Combined Science key terms

Plant transport tissue consisting of tubes of elongated cells with pores in their end walls, carrying dissolved sugars.

The process by which plants and algae use light energy to make glucose from carbon dioxide and water, releasing oxygen.

A structure that blocks pathogen entry or traps and removes pathogens.

A change in which no new substance forms. When a change of state is reversed, the material recovers its original properties.

A change that does not produce new substances, such as dissolving, evaporating or separating the components of a mixture.

A measurable property, such as mass, time or electric current, expressed using a numerical value and a unit.

The form of a substance: solid, liquid or gas, at a stated temperature.

A biological extraction method in which plants absorb metal ions through their roots and are harvested and burned to produce ash containing metal compounds.

A method of extracting metals using plants to absorb metal compounds, followed by harvesting and burning the plants and processing the ash.

A unit of length equal to $10^{-12}$ metres. Its symbol is pm.

An endocrine gland at the base of the brain that releases several hormones, including hormones that stimulate other endocrine glands.

A treatment resembling the medicine being tested but containing none of its active drug, used as a comparison in a trial.

Small organisms that drift in water, including microscopic aquatic plants and animals.

The liquid component of blood, mainly water, which transports dissolved substances and suspends blood cells and platelets.

A small ring of DNA, separate from the main bacterial chromosome, that can carry additional genes such as those for antibiotic resistance.

A flat section of a graph. On a temperature–time graph for melting ice, it shows that the temperature remains approximately constant during melting.

A small cell fragment involved in blood clotting.

A small compass containing a freely turning magnetic needle, used to find the direction of a magnetic field at a point.

An early model of the atom consisting of a ball of positive charge with negative electrons embedded throughout it.

The addition of harmful substances to the environment.

A charged group of atoms that acts as a single ion, such as nitrate, $\mathrm{NO_3^-}$, or sulfate, $\mathrm{SO_4^{2-}}$.

Having extra fingers or toes; the inherited form studied here is caused by a dominant allele.

The inheritance of a characteristic controlled by more than one gene.

A large molecule made from many smaller repeating units joined together.

A group of individuals of the same species living in an area.

The number of organisms per unit area, for example plants per square metre.

The number of organisms in a population.