# MCAT: the science parts

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.

#### MikeS 78

##### Senior Member
10+ Year Member
15+ Year Member

This is my follow up to the verbal section that I wrote over a year ago. I hope that its comprehensive enough, because I am rushed (angiogenesis isn't going to inhibit itself)

Physical
There are only two types of questions....and they are not physics and chem
Type 2- comparison questions

I will explain what these are in a bit however I will explain the rationale behind these types

Type 1- alot of times, doctors have to crunch out numbers (ie cardiac output, drug calc's etc) it is rather helpful if you aren't a slave to the calculator and have a decent grasp of numbers
Type 2- these encompass about 80-90% of all Mcat questions...there is a reason for this.......anyone who has even taken pathphysiology/physio...knows that pretty much all it is the study of how one variable is changed with the change of another (well that and how the body prevents this change) if you don't have a solid grasp changing variables in scientific models, then life will be tough

ok what are these questions and how do we tackle them

type 1- believe it or not these are far far in the minority, you really dont have to do many calculations to do well....the big this is estimate simplify estimate simplify....do not sit there calculating out to the 4th decimal, estimate crank out a number and check this probability

type 2- this is where you will make your money...now what do i mean by comparison

A comparison question, by definition, is any question that descibes a factor in the system changing...sometimes this occurs

they come in three flavors
1) the direct approach- in this one the question explicitly asks "If variable A is doubled what happens to variable B"
2) the variable approach-If the answer is in variables, then it is always, always, always a comparison.....always
3) The sneak attack- this is the primary claim that I make that few others make.....that a good portion of questions that do not fit the 1st two formats......alot of times these never state explicitly that any of the variables are even changing.....sometimes you have to pull that from the passage.....even worse is when they don't even tell you that the variables are related, or even that the things they are describing are variables

it is absolutely critical that you can differentiate type 1 from the third one the third type of comparison is about 45% of the phy sci....practice, and when you go back and look at the test.....determine if the question that has you stumped is in fact a comparison.....learn to spot these and you will prosper

here is the algorhythm....and note that I called it an algorhythm...meaning you should do this every single time

Step One- write next to the question the changing variable and the affected variable........you must write this out each time or it will become easy to get lost in the melee

the affected variable is usually the easier of the two to spot......is is usually the variable that they send you on the hunt for
the change is usually the tougher of the two.....sometimes you have to figure out from the passage that a variable even changes at all....however once you see that something in the system changes from the reference point (as decribed in the passage or if stated from the previous question) you write out exactly what they are asking

Step 2- ASSEMBLE AN EQUATION THAT DIRECTLY RELATES THESE TWO VARIABLES

This is the tough part there are four places to get this equation from
1) the passage
3) The synthesis of two and sometimes 3 (never more than 3) equations from your knowledge
4) sythesis of some equation from the passage and your opwn knowledge

typically when you must synthesize, the equations you must pull from your head are simple ones F=ma V=IR stuff like that...no poisseilles law or the equation for double slit diffraction

if nothing pops out immediately...start writing out every equation you can thing of or see that has the variables in it till something overlaps

Step 3-Find a way to hold everything constant
1) the passage states that the variable is being held constant (occasionally that requires you to turn words into variables...hey never said it was easy just consistent)
2) the variable is a constant
3) if 1 and 2 fail you need another equation write out any equation you can think of, until you can work that nasty variable out of the equation
repeat these steps until the only things that are not held constant

Step four- plug and chug

the key to these questions is to explicate your reasoning on paper so that you don't
formulate some bogus equations and run with them...the key is to quickly classify all questions as type one or two and if type one estimate and solve.....if type two write things out and pound away with the algorhythm described there is no question that wont fold if you try enough tricks

as for which equations to focus on simplicity is key....5 areas to know cold
1) circuits-this is so crucial for understaning neurophysio and blood flow...plus lends itself to comparison questions
2) lens optics
3) universal gravitation
4) buoyancy problems (this what my MCAT had all over its phy sci)
5) heat transfer

of course there are others, however these questions are the types that really easily can be written into change format
the Princeton review science review is a pretty decent listing of equations.....nothing you need is missing from their sections and they dont have too much extraneous.....and no I am not employed by them these days....

Biology

much shorter

BLOW OFF ORGANIC CHEM
it is really not tested at all on this test the major aim of the stuff that they do test is to see if you have the key concepts down (ie the 1st 6-7 chapters of your org text-sn1/sn2 stuff)....I would know that like the back of my hand

as far as reactions, do not cram....repeat do not cram....don't attempt to cram the electronic details of the diels-alder reaction into your head...the reactions that they stress all have analogues in biochemistry
1) free radicals-guys these reactions form some of the most fundamental basis of pathophysiology....and if you don't learn it for the mcat- trust me you will become pals with it again
2) carbonyl chemistry-aldehydes, ketones etc- pay particular attention to the reaction of Lithium aluminum hydride with carbonyls.....because its analog reaction in the body is the dehydrogenase reactions involving NADH and NADPH
3) esters, carboxylic acids
4) hydrolysis rxn's
5) amines (a little)

YOUR MAIN BIO SCI FOCUS IS ON HUMAN PHYSIOLOGY

if you don't have any idea of the basic issues on how the major organs work....then you might never know because you might not pass the mcat....here are the one i'd focus on
1) the Kidney
2) the kidney
3) the kidney
4) the endocrine hormones (renin-angiotensin is good to know a little about)
5) the GI tract and digestion
6) female reporductive cycles

what do these things have in common
1) they tend to be complicated
2) they have numerous interelated parts
3) they often demonstrate aspects of negative feedback, homeostasis etc, which test
4) they have conceptualization that does not require one to know the relevent equations (unlike cardio/respiratory which are rather devoid of interesting info without them)

the big thing MCAT biology is all about, is to test whether or not you can decipher complex biological systems and get to the heart of the matter.....it is not testing if you know the pathway by which cdk-2 is activated or the equation for the fractional excretion of sodium....there is not trivia on this test....and believe it or not you really don't have to know all that much human physio to do really really well.....just understand the concept and you will do fine

granted there is non physiological based questions on the mcat, however chances are good you have encountered most of the material that will be asked in areas such as cell biology and mendelian genetics...advanced biology classes, cell bio and the like are not really tested on the MCAT, anyone who tells you that this material is necessary, really didn't understand the test very well....yes it does help when you reach the part about lysosomal protein targeting, if you know about mannose-6 phosphate and its role in depth.....however the return on investment is rather low

#### dtreese

##### Caramel Gollum
10+ Year Member
15+ Year Member
Nice perspective. I'm prepping for a retake & I definitely like your way of thinking.
I would add one thing to the physio, though -- they LOVE the O2-hemoglobin dissociation curve. It's almost always there, so know the effects of pH, pO2, pCO2, etc. UNDERSTAND THE Bohr & Haldane effects.

10+ Year Member
5+ Year Member
BUMP

#### MikeS 78

##### Senior Member
10+ Year Member
15+ Year Member
I am going to bump this as I keep getting asked about it...for some reason no one ever can find it even though they find the verbal part

M

#### Forkit

##### Full Member
10+ Year Member
7+ Year Member
Why aren't you a mod here at SDN yet, Mike S? Your posts are all gold

#### Dynamo24

##### Full Member
Sticky worthy.

Sent from my SAMSUNG-SGH-I777 using SDN Mobile

#### silverice

##### Full Member
5+ Year Member
what a precious post! I've been looking for something like this forever. Thanks!!