AQA GCSE Science Glossary

AQA GCSE Combined Science – Core Glossary

This glossary is designed for AQA GCSE Combined Science (Trilogy). It explains key words from Biology, Chemistry and Physics in calm, clear language to support confident, neuro-inclusive revision.

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Biology Glossary (AQA Combined Science)

These terms link to topics such as cell biology, organisation, infection and response, bioenergetics, homeostasis, inheritance and ecology.

Active transport: Movement of particles from a low to a high concentration using energy from respiration.
Active site: The part of an enzyme where the substrate fits and the reaction happens.
Aerobic respiration: Release of energy from glucose using oxygen. Word equation: glucose + oxygen → carbon dioxide + water.
Anaerobic respiration: Release of energy from glucose without oxygen, making lactic acid in muscles.
Antibody: A protein made by white blood cells that sticks to a specific antigen and helps destroy pathogens.
Antigen: A molecule on the surface of a pathogen that triggers an immune response.
Artery: Blood vessel with thick muscular walls that carries blood away from the heart at high pressure.
Bacteria: Single-celled prokaryotic organisms. Some cause disease; others are useful.
Benign tumour: A growth of abnormal cells that stays in one place and does not spread to other parts of the body.
Capillary: Very thin blood vessel where substances like oxygen and glucose diffuse in and out of cells.
Cell membrane: Thin layer surrounding the cell that controls what enters and leaves.
Cell wall: Rigid layer made of cellulose in plant and algal cells that supports and strengthens the cell.
Chloroplast: Plant cell organelle containing chlorophyll where photosynthesis happens.
Communicable disease: A disease that can spread between people or animals, caused by pathogens.
Diffusion: Net movement of particles from an area of higher concentration to an area of lower concentration.
Enzyme: A biological catalyst made of protein that speeds up chemical reactions in the body.
Eukaryotic cell: Cell that has a nucleus and membrane-bound organelles, e.g. animal and plant cells.
Prokaryotic cell: Smaller cell without a nucleus, e.g. bacterial cell.
Glucose: A simple sugar used in respiration and made in photosynthesis.
Haemoglobin: Red pigment in red blood cells that carries oxygen.
Homeostasis: Maintaining a stable internal environment in the body.
Hormone: Chemical messenger released into the blood by glands and carried to target organs.
Mitochondria: Organelles where most aerobic respiration happens, releasing energy for the cell.
Mitosis: Type of cell division that makes two identical daughter cells for growth or repair.
Non-communicable disease: A disease that cannot be passed from person to person, e.g. coronary heart disease.
Osmosis: Diffusion of water through a partially permeable membrane from high to low water concentration.
Pathogen: Microorganism that causes disease, such as certain bacteria, viruses, fungi or protists.
Photosynthesis: Process in plants that uses light energy to convert carbon dioxide and water into glucose and oxygen.
Plasma: Liquid part of the blood that carries cells and dissolved substances.
Platelets: Cell fragments in the blood that help with clotting at wounds.
Respiration: Process that releases energy from food molecules in cells.
Vaccination: Giving a dead, weakened, or part of a pathogen to stimulate immunity.
Vector (disease): An organism that carries a pathogen from one host to another, e.g. a mosquito.

Chemistry Glossary (AQA Combined Science)

These terms support topics such as atomic structure, bonding, quantitative chemistry, chemical changes, energy changes, rates, organic chemistry and the atmosphere.

Acid: A substance that forms H⁺ ions in solution and has a pH less than 7.
Alkali: A soluble base that forms OH⁻ ions in solution and has a pH greater than 7.
Alloy: A mixture of a metal with other elements to improve properties.
Atom: Smallest part of an element that can still be recognised as that element.
Base: Substance that can neutralise an acid, forming a salt and water.
Catalyst: Substance that speeds up a reaction without being used up.
Concentration: Amount of solute dissolved in a given volume of solution.
Compound: Substance made when atoms of two or more elements are chemically bonded.
Covalent bond: Bond formed when atoms share pairs of electrons.
Crude oil: Mixture of many hydrocarbons, mainly alkanes, formed from ancient biomass.
Electrolysis: Decomposition of an ionic compound using electricity.
Element: Pure substance made of only one type of atom.
Endothermic reaction: Reaction that takes in energy from the surroundings, causing a temperature decrease.
Exothermic reaction: Reaction that releases energy to the surroundings, causing a temperature increase.
Formula: Representation of a substance using chemical symbols, e.g. H₂O.
Group (periodic table): Vertical column of elements that have similar chemical properties.
Hydrocarbon: Compound made only of hydrogen and carbon atoms.
Ion: Charged particle formed when atoms or groups of atoms lose or gain electrons.
Ionic bond: Electrostatic attraction between oppositely charged ions.
Isotope: Atoms of the same element with the same number of protons but different numbers of neutrons.
Mixture: Two or more substances not chemically bonded and easily separated.
Neutralisation: Reaction between an acid and a base to form a salt and water.
Oxidation: Reaction involving gain of oxygen or loss of electrons.
Periodic table: Chart of elements arranged in order of atomic (proton) number.
pH scale: Scale from 0 to 14 showing how acidic or alkaline a solution is.
Product: Substance made in a chemical reaction.
Reactant: Starting substance in a chemical reaction.
Reduction: Reaction involving loss of oxygen or gain of electrons.
Relative formula mass (Mr): Sum of the relative atomic masses of all atoms in a formula; unit-less.
State symbol: Letter in brackets after a formula showing physical state: (s), (l), (g), (aq).
Thermal decomposition: Breaking down a compound using heat.

Physics Glossary (AQA Combined Science)

These terms support topics such as energy, electricity, particle model, atomic structure, forces, waves and magnetism.

Acceleration: Change in velocity per second. Measured in m/s².
Amplitude: Maximum displacement of a wave from its rest position.
Atomic number: Number of protons in the nucleus of an atom.
Beta radiation: Radiation made of fast-moving electrons from the nucleus.
Current: Flow of electric charge per second. Measured in amperes (A).
Density: Mass per unit volume of a substance. Density = mass ÷ volume.
Efficiency: Useful energy output ÷ total energy input (often as a percentage).
Energy store: Way energy is kept, e.g. kinetic, gravitational, thermal, elastic, chemical.
Frequency: Number of wave cycles per second. Measured in hertz (Hz).
Gravitational field strength: Force on 1 kg in a gravitational field. Measured in N/kg.
Half-life: Time for the activity or number of radioactive nuclei to halve.
Joule (J): Unit of energy and work.
Kinetic energy: Energy an object has because it is moving.
Longitudinal wave: Wave where vibrations are parallel to the direction of energy transfer, e.g. sound.
Magnetic field: Region where a magnetic material or moving charge experiences a force.
Mass: Amount of matter in an object. Measured in kilograms (kg).
Newton’s first law: If the resultant force is zero, an object stays at rest or moves at constant velocity.
Potential difference (voltage): Energy transferred per coulomb of charge. Measured in volts (V).
Power: Rate of energy transfer or work done per second. Measured in watts (W).
Resistance: How much a component opposes current. Measured in ohms (Ω).
Resultant force: Single force that has the same effect as all the forces acting on an object.
Scalar quantity: Quantity with magnitude only, e.g. speed, distance, mass.
Vector quantity: Quantity with magnitude and direction, e.g. velocity, force.
Specific heat capacity: Energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Speed: Distance travelled per unit time. Measured in m/s.
Transverse wave: Wave where vibrations are at right angles to the direction of energy transfer, e.g. light.
Velocity: Speed in a given direction.
Work done: Energy transferred when a force moves an object. Work = force × distance.

Working Scientifically & Exam Language

These words appear in practical work and exam questions across all three sciences.

Accuracy: How close a measurement is to the true value.
Anomalous result: A result that does not fit the pattern of the other data.
Calibration: Checking or setting a measuring instrument using known values.
Control variable: A variable that must be kept the same to make a test fair.
Dependent variable: The variable that is measured in an investigation.
Independent variable: The variable that is changed on purpose in an investigation.
Hypothesis: A testable idea or prediction about what you think will happen.
Precision: How close repeated measurements are to each other.
Prediction: Statement suggesting what will happen in a new situation, based on evidence.
Reliability: How consistent results are when an investigation is repeated.
Repeatable: When the same person gets similar results using the same method and equipment.
Reproducible: When different people or methods give similar results.
Resolution: The smallest change a measuring instrument can detect.
Risk assessment: Identifying possible dangers and how to reduce them before a practical.
Systematic error: Error that shifts all results in one direction, often due to faulty equipment or method.
Random error: Error that causes results to vary in an unpredictable way from measurement to measurement.
Uncertainty: The range within which the true value is expected to lie.

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This glossary is designed to support AQA GCSE Combined Science: Trilogy. It is for learning support only and does not replace the official specification or exam materials.