Combined Science key terms

A single layer of graphite, consisting of a flat sheet of covalently bonded carbon atoms one atom thick.

A form of carbon with a giant covalent structure consisting of layers of hexagonal rings. Each carbon atom bonds to three others and contributes one delocalised electron.

The gravitational force per kilogram of mass at a particular location, measured in newtons per kilogram (N/kg).

An attractive non-contact force between objects with mass.

The energy associated with an object's position in a gravitational field. Raising an object increases the gravitational potential energy of the object–Earth system.

Energy stored because of the positions of objects in a gravitational field, such as an object raised above the ground.

The natural warming of the Earth's surface and atmosphere because greenhouse gases absorb outgoing infrared radiation and re-emit some towards the surface, reducing energy loss to space.

A gas that absorbs radiation emitted by the Earth and re-radiates energy, helping to warm the surface and atmosphere. Carbon dioxide and methane are examples.

Water stored underground in soil and rocks.

A vertical column of the periodic table containing elements with similar chemical properties.

A permanent increase in the size or mass of an organism.

One of a pair of specialised cells surrounding a leaf pore and controlling whether it is open or closed.

The industrial manufacture of ammonia by reacting nitrogen with hydrogen using an iron catalyst at 450 °C and 200 atmospheres.

The place where an organism lives.

A protein in red blood cells that binds reversibly to oxygen.

An equation showing the reaction at one electrode, including the electrons gained or lost. Both atoms and total charge must balance.

The time taken for the number of nuclei of a radioactive isotope in a sample to halve, or for the sample’s count rate or activity to fall to half its initial level.

A compound containing a halogen combined with another element, such as sodium chloride or hydrogen bromide.

A negatively charged ion formed when a halogen atom gains one electron, such as $\mathrm{Cl^-}$.

An element in Group 7 of the periodic table. Halogen atoms have seven electrons in their outer shell.

Describes a cell or nucleus containing a single set of chromosomes.

A nucleus containing one set of chromosomes: half the normal number found in body cells.

A substance, object or situation that could cause harm, such as a corrosive chemical or hot apparatus.

A pictogram used to warn people about the dangers associated with a substance.

The state of physical and mental well-being.

A condition in which the heart cannot pump blood around the body effectively.

The number of times the heart beats per minute.