| the movement of ions or molecules across a cellular membrane from a lower to a higher concentration, requiring the consumption of energy. |
| active transport n. The movement of a chemical substance through a gradient of concentration or electrical potential in the direction opposite to normal diffusion, requiring the expenditure of energy: active transport across a cell membrane. |
active transport n.
The passage of ions or molecules across a cell membrane against an electrochemical or concentration gradient, or against the normal direction of diffusion.
| active transport
The movement of ions or molecules across a cell membrane in the direction opposite that of diffusion, that is, from an area of lower concentration to one of higher concentration. Active transport requires the assistance of a type of protein called a carrier protein, using energy supplied by ATP. |