NEET UG key terms

An expression showing which base quantities (mass, length, time, current, temperature, amount, luminous intensity) make up a physical quantity, written with their exponents, such as force as M L T^-2. It is used to check equation consistency and convert units.

The digits in a measured value that carry meaningful information about its precision, including all certain digits plus one estimated digit. Rules govern rounding, zeros, and results of multiplication or addition, controlling how answers are reported.

Two-dimensional motion of an object launched into the air and then moving only under gravity, with constant horizontal velocity and constant vertical acceleration. Range, maximum height, and time of flight follow from the launch speed and angle.

The velocity of one body measured from a frame attached to another moving body, found by vector subtraction of the two velocities. It explains river-boat, rain-man, and approach problems where the observer is itself moving.

The acceleration of a body moving on a circular path, directed toward the centre, with magnitude v squared divided by radius. It changes only the direction of velocity, not its magnitude, and requires a centripetal force.

Tilting the outer edge of a curved road so that the horizontal component of the normal reaction supplies part or all of the centripetal force. At the design speed, friction is not needed to keep a vehicle on the curve.

The net work done by all forces on a body equals the change in its kinetic energy. It links force, displacement, and speed without tracking time, and holds for both constant and varying forces.

In a system where only conservative forces do work, the sum of kinetic and potential energy stays constant. Energy shifts between the two forms, as in a pendulum or a freely falling body.

A collision in which both total linear momentum and total kinetic energy are conserved. In one dimension with equal masses, the bodies simply exchange velocities; inelastic collisions conserve momentum but lose kinetic energy.

A body's resistance to change in its rotational motion, equal to the sum of mass times squared distance from the axis for all particles. Its value depends on the axis chosen and on how mass is distributed.

If no external torque acts on a system, its total angular momentum stays constant. Because angular momentum is moment of inertia times angular velocity, a skater pulling in her arms spins faster.

The minimum launch speed needed for a body to leave a planet's gravitational field without further propulsion, equal to the square root of twice gravitational parameter divided by radius. It is independent of launch direction and of the body's mass.

Three statements describing planetary motion: orbits are ellipses with the Sun at one focus; the radius vector sweeps equal areas in equal times; and the square of the period is proportional to the cube of the semi-major axis.

The speed required for a satellite to stay in a given circular orbit, equal to the square root of gravitational parameter divided by orbital radius. It decreases as the orbit becomes higher and is independent of satellite mass.

Oscillation in which restoring acceleration is directly proportional to displacement from equilibrium and directed opposite to it. Displacement follows a sine or cosine in time, and period is independent of amplitude.

A large-amplitude response that occurs when an external periodic force's frequency matches a system's natural frequency. Damping lowers and broadens the peak; it underlies tuning circuits and some mechanical failures.

The apparent change in observed frequency when source and observer move relative to each other: higher when approaching, lower when receding. It applies to sound and light and is used in radar and astronomy.

Complete reflection of light back into a denser medium when it strikes a boundary with a rarer medium beyond the critical angle. It requires travel from denser to rarer medium and underlies optical fibres.

The treatment of amount of substance in moles, where one mole contains Avogadro's number of particles and has a mass in grams equal to the molar mass. It converts between particle counts, masses, and gas volumes.

The simplest whole-number ratio of atoms of each element in a compound, obtained from percentage composition by mass. The molecular formula is a whole-number multiple of it, found using molar mass.

The reactant that is completely consumed first in a chemical reaction and therefore fixes the maximum amount of product formed. Others remain in excess; calculations use moles of this reagent.

Concentration expressed as moles of solute per litre of solution. It changes with temperature because solution volume expands; molality, by contrast, uses kilograms of solvent and is temperature independent.

The minimum energy needed to remove the most loosely bound electron from an isolated gaseous atom or ion. It increases across a period and decreases down a group, with exceptions at half-filled and filled subshells.

A measure of how strongly an atom in a bond attracts the shared electron pair. Differences between bonded atoms create polar bonds and predict bond character, from nonpolar covalent to ionic.

A measure of the size of an atom, usually half the distance between neighbouring nuclei in an element or compound. It generally decreases across a period and increases down a group as shells are added.

An unusually strong intermolecular attraction between a hydrogen atom bonded to N, O, or F and a lone pair on a nearby electronegative atom. It raises boiling points and shapes proteins and DNA.

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts in the direction that partly opposes the change. It predicts how yields respond to altered conditions.

The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric coefficient, at equilibrium for a given temperature. Its size indicates whether products or reactants dominate.

A solution that resists a change in pH when small amounts of acid or base are added, usually made from a weak acid with its conjugate base. Its pH follows the Henderson-Hasselbalch relation.

A logarithmic scale of hydrogen ion activity, with pH equal to the negative logarithm of hydrogen ion concentration. Values below 7 are acidic, above 7 basic, at about 25 degrees Celsius.

A form of stereoisomerism in which molecules are non-superimposable mirror images called enantiomers, usually because a carbon atom carries four different groups. Enantiomers rotate plane-polarised light in opposite directions.

When a hydrogen halide adds to an unsymmetrical alkene, the hydrogen adds to the carbon bearing more hydrogens, giving the more stable carbocation intermediate. Peroxide conditions can reverse this outcome.

The light-driven synthesis of organic compounds from carbon dioxide and water in chloroplasts, releasing oxygen. Light reactions make ATP and NADPH, which the Calvin cycle uses to fix carbon.

A wasteful process in which RuBisCO binds oxygen instead of carbon dioxide, consuming ATP and releasing carbon dioxide without producing sugar. It rises in hot, dry conditions when stomata close.

Loss of water vapour from aerial plant parts, mainly through stomata. It drives upward water movement in the xylem, cools leaves, and is regulated by guard cell turgor.

Shrinking of the protoplast away from the cell wall when a plant cell loses water to a hypertonic solution. It demonstrates osmosis and is reversed by placing the cell in a hypotonic solution.

The response of plants to the relative lengths of day and night, controlling flowering in short-day and long-day plants. Night length is usually the decisive factor, sensed by phytochrome pigments.

Conversion of atmospheric nitrogen gas into ammonia or other usable nitrogen compounds, carried out by free-living bacteria and by symbiotic bacteria such as Rhizobium in root nodules. The enzyme nitrogenase catalyses it.

The two alleles of a gene separate during gamete formation, so each gamete receives only one allele. Random union of gametes at fertilisation then restores the pair in offspring.

A cross between an individual of unknown genotype and one homozygous recessive for the trait. The phenotypes of the offspring reveal whether the unknown parent was homozygous or heterozygous.

The tendency of genes located close together on the same chromosome to be inherited together rather than assorting independently. Recombination frequency between them reflects their distance apart.

Differential survival and reproduction of individuals because of heritable variation, so traits that improve fitness become more common over generations. It is a mechanism of evolutionary change, not a goal-directed process.

Random change in allele frequencies in a population from generation to generation, especially strong in small populations. Unlike natural selection, it is not driven by fitness differences.

The maintenance of a stable internal environment within narrow limits despite external change, achieved by negative feedback involving sensors, control centres, and effectors. Examples include blood glucose and body temperature regulation.

The functional unit of the kidney, consisting of a glomerulus, Bowman's capsule, and tubules. Filtration, selective reabsorption, and secretion together form urine and maintain water and ion balance.

A rapid, self-propagating change in membrane potential of a neuron or muscle cell caused by sequential opening of sodium and potassium channels. It travels along axons and triggers neurotransmitter release.