Which of the following is not considered a form of passive transport?

Endocytosis is a process that involves the active transport of substances into a cell by engulfing them in a portion of the cell membrane, which then pinches off to form a vesicle inside the cell. This mechanism requires energy in the form of ATP because it is moving materials against their concentration gradient or into the cell in a way that is not inherently spontaneous.

In contrast, diffusion, facilitated diffusion, and osmosis are all considered forms of passive transport. They occur naturally without the input of energy, relying instead on the concentration gradients of substances. Diffusion involves the movement of molecules from an area of higher concentration to an area of lower concentration. Facilitated diffusion is similar but involves specific carrier proteins assisting certain molecules across the cell membrane. Osmosis specifically refers to the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. All these processes occur until equilibrium is reached, emphasizing their nature as passive transport mechanisms.