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

Active transport is the process that requires energy to move substances across a cell membrane. This energy is often derived from the hydrolysis of ATP (adenosine triphosphate). Unlike passive transport methods such as diffusion and osmosis, which rely on the natural concentration gradient (moving substances from an area of higher concentration to an area of lower concentration without expending energy), active transport works against the gradient.

This means that substances are moved from regions of lower concentration to regions of higher concentration. This is crucial for maintaining cellular functions, as it allows cells to uptake necessary nutrients or ions that are in lower concentrations outside the cell compared to the inside. For example, in a nerve cell, active transport is used to maintain a difference in ion concentrations, which is essential for generating nerve impulses.

Osmosis, while it involves the movement of water across a semipermeable membrane, is also considered a passive transport mechanism. Therefore, active transport is distinct in that it directly requires energy to facilitate the movement of molecules across the membrane.