OCR GCSE Combined Science A key terms

An operation intended to permanently prevent pregnancy by blocking or cutting the sperm ducts or oviducts.

Short sections of unpaired DNA bases at the ends of cut DNA that can pair with complementary bases on another DNA fragment.

A change in the internal or external environment that can be detected by a receptor.

The relative amounts of reactants and products involved in a reaction, expressed by the mole ratios in its balanced chemical equation.

A small pore in the surface of a leaf that allows gas exchange. Two guard cells control its opening and closing; the plural is stomata.

The total distance a vehicle travels from when the driver recognises the need to stop until the vehicle comes to rest. It is thinking distance plus braking distance.

Shaping an object so that it experiences less resistance as it moves through air or another fluid.

A change in shape in which an object becomes longer because forces pull its parts apart.

An acid that ionises completely in water.

A particle smaller than an atom that forms part of its structure, such as a proton, neutron or electron.

A structure within a cell, such as a nucleus, mitochondrion or ribosome.

The change directly from solid to gas, without passing through the liquid state.

A small number written below and to the right of a chemical symbol or bracket, showing how many atoms or groups are represented.

The substance on which an enzyme acts.

A collision between reactant particles that results in a chemical reaction.

An acidic gas, $\mathrm{SO_2}$, produced when sulfur burns in oxygen, including sulfur impurities in fossil fuels.

The total area of an object's outer surface.

The surface area of an object divided by its volume: $\text{surface area to volume ratio} = \frac{\text{surface area}}{\text{volume}}$.

The exposed surface area of an object divided by its volume. Smaller pieces have a larger surface area-to-volume ratio than larger pieces of the same shape.

The surface area of an object divided by its volume: a measure of how much surface is available per unit of volume.

Water flowing over the land surface into streams, rivers and other bodies of water.

Everything outside the reacting chemical system that can exchange energy with it, including the solution, container and nearby air.

Meeting present needs without compromising future generations’ ability to meet their own needs.

A component that opens or closes a conducting path in a circuit.

A change experienced by an infected person, such as pain or tiredness, that indicates illness.

A junction between neurones where a neurotransmitter carries the signal across a small gap.

The building of a larger molecule from smaller molecules, such as making a lipid from fatty acids and glycerol.