SPM Additional Science key terms

A testable statement predicting the relationship between variables, written before an experiment so that results can be judged as supporting or contradicting it rather than interpreted after the fact.

The factor the experimenter deliberately changes between trials so its effect on the outcome can be observed; it is plotted on the horizontal axis of a graph.

The factor measured in an experiment because it is expected to respond to the change made by the experimenter; it is plotted on the vertical axis.

Any factor other than the independent variable that is kept the same across all trials, so that observed changes can be attributed to the intended cause.

The number of protons in the nucleus of an atom, which fixes the element's identity and its position in the periodic table; also called atomic number.

The total number of protons and neutrons in an atomic nucleus, also called mass number; subtracting the proton number gives the number of neutrons.

One of two or more atoms of the same element with identical proton numbers but different numbers of neutrons, so they share chemical properties yet differ in mass.

The strong electrostatic attraction formed when a metal atom transfers electrons to a non-metal atom, producing oppositely charged ions that pack into a giant lattice.

A bond formed when two atoms share one or more pairs of electrons, typically between non-metal atoms, giving discrete molecules or giant covalent structures.

The amount of substance containing 6.02 x 10^23 particles, allowing masses in grams to be converted into numbers of particles for stoichiometric calculation.

The mass of one mole of a substance in grams per mole, obtained by adding the relative atomic masses of all atoms shown in its formula.

A chemical equation in which the number of atoms of each element is equal on both sides, reflecting conservation of mass and giving usable mole ratios.

The decomposition of an ionic compound, molten or in aqueous solution, by passing a direct electric current through it using inert or reactive electrodes.

The change in amount of reactant used or product formed per unit time; increased by higher concentration, higher temperature, larger surface area or a catalyst.

A substance that speeds up a chemical reaction by providing an alternative pathway of lower activation energy, while remaining chemically unchanged in mass and composition at the end.

The single force that has the same effect as all the individual forces acting on an object combined; a zero resultant means the object's motion does not change.

The rate at which velocity changes with time, measured in metres per second squared; it occurs whenever a resultant force acts on an object with mass.

The product of an object's mass and its velocity, a vector quantity conserved in collisions and explosions when no external resultant force acts on the system.

The energy an object possesses because of its motion, calculated as one half of its mass multiplied by the square of its speed, measured in joules.

The statement that the current through a metallic conductor at constant temperature is directly proportional to the potential difference across it, so resistance stays constant.

A measure of how strongly a component opposes current, equal to potential difference divided by current, measured in ohms and increased by longer or thinner wires.

The energy transferred per unit charge between two points in a circuit, measured in volts; it is supplied by a source and dropped across components.

A temporary magnet made by winding a coil around a soft iron core and passing current through it; its strength rises with current, turns and the presence of the core.

The generation of a potential difference in a conductor when it experiences a changing magnetic field, the principle behind generators and transformers.

The number of complete waves passing a fixed point each second, measured in hertz; it determines pitch for sound and colour for visible light.

The distance between two consecutive corresponding points on a wave, such as crest to crest, measured in metres and related to frequency through wave speed.

The maximum displacement of a wave from its rest position; for sound it relates to loudness, and for light to brightness.

The bending of a wave as it passes from one medium into another of different optical density, caused by a change in wave speed at the boundary.

The complete reflection of light inside a denser medium when it strikes a boundary beyond the critical angle, used in optical fibres and reflecting prisms.

The net movement of water molecules across a partially permeable membrane from a dilute solution to a more concentrated one, down a water potential gradient.

The net spreading of particles from a region of higher concentration to one of lower concentration, caused by random motion and requiring no energy input.

The movement of ions or molecules across a cell membrane against a concentration gradient using energy from respiration and carrier proteins.

A rapid, involuntary response to a stimulus that travels through a reflex arc without involving conscious decision-making in the brain.

A specialised nerve cell that carries electrical impulses, consisting of a cell body, dendrites and a long axon insulated by a myelin sheath.

The maintenance of a stable internal environment, such as constant body temperature and blood glucose, through negative feedback involving receptors and effectors.

A control mechanism in which a deviation from the normal value triggers a response that reverses the deviation, restoring the set point.

The position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer, determined by how it obtains energy.

A diagram showing the many interconnected food chains in a habitat, illustrating how energy flows between organisms and how populations depend on one another.

The enrichment of water with nutrients such as nitrates, leading to algal blooms, oxygen depletion and the death of aquatic organisms.