MCAT Study Guide

Chemical & Physical Foundations of Biological Systems 95 min -- 59 Q

Roughly a quarter general chemistry, a quarter physics, a quarter organic chemistry, and a quarter biochemistry, all wrapped in experimental passages. Most questions are passage-based; about a quarter are discrete. You are rewarded for reasoning, dimensional analysis, and estimation -- not heavy computation. No calculator is allowed, so practice arithmetic with scientific notation and clean round numbers.

General Chemistry -- Atomic Structure & Periodic Trends

• Quantum numbers: n (shell), l (subshell: s=0, p=1, d=2, f=3), m_l (orbital), m_s (spin, +/-1/2). No two electrons share all four (Pauli).
• Filling rules: Aufbau (low energy first), Hund (singly fill degenerate orbitals before pairing), Pauli. Watch the Cr and Cu exceptions (half-filled and filled d are extra-stable).
• Effective nuclear charge (Z_eff) rises across a period -> drives every trend.
• Atomic radius: decreases left-to-right, increases top-to-bottom. Ionization energy and electronegativity do the opposite (up and right = highest, F is the most electronegative). Electron affinity is most negative near the halogens.

Bonding & Molecular Structure

• Ionic (metal + nonmetal, electron transfer) vs covalent (shared) vs metallic (delocalized sea). EN difference >~1.7 leans ionic.
• VSEPR: count electron domains. 2 = linear, 3 = trigonal planar, 4 = tetrahedral, 5 = trigonal bipyramidal, 6 = octahedral. Lone pairs compress bond angles (e.g. water ~104.5 deg).
• Hybridization: sp (linear), sp2 (trigonal planar), sp3 (tetrahedral). Sigma bonds = head-on overlap; pi bonds = sideways p overlap and prevent rotation.
• Formal charge = valence e- minus (lone e- + 1/2 bonding e-). Pick resonance structures with low/zero formal charges and negative charge on the most electronegative atom.
• Intermolecular forces (strength order): ion-dipole > H-bond (N/O/F-H) > dipole-dipole > London dispersion. These set boiling point, viscosity, and solubility.

Stoichiometry, Gases & Phases

• Mole = 6.022 x 10^23. Empirical vs molecular formula. Identify the limiting reagent by dividing moles by coefficients.
• Ideal gas: PV = nRT. At STP one mole occupies 22.4 L. Real gases deviate at high P / low T (finite volume + attractions).
• Colligative properties depend on particle count, not identity: boiling-point elevation, zing-point depression (Delta T = i K m), osmotic pressure (Pi = iMRT). i = van't Hoff factor (NaCl ~ 2).

Thermochemistry & Thermodynamics

• Delta G = Delta H - T Delta S. Negative Delta G = spontaneous. Memorize the sign chart: -H/+S is always spontaneous; +H/-S never; the mixed cases flip with temperature.
• Delta G = Delta G(deg) + RT ln Q and Delta G(deg) = -RT ln K = -nFE(deg) tie thermo, equilibrium, and electrochemistry together.
• Hess's law: enthalpy is a state function -- sum reaction steps. Delta H(rxn) = bonds broken (endo, +) minus bonds formed (exo, -).
• Calorimetry: q = mc Delta T (sensible heat) and q = m L (phase change, constant T). First law: Delta U = q + w.

Kinetics

• Rate law = k[A]^x[B]^y; orders come from experiment, not coefficients. Determine them by comparing initial-rate trials.
• Catalysts lower activation energy and speed both directions equally; they do not change Delta G, K, or equilibrium position.
• The rate-determining step is the slowest step. Arrhenius: higher T or lower Ea -> larger k.

Equilibrium

• K = products/reactants (each raised to its coefficient); pure solids/liquids excluded. Compare Q to K: Q<K shifts right, Q>K shifts left.
• Le Chatelier: stress (concentration, pressure/volume, temperature) shifts equilibrium to relieve it. Treat heat as a reactant (endothermic) or product (exothermic).
• Solubility: Ksp and the common-ion effect (added shared ion lowers solubility).

Acids, Bases & Buffers

• pH = -log[H+], pOH = -log[OH-], pH + pOH = 14. Strong acids/bases fully dissociate; weak ones use Ka/Kb (Ka x Kb = Kw = 1.0 x 10^-14).
• Henderson-Hasselbalch: pH = pKa + log([A-]/[HA]). A buffer is strongest when pH = pKa ([HA] = [A-]).
• Titrations: at the half-equivalence point pH = pKa; at the equivalence point moles acid = moles base (and the salt's hydrolysis sets the pH -- e.g. weak acid + strong base gives a basic endpoint).

Electrochemistry

• Redox: "OIL RIG" -- Oxidation Is Loss, Reduction Is Gain of electrons. Track oxidation states.
• Galvanic/voltaic cell: spontaneous, E(cell) > 0, Delta G < 0, makes electricity. Electrolytic cell: non-spontaneous, driven by external power.
• Anode = oxidation, Cathode = reduction (in BOTH cell types). "An Ox, Red Cat." In a galvanic cell the anode is negative; in an electrolytic cell it is positive.
• E(cell) = E(cathode) - E(anode) from a reduction-potential table.

Physics -- Kinematics & Dynamics

• Big four: v = v0 + at; x = v0 t + 1/2 a t^2; v^2 = v0^2 + 2a Delta x; x = 1/2 (v0 + v) t. Projectiles: x and y are independent; g = ~10 m/s^2 down.
• Newton's laws: F = ma; action-reaction pairs act on different bodies. Friction f = mu N; static friction self-adjusts up to mu_s N.
• Inclines: gravity component along the plane = mg sin(theta); normal-direction = mg cos(theta).
• Circular/centripetal: a_c = v^2/r toward the center; torque tau = rF sin(theta). Equilibrium = net force and net torque both zero.

Physics -- Energy, Work & Momentum

• Work W = Fd cos(theta); KE = 1/2 mv^2; gravitational PE = mgh; spring PE = 1/2 k x^2. Power = W/t.
• Conservation of energy: total mechanical energy is constant without friction (a non-conservative force). Work-energy theorem: W_net = Delta KE.
• Momentum p = mv is conserved in all collisions. Elastic conserves KE too; inelastic does not (perfectly inelastic = objects stick). Impulse = F Delta t = Delta p.

Physics -- Fluids

• Density rho = m/V; pressure P = F/A; hydrostatic gauge pressure P = rho g h.
• Buoyancy (Archimedes): F_b = rho_fluid V_displaced g. Floats when object density < fluid density.
• Continuity: A1 v1 = A2 v2 (narrow = faster). Bernoulli: faster flow -> lower pressure (P + 1/2 rho v^2 + rho g h = constant).
• Pascal's principle (hydraulics) multiplies force; Poiseuille: flow scales with r^4 (tiny radius change, huge resistance change -- key for vessels).

Physics -- Electrostatics & Circuits

• Coulomb: F = kq1q2/r^2. Field E = F/q = kQ/r^2 (points away from +). Potential V = kQ/r; potential energy U = kq1q2/r.
• Ohm's law V = IR; power P = IV = I^2R = V^2/R.
• Series: resistors add, current shared, voltage splits. Parallel: 1/R_eq sums, voltage shared, current splits. Capacitors behave oppositely.
• Capacitor C = Q/V; energy = 1/2 CV^2. A dielectric raises C.

Physics -- Waves, Sound & Optics

• v = f lambda; period T = 1/f. Sound is a longitudinal pressure wave; light is transverse and electromagnetic.
• Intensity follows 1/r^2; the decibel scale is logarithmic (every +10 dB = 10x intensity). Doppler: approaching -> higher perceived frequency.
• Standing waves/resonance: open pipes and strings fixed at both ends support all harmonics; a pipe closed at one end only supports odd harmonics.
• Optics: 1/f = 1/o + 1/i; magnification m = -i/o. Converging (convex) lens / concave mirror have +f. Snell: n1 sin(theta1) = n2 sin(theta2); total internal reflection beyond the critical angle.

Organic Chemistry -- Functional Groups & Nomenclature

• Know the priority/oxidation ladder: alkane -> alcohol -> aldehyde/ketone -> carboxylic acid. Carboxylic-acid derivatives by reactivity: acyl halide > anhydride > ester ~ acid > amide.
• Recognize on sight: hydroxyl, carbonyl, carboxyl, amino, amide, ester, ether, thiol, phosphate. IUPAC: lowest locants to the highest-priority group.

Isomerism & Stereochemistry

• Constitutional (different connectivity) vs stereoisomers (same connectivity, different 3-D).
• Enantiomers = non-superimposable mirror images (opposite at every chiral center, identical physical properties except optical rotation). Diastereomers differ at some but not all centers (different physical properties). Meso compounds have chiral centers but an internal mirror plane -> achiral.
• R/S by CIP priority (highest atomic number first); n chiral centers -> up to 2^n stereoisomers.

Key Reactions & Mechanisms

• SN1/E1 (carbocation, favored by 3 deg substrates and polar protic solvent, racemization) vs SN2/E2 (one-step backside attack, 1 deg substrate, strong nucleophile/base, inversion).
• Nucleophilic addition to carbonyls (Grignard, hydride, hydrate/hemiacetal/acetal). Nucleophilic acyl substitution for carboxylic-acid derivatives.
• Aldol, esterification (Fischer), saponification, oxidation/reduction (PCC stops at aldehyde; LiAlH4 is strong, NaBH4 mild), and imine/enamine formation.

Separations & Spectroscopy

• Extraction: separate by acid-base properties / polarity into immiscible layers. Distillation: by boiling point. Chromatography (TLC, column, GC, HPLC): by polarity / affinity for stationary vs mobile phase.
• IR: functional groups. Broad O-H ~3300, sharp C=O ~1700, N-H, C(triple)N ~2200 cm^-1.
• 1H NMR: number of signals = chemically distinct H's; chemical shift = electronic environment (deshielded downfield); integration = relative H count; n+1 splitting = neighboring H's.
• Mass spec: molecular ion (M+) gives molecular weight; fragmentation patterns identify structure.

Where Biochemistry Shows Up Here

Expect thermodynamics and kinetics applied to enzymes (lowering Ea, Michaelis-Menten), acid-base chemistry applied to amino acid side chains and physiological buffers (the bicarbonate buffer, pKa-driven protonation), and IMFs / pH applied to protein folding and membrane behavior. Treat the biological molecule as just another chemical system.

Critical Analysis & Reasoning Skills (CARS) 90 min -- 53 Q

Nine passages (~500-600 words each) drawn from the humanities and social sciences -- philosophy, ethics, history, literature, art, cultural studies, economics, political theory. There is no outside content to memorize. Every answer is supported by the passage in front of you. This is the section that rewards deliberate reading practice more than studying, and it is the hardest to cram for, so start it early.

The Three Question Categories

• Foundations of Comprehension (~30%): What does the passage say or mean? Main idea, the author's tone, the meaning of a word/phrase in context, and the function of a paragraph. The answer is paraphrased directly from the text.
• Reasoning Within the Text (~30%): How does the argument work? Identify the author's central claim, the evidence, assumptions, and whether parts strengthen or weaken the argument. You judge the internal logic, not the truth.
• Reasoning Beyond the Text (~40%): Apply or extend. Take the author's reasoning to a brand-new situation, or introduce new information and ask how it affects the argument. The "right answer" lives outside the passage but must follow from the author's logic.

An Active-Reading Approach

• Read for structure, not facts. After each paragraph, ask "what is the author DOING here?" -- introducing a claim, conceding a point, raising a counterargument, giving an example. Track the argument's spine, not the details.
• Find the thesis and the tone. Most passages have one main point and an attitude (approving, skeptical, neutral, critical). Lock both in before the questions.
• Watch the signposts: "however / but / yet" (a turn), "therefore / thus" (a conclusion), "for example" (support), "although / despite" (concession). These tell you where the argument bends.
• Anticipate the answer in your own words before reading the choices, then match. This inoculates you against tempting distractors.

Common Wrong-Answer Traps

• Too extreme: absolute words (always, never, all, none, impossible) when the author was measured. CARS authors are usually nuanced.
• Out of scope / outside knowledge: true in the real world but never argued in the passage.
• Half-right: one clause matches the text, the other distorts it. A choice is only correct if the WHOLE thing is supported.
• Opposite / distortion: reverses the author's stance or subtly twists a claim.
• Right answer, wrong question: a true statement that doesn't answer what was asked.

Timing

• ~10 minutes per passage (read ~4 min, answer ~6 min). Never sink 3 minutes into one question -- flag and move.
• Consider doing your strongest passage types first and saving dense/abstract philosophy for last; partial credit doesn't exist, so bank the easy points.
• Answer every question -- there is no wrong-answer penalty. Guess your pre-committed letter on anything you can't reach.

Biological & Biochemical Foundations of Living Systems 95 min -- 59 Q

About 65% biology and 25% biochemistry, with a little gen-chem and organic mixed in. Heavily experiment- and figure-based: you will interpret data, controls, and pathways more than recall isolated facts. The single highest-yield cluster is amino acids, enzymes, and metabolism.

Biochemistry -- Amino Acids & Proteins

• 20 amino acids: central carbon + amino group + carboxyl + R group. Group them by side chain: nonpolar, polar uncharged, acidic (Asp, Glu), basic (Lys, Arg, His). Know the special ones: Gly (smallest, flexible), Pro (kink, no rotation), Cys (disulfide bonds).
• pI = pH at which the amino acid is neutral (zwitterion); side-chain pKa values drive charge at a given pH.
• Structure levels: primary (sequence) -> secondary (alpha-helix, beta-sheet via backbone H-bonds) -> tertiary (3-D fold, R-group interactions) -> quaternary (multiple subunits, e.g. hemoglobin). Denaturation disrupts everything but the primary sequence.
• The peptide bond is a partial-double-bond amide -> planar and rigid.

Enzymes & Kinetics

• Enzymes lower activation energy; they don't change Delta G or equilibrium. Lock-and-key vs induced fit.
• Michaelis-Menten: v = Vmax[S]/(Km + [S]). Km = [S] at half Vmax and inversely reflects affinity (low Km = high affinity). The Lineweaver-Burk double-reciprocal plot linearizes this.
• Inhibition: competitive (raises Km, Vmax unchanged, outcompeted by substrate) vs noncompetitive (lowers Vmax, Km unchanged) vs uncompetitive (lowers both).
• Regulation: allosteric (cooperative, sigmoidal curve -- think hemoglobin), feedback inhibition, covalent modification (phosphorylation), zymogen activation. Cofactors/coenzymes (many from vitamins) assist catalysis.

Metabolism Overview

• Glycolysis (cytoplasm): glucose -> 2 pyruvate, net 2 ATP + 2 NADH; anaerobic.
• Pyruvate -> acetyl-CoA, then the Citric Acid (Krebs) cycle (mitochondrial matrix): produces NADH, FADH2, GTP, and CO2.
• Oxidative phosphorylation / electron transport chain (inner mitochondrial membrane): NADH/FADH2 drive a proton gradient; ATP synthase makes the bulk of ATP (~30-32 total per glucose). O2 is the final electron acceptor.
• Other fuels: beta-oxidation of fats (high ATP yield), gluconeogenesis, glycogenesis/glycogenolysis, the pentose phosphate pathway (NADPH + ribose), and ketones during starvation. Insulin = fed/storage; glucagon and epinephrine = fasting/mobilization.

Molecular Biology & the Central Dogma

• DNA -> RNA -> protein. DNA is antiparallel, complementary (A-T, G-C), replicated semiconservatively (helicase, polymerase 5'->3', leading vs lagging/Okazaki, primase, ligase).
• Transcription (RNA polymerase) then eukaryotic processing: 5' cap, poly-A tail, splicing out introns. Translation at the ribosome: codons -> amino acids; the genetic code is degenerate, with start (AUG) and stop codons.
• Mutations: silent, missense, nonsense, frameshift (insertion/deletion). Gene regulation: operons (lac/trp) in prokaryotes; promoters, enhancers, transcription factors, epigenetics (methylation, histones) in eukaryotes.

Lab Techniques

• PCR amplifies DNA; gel electrophoresis separates by size (small = farther). Blots: Southern (DNA), Northern (RNA), Western (protein).
• Sanger sequencing, restriction enzymes, cloning vectors/plasmids, CRISPR for editing, and ELISA for detecting specific proteins.

Cell Biology

• Eukaryote vs prokaryote (nucleus, membrane-bound organelles). Know organelle jobs: mitochondria (ATP), rough/smooth ER (protein + lipid synthesis), Golgi (modify/ship), lysosome (digest), peroxisome (detox).
• Membranes: fluid mosaic, phospholipid bilayer; transport by simple/facilitated diffusion, osmosis, and active transport (Na+/K+ ATPase). Endo/exocytosis for big cargo.
• Cell cycle: G1-S-G2-M with checkpoints; mitosis (PMAT) yields identical diploid cells; meiosis yields four haploid gametes with crossing over and independent assortment (the engines of genetic variation).

Genetics

• Mendel: segregation and independent assortment; dominant/recessive, Punnett squares, test crosses. Beyond simple dominance: incomplete dominance, codominance, polygenic, pleiotropy, epistasis.
• Sex-linked (X-linked recessive hits males more) and pedigree analysis. Hardy-Weinberg: p + q = 1 and p^2 + 2pq + q^2 = 1 at equilibrium (no selection, mutation, migration, drift, random mating).

Organ Systems -- High-Yield Facts

• Nervous: resting potential ~ -70 mV; action potential = depolarization (Na+ in) then repolarization (K+ out), all-or-none, restored by Na+/K+ ATPase. Saltatory conduction along myelin. CNS vs PNS; autonomic = sympathetic ("fight or flight") vs parasympathetic ("rest and digest").
• Endocrine: hypothalamus -> anterior/posterior pituitary -> target glands, with negative feedback. Peptide hormones (fast, surface receptors, second messengers like cAMP) vs steroid hormones (slow, lipid-soluble, intracellular receptors). Insulin/glucagon, thyroid, cortisol, ADH, aldosterone.
• Cardiovascular: right heart -> lungs -> left heart -> body. SA node sets the pace -> AV node -> Purkinje. Cardiac output = HR x stroke volume. Arteries (away, high pressure), veins (toward, valves), capillaries (exchange). O2/CO2 transport on hemoglobin (cooperative; Bohr effect shifts the curve).
• Respiratory: gas exchange at alveoli by diffusion; diaphragm drives ventilation. CO2/pH (not O2) is the primary breathing-rate driver via the bicarbonate buffer.
• Renal: nephron = filtration (glomerulus) -> reabsorption (proximal tubule, loop of Henle countercurrent) -> secretion -> excretion. ADH (water) and aldosterone (Na+) fine-tune blood pressure and osmolarity; kidneys also balance pH.
• Immune: innate (fast, nonspecific: skin, phagocytes, inflammation, complement) vs adaptive (specific, memory: B cells/antibodies = humoral; T cells = cell-mediated; helper vs cytotoxic). Antigen presentation via MHC.
• Digestive: mechanical + chemical breakdown; mouth (amylase) -> stomach (acid, pepsin) -> small intestine (most digestion/absorption, with pancreatic enzymes and bile from the liver/gallbladder) -> large intestine (water + electrolytes).
• Reproductive: spermatogenesis (continuous) vs oogenesis (cyclical); the menstrual cycle (FSH, LH, estrogen, progesterone) with ovulation at the LH surge. Fertilization -> zygote -> blastocyst -> implantation.
• Musculoskeletal: sarcomere sliding-filament (actin/myosin), Ca2+-triggered contraction; skeletal (voluntary, striated), cardiac (involuntary, striated, gap junctions), smooth (involuntary). Bone provides support, mineral storage, and hematopoiesis.

Psychological, Social & Biological Foundations of Behavior 95 min -- 59 Q

Roughly 65% psychology, 30% sociology, and 5% biology. The biggest challenge is vocabulary -- the section is dense with named theories, theorists, and terms that look alike. The fastest gains come from flashcarding the terminology and the people attached to each idea.

Sensation & Perception

• Sensation = detecting stimuli (transduction); perception = organizing/interpreting them. Absolute threshold (minimum detectable) vs difference threshold/JND (Weber's law: proportional). Signal detection theory separates sensitivity from response bias.
• Bottom-up (data-driven) vs top-down (expectation-driven) processing. Gestalt principles (proximity, similarity, closure, continuity) explain grouping.

Learning

• Classical conditioning (Pavlov): neutral stimulus -> conditioned stimulus via association (acquisition, extinction, spontaneous recovery, generalization, discrimination).
• Operant conditioning (Skinner): behavior shaped by consequences. Reinforcement increases behavior, punishment decreases it; each can be positive (add) or negative (remove). Variable-ratio schedules are the most resistant to extinction.
• Observational learning (Bandura, Bobo doll) and latent learning round out the theories.

Memory & Cognition

• Stages: sensory -> short-term/working (~7 items, Miller) -> long-term (explicit/declarative vs implicit/procedural). Encoding (elaborative > shallow), storage, retrieval (recall vs recognition, context/state-dependent cues).
• Forgetting: decay, proactive/retroactive interference, the misinformation effect (Loftus). Problem solving: algorithms vs heuristics; biases (availability, representativeness, confirmation, anchoring), framing, and fixation. Language: Whorf's linguistic relativity; Chomsky's universal grammar.

Motivation & Emotion

• Theories of motivation: drive-reduction, arousal (Yerkes-Dodson optimal arousal), incentive, and Maslow's hierarchy (physiological -> safety -> love -> esteem -> self-actualization).
• Theories of emotion: James-Lange (body first -> emotion), Cannon-Bard (simultaneous), Schachter-Singer two-factor (arousal + cognitive label). Amygdala = fear; limbic system processes emotion.

Personality & Development

• Personality: psychoanalytic (Freud: id/ego/superego, defense mechanisms), humanistic (Rogers, Maslow), trait (Big Five: OCEAN), and social-cognitive (Bandura's reciprocal determinism).
• Development: Piaget's cognitive stages (sensorimotor -> preoperational -> concrete -> formal operational), Erikson's psychosocial stages (e.g. trust vs mistrust, identity vs role confusion), Kohlberg's moral reasoning (preconventional -> conventional -> postconventional), Vygotsky (zone of proximal development).

Psychological Disorders & Biological Bases

• Categories: anxiety, depressive/bipolar, schizophrenia (positive vs negative symptoms, dopamine), OCD, personality disorders, dissociative. The biomedical, biopsychosocial, and diathesis-stress models explain causes.
• Brain: frontal lobe (executive/planning), parietal (touch/spatial), temporal (hearing, memory, Wernicke's), occipital (vision), cerebellum (coordination), hippocampus (memory formation), hypothalamus (homeostasis).
• Neurotransmitters: dopamine (reward/movement), serotonin (mood/sleep), GABA (inhibition), glutamate (excitation), acetylcholine (muscle/memory), norepinephrine (arousal).

Sociology -- Social Structure & Interaction

• Status (ascribed vs achieved), role (and role strain/conflict), groups (primary vs secondary, in-group/out-group, reference groups), networks, and organizations (bureaucracy -- Weber).
• Socialization: agents (family, school, peers, media); the self via Cooley's looking-glass self and Mead's I/me. Deviance: labeling theory, strain theory (Merton), differential association.

Stratification & Demographics

• Social stratification: class, caste, socioeconomic status, social mobility, and reproduction of inequality. Concepts: social capital, cultural capital, the power elite, prestige, privilege.
• Demographics: age, gender, race/ethnicity, immigration; demographic transition, fertility/mortality/migration, population pyramids. Theories: Malthusian limits vs the demographic transition model.
• Health disparities and the social determinants of health are repeatedly tested.

Culture & Institutions

• Culture: material vs nonmaterial, values, norms (folkways, mores, taboos), symbols, language; ethnocentrism vs cultural relativism; subcultures and countercultures.
• Social institutions: family, education (hidden curriculum), religion, government/economy, and medicine (the sick role -- Parsons; medicalization).

Sociological Theories & Named Theorists

• Functionalism (Durkheim): society as interdependent parts maintaining stability; manifest vs latent functions.
• Conflict theory (Marx): society as competition over scarce resources; power, inequality, and class struggle.
• Symbolic interactionism (Weber, Mead, Goffman): meaning built through everyday interaction and symbols; Goffman's dramaturgy (front/back stage).