IISER IAT key terms

The movement of solvent, usually water, across a semipermeable membrane from a region of lower solute concentration to one of higher solute concentration, driven by a chemical potential gradient.

The potential energy of water per unit volume relative to pure water at the same temperature and pressure; solutes lower it, and water moves toward regions of lower water potential.

The effective osmotic pressure gradient between two solutions separated by a membrane, describing whether a cell gains, loses, or maintains its volume in that solution.

The study of how reaction rates depend on substrate concentration, enzyme concentration, and inhibitors, often described by the Michaelis–Menten model and its parameters.

The substrate concentration at which an enzyme-catalysed reaction proceeds at half its maximum velocity; a low value indicates high apparent affinity of the enzyme for the substrate.

Reversible inhibition in which an inhibitor resembling the substrate binds the active site, raising the apparent Michaelis constant while leaving maximum velocity unchanged at saturating substrate.

The tendency of genes located close together on the same chromosome to be inherited together, producing offspring genotype ratios that deviate from independent assortment.

The proportion of offspring showing recombination between two loci; values below fifty percent indicate linkage and are used as a measure of genetic distance.

The reciprocal exchange of chromosome segments between homologous chromatids during prophase of meiosis, generating new combinations of alleles on a chromosome.

The condition in which allele and genotype frequencies in a population remain constant across generations in the absence of selection, mutation, migration, drift, and non-random mating.

Random fluctuation of allele frequencies between generations due to sampling of gametes, whose effects are strongest in small populations and can fix or eliminate alleles.

The proportion of all copies of a gene in a population that are represented by a particular allele, usually expressed as a fraction or percentage.

The steady electrical potential difference across a cell membrane at rest, set mainly by potassium permeability and maintained by ion pumps and selective ion channels.

A rapid, self-propagating change in membrane voltage caused by sequential opening of voltage-gated sodium and potassium channels, used for signalling along axons.

An expression giving the equilibrium potential for a single ion across a membrane from its concentration ratio and charge, using temperature and the gas constant.

A concentration unit equal to the number of moles of solute dissolved per litre of solution, commonly denoted M and used in stoichiometric and equilibrium calculations.

The amount of substance containing exactly the Avogadro number of elementary entities, used to convert between particle counts and measurable masses.

The reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can form according to the stoichiometry.

The ratio of product activities to reactant activities, each raised to its stoichiometric coefficient, at equilibrium; its value indicates the extent of reaction at a given temperature.

A rule stating that a system at equilibrium shifts to oppose a change in concentration, pressure, or temperature, thereby partially counteracting the imposed disturbance.

The same ratio of product to reactant activities as the equilibrium constant but evaluated at any instant; comparing it with the equilibrium constant predicts the direction of change.

A solution of a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists large pH changes on addition of small amounts of acid or alkali.

A relation linking the pH of a buffer to the acid dissociation constant and the ratio of conjugate base to weak acid concentrations.

The negative logarithm to base ten of hydrogen ion activity in a solution, giving a scale on which values below seven are acidic at standard conditions.

The property of a molecule that is not superimposable on its mirror image, usually due to a carbon bearing four different substituents, giving rise to enantiomers with distinct optical behaviour.

One of a pair of stereoisomers that are non-superimposable mirror images of each other and rotate plane-polarised light in opposite directions when pure.

The branch of chemistry concerned with the three-dimensional arrangement of atoms in molecules and how that arrangement affects properties and reactions.

A guideline for addition of a hydrogen halide to an unsymmetrical alkene stating that the hydrogen adds to the carbon bearing more hydrogens, giving the more substituted product.

A positively charged carbon species with an incomplete octet, stabilised by electron-donating groups and hyperconjugation; stability increases from primary to tertiary.

A reaction in which an electron-rich multiple bond attacks an electrophile, forming a new sigma bond and generating an intermediate that is then captured by a nucleophile.

The value a function approaches as its input approaches a specified point; it underlies continuity, differentiation, and integration in calculus.

The property of a function whose value at a point equals the limit of the function there, so that its graph has no break or jump at that point.

The instantaneous rate of change of a function with respect to its variable, defined as the limit of a difference quotient and interpreted geometrically as the slope of the tangent.

The limit of a sum of rectangular areas under a curve between two bounds, interpreted as signed area and evaluated using an antiderivative via the fundamental theorem of calculus.

A scalar associated with a square matrix that indicates whether the matrix is invertible and, in two or three dimensions, gives the signed area or volume scaling of the transformation.

A scalar for which a nonzero vector is mapped to a scalar multiple of itself by a linear transformation, found by solving the characteristic equation.

The matrix that multiplies a given square matrix to produce the identity matrix; it exists exactly when the determinant is nonzero.

An arrangement of objects in a definite order; the number of arrangements of n distinct objects taken r at a time is written as nPr.

A selection of objects in which order does not matter; the number of ways to choose r objects from n is written as nCr and equals nPr divided by r factorial.

A number between zero and one measuring how likely an event is, defined for equally likely outcomes as the ratio of favourable outcomes to total outcomes.

The statement that the net force on a body equals the rate of change of its momentum, reducing to mass times acceleration for constant mass.

The product of a body's mass and velocity; the total momentum of an isolated system is conserved in all collisions.

The principle that total energy in an isolated system remains constant, though it may transform between kinetic, potential, thermal, and other forms.

The energy transferred to a body by a force acting through a displacement, calculated as the scalar product of force and displacement.

A sketch showing a single body isolated from its surroundings with all external forces drawn as arrows indicating magnitude and direction, used to apply Newton's laws.

A contact force opposing relative motion or its tendency between surfaces; kinetic friction is roughly constant while static friction adjusts up to a maximum value.

A vector field giving the force per unit positive charge at each point in space, directed away from positive charge and toward negative charge.

The work done per unit positive charge in bringing a test charge from infinity to a point; it is a scalar and the field equals its negative gradient.

The statement that the electric flux through a closed surface equals the enclosed charge divided by the permittivity, useful for highly symmetric charge distributions.

The ratio of charge stored on a conductor to the potential difference across it; for a parallel-plate capacitor it depends on plate area, separation, and the dielectric.

The emission of electrons from a metal surface when light above a threshold frequency strikes it, explained by quantised photons transferring energy to electrons.

The minimum energy needed to remove an electron from a metal surface; in the photoelectric effect it sets the threshold frequency for emission.

The wavelength associated with a moving particle, equal to Planck's constant divided by the particle's momentum, observable for electrons and other small particles.