OCR GCSE Science Glossary

OCR GCSE Combined Science (Gateway) – Core Glossary

This glossary is designed for OCR GCSE Combined Science A (Gateway, J250). 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 (OCR Combined Science)

These terms link to OCR Biology topics B1–B6, including cell level systems, scaling up, organism level systems, communities, genes and global challenges.

Cell: The basic structural and functional unit of all living organisms.
Nucleus: Organelle containing DNA that controls the activities of a eukaryotic cell.
Mitochondria: Organelles where most aerobic respiration happens, releasing energy for the cell.
Ribosome: Tiny structure in the cytoplasm where proteins are made.
Chloroplast: Plant cell organelle containing chlorophyll where photosynthesis takes place.
Eukaryotic cell: Cell with a nucleus and membrane-bound organelles, e.g. animal and plant cells.
Prokaryotic cell: Smaller cell without a nucleus; genetic material is free in the cytoplasm, e.g. bacteria.
Diffusion: Spreading out of particles from an area of higher concentration to an area of lower concentration.
Osmosis: Diffusion of water through a partially permeable membrane from high to low water concentration.
Active transport: Movement of substances from a low to a high concentration using energy from respiration.
Enzyme: A biological catalyst made of protein that speeds up chemical reactions in cells.
DNA: Long molecule with a double-helix structure that carries genetic information.
Gene: A small section of DNA that codes for a particular protein or characteristic.
Chromosome: Long DNA molecule found in the nucleus, carrying many genes.
Allele: Different version of the same gene, which may give different characteristics.
Dominant allele: Allele that is expressed in the phenotype even if only one copy is present.
Recessive allele: Allele that is only expressed in the phenotype when two copies are present.
Mutation: A change in the DNA sequence which may lead to a new allele.
Natural selection: Process where individuals with better adaptations are more likely to survive and reproduce.
Variation: Differences in characteristics between individuals of the same species.
Organ system: Group of organs working together to carry out a particular function.
Surface area to volume ratio: Comparison of the size of an object’s surface to its volume, affecting rates of exchange.
Reflex arc: Pathway of neurons that produces a rapid, automatic response to a stimulus.
Hormone: Chemical messenger released by endocrine glands and carried in the blood to target organs.
Homeostasis: Maintaining stable internal conditions in the body, such as temperature and blood glucose.
Pathogen: Microorganism that causes disease, such as certain bacteria, viruses, fungi or protists.
Population: All the organisms of the same species living in a particular area at the same time.
Community: All the different populations of organisms living and interacting in a habitat.
Ecosystem: The community of organisms and the non-living conditions in an area.
Biodiversity: The variety of different species and habitats in an ecosystem or on Earth.
Food security: Having reliable access to enough safe, nutritious food for a population.

Chemistry Glossary (OCR Combined Science)

These terms support OCR Chemistry topics C1–C6, including particles, elements and compounds, reactions, predicting products, controlling reactions and global challenges.

Particle model: Idea that all substances are made of tiny particles whose arrangement and movement explain their properties.
State of matter: The physical form of a substance: solid, liquid or gas.
Element: Pure substance made of only one type of atom.
Compound: Substance formed when atoms of two or more elements are chemically bonded together.
Mixture: Two or more substances not chemically bonded, which can be separated by physical methods.
Atom: Smallest part of an element that can still be recognised as that element.
Ion: Charged particle formed when an atom or group of atoms loses or gains electrons.
Ionic bond: Electrostatic attraction between oppositely charged ions, usually metal and non-metal.
Covalent bond: Bond formed when non-metal atoms share pairs of electrons.
Balanced symbol equation: Symbol equation that shows the correct formulas and equal numbers of each atom on both sides.
Reactant: Substance present at the start of a chemical reaction.
Product: Substance formed in a chemical reaction.
Exothermic reaction: Reaction that transfers energy to the surroundings, usually causing a temperature rise.
Endothermic reaction: Reaction that takes in energy from the surroundings, usually causing a temperature drop.
Conservation of mass: Principle that the total mass of reactants equals the total mass of products in a closed system.
Concentration: The amount of solute dissolved in a given volume of solution.
Rate of reaction: How quickly reactants are used up or products are formed.
Catalyst: Substance that speeds up a reaction without being used up.
Precipitate: An insoluble solid that forms when two solutions react together.
Indicator: Substance that changes colour depending on whether a solution is acidic or alkaline.
pH scale: Scale from 0 to 14 that shows how acidic or alkaline a solution is.
Neutralisation: Reaction between an acid and an alkali or base to form a salt and water.
Electrolysis: Breaking down of an ionic compound using an electric current.
Oxidation: Reaction where a substance gains oxygen or loses electrons.
Reduction: Reaction where a substance loses oxygen or gains electrons.
Ore: Rock that contains enough of a metal or metal compound to make extraction economical.
Finite resource: Resource that is being used up faster than it is formed and will eventually run out.
Sustainable development: Meeting present needs without reducing the ability of future generations to meet theirs.

Physics Glossary (OCR Combined Science)

These terms support OCR Physics topics P1–P6, including matter, forces, electricity and magnetism, waves and radioactivity, energy and global challenges.

Density: Mass per unit volume of a substance. Density = mass ÷ volume.
Specific latent heat: Energy needed to change the state of 1 kg of a substance without changing its temperature.
Specific heat capacity: Energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Force: A push or pull that can change the motion or shape of an object. Measured in newtons (N).
Resultant force: Single force that has the same effect as all the forces acting on an object.
Weight: Force acting on an object due to gravity. Weight = mass × gravitational field strength.
Acceleration: Change in velocity per second. Measured in m/s².
Scalar quantity: Quantity with magnitude only, e.g. speed, distance, mass.
Vector quantity: Quantity with magnitude and direction, e.g. velocity, force.
Work done: Energy transferred when a force moves an object. Work = force × distance moved.
Energy store: Way energy is kept, such as kinetic, gravitational, thermal, elastic or chemical.
Power: Rate of energy transfer or work done per second. Measured in watts (W).
Efficiency: Ratio of useful output energy to total input energy, often given as a percentage.
Current: Flow of electric charge per second in a circuit. Measured in amperes (A).
Potential difference (voltage): Energy transferred per coulomb of charge between two points. Measured in volts (V).
Resistance: How much a component opposes the flow of current. Measured in ohms (Ω).
Ohm’s law: For a fixed temperature, current through a resistor is directly proportional to the potential difference across it.
Amplitude: Maximum displacement of a wave from its rest position.
Frequency: Number of wave cycles passing a point each second. Measured in hertz (Hz).
Wavelength: Distance between the same point on two neighbouring waves, such as crest to crest.
Transverse wave: Wave where vibrations are at right angles to the direction of energy transfer, e.g. light waves.
Longitudinal wave: Wave where vibrations are parallel to the direction of energy transfer, e.g. sound waves.
Half-life: Time taken for the activity or number of radioactive nuclei in a sample to halve.
Ionising radiation: Radiation that can remove electrons from atoms or molecules to form ions, such as alpha, beta and gamma.
Renewable energy resource: Energy source that will not run out on a human timescale, e.g. wind, solar and tidal.
Non-renewable energy resource: Energy source that will run out, such as coal, oil and gas.

Working Scientifically & Exam Language (OCR)

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

Accuracy: How close a measured value is to the true or accepted value.
Precision: How close repeated measurements are to each other.
Repeatable: When the same person using the same method and equipment gets similar results.
Reproducible: When different people or methods give similar results.
Independent variable: The variable that is deliberately changed in an investigation.
Dependent variable: The variable that is measured in response to changes in the independent variable.
Control variable: Variable that must be kept the same to make the test fair.
Hypothesis: A testable idea or prediction about what you think will happen.
Anomalous result: Result that does not fit the pattern of the other data points.
Random error: Error that causes results to vary in an unpredictable way from measurement to measurement.
Systematic error: Error that shifts all results in one direction, often due to a fault in equipment or method.
Resolution: The smallest change a measuring instrument can detect.
Uncertainty: The range within which the true value is expected to lie.
Risk assessment: Process of identifying hazards and deciding how to reduce risks in practical work.

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This glossary is designed to support OCR GCSE Combined Science A (Gateway, J250). It is for learning support only and does not replace the official specification or exam materials.