Edexcel GCSE Combined Science key terms

A temperature-sensitive resistor whose resistance decreases as its temperature increases.

The resistance of a single resistor that would draw the same total current as a combination of resistors at the same potential difference.

A specialised nerve cell that transmits electrical impulses.

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

An atom with no overall electric charge because it contains equal numbers of protons and electrons.

A reaction between an acid and a base. In acid–alkali neutralisation, hydrogen ions react with hydroxide ions to form water.

The mains wire that completes the circuit with the live wire and is normally close to earth potential.

A particle in an atom’s nucleus with relative mass 1 and no electric charge.

An instrument that measures force using a calibrated spring and a scale marked in newtons; also called a spring balance.

When two objects interact, each exerts a force on the other that is equal in magnitude and opposite in direction. These forces act on different objects and are the same type of force.

A nitrogen-containing mineral ion, $\mathrm{NO_3^-}$, absorbed by plant roots and used to make amino acids and proteins.

The conversion of ammonium compounds into nitrites and then nitrates by nitrifying bacteria in soil.

The conversion of atmospheric nitrogen gas into nitrogen compounds by nitrogen-fixing bacteria.

An element in Group 0 of the periodic table. Noble gases have full outer electron shells and are very unreactive.

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

Unable to burn.

A species that does not occur naturally in a particular area and has been introduced there.

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

A resource that cannot be replaced as quickly as it is used.

An imaginary line drawn at right angles to a surface at the point where a ray meets it.

The supporting force exerted by a surface on an object, acting perpendicular to the surface.

An equation showing a nuclear change, with the total nucleon number and total electrical charge balanced on both sides.

An atomic model with a small, positively charged central nucleus containing nearly all the atom’s mass, surrounded by electrons, with most of the atom being empty space.

A proton or neutron in an atomic nucleus.

A subunit of DNA consisting of a sugar, a phosphate group and one of four bases attached to the sugar.

The tiny, positively charged central part of an atom, containing protons and neutrons and almost all the atom's mass.

A condition in which excess body fat can damage health.

A hormone produced by the ovaries that repairs and thickens the uterus lining. It also inhibits FSH release and, at high levels before ovulation, stimulates LH release.