How is energy used in active transport across cell membranes?

Energy is used in active transport to move molecules against their concentration gradient across cell membranes.

Active transport is a process that enables cells to move substances across the cell membrane against their concentration gradient, from an area of lower concentration to an area of higher concentration. This process is vital for maintaining the cell's internal environment and for specific functions such as nerve transmission. However, unlike passive transport, which relies on the natural movement of substances down their concentration gradient, active transport requires energy.

The energy used in active transport is typically derived from adenosine triphosphate (ATP), a molecule that stores and releases energy within cells. When a cell needs to transport a substance against its concentration gradient, it uses an enzyme called ATPase to break down ATP, releasing energy. This energy is then used to change the shape of a transport protein embedded in the cell membrane, allowing the substance to be moved across.

There are two main types of active transport: primary and secondary. In primary active transport, the energy from ATP is used directly to transport substances across the membrane. An example of this is the sodium-potassium pump, which uses ATP to pump sodium ions out of the cell and potassium ions into the cell.

In secondary active transport, the energy from ATP is used indirectly. Instead of powering the transport directly, ATP is used to create a concentration gradient for one substance, and this gradient is then used to transport another substance. An example of this is the glucose-sodium symporter, which uses the sodium gradient created by the sodium-potassium pump to transport glucose into the cell.

In summary, energy is crucial for active transport as it enables cells to move substances against their concentration gradient, maintaining the cell's internal environment and enabling specific functions. This energy is typically derived from ATP and is used to change the shape of transport proteins or to create concentration gradients that power transport.