## Chem/Phys Questions

jeffbassett87
Posts: 13
Joined: Mon Jan 13, 2020 7:38 pm

### Chem/Phys Questions

I'm posting this here because nobody is responding in the AAMC section.

I have questions from the AAMC full length #4 all from the chem/phys section.

#7-I made an educated guess and got it correct going off the "1/30" part in the passage, but I don't understand the AAMC explanation at all and the math.

#35-I had no idea what all the answer terms meant, but I also have no idea how to interpret Figure 1.

#38-I knew how to apply the formula, but I struggled with the actual math without a calculator. What is the trick to doing this?
NS_Tutor_Nancy
Posts: 17
Joined: Wed May 27, 2020 7:25 pm

### Re: Chem/Phys Questions

Hello!

I'm sorry if your post in the AAMC section somehow got missed, as for your questions:

Q7: You can tell from the other values in table 1 that absorbance and glucose concentration have a direct, linear relationship. So you can say the ratio of absorbances equals the corresponding ration of glucose concentrations: 0.20/0.24 = x/6 >>> x =(0.20/0.24) * 6 = 5. Then because the dilution from the blood is 1/30, multiply by 30 to get 150.
Q35: As far as what everything means, ping pong is another way to say double displacement, and it refers to a substrate binding mechanism where one or more products are released before all substrates bind the enzyme. Random order means either substrate could bind the enzyme first, whereas ordered means that a particular substrate needs to bind before the other. The figure shows the formation of the enzyme/substrate complex that occurs in a specific order with no product being released in the middle, making ordered the correct choice.
Q38: So the math is 0.7 / (1367x1) = 0.7/1367. Here it is time to do some strategic rounding. The MCAT is designed to not need a calculator, they know that you are rounding, so usually the answer choices are far enough apart to allow for this. We'll round to 0.7/1400 = 7/14000 = 1/2000 = 0.5/1000 = 0.0005 M = 500uM. In general for fractions, try to get a denominator of 10, 100, 1000, etc.

I hope this helps!