OCR GCSE Combined Science B key terms

A unit of length equal to $10^{-9}$ metres. There are 1000 nanometres in one micrometre.

A particle approximately 1–100 nanometres in size. Its properties may differ from those of the same material in bulk.

The use and control of structures between 1 and 100 nanometres in size.

The network of cables and transformers that distributes electrical power from power stations to users.

The process in which organisms with inherited characteristics better suited to their environment are more likely to survive and reproduce, making those characteristics more common over generations.

A relationship in which higher values of one variable tend to occur with lower values of another.

A control mechanism in which a change triggers responses that oppose the change, returning a condition towards its normal level.

A flat arrangement of faces that can be folded to form a three-dimensional solid.

The overall decrease in a quantity: its initial value minus its final value. For radioactive emission, the fractional net decline is the decrease in activity divided by the initial activity.

The overall gas exchange remaining after the effects of photosynthesis and respiration have both been taken into account.

A specialised nerve cell that carries electrical impulses.

A chemical messenger released by a neurone that diffuses across a synaptic gap and binds to receptors on the next cell.

A reaction in which an acid reacts with a base to form a salt and water.

The condition in which hydrogen ions and hydroxide ions have equal concentrations. In the usual school pH scale, a neutral solution has pH 7.

The mains wire that completes the normal circuit through an appliance and is at approximately the same potential as earth.

A particle in the nucleus with no electrical charge and relative mass approximately 1.

An object remains at rest or moves with constant velocity unless a non-zero resultant force acts on it.

The resultant force on an object equals its mass multiplied by its acceleration: $F = ma$.

Whenever two objects interact, they exert equal and opposite forces on each other.

A Group 0 element whose atoms have a full outer electron shell and are generally chemically unreactive.

A fixed point on a stationary wave where there is no vibration.

A solvent that is not water-based, such as ethanol.

Not readily broken down by microorganisms, so it can persist in the environment.

A disease that cannot be passed from one individual to another.

A force that acts between objects without them touching, through a field.

A system in which substances can enter or leave, for example through the open neck of a flask.

A circuit component whose current is not directly proportional to the potential difference across it; its I–V characteristic is not a straight line through the origin.

An energy resource with a finite supply that is not replaced on a human timescale.