Active transport is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration, which is against their concentration gradient. This process requires cellular energy, usually in the form of ATP, because it moves substances "uphill" against their natural diffusion direction

. There are two main types of active transport:

• Primary active transport , which directly uses chemical energy (ATP) to transport molecules. An example is the sodium-potassium pump that moves sodium ions out of the cell and potassium ions into the cell

• Secondary active transport , which uses the energy stored in an electrochemical gradient created by primary active transport to move other substances against their gradient

Active transport is essential for physiological functions such as nutrient uptake in the intestines, ion absorption in plant root hairs, hormone secretion, and nerve impulse transmission. It involves specific carrier proteins or pumps that selectively transport molecules like glucose, ions, and amino acids

. Additionally, active transport can include processes like endocytosis (cell intake of large particles or fluids) and exocytosis (removal of substances from the cell), which also require energy

. In summary, active transport is a vital cellular mechanism that moves substances against their concentration gradient using energy, enabling cells to maintain necessary concentrations of molecules for proper function