MP 28 : We Break Down Biology Discrete Questions for the MCAT

Session 28

This week Bryan and I are breaking down discrete questions from the MCAT. These questions are taken directly from Next Step MCAT Full-length Exams

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Transcript

Introduction

Dr. Ryan Gray: The MCAT Podcast is part of the Med Ed Media network at www.MedEdMedia.com.

The MCAT Podcast, session number 28.

A collaboration between the Medical School Headquarters and Next Step Test Prep, The MCAT Podcast is here to make sure you have the information you need to succeed on your MCAT test day. We all know that the MCAT is one of the biggest hurdles as a premed, and this podcast will give you the motivation and information you need to know to help get you the score you deserve so you can one day call yourself a physician.

Welcome to The MCAT Podcast, we are part of the Med Ed Media network. We have several podcasts for you, the premed student. Go check out everything we do over at www.MedEdMedia.com. This week we're going to jump right into another exciting episode of The MCAT Podcast.

Alright Bryan, we're back with more MCAT questions. Are you excited?

Question #1

Bryan Schnedeker: I am very excited, and what I want to start us off with for today's podcast is a bunch of bio discrete questions. Of course everybody knows that there's biology- number one with the bullet in terms of the content, you have to know it. The discrete questions are really going to test the application and recall of that information. And so Ryan, after all the challenging stuff we looked at in the past few podcasts, I decided to change it up a little. And what we're going to look at- and of course the listeners can download the handout, is actually some more straightforward questions, meaning these are questions that in our test system generally 80% or even more than 80% of students are getting right. So I'm not going to call them easy because of course they're only easy if you know the answer, but the point of us doing some more straightforward questions together is just to illustrate that in the competitive world of MCAT prep, you can't leave any of these points on the table. If you get a question that seems fairly straightforward from a fact, then you have to get it because everyone else is.

Dr. Ryan Gray: Yeah so these ones are just the fat slow pitch softball thrown right there for you to hit out of the park.

Bryan Schnedeker: Yeah or at least make contact. You've got to get on base with these questions. And Ryan, you want to lead us off with number 29 here?

Dr. Ryan Gray: Yeah so question 29. When normal human cells are grown in culture they will divide a limited number of times, typically fifty rounds of mitosis. After this number is reached, the cells become apoptotic. This cell death is a result of- and then we have decreasing number of membrane bound organelles per cell. Decreasing number of non-membrane bound organelles per cell. Decreasing levels of growth hormone. Chromosomal telomeres shortening after each round of division. Now Bryan, I want to try to answer this, and just from my limited knowledge going back to this, I have an understanding that it's the shortening telomeres that are causing issues with aging. So I'm going to go with D.

Bryan Schnedeker: And perfect, there you go. Exactly. So you and 83% of Next Step students got that one right. And this is just an important bio biochem genetic fact. That [Inaudible 00:03:28], that aging process in cells is due to telomere shortening, absolutely right.

Dr. Ryan Gray: Yeah and there's lots of interesting science behind trying to prevent that and lengthen our lives.

Bryan Schnedeker: Yeah absolutely. And of course the question is, ‘Well why can't you just make them longer?' And of course uncontrolled chromosomal alteration in lengthening and addition is what we know is cancer, right? So you can't just go in there and muck about with no problem.

Dr. Ryan Gray: Yeah.

Question #2

Bryan Schnedeker: Okay I'll read number thirty for us. A student finishes an experiment involving several bacteria which are highly pathologic in humans. She wishes to dispose of the agar plates and [Inaudible 00:04:06] she used. Which of the following procedures should she carry out? A, microwave all materials for more than sixty seconds. B, wipe down all materials with a 100% ethanol solution. C, place all materials in a biohazard bag and autoclave the bag. And D, place all materials under a UV light for ninety seconds. So Ryan, what do you think?

Dr. Ryan Gray: Interesting. She wants to dispose of them- oh man. I would- I don't know. I don't know, I'm not going to embarrass myself if I don't know it.

Bryan Schnedeker: Okay, no fair enough. So this is one of the classic just lab procedure questions, right? You have to know kind of the mechanics of life in the lab, and this is one of the hallmarks of the new version, the post-2015 version of the MCAT as opposed to the old version which was more textbook. So there's a lot of these questions where it's just, ‘Have you spent time in the lab recently? Do you know how that works?' And so in this case if you ever have biohazard that you have to dispose of, you absolutely autoclave it. I mean there's no second best choice, there's no alternative, every lab in the universe has an autoclave for a reason, and it's to dispose of biohazard like this. And so the right answer would be C, place all of the materials in a biohazard bag and autoclave the bag.

Dr. Ryan Gray: That's what I would have gone with if I wanted to guess.

Bryan Schnedeker: Yeah there you go. You want to give us number 45 there?

Dr. Ryan Gray: Sure it says, ‘In a population of Amish people the frequency of the recessive autosomal allele for polydactyly is 1.2%. What percent of the population are carriers for this gene? Oh you're going to make me do this one, too?

Bryan Schnedeker: No this is actually the hardest one of the set we're going to look at. Only about 70%- a little less than 70% of students got this one right. And so this one is what we call a Hardy Weinberg Equilibrium, there's a bunch of different percentages as an answer, and we're told that the recessive allele has a frequency of 1.2%. And since all of the recessive and all the dominant alleles in the universe have to add up to 100%, that means the frequency of the dominant allele is 98.8%. Right so you've got the 98.8% dominant plus 1.2% recessive, given you 100% of all the people. The extra bit is just remembering what the mathematical term is for the carriers in the Hardy Weinberg Equilibrium. So the equation- the listeners may remember is usually expressed as P squared plus 2PQ plus Q squared equals one, or 100%. And so in that, to be a carrier means to be a heterozygote, to have both of the genes, so that is that term in the middle of the equation usually written as 2PQ, where two is just the number two, P is the percentage of dominant, and Q is the percentage of recessive. So in this case, the dominant was 98.8% or 0.988. The recessive was 1.2% or 0.012. And thing about these calculations for the MCAT is you don't have to go into super detail. You can kind of round things off. So 2PQ is two times 0.988 times 0.012, and that 0.988 in the middle, we'll just round that up to one. So the equation because two times one times 1% roughly. In other words 2%, right? Two times one times one. So you can ignore all the little decimals, all the little fiddly bits, and just say, ‘Well it's going to be about 2% of carriers.' And when you look at the answer choices the answer choices are really spread out. Choice A is .01%. Choice B is 1%. Choice B is 2%. Choice D is 97%. And again there are some decimals there but we're going to ignore them because answer choice C is the only one that's anywhere close, that's a little over 2%.

Dr. Ryan Gray: At what point for these types of equations do you get in trouble by rounding like that?

Bryan Schnedeker: It depends entirely on how spread out the answer choices are. So you'll see some physics problems for example where the answer choices are literally thousands of times bigger and smaller than each other. Blah, blah, blah times ten to the ten. Blah, blah, blah times ten to the fifteen. You're like, “Oh wow that's 10,000 times different from each other.' So in that case you can afford to round off ruthlessly. Here where the answers were 0.01, 1, 2, and 98; even the two answer choices that were closest together, 1 and 2, is a 100% difference, right? Double one answer choice to the next. So you can round off pretty aggressively.

Dr. Ryan Gray: Okay. Alright, last one?

Question #3

Bryan Schnedeker: Alright last one, 46. Ryan why don't you take a crack at that one?

Dr. Ryan Gray: Alrighty. I think people listening to this are going to be like, ‘Wow Dr. Gray doesn't know anything,' but that's okay. I'm here for you. It says, ‘Those species that are capable of both sexual and asexual reproduction will typically prefer sexual reproduction because it A, increases the likelihood of each individual offspring surviving. B, increases the likelihood of beneficial mutations. C, creates more variation in the next generation. Or D, takes less time to complete.

Bryan Schnedeker: What do you think? What would you go with there?

Dr. Ryan Gray: Let's see, let me read the question again, ‘Capable of both sexual and asexual reproduction.' I want to know what species those are.

Bryan Schnedeker: It's like bugs mostly.

Dr. Ryan Gray: Slugs or something I think. ‘Typically prefer sexual reproduction because it-‘ I would say C.

Bryan Schnedeker: There you go, more variety in the next generation.

Dr. Ryan Gray: More variety in the next generation.

Bryan Schnedeker: Absolutely. And the trap answer here, the one that gets maybe 10% or 15% of students to pick it is choice A, that it increases the likelihood of each individual offspring surviving. But of course we know evolution doesn't work on that level, right? It cares about whole populations, whole cohorts of individuals and the likelihood of survival, not one the individual necessarily surviving. And so when we think about the genetics that's on the MCAT, it's not really any college-y question, it's not even so much an evolution question as it is just understanding the mechanics of that genetic re-shuffling that happens during sexual reproduction, and why we go to so much effort, right? I mean peacocks growing those enormous tails, and bowerbirds building those huge nests, and these enormous metabolic costs that animals put into the entire dance of sexual reproduction, and what's the point? The point is so that the next generation of animals has more variety, is more adaptable to changing environmental conditions. And in fact that variety is so critically important that sexual reproduction strategies, as we know just from looking at nature, are vastly more successful.

Dr. Ryan Gray: Yeah, alright. We've gone from MCAT to talking about sexual reproduction.

Bryan Schnedeker: There you go. Always a good note to end a podcast on.

Dr. Ryan Gray: Another great discussion, thanks Bryan.

Bryan Schnedeker: Sure thing.

Final Thoughts

Dr. Ryan Gray: Alright there you go. Again you can find out everything that we talked about, the questions and everything, you can get on the show notes page at www.TheMCATPodcast.com. Each episode has its own page, go find this episode and download the actual questions from that page.

I want to take a second and thank a few people that have left us ratings and reviews in iTunes. If you would like to do that, go into iTunes, search for ‘The MCAT Podcast,' and click ratings and reviews, and then write a review.

We have one here from LanyeBush that says, ‘A must. I'm so excited about this podcast with the amazing Ryan Gray at the helm.' Okay. ‘I'm sure The MCAT Podcast will be just as helpful as The Premed Years. If you're not taking the MCAT you should be- if you are taking the MCAT you should be waiting with bated breath for every episode.' Thanks Lanye for that.

We have one here from Sarxws that says, ‘Gonna be amazing!' So I guess these people- these are older reviews that left- I haven't read any yet. These were left before I actually launched The MCAT Podcast so people that were listening before. Thank you for that.

We have one here from zick8072 that says, ‘Full of great info. I always imagine Dr. Gray's podcast to be like a personal weekly phone call from a very knowledgeable mentor.' Thank you for that review, that's awesome.

And we have one here from Burhan22 that says, ‘I appreciate the hard work that Dr. Ryan Gray and his fellow partners have put on this podcast.' So yes, thank you Bryan and Next Step Test Prep for doing this podcast with me. I couldn't do it literally without you.

Alright if you would like to leave a rating and review, again go into iTunes, search for The MCAT Podcast and click on ‘Write a Review.'

I appreciate you, I hope you have a great week, and I hope you join us next week here at The MCAT Podcast.

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