How does active transport occur across the cell membrane?

Active transport occurs across the cell membrane through the use of energy to move substances against their concentration gradient.

Active transport is a vital process that allows cells to maintain their internal environment, different from the external one. This process involves the movement of molecules or ions across the cell membrane from a region of lower concentration to a region of higher concentration. Unlike passive transport, which relies on the natural diffusion of substances, active transport requires energy, usually in the form of adenosine triphosphate (ATP).

The process of active transport is facilitated by specific proteins embedded in the cell membrane, known as carrier proteins or transport proteins. These proteins act as pumps, binding to the molecules or ions to be transported, and using energy to change their shape and move the substances across the membrane. This is often referred to as primary active transport.

There are two main types of active transport: primary and secondary. Primary active transport directly uses energy to transport molecules across a membrane. A well-known example of this is the sodium-potassium pump in animal cells, which uses ATP to pump sodium ions out of the cell and potassium ions into the cell.

Secondary active transport, on the other hand, involves the use of an electrochemical gradient. This gradient is created by primary active transport and is then used to drive the transport of other substances against their own concentration gradients. This is often coupled with the movement of another molecule that is moving down its concentration gradient, providing the energy for the transport of the other molecule.

In summary, active transport is a crucial cellular process that uses energy to move substances against their concentration gradient, allowing cells to maintain their internal environment. This process is facilitated by carrier proteins in the cell membrane and can involve either direct use of energy (primary active transport) or the use of an electrochemical gradient (secondary active transport).