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Definition

noun

A kind of transport wherein ions or molecules move against a concentration gradient, which means movement in the direction opposite that of diffusion – or – movement from an area of lower concentration to an area of higher concentration. Hence, this process will require expenditure of energy, and the assistance of a type of protein called a carrier protein.

Supplement

The movement of a substance across a membrane from a region of its lower concentration to a region of its higher concentration against a concentration gradient, using energy. This energy is supplied through respiration using ATP. Mitochondria ( cell organelles in the cytoplasm) control energy release. Respiratory poisons block energy release, so they can prevent active transport.

Common sites of active transport are root hair cells the wall of small intestine(villi).

Compare: passive transport, diffusion.
See also: concentration gradient.