active transport n movement of a chemical substance by the expenditure of energy against a gradient in concentration or electrical potential across a plasma membrane
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(in biochemistry) an energy-dependent process in which certain substances (including ions, some drugs, and amino acids) are able to cross cell membranes against a concentration gradient. The process is inhibited by substances that interfere with cellular metabolism (e.g. high doses of digitalis).
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the movement of substances across the cell membrane, usually up a concentration gradient, produced by the expenditure of metabolic energy. See primary active t. and secondary active t. and cf. passive t.
(A) Passive transport exemplified by diffusion of potassium ions across the plasma membrane, through specific ion channels, down a concentration gradient; (B) active transport exemplified by the cellular sodium pump, which uses ATP hydrolysis to create gradients of sodium and potassium across the plasma membrane.
Medical dictionary. 2011.