OCR GCSE Combined Science A key terms

The organisation of organisms into groups according to shared characteristics.

A long-term change in weather patterns, including average temperatures and rainfall.

Testing a potential medicine in human volunteers and patients to investigate its safety, effectiveness and suitable dose.

A complete conducting path through which charge can flow.

A system in which no substances can enter or leave.

A number placed before a chemical formula in an equation to show the relative amount of that substance. It multiplies every atom in the formula.

A loop, or several turns, of conducting wire through which current can flow.

An encounter in which particles come into contact with one another.

The number of collisions occurring in a given time.

The explanation that reactant particles must collide with sufficient energy for a chemical reaction to occur.

Burning a fuel in oxygen, transferring energy to the surroundings. Complete combustion of carbon-containing fuels produces carbon dioxide.

An ancestral organism from which two or more groups of organisms evolved.

A disease caused by a pathogen that can spread between organisms.

All the populations of different species living in the same area at the same time.

A living cell alongside a sieve-tube element that supports its living functions and provides energy needed for transport.

A small permanent magnet free to turn and align with the magnetic field around it.

An interaction between organisms that need the same resource when its supply is limited.

A substance containing two or more different elements chemically combined in fixed proportions.

A charged group of covalently bonded atoms, such as the nitrate ion, $\mathrm{NO_3^-}$.

A unit formed by combining units, such as metres per second (m/s).

A region of a longitudinal wave where particles are closer together than usual.

A model that uses a computer to apply rules or equations to input data and calculate possible outcomes.

Describes a solution containing a relatively large amount of dissolved substance per unit volume.

The amount of dissolved substance per unit volume of solution. For an acid, $c = n/V$, where $n$ is the amount of acid and $V$ is the solution volume.

A difference in the concentration of a substance between two regions. Net diffusion occurs from higher to lower concentration.

Circles with the same centre. Around a straight current-carrying wire, the wire passes through their common centre.

A judgement about what the evidence shows, limited to what the data can support.