Which type of transport requires energy to move substances across a cell membrane?

Active transport requires energy to move substances across a cell membrane. This process is necessary for transporting molecules against their concentration gradient, meaning from an area of lower concentration to an area of higher concentration. Cells often utilize ATP (adenosine triphosphate) as the energy source for active transport mechanisms.

This is particularly important for the maintenance of cellular function and homeostasis, as it allows cells to accumulate nutrients and other essential substances despite unfavorable concentration differences. For instance, the sodium-potassium pump is a well-known example of active transport, as it moves sodium ions out of the cell and potassium ions into the cell, which is vital for various cellular processes, including maintaining membrane potential and cell volume.