Is endocytosis an active or passive process?

Endocytosis is considered an active process because it requires the expenditure of energy, typically in the form of ATP (adenosine triphosphate). During endocytosis, the cell membrane engulfs extracellular material, forming a vesicle that brings the material into the cell. This process involves various proteins and cellular machinery, which are dependent on energy to facilitate the movement and deformation of the cell membrane.

In contrast, passive processes, such as diffusion or osmosis, do not require energy as they rely on the natural movement of particles from areas of higher concentration to areas of lower concentration. Since endocytosis actively transports substances into the cell against their concentration gradients and involves significant cellular work, it is classified strictly as an active process.

The other options suggest either a passive mechanism or a combination of processes, neither of which accurately describes the energy demands and mechanisms involved in endocytosis.