OCR GCSE Combined Science A key terms

A compound containing only carbon and hydrogen atoms.

A solution whose colour responds to changes in carbon dioxide concentration through changes in pH.

A positively charged ion, $\mathrm{H^+}$, supplied by an acid in aqueous solution.

The amount of hydrogen ions, $\mathrm{H^+}$, per unit volume of a solution. A higher hydrogen ion concentration gives a lower pH.

A negatively charged ion, $\mathrm{OH^-}$, consisting of an oxygen atom and a hydrogen atom bonded together.

A proposed explanation or prediction that can be tested using evidence.

A transformer assumed to transfer all its input power to its output, with no energy dissipated to the surroundings.

A series of choices about observable features used to identify an organism.

Describes liquids that do not mix and instead form separate layers.

The body's defence system against pathogens, involving white blood cells.

A medicine that reduces immune-system activity, helping to prevent transplant rejection but increasing susceptibility to infection.

The attachment and embedding of an embryo in the lining of the uterus.

A sample containing more than one substance; chemically, it is a mixture.

An unwanted substance mixed with the substance being examined.

Breeding between closely related organisms.

The number of new cases of a disease in a stated population during a stated period, often expressed per fixed number of people.

The number of new cases of a disease relative to the population size during a stated period, often expressed per 100,000 people per year.

Burning in an insufficient supply of oxygen. Carbon-containing fuels can produce carbon monoxide and solid carbon particles rather than all their carbon forming carbon dioxide.

The factor deliberately changed in an investigation to find out how it affects the results.

A substance that changes colour depending on the pH of a solution.

An observation used to infer something that cannot be observed directly, such as using present-day volcanic gases to help explain the earliest atmosphere.

An object that becomes magnetic when placed in an external magnetic field, usually losing most or all of its magnetism when that field is removed.

The process by which a magnetic material becomes a magnet when placed in a magnetic field.

A ball-shaped object whose collisions do not conserve all the kinetic energy of the colliding objects; bowling balls are a simple comparison used to represent particles.

Chemically unreactive under the conditions used. An inert electrode conducts electricity without taking part in the intended reaction.

An electrode that conducts electricity and provides a surface for reactions without itself taking part in the electrolysis reaction.

An object's resistance to a change in its velocity.