1,800+ MCAT terms, defined.

Ohm's law states that the potential difference across a conductor equals the current through it times its resistance, V = IR. It holds for ohmic materials, where R stays constant, but not for every device. The MCAT tests how current chan...

An electrochemical cell links a redox reaction to electron flow through an external circuit. Galvanic cells run spontaneously (E°cell > 0) and make current; electrolytic cells use a power source to drive a nonspontaneous reaction. Oxidat...

A chiral molecule cannot be superimposed on its mirror image, so it exists as a pair of enantiomers. Usually this comes from a carbon bonded to four different groups, but a molecule with stereocenters and an internal mirror plane (a meso...

A personality trait is a relatively stable tendency to think, feel, and act in a certain way across many situations and over time. The MCAT tests trait theories, especially the Big Five, which place people along continuous dimensions, an...

Mutarotation is the gradual change in optical rotation when a pure anomer of a sugar dissolves and equilibrates with its other anomer through the open-chain form. Starting from either pure α- or β-D-glucose, the rotation drifts to the sa...

Viscosity (η) is a fluid's internal resistance to flow, caused by friction between layers moving at different speeds; its SI unit is Pa·s. The most testable point: in Poiseuille's law, flow rate is inversely proportional to η and proport...

Insoluble means a substance dissolves so little in a solvent, usually water, that it is treated as not dissolving. It is a relative label for a very small Ksp, not zero solubility. The MCAT tests it through solubility rules and by compar...

Attachment is the enduring emotional bond between an infant and a caregiver, which gives the infant a secure base for exploring. The most testable point is Ainsworth's Strange Situation, which classifies infants as secure, avoidant, ambi...

A phenotype is an organism's observable or measurable trait, produced by its genotype together with the environment. Testable point: different genotypes can give the same phenotype (AA and Aa under complete dominance), so phenotype does...

Saponification is base-promoted hydrolysis of an ester, classically a triglyceride with NaOH or KOH, giving glycerol and carboxylate salts (soap). The carboxylic acid is deprotonated as it forms, so the reaction is effectively irreversib...

Inclusive fitness is an individual's genetic success counted through its own offspring plus the extra offspring of relatives it helps, weighted by relatedness. It explains how altruism toward kin can evolve even when helping costs the he...

The electric dipole moment p measures a pair of equal and opposite charges separated by a distance: p = qd, in C·m, pointing from the negative to the positive charge in the physics convention. In a uniform electric field the dipole feels...

Ksp is the solubility product constant: the equilibrium constant for a slightly soluble ionic solid dissolving into its ions. Comparing the ion product Q with Ksp predicts whether a precipitate forms (Q > Ksp) or more solid can dissolve...

A reducing sugar has a free anomeric carbon (hemiacetal or hemiketal) that can open to an aldehyde and be oxidized, reducing an agent such as Cu²⁺ in Benedict's or Ag⁺ in Tollens' reagent. Testable point: sucrose is non-reducing because...

Migration is the movement of people from one place to another to settle, and it is one of the three demographic processes, with birth and death, that change a population. Immigration is movement into a region and emigration is movement o...

Splitting is the division of a ¹H NMR signal into a multiplet by coupling to nonequivalent protons on neighboring atoms, usually the adjacent carbon. A proton with n equivalent neighbors usually gives n + 1 peaks (the n + 1 rule), so the...

A drive is an internal state of tension, produced by an unmet biological need such as hunger or thirst, that pushes an organism to act to reduce it. In drive-reduction theory, reducing the drive restores homeostasis, but the theory does...

Incomplete dominance is when a heterozygote shows a phenotype intermediate between the two homozygotes, because neither allele fully masks the other. The classic case is red × white flowers giving pink, with a 1:2:1 phenotypic ratio in t...

Total internal reflection is the complete reflection of light back into its original medium when it meets a boundary with a lower-index medium at an angle of incidence greater than the critical angle. It needs n₁ > n₂ and θ > θc, and the...

Reduction is the gain of electrons by a species, which lowers its oxidation number. It always occurs at the cathode, in galvanic and electrolytic cells alike, and the species reduced is the oxidizing agent. In organic chemistry it often...

Mass hysteria is a form of collective behavior in which a fear, belief, or physical symptom spreads quickly through a group, usually with no physical cause found. The testable point is that it is explained by social contagion, meaning pe...

SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) separates denatured proteins mainly by size. SDS gives proteins a similar charge-to-mass ratio, so smaller proteins migrate farther toward the positive electrode (anode).

Recall is retrieving stored information from memory without being shown the item, as in a short-answer question. It is typically harder than recognition, where you only pick out the correct item from options.

A phenol is a compound with an OH group bonded directly to a benzene ring; C₆H₅OH is the parent. It is much more acidic than an aliphatic alcohol (pKa about 10 versus roughly 16 to 18) because phenoxide is resonance-stabilized, but it is...

Hooke's law says an ideal spring exerts a restoring force proportional to its displacement from equilibrium and opposite in direction: F = −kx. It holds within the elastic limit; doubling the stretch doubles the force but quadruples the...

A titration finds an unknown concentration by adding a solution of known concentration until the reaction is stoichiometrically complete (the equivalence point). Testable point: equivalence means equal moles of H⁺ and OH⁻ have reacted, b...

A social movement is a sustained, organized effort by a large group to bring about or resist social change, usually through channels outside routine institutions. The MCAT tests why movements arise and succeed: relative deprivation stres...

The peripheral nervous system (PNS) is all nervous tissue outside the brain and spinal cord (the CNS): the nerves and ganglia. Sensory neurons are afferent (toward the CNS) and motor neurons are efferent (away), and the motor part divide...

The active site is the pocket or cleft on an enzyme where the substrate binds and the reaction is catalyzed. Its shape and chemistry match the substrate (lock-and-key or induced fit). Competitive inhibitors bind here, and denaturation th...

A vacuum is a region with no matter, ideally at zero absolute pressure. Electromagnetic waves, including light at c = 3.00 × 10⁸ m/s, travel through it, but sound and other mechanical waves cannot, and with no air resistance, objects fal...

Isotopes are atoms of the same element (same number of protons, same atomic number Z) with different numbers of neutrons, so different mass numbers A. They behave almost identically in chemistry but differ in mass, and some are radioacti...

Social loafing is the tendency for individuals to put in less effort on a task when working in a group than when working alone. It is most likely when individual contributions cannot be identified or evaluated, and it tends to shrink whe...

A racemic mixture (racemate) is an equal, 50:50 mixture of two enantiomers. Their optical rotations cancel, so it shows zero net rotation and is optically inactive. It typically forms when a new stereocenter is made from achiral reactant...

In Piaget's theory, assimilation is fitting new information into an existing schema without changing that schema. The key contrast is accommodation, where the schema itself is modified. In sociology, assimilation means a minority group a...

Perpendicular means at a 90° angle to a line, surface, or vector. The most testable consequence is that a force perpendicular to the displacement does no work (cos 90° = 0), so it can change direction without changing speed.

Hess's law says the enthalpy change of an overall reaction equals the sum of the enthalpy changes of its steps, because enthalpy is a state function. Most testable: reversing a step flips the sign of ΔH, and scaling the coefficients scal...

Problem solving is the cognitive process of finding a way to reach a goal when the route is not obvious. The most testable point is algorithm versus heuristic: an algorithm is a step-by-step procedure that gives the correct answer if fol...

Pancreatic juice is the exocrine secretion of the pancreas, sent through the pancreatic duct into the duodenum. It contains bicarbonate, which neutralizes acidic chyme, and digestive enzymes (amylase, lipase, nucleases, proteases). Prote...

The cytosol is the water-based fluid inside the plasma membrane but outside the organelles, holding enzymes, ions and metabolites. Its most testable point is pathway location: glycolysis and fatty acid synthesis occur here, while the cit...

Induction (the inductive effect) is the shift of electron density along sigma bonds toward or away from an electronegative or electropositive group. Electron-withdrawing groups stabilize nearby negative charge, so they strengthen acids,...

Role conflict is the tension that arises when the expectations of two or more roles a person holds at the same time are incompatible, such as worker and parent. The key test point: conflict spans different roles, whereas role strain is s...

Poiseuille's law gives the volume flow rate of a viscous fluid in steady laminar flow through a long cylindrical tube: Q = πr⁴ΔP / (8ηL). Most testable point: flow depends on the fourth power of the radius, so a small change in radius ch...

Chemical equilibrium is the state of a reversible reaction where forward and reverse rates are equal, so concentrations stay constant (a dynamic state, not a stopped reaction). Most testable: Le Châtelier's principle predicts the directi...

Role strain is stress that arises from incompatible or excessive demands within a single social role, such as a teacher expected to be both friendly mentor and impartial grader. The testable contrast: strain involves one role, while role...

Extraction separates compounds by their different solubilities in two immiscible liquids, usually water and an organic solvent. In acid-base extraction, converting an acid or base to its charged salt moves it into the water layer. Neutra...

The anomeric carbon is the former carbonyl carbon of a sugar, which becomes a new stereocenter (a hemiacetal or hemiketal carbon) when the sugar cyclizes. Its OH can point either way, giving α and β anomers. A free anomeric OH makes a su...

A bureaucracy is a formal organization run by written rules, a hierarchy of offices, specialized roles, and impersonal, merit-based treatment of members. Weber presented it as an ideal type of rational-legal authority that favors efficie...

GPCRs (G protein-coupled receptors) are seven-transmembrane-helix receptors that, when a ligand binds, activate an associated G protein by swapping GDP for GTP. The G protein then changes an effector such as adenylyl cyclase or phospholi...

Centripetal force is the net force directed toward the center of a circular path that keeps an object in circular motion. It is not a new kind of force but the net of real forces (tension, gravity, friction, normal force), and it is alwa...

The equilibrium constant, Keq, is the ratio of product to reactant concentrations, each raised to its coefficient, once a reversible reaction reaches equilibrium. Most testable: temperature changes Keq, but added reactant, pressure chang...