OCR GCSE Combined Science A key terms

Growing several crop species or varieties together rather than a single crop.

Inheritance in which more than one gene contributes to a characteristic.

A substance made of very large molecules containing repeating units, with strong covalent bonds between the atoms within each molecule.

A suction device with a collecting chamber and two tubes, used to collect small invertebrates.

All the organisms of one species living in a defined area at the same time.

The number of individuals of a species per unit area, for example per square metre.

A relationship in which two quantities tend to increase together or decrease together. It does not, by itself, prove that one causes the other.

An atom or group of atoms with an overall positive electrical charge. A metal atom becomes a positive ion when it loses electrons.

Water that is safe to drink. It may contain dissolved substances at safe concentrations, so it need not be chemically pure.

The energy transferred per unit charge between two points, measured in volts (V).

Energy particles have because of their positions relative to one another and the forces between them.

An apparatus used to measure the rate at which a cut plant shoot takes up water.

The rate of doing work or transferring energy, measured in watts (W).

A number written as ten raised to an exponent. Positive exponents represent repeated multiplication by ten; negative exponents represent reciprocals, such as $10^{-3}=1/1000$.

The stated power of an appliance when operating under its specified conditions, indicating how much energy it transfers per unit time.

A device that provides a potential difference to a circuit; a d.c. supply has positive and negative terminals.

A unit of concentration meaning parts per million. An atmospheric CO₂ concentration of 420 ppm means approximately 420 CO₂ molecules in every million air molecules.

A measure taken to reduce the likelihood or severity of harm.

An insoluble solid that forms during a reaction in solution.

Water falling from clouds as rain, snow, sleet or hail.

How close repeated measurements are to one another.

Testing a potential medicine before human trials, using laboratory cells, tissues and live animals; computer models may also help.

An interaction in which a predator hunts, kills and eats another organism, its prey.

An expected observation or result deduced from a hypothesis or scientific explanation.

A word or symbol placed before a unit to indicate a particular multiplier, such as kilo (k), meaning $10^3$.

The force exerted per unit area on a surface, measured in pascals (Pa).

The input coil of a transformer, connected to the alternating-current supply.

The chance of an outcome occurring, expressed as a fraction, decimal or percentage.