep at 1 hour and 2 hours, but that the mild and deep were statistically not differentiable in either setting.
#42: Which table or figure suggests that the CAC is effected and how? Also, what do the plaques mean in Table 1?
#44: Are there any cells in the bloodstream that would be harmed besides RBCs? Couldn't the other cells switch to using fats and ketones and make it out ok?

Psych/Sociology

#3: The wikipedia article for feature detection features multiple examples from the auditory systems of different animals, and the answer key mentions that feature detection is "mainly" a visual skill. For the MCAT are there any important examples I should know of feature detection outside the visual system, or is it fair to assume that feature detection = visual system?
#13: I had trouble deciding between A and C. Couldn't you also argue that someone who is disabled is obliged to play the sick role and is therefore not being deviant by deciding to remain unemployed?
#50: I had assumed that serotonin could cross the BBB because it's so structurally similar to tryptophan. Is it safe to assume for the MCAT that amino acids have their own transporters in the BBB and that as a result, even stuff that highly resembles them can't get in?
z3lan
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Joined: Thu Feb 28, 2019 5:24 pm

Re: FL 7 Questions

Post by z3lan » Wed May 15, 2019 7:22 pm

This is a tangential question to Chem/Phys #2. I know the typical way you find pIs is to average the bottom two or top two pKas, depending on whether you're an acidic or basic amino acid respectively. But what do you do about the more ambiguous ones like T, Y, S, M, and C? Do you just have to draw them and logic out what'll be charged at what pH, or is there a systematic way to deal with them?
NS_Tutor_Will
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Re: FL 7 Questions

Post by NS_Tutor_Will » Thu May 16, 2019 7:49 am

For the leaf, thinking about it as the leaf doing work against gravity probably makes the most sense in a common sense way. Remember, there's no net force necessary to keep an object moving or stationary, we only need a net force for changing the motion of the object. Lots more discussion if you're curious here: https://www.quora.com/Is-work-done-unde ... y-negative
NS_Tutor_Will
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Joined: Fri May 25, 2018 9:15 am

Re: FL 7 Questions

Post by NS_Tutor_Will » Thu May 16, 2019 8:10 am

Thanks for the questions!

Bio/Biochem
#20: Don't cancer cells tend to like glycolysis as a source of energy as opposed to oxidative phosphorylation due to the danger of messing with cytochrome c, a mediator of apoptosis? Therefore wouldn't we expect oncogenic proteins to inhibit the ETC?
Many cancer cells do rely on glycolysis for many reasons in addition to the one you mentioned (sometimes lack of oxygen in rapidly growing cells requires glycolysis). We want to choose the most straightforward answer, though. Since cancer is essentially uncontrolled cellular growth and division, A, C, and D are all obviously correct. ETC inhibition is a possibility but a cancer wouldn't "prefer" to get rid of the ETC if it had the ability to use that as a means to generate necessary energy.
#37: What do the asterisks mean on Figure 1? I had interpreted them as meaning the control was significantly different from the mild and deep at 1 hour and 2 hours, but that the mild and deep were statistically not differentiable in either setting.
Well we have error bars here, so we can distinguish between the mild and the deep in the 2 hour condition because these bars aren't overlapping. The asterisk refers to the differences in the control groups across different time periods.
#42: Which table or figure suggests that the CAC is effected and how? Also, what do the plaques mean in Table 1?


It's more that the passage tells us that the virus affects mitochondrial function, which is where the CAC takes place. The other options all include pathways that aren't as bound to the mitochondria in terms of location. Plaques refer to cells that have been destroyed by viruses (it's what's leftover).
#44: Are there any cells in the bloodstream that would be harmed besides RBCs? Couldn't the other cells switch to using fats and ketones and make it out ok?
It's likely that many cells would be damaged, whether or not the organism was able to survive. Lots of cells uptake glucose and would prefer to continue doing that if they were able! There may be some cells that could survive via other means, but ultimately this is not a targeted enough recipe. If we want to starve out the cancer cells, we want to choose a means that won't also starve out healthy cells (as much as possible).

Psych/Sociology
#3: The wikipedia article for feature detection features multiple examples from the auditory systems of different animals, and the answer key mentions that feature detection is "mainly" a visual skill. For the MCAT are there any important examples I should know of feature detection outside the visual system, or is it fair to assume that feature detection = visual system?


Yes, it's most commonly considered in the visual system, so I'd lean toward that as a good rule to follow. Again, though, this is one where B (from the passage), and C and D (from outside knowledge) are all fairly straightforward functions of the ear, so A is our safest bet.
#13: I had trouble deciding between A and C. Couldn't you also argue that someone who is disabled is obliged to play the sick role and is therefore not being deviant by deciding to remain unemployed?
I think the idea here is more about the individualistic society and the fact that this person wants to remain on disability and not provide for themselves thus violating the values that the individualistic society holds ("independence and self-reliance"). The sick role is almost like an "exemption" from social norms/values, so conforming wouldn't be quite right either -- it's more like "opting out" while sick.
#50: I had assumed that serotonin could cross the BBB because it's so structurally similar to tryptophan. Is it safe to assume for the MCAT that amino acids have their own transporters in the BBB and that as a result, even stuff that highly resembles them can't get in?
Here's text from an earlier post I made about serotonin that might be helpful:

"These can be tricky since it can feel like a judgment call, but no, the polar components of serotonin make it function as a polar molecule. Each time you get a question like this you can update your model of how you draw the line between polar and non-polar. With serotonin, we also know it's a neurotransmitter, which should point us toward the fact that it'd be secreted by a presynaptic neuron and then stimulate a receptor on the postsynaptic receptor. That it can't cross the membrane may come naturally out of its function of NT."

Also, I suppose there are amino acid transporters, but like it says in the explanation "details of amino acid transporters are beyond the direct scope of the MCAT," so don't worry too much about them!
I know the typical way you find pIs is to average the bottom two or top two pKas, depending on whether you're an acidic or basic amino acid respectively. But what do you do about the more ambiguous ones like T, Y, S, M, and C? Do you just have to draw them and logic out what'll be charged at what pH, or is there a systematic way to deal with them
These amino acids will typically still be neutrally charged according to the C-terminus and the N-terminus. If you image search some of them, you'll see which transition happens at what pH and that should help visualize it. Also, here's a table showing the pKa1, pKa2, pKa3 (where relevant), and pI of the amino acids: http://www.chem.ucalgary.ca/courses/351 ... 1-4-2.html

I hope this is helpful! Good luck!
z3lan
Posts: 101
Joined: Thu Feb 28, 2019 5:24 pm

Re: FL 7 Questions

Post by z3lan » Thu May 16, 2019 11:07 pm

Yep, that's helpful. Thank you!
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