OCR GCSE Combined Science A key terms

Equipment used to carry out an experiment or make a measurement.

A practical use of scientific knowledge to achieve a particular purpose.

Dissolved in water; represented by the state symbol $(\mathrm{aq})$ in a chemical equation.

A solution in which water is the solvent.

A solvent in which water is the solvent or a main part of the solvent mixture.

A measure of central tendency calculated by adding all the values and dividing by the number of values included.

A blood vessel that carries blood away from the heart.

A system that groups organisms using selected convenient features rather than their evolutionary relationships.

A set of working methods that prevents unwanted microorganisms contaminating a culture and reduces the risk of the cultured microorganisms spreading.

A condition or simplification accepted when using a model, which may restrict where its predictions are useful.

The layer of gases surrounding the Earth.

A tiny particle that is the basic building block of an element, consisting of a nucleus surrounded by electrons.

The number of protons in the nucleus of an atom. Each element has a different atomic number.

An approximate distance from the centre of an atom to the outer extent of its electron region.

Adenosine triphosphate: a molecule that transfers energy for processes within cells.

A valve between an atrium and a ventricle that prevents blood flowing back into the atrium when the ventricle contracts.

An upper chamber of the heart that receives blood from veins and passes it into a ventricle.

A force that pulls objects towards one another.

A condition in which the immune system attacks the body's own cells.

An organism that makes its own food from simple substances rather than obtaining food by eating other organisms.

The total distance travelled divided by the total time taken.

The number of specified elementary entities per mole, symbol $N_{\mathrm A}$. Its exact value is $6.022\,140\,76 \times 10^{23}\ \mathrm{mol^{-1}}$, usually rounded to $6.02 \times 10^{23}\ \mathrm{mol^{-1}}$ in GCSE calculations.

A long neurone fibre that carries impulses away from the cell body.

A chemical equation with the same number of atoms of each element on both sides of the reaction arrow.

Forces acting on an object that cancel overall, giving a resultant force of zero.

The number placed before a chemical formula to show the relative number of particles or amounts of substance involved.

A representation in which balls stand for atoms or ions and sticks indicate bonds or connections within the structure.