OCR GCSE Combined Science A key terms

A three-dimensional molecular representation using touching or overlapping spheres to show the space occupied by atoms.

A model that shows how parts are arranged or positioned relative to one another.

A cell with structures suited to carrying out a particular function.

The formation of new species from an existing species.

A group of organisms that can interbreed to produce fertile offspring.

The number of different species present in an area.

The energy needed to raise the temperature of 1 kg of a substance by 1°C, without a change of state. Its unit is J/(kg °C).

The thermal energy required to change the state of 1 kg of a substance without changing its temperature. Its SI unit is J/kg.

The thermal energy required to change 1 kg of a substance from solid to liquid without changing its temperature. The same amount is released when 1 kg freezes.

The thermal energy required to change 1 kg of a substance from liquid to gas without changing its temperature. The same amount is released when 1 kg condenses.

A sample of biological material selected for observation, such as a thin layer of onion tissue.

An ion that remains unchanged in solution during a reaction.

The distance travelled per unit time, measured in metres per second (m/s).

A thin strip of wood used to test gases, either while burning with a flame or while glowing without a flame.

A reproductive unit of a fungus that can develop into new fungal growth in suitable conditions.

A measure of a spring's stiffness, represented by $k$ and measured in newtons per metre (N/m). A larger spring constant means more force is needed for the same extension.

A substance that increases contrast between parts of a specimen, making some structures easier to distinguish.

A way of writing a number as $a \times 10^k$, where $1 \leq a < 10$ and $k$ is an integer.

A stable pattern of oscillation that does not appear to travel along the material carrying the wave.

A test using iodine solution: a blue-black colour indicates starch is present; an orange-brown colour indicates starch is absent.

A physical form of a substance, such as solid, liquid or gas.

A label written after a chemical formula in an equation to show whether the substance is solid, liquid, gaseous or dissolved in water.

A sudden movement of accumulated electric charge that reduces a build-up of static charge and may produce a spark.

A build-up of electric charge on an object.

A medicine that lowers blood LDL cholesterol, helping slow the build-up of fatty deposits in arteries.

The phase that stays in place during chromatography and interacts with the components of the mixture.

An undifferentiated cell that can divide to produce more stem cells and can differentiate into specialised cells.