BerkReviewTeach thank you for the input, my major problem is not catching which concept the question is asking about, missing where the conceptual ties are, and how certain parts of the experiment is needed to fulfill the experiment.
My fundamental understanding is weak despite the fact that i have devoted most of my prep time to this section and it's hard to improve with practice questions since there are plethora of ways to apply the fundamentals.
Is there something that I could do the last 2 weeks to improve at least a little?
The key thing here is that you recognize what is going awry on your exams, which it sounds like you know well. The conclusion most people reach is that they don't know their content well enough, and this no doubt stems from their experiences in college. A good grade directly resulted from a bigger volume of memorized information, so their line of reasoning is that a lower MCAT score must mean they don't know the material well enough. After many years of doing this, I can tell you for sure that knowledge base is hardly ever the reason for someone's low scores.
In your case, I would highly recommend you sit down and slowly take a PS section (untimed) where you make a thought flowchart for every question. In essence you will be writing a highly detailed, systematic answer explanation for 59 questions. Starting slow and building good habits is the goal here. Over time, you get a little faster and a little faster and it becomes second nature. For example, here is a question from one of the practice tests in our g chem book.
Qu) Based on the arrangement of the electrochemical cell in Figure 1, what can be concluded about the migration of lysine and aspartic acid at pH = 7 through the gel?
A) Lysine will migrate to the right; aspartic acid will migrate to the left.
B) Lysine will migrate to the left; aspartic acid will migrate to the right.
C) Both lysine and aspartic acid will migrate to the right.
D) Both lysine and aspartic acid will migrate to the left.
Your first thought is your most important thought. This thought needs to be based on the answer choices and not the passage or the question itself. The answer choices involve two amino acids and their respective directions, so your first thought (question) needs to be "
how do these two amino acids relate?" Lysine is a basic amino acid and aspartic acid is an acidic amino acid.
They are different (opposites) in terms of charges at a given pH. Without any detailed reasoning, you need to consider that opposite charges will have opposite behaviors, so they will migrate in opposite directions. Choices C and D are systematically eliminated with little time invested.
Now comes the detailed part. You need to know which way anionic amino acids and cationic amino acids migrate in electric fields (such as the one in which the gel resides). This is memorization based. I assume you haven't used our books, so the BR mnemonic is likely unfamiliar. What you need to remember is that
anions migrate towards the anode and cations migrate towards the cathode. Keep it simple.
The next step is to determine which plate of the electric field surrounding the gel is the anode and which is the cathode. To do this, you need to ask "
what are they connected to?" The plate on the left is connected to the half-cell containing the zinc oxidation half-reaction while the plate on the right is connected to the copper reduction half-reaction. This is where another mnemonic would be helpful (and there are plenty). Oxidation occurs at the anode and reduction occurs at the cathode (oxan and redcat), so the
left plate is connected to the anode (making it a cathode) and the right plate is connected to the cathode (making it an anode.)
Now it's a matter of combining our two mnemonic driven thoughts. Cations migrate to the cathode, and lysine is our cation, so lysine must be migrating to the left (the cathode, which is connected to the zinc anode). We have done all we needed to do in order to systematically narrow down to choice B.
This didn't require detailed reasoning; it required keeping it simple. This is generally considered a tough question by many people, and I think this has to do with being overwhelmed by (1) the lack of familiarity with the combining of a redox cell and gel electrophoresis and (2) multiple disciplines being tested in the same question. If you stay calm and systematic, then you will do well on this passage. That is the biggest thing you can do to improve. DO NOT go back and try to read and absorb more information. You need to organize the information you already have.
You asked what you can do over the last two weeks, and I have a suggestion, but do not want to sound like I'm promoting. The BR books have a unique and systematic way of answering questions. I think doing the above process for roughly 20 questions in each of the sections in the BR books for this part of the exam and then reading the answer explanations to see if your reasoning was similar will do wonders for your score. You should also keep a running list of mnemonics and shortcuts you pick up from the books. They really save a huge amount of time.
Good luck.
(lol this thing is so cute. I always wanted to use it if i post lol!)
