Each entry shows which science it belongs to in brackets. Boards phrase things slightly differently, so if your school or specification words a definition another way, learn that wording for your exam.
A
- Alkali (chemistry)
- A base that dissolves in water, producing hydroxide ions (OH-) and a pH above 7. See also: Neutralisation.
- Allele (biology)
- One version of a gene. A person inherits two alleles of each gene, one from each parent. See also: Gene, Phenotype.
- Alternating current (physics)
- Electric current that repeatedly reverses direction. Mains electricity in the UK is of this kind. See also: Potential difference.
- Amplitude (physics)
- Largest displacement of a wave from its rest position. Greater amplitude means the wave carries more energy. See also: Frequency, Wavelength.
- Antibody (biology)
- A protein made by white blood cells that fits one specific antigen on a pathogen and helps to destroy it. See also: Pathogen.
- Atomic number (chemistry)
- Number of protons in the nucleus of an atom. It decides which element the atom belongs to. See also: Isotope, Mass number.
C
- Catalyst (chemistry)
- A substance that speeds up a reaction without being used up. It does this by offering a route with lower activation energy. See also: Enzyme.
- Cell membrane (biology)
- Thin layer around a cell that controls which substances pass in and out. See also: Diffusion, Osmosis.
- Compound (chemistry)
- Substance made of two or more elements chemically joined in a fixed ratio. See also: Ion.
- Conduction (physics)
- Transfer of thermal energy through a solid as vibrating particles pass energy to their neighbours. Metals do it well. See also: Convection.
- Convection (physics)
- Transfer of thermal energy in a liquid or gas as warmer, less dense fluid rises and cooler fluid sinks to replace it. See also: Conduction, Density.
D
- Decomposer (biology)
- An organism, such as a fungus or bacterium, that breaks down dead material and returns nutrients to the soil. See also: Producer.
- Density (physics)
- Mass in a given volume of a material, found by dividing mass by volume. Typical units are g/cm3 or kg/m3. See also: Convection.
- Diffusion (biology)
- Net movement of particles from where they are more concentrated to where they are less concentrated, with no energy supplied by the cell. See also: Osmosis, Cell membrane.
- Displacement reaction (chemistry)
- A reaction in which a more reactive element takes the place of a less reactive one in a compound. See also: Reactivity series.
E
- Electrolysis (chemistry)
- Splitting a molten or dissolved ionic compound into elements by passing a direct current through it. See also: Ion.
- Endothermic (chemistry)
- Describes a change that takes in energy from its surroundings, so the surroundings get colder. See also: Exothermic.
- Enzyme (biology)
- A biological catalyst, made of protein, whose shape suits one type of reaction. Heat or extreme pH can change its shape and stop it working. See also: Catalyst.
- Exothermic (chemistry)
- Describes a change that releases energy to its surroundings, so the surroundings get warmer. Burning fuel is an example. See also: Endothermic.
F
- Frequency (physics)
- Number of complete waves passing a point each second, measured in hertz (Hz). See also: Wavelength, Amplitude.
G
- Gene (biology)
- A short section of DNA that carries the instructions for making one protein. See also: Allele.
H
- Half-life (physics)
- Time taken for half of the unstable nuclei in a sample to decay, or for the count rate from the sample to halve. See also: Isotope.
- Homeostasis (biology)
- Keeping conditions inside the body, such as temperature and blood glucose, within a narrow range despite changes outside. See also: Respiration.
- Hydrocarbon (chemistry)
- A compound containing only hydrogen and carbon atoms. Alkanes such as methane are examples. See also: Polymer.
I
- Ion (chemistry)
- An atom or group of atoms that has gained or lost electrons and so carries an electrical charge. See also: Electrolysis, Compound.
- Isotope (chemistry)
- One of several forms of an element with the same number of protons but a different number of neutrons. See also: Atomic number, Mass number, Half-life.
K
- Kinetic energy (physics)
- Energy an object has because it is moving. It depends on the object's mass and on the square of its speed. See also: Work done.
L
- Limiting reactant (chemistry)
- Reactant that is used up first, so it decides how much product can form. Not every combined course expects it: AQA Trilogy lists it for higher tier only, and OCR (J250 and J260) refers to the effect of a limiting quantity of a reactant.
M
- Mass number (chemistry)
- Total number of protons and neutrons in the nucleus of an atom. See also: Atomic number, Isotope.
- Mitosis (biology)
- Cell division that produces two genetically identical daughter cells. It is used for growth and repair. See also: Stem cell.
N
- Natural selection (biology)
- Process in which individuals with characteristics that suit their environment are more likely to survive and breed, passing those characteristics on. See also: Allele, Phenotype.
- Neutralisation (chemistry)
- Reaction between an acid and a base that forms a salt and water, moving the pH towards 7. See also: Alkali.
O
- Osmosis (biology)
- Net movement of water across a partially permeable membrane from a dilute solution to a more concentrated one. See also: Diffusion, Cell membrane.
P
- Pathogen (biology)
- A microorganism that causes disease, such as a bacterium, virus, fungus or protist. See also: Antibody.
- Phenotype (biology)
- Observable characteristics of an organism, produced by its genes together with its environment. See also: Allele, Gene.
- Photosynthesis (biology)
- Process in which plants and algae use light energy to turn carbon dioxide and water into glucose and oxygen. See also: Respiration, Producer.
- Polymer (chemistry)
- A very long molecule made by joining many small repeating units called monomers. See also: Hydrocarbon.
- Potential difference (physics)
- Energy transferred per unit of charge as it moves between two points in a circuit, measured in volts. See also: Resistance, Alternating current.
- Producer (biology)
- An organism, usually a green plant or alga, that makes its own food by photosynthesis and so starts a food chain. See also: Photosynthesis, Decomposer.
R
- Reactivity series (chemistry)
- A list of metals in order of how readily they react. A metal can displace any metal lower in the list from its compounds. See also: Displacement reaction.
- Resistance (physics)
- How strongly a component opposes the flow of current, found by dividing potential difference by current. Measured in ohms. See also: Potential difference.
- Respiration (biology)
- Chemical reactions in living cells that release energy from glucose. Aerobic respiration uses oxygen. See also: Photosynthesis, Homeostasis.
- Resultant force (physics)
- Single force that has the same effect as all the forces on an object added together, taking direction into account. See also: Velocity.
S
- Specific heat capacity (physics)
- Energy needed to raise the temperature of 1 kg of a substance by 1 degree Celsius. See also: Conduction.
- Stem cell (biology)
- An undifferentiated cell that can divide and turn into specialised cell types. See also: Mitosis.
T
- Transpiration (biology)
- Loss of water vapour from a plant, mainly through the stomata in the leaves, which draws water up from the roots. See also: Diffusion, Osmosis.
V
- Velocity (physics)
- Speed in a stated direction. Two objects can have the same speed but different velocities. See also: Resultant force.
W
- Wavelength (physics)
- Distance from a point on one wave to the same point on the next, such as crest to crest. See also: Frequency, Amplitude.
- Work done (physics)
- Energy transferred when a force moves an object. It equals force multiplied by the distance moved in the direction of the force. See also: Kinetic energy.
Part of the GCSE Combined Science revision set: the revision guide, self-marking quiz and comparison of the three exam boards.