OCR GCSE Combined Science A key terms

A protective mechanism that acts against a range of pathogens rather than targeting one particular pathogen.

Motion in which an object’s speed, direction or both change.

An imaginary line perpendicular to a surface at the point where a ray meets it.

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

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

A temperature-dependent resistor with a negative temperature coefficient: its resistance decreases as its temperature increases.

The total positive charge of an atomic nucleus, determined by its number of protons.

The mass of an atom’s nucleus, contributed by the protons and neutrons it contains.

An atomic model with a small, positively charged nucleus surrounded by electrons, with most of the atom being empty space.

A way of representing a nucleus using its element symbol, mass number and atomic number: ${}^{A}_{Z}\mathrm{X}$.

A proton or neutron in an atomic nucleus.

A molecular subunit of DNA; many nucleotides join together to form a DNA strand.

The small, positively charged central region of an atom, containing protons and neutrons and almost all of the atom’s mass.

Having excessive body fat, which increases the risk of conditions including type 2 diabetes and cardiovascular disease.

The microscope lens closest to the specimen, which provides the first magnification of its image.

Judging evidence without allowing personal preferences or expectations to influence the conclusion.

Something directly noticed or measured, rather than an explanation of what caused it.

A hormone produced by the ovaries that builds up the uterus lining, inhibits FSH release and, at a high level before ovulation, stimulates LH release.

A conductor for which current is directly proportional to potential difference at constant temperature.

The current through a conductor is directly proportional to the potential difference across it, provided its temperature remains constant.

A thin, transparent fibre along which light signals travel to carry information.

The temperature or pH at which an enzyme-controlled reaction has its highest rate.

The temperature at which an enzyme-controlled process works at its fastest rate.

The characteristic scale of a quantity, expressed as a power of ten rather than an exact value.

A rock containing enough metal or metal compound to make extracting the metal worthwhile.

A member of the large class of carbon-based compounds, usually containing carbon bonded to hydrogen; not every carbon-containing compound is classified as organic.

A single living thing.

A repeated variation or back-and-forth movement. In a radio aerial, electric charges move back and forth.