Respuesta :
Answer:
See below
Explanation:
Active transport is the movement of materials across a membrane that requires an input of energy from a cell. This is because ions move into and out of cells and because cells contain proteins that do not move across the membrane and are mostly negatively charged, there is also an electrical gradient, a difference of charge, across the plasma membrane. the interior of living cells is electrically negative with respect to the extracellular fluid in which they are bathed.
At the same time, cells have higher concentrations of potassium (K+) and lower concentrations of sodium (Na+) than does the extracellular fluid. In a living cell, the concentration gradient of Na+ tends to drive it into the cell, and the electrical gradient of Na+ (a positive ion) also tends to drive it inward to the negatively-charged interior. The situation is more complex, however, for other elements such as potassium.
To move substances against a concentration or electrochemical gradient, the cell must use energy. This energy is harvested from adenosine triphosphate (ATP) generated through the cell’s metabolism. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. Small substances constantly pass through plasma membranes. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements.