Active transport is essential when cells need to move substances against their concentration gradient. This process requires energy, typically in the form of ATP. There are two main types of active transport: Primary Active Transport: Directly uses energy to transport molecules. An example is the sodium-potassium pump, which maintains the proper concentration of sodium and potassium ions inside and outside the cell. Secondary Active Transport: Also known as co-transport, this mechanism uses the energy stored in the concentration gradient of one molecule to move another molecule against its gradient. This often involves symporters and antiporters.
