OCR GCSE Combined Science A key terms

One of two or more different structural forms of the same element.

A mixture of a metal with one or more other elements, made to obtain useful properties.

A positively charged particle used to probe atoms in the gold-foil scattering experiment.

An electric current that repeatedly reverses direction.

An electric current that repeatedly changes direction, supplied to domestic appliances by the mains.

A potential difference that repeatedly reverses polarity, alternating between positive and negative values when measured in a fixed direction.

A small molecule that acts as a monomer in the formation of proteins.

An instrument that measures current and is connected in series with the component being tested.

A measure of how many specified particles a sample contains, measured in moles (mol).

The SI unit of electric current. A current of one ampere means one coulomb of charge passes a point each second.

The maximum distance a vibrating point moves from its undisturbed position, measured in metres (m). Its symbol is $A$.

An enzyme that breaks down starch into maltose.

Respiration that breaks down glucose without using oxygen, yielding much less ATP per molecule of glucose than aerobic respiration.

The angle between an incoming ray and the normal to the surface.

A negatively charged ion.

The positive electrode in electrolysis, towards which negative ions move.

A result that does not fit the overall pattern of the other results.

A result that does not fit the pattern of the other results and may not be part of their ordinary variation.

The opposing effects of two substances or processes, such as insulin lowering blood glucose concentration and glucagon raising it.

Originating from human activity, rather than solely from natural processes.

A medicine that kills bacteria or stops their growth.

The ability of bacteria to survive treatment with an antibiotic that would normally kill them or stop their growth.

A gene that allows cells carrying it to survive exposure to a particular antibiotic, enabling their selection.

A protein produced by lymphocytes that binds to a specific antigen because their shapes are complementary.

Predicting when an event will happen, allowing a person to begin responding before they actually detect it.

A molecule, such as one on a pathogen’s surface, that can be recognised by the immune system and trigger a specific immune response.

A medicine used to lower high blood pressure.