| 释义 |
active transport
active transportn. 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 (Biochemistry) biochem physiol a process by which molecules are enabled to pass across a membrane from a region in which they are in a low concentration to one of high concentration; this requires the expenditure of energy in metabolism and is assisted by carrier proteins, commonly referred to as pumps ac′tive trans′port
n. the movement of ions or molecules across a cellular membrane from a lower to a higher concentration. [1960–65] 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. The energy needed for active transport is supplied by ATP.active transportAn energy-requiring process which carries substances across cell membrane against a concentration gradient.Thesaurus| Noun | 1. |  active transport - transport of a substance (as a protein or drug) across a cell membrane against the concentration gradient; requires an expenditure of energydrug - a substance that is used as a medicine or narcotictransport - an exchange of molecules (and their kinetic energy and momentum) across the boundary between adjacent layers of a fluid or across cell membranes |
active transport
active transport[′ak·tiv ′tranz‚pȯrt] (physiology) The pumping of ions or other substances across a cell membrane against an osmotic gradient, that is, from a lower to a higher concentration. active transport
active transport [ak´tiv trans´port] the movement of ions or molecules across membranes" >cell membranes and epithelial layers, usually against a concentration gradient, as a direct result of the expenditure of metabolic energy. For example, under normal circumstances more potassium ions are present within the cell and more sodium ions are present extracellularly. The process of maintaining these normal differences in electrolytic composition between the intracellular and extracellular fluids is active transport. The process differs from transport" >passive transport, simple diffusion, and osmosis in that it requires the expenditure of metabolic energy.ac·tive trans·portthe passage of ions or molecules across a cell membrane, not by passive diffusion but by an energy-consuming process at the expense of catabolic processes proceeding within the cell; in active transport, movement takes place against an electrochemical gradient.active transportn. 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 The transportation across membranes by a membrane-bound protein complex of ions, nutrients or other molecules against a concentration gradient, which requires hydrolysis of high-energy phosphate bonds—e.g., ATP.ac·tive trans·port (ak'tiv trans'pōrt) The passage of ions or molecules across a cell membrane, not by passive diffusion but by an energy-consuming process against an electrochemical gradient. active transport The movement of dissolved substances across a membrane in the direction opposite to that of normal diffusion. Active transport operates against gradients of chemical concentration, electrical charge or electrochemical state. It requires the expenditure of energy. Fig. 12 Active transport . Active transport across a membrane. active transport movement of a substance from a region of low concentration to another of higher concentration, i.e. against the CONCENTRATION GRADIENT. Such transport typically occurs in cell membranes, which are thought to contain carriers which move molecules from one side of the membrane to the other. Since these processes involve movement up a free-energy gradient, they require the expenditure of energy from the breakdown of ATP and are therefore sensitive to factors affecting metabolism (temperature, oxygen, pH, etc.). Compare DIFFUSION. See ACTIVE ABSORPTION.transport, active A process by which particles (e.g. ions, molecules) are transported across cell membranes, against, in almost all instances, the concentration gradient. It requires energy, which is provided by the metabolism of carbohydrates, proteins or lipids and cellular energy, which is obtained from splitting adenosine triphosphate (ATP).(Example: the sodium/ potassium pump that keeps sodium ions out of a cell and potassium ions in). When this process results in a compound being released, it is termed 'secretion'. This process is one of the mechanisms by which aqueous humour is produced in the ciliary body. See action potential; ultrafiltration.ac·tive trans·port (ak'tiv trans'pōrt) Passage of ions or molecules across a cell membrane by an energy-consuming process at the expense of catabolic processes proceeding within the cell. FinancialSeeActiveactive transport
Words related to active transportnoun transport of a substance (as a protein or drug) across a cell membrane against the concentration gradientRelated Words |