1,800+ MCAT terms, defined.

Cultural imperialism is the promotion or imposition of one society's culture, usually a economically or politically powerful one, on other societies, often displacing local practices. The testable point is that it operates through media,...

The refractive index n = c/v compares the speed of light in a vacuum with its speed in a medium, so n is unitless and at least 1. A higher n means slower light. A ray entering a higher-n medium bends toward the normal.

Metalloids are elements with properties intermediate between metals and nonmetals, found along the diagonal staircase of the periodic table (B, Si, Ge, As, Sb, Te are the usual list). Most testable: many are semiconductors, whose conduct...

Protein folding is the process by which a polypeptide chain adopts its functional three-dimensional (native) shape. The primary sequence largely determines the fold, and the hydrophobic effect is a major driving force. Denaturation unfol...

Ego depletion is the proposal that self-control draws on a limited mental resource, so using willpower on one task leaves less for a later one. The classic result is reduced persistence on a second task, but replications and motivation-b...

An extinction burst is a temporary increase in the frequency, intensity, or variety of a previously reinforced behavior right after reinforcement is first withheld. It signals that extinction is under way, and the behavior typically decl...

Implantation is the embedding of the blastocyst into the endometrium of the uterus about a week after fertilization. The testable point: trophoblast cells then secrete hCG, which maintains the corpus luteum and its progesterone until the...

Ortho (o-) describes two substituents on adjacent carbons of a benzene ring, a 1,2 relationship. Most testable: electron-donating groups and halogens direct an incoming electrophile to the ortho and para positions, while strongly electro...

An ammeter is a meter that measures the current through a circuit element, and it is connected in series with that element. An ideal ammeter has zero resistance, so it does not change the current it measures.

ΔG is the change in Gibbs free energy, the energy available to do useful work at constant temperature and pressure. A negative ΔG means a process is spontaneous (thermodynamically favorable) as written, ΔG = 0 means equilibrium, and ΔG s...

Gender schema theory says children learn gender through cognitive schemas, which are mental frameworks that organize information about what is male or female. These schemas then guide attention, memory, and behavior. Testable point: gend...

Cooperative binding means binding of a ligand to one subunit of a multisubunit protein changes the affinity of the other subunits for that ligand. In hemoglobin, O₂ binding raises affinity at the remaining sites, giving a sigmoidal (S-sh...

The hidden curriculum is the unofficial set of norms, values, and expectations students learn through schooling, beyond the formal academic lessons. Its most testable point: it socializes students into roles such as punctuality, obedienc...

Gauche is a staggered conformation in which two substituents on adjacent carbons are 60° apart in a Newman projection. It is slightly higher in energy than anti (180°) because of steric strain, so anti is the most stable conformer of but...

Kinetic friction is the force along the contact surface that opposes the relative sliding of two surfaces. Its magnitude is fk = μk N, which depends on the normal force but not on speed or contact area, and μk is usually smaller than μs.

Bond energy is the energy needed to break one mole of a particular bond in the gas phase, usually in kJ/mol. A higher value means a stronger bond, which is usually shorter. Most testable: ΔH ≈ energy of bonds broken − energy of bonds for...

Low-effort syndrome is a phrase from John Ogbu's work on school achievement gaps: students say education matters but put in little effort, which he tied to perceived blocked opportunity and peer norms. It is niche; the MCAT more often te...

Linked genes are loci close together on the same chromosome, so they tend to be inherited together instead of assorting independently. Crossing over can still separate them, and the recombination frequency stays below 50% and rises with...

DHAP (dihydroxyacetone phosphate) is a three-carbon glycolytic intermediate made when aldolase splits fructose 1,6-bisphosphate. Triose phosphate isomerase converts it to glyceraldehyde 3-phosphate, so both halves of glucose go through t...

The ohm (Ω) is the SI unit of electrical resistance, equal to one volt per ampere. In an ohmic conductor, a larger resistance in ohms means less current for the same potential difference, and resistances in series add.

A spontaneous process proceeds in the forward direction on its own, without continuous outside energy input. At constant T and P it has ΔG < 0, equivalently the entropy of the universe increases. Spontaneous says nothing about speed, whi...

Mass society theory says industrialization, urbanization, and large bureaucracies weaken close community ties, leaving individuals isolated and more open to influence by impersonal institutions and mass media. Testable point: it is the l...

Spin-spin coupling is the interaction between nonequivalent hydrogens on neighboring carbons in ¹H NMR that splits one signal into a multiplet. By the n + 1 rule, n equivalent neighboring hydrogens give n + 1 peaks; equivalent hydrogens...

Motivational interviewing is a collaborative, client-centered counseling style that helps people resolve ambivalence and build their own motivation to change a behavior. Testable point: the counselor uses open-ended questions and reflect...

An attractive force pulls two objects toward each other along the line joining them. Gravity between masses and the Coulomb force between opposite charges are attractive. The most testable point is that these forces weaken as 1/r², so do...

Disproportionation is a redox reaction in which one species is both oxidized and reduced, so an element in an intermediate oxidation state forms products with a higher and a lower oxidation number. Example: 2H₂O₂ → 2H₂O + O₂. Spot it by...

Optimism bias is the tendency to judge your own chances of good outcomes as higher, and of bad outcomes as lower, than the evidence or other people's outcomes support. The exam treats it as a systematic error in judgment about future eve...

A heme group is a porphyrin ring holding a central iron ion, the site where hemoglobin and myoglobin bind O₂ reversibly. Testable point: the iron stays Fe²⁺ when O₂ binds (oxygenation, not oxidation), and hemoglobin has four hemes, so it...

Fluidity is how easily lipids and proteins move sideways within the membrane bilayer. Higher temperature, shorter chains and more cis double bonds (unsaturation) increase it. Cholesterol is a buffer: it lowers fluidity when warm and keep...

An alkyl halide (haloalkane) is R–X, with a halogen (F, Cl, Br, I) bonded to an sp³ carbon. The polar C–X bond makes that carbon electrophilic, so alkyl halides undergo SN1, SN2, E1 and E2 reactions. Leaving-group ability runs I⁻ > Br⁻ >...

Parallel processing is the brain's simultaneous analysis of different features of a stimulus, such as color, shape, and motion, through separate pathways. Serial processing works one step at a time. Automatic tasks tend to be parallel; e...

A closed pipe is closed at one end and open at the other, so it has a displacement node at the closed end and an antinode at the open end. Its resonances are only odd harmonics, f = nv/4L with n = 1, 3, 5, …, so its fundamental is half t...

Peroxides are compounds containing an O–O single bond, such as H₂O₂ and Na₂O₂, with oxygen in the −1 oxidation state instead of the usual −2. The most testable point is that this is the standard exception when assigning oxidation numbers.

Racial formation theory (Omi and Winant) holds that race is a socially constructed category, continually created and reshaped by social, economic, and political forces rather than fixed by biology. Testable point: racial categories and m...

A hemiketal is a carbon bonded to one OH, one OR, and two carbon groups, formed when an alcohol adds to a ketone. The reaction is reversible, and the intramolecular version gives the ring form of ketoses such as fructose. A second alcoho...

The enzyme-substrate complex (ES) is the intermediate formed when a substrate binds noncovalently at an enzyme's active site, before product forms. Most testable: at high [S] nearly all enzyme is in ES form, so the rate levels off at Vmax.

Social desirability bias is the tendency of respondents to answer in ways they think will be viewed favorably, overreporting good behavior and underreporting bad. It threatens the validity of self-report data, especially on sensitive top...

A self-antigen is a molecule made by the body's own cells that lymphocyte receptors could bind but that the immune system normally tolerates. Most self-reactive T and B cells are eliminated or silenced (negative selection in the thymus f...

Electric field lines are drawn curves whose tangent at any point shows the direction of the force on a positive test charge. They leave positive charges and end on negative charges, and closer spacing means a stronger field. Lines do not...

A real gas is a gas whose behavior departs from PV = nRT because its particles take up volume and attract one another. The deviation is generally largest at high pressure and low temperature, and smallest for small, nonpolar gases such a...

Spontaneous recovery is the reappearance of an extinguished conditioned response when the conditioned stimulus is presented again after a rest period. The recovered response is typically weaker than the original. It suggests extinction s...

The N-terminus is the end of a peptide or protein that has a free α-amino group (–NH₃⁺ at physiological pH). Sequences are written and numbered from the N-terminus (left) to the C-terminus (right), so the first residue listed is the N-te...

Synaptic pruning is the normal elimination of little-used synapses during development, while frequently used connections are kept and strengthened. It makes neural circuits more efficient, and the testable idea is "use it or lose it": ex...

A paramagnetic material is weakly attracted to a magnetic field because its atoms have unpaired electrons whose magnetic moments partly align with the field. The alignment fades when the field is removed. Diamagnetic materials are weakly...

A coordination complex is a central metal ion bonded to ligands, each of which donates a lone pair to the metal in a coordinate covalent bond (Lewis base to Lewis acid). Testable point: forming a complex with a large Kf lowers free metal...

Orexin (hypocretin) is a neuropeptide made in the lateral hypothalamus that promotes wakefulness and stimulates appetite, acting through G protein-coupled receptors. Most testable: losing orexin neurons or signaling causes narcolepsy-lik...

A token economy is an operant conditioning system in which desired behaviors earn tokens (points, stickers, chips) that can later be exchanged for backup reinforcers like privileges or treats. Tokens are secondary (conditioned) reinforce...

The resting potential is the steady membrane voltage of an unstimulated excitable cell, about −70 mV (inside negative) in a typical neuron. It arises mainly because K⁺ leaks out through open channels while the membrane is far less permea...

Bulk modulus (B) measures how strongly a material resists uniform compression: the pressure change divided by the fractional volume change. A larger B means the material is harder to compress. Liquids and solids generally have much large...

Van der Waals forces are weak attractions between molecules or nonbonded atoms. Broadly they include London dispersion and dipole-dipole forces; some texts mean dispersion alone. Testable point: dispersion forces strengthen with size and...