Good morning! Hope anyone could help me out for these two questions! I am really struggling and couldn't understand AAMC explanation.
Q38. How do we keep tracking of 14C labeled during these reaction? Could you please explain in different ways? I always spend a lot of time at this kind of question because I am so weak at this.
Q46. Could you also explain what equation we have to know in order to solve this question? I am not still sure about why the correct answer is A.
Thank you so much!
AAMC Sample test C/P Q38, Q46

 Posts: 10
 Joined: Tue Mar 06, 2018 9:49 pm

 Posts: 271
 Joined: Fri May 25, 2018 9:15 am
Re: AAMC Sample test C/P Q38, Q46
Q38 is a little tough to explain in writing, but I'll try my best. We need to follow the 14C carbons on the acetylCoA molecules. Reaction 1 gives us the first two and they don't change after that reaction (positions 2 and 4). In the second reaction, acetylCoA attacks the carbonyl to the left of acetoacetylCoA. The steps of that reaction aren't too important, but we end up with another 14C next to the old carbonyl (position 5). The decarboxylation is the final step, but it doesn't involved the 14C labeled positions.
For Q51, you need to understand Archimedes' principle. The AAMC summarizes it this way:
For fluids, I find it helpful to watch videos explaining the concepts because, at least for me, they are often counter intuitive and difficult to visualize. I'd suggest watching some of those and following along conceptually rather than focusing on just the equations which are often pretty confusing!
For Q51, you need to understand Archimedes' principle. The AAMC summarizes it this way:
So, the equation: ρobj / ρfluid = weight(obj) / (weight(obj)  weight(sub))The ratio of the density of an object to the density of the fluid it is submersed in is equal to the ratio of the weight of the object in air to the difference of submersed weight and weight in air
For fluids, I find it helpful to watch videos explaining the concepts because, at least for me, they are often counter intuitive and difficult to visualize. I'd suggest watching some of those and following along conceptually rather than focusing on just the equations which are often pretty confusing!
Re: AAMC Sample test C/P Q38, Q46
Regarding the quote you posted (the AAMC explanation to the question) how do we arrive at that equation? I've tried deriving it and have been having no luck and I can't find that anywhere online!

 Posts: 271
 Joined: Fri May 25, 2018 9:15 am
Re: AAMC Sample test C/P Q38, Q46
I'll try to derive it here from a few other fluids formulas, but the notation is a little tricky with the forum formatting!
Start with two equations:
Wwater = Wair  Fbuoyant (weight in water equals weight in air minus the buoyant force)
Wair = Fg = mg (weight in air equals the force of gravity equals mass times gravitational acceleration)
Then work with the first equation to get:
Wair  Wwater = Fbuoyant
WairWwater = density(water) * Vol(submerged) * g
Then we can use that derivation along with the second equation from above:
Wair=mg
WairWwater = density(water) * Vol(human) * g
(Wair)/(WairWwater) = (mg)/(density(water) * Vol(human) * g)
...which simplifies to...
(Wair)/(WairWwater) = mass(human) / Vol(human)
Note that we can cancel the density of water because it is taken to be one (1 g/cm^3).
That final equation states that Density(human) = Wair / WairWwater
I hope this helps!
Start with two equations:
Wwater = Wair  Fbuoyant (weight in water equals weight in air minus the buoyant force)
Wair = Fg = mg (weight in air equals the force of gravity equals mass times gravitational acceleration)
Then work with the first equation to get:
Wair  Wwater = Fbuoyant
WairWwater = density(water) * Vol(submerged) * g
Then we can use that derivation along with the second equation from above:
Wair=mg
WairWwater = density(water) * Vol(human) * g
(Wair)/(WairWwater) = (mg)/(density(water) * Vol(human) * g)
...which simplifies to...
(Wair)/(WairWwater) = mass(human) / Vol(human)
Note that we can cancel the density of water because it is taken to be one (1 g/cm^3).
That final equation states that Density(human) = Wair / WairWwater
I hope this helps!