What is the process called when large substances are actively taken into the cell?

The process of actively taking large substances into a cell is known as endocytosis. During endocytosis, the cell membrane engulfs extracellular material, forming a pocket that eventually pinches off to create a vesicle within the cell. This mechanism is essential for cells to absorb macromolecules, particles, and even other cells, allowing them to take in nutrients, pathogens, or signaling molecules that are too large to pass through the membrane by simple diffusion.

In contrast, exocytosis is the process of expelling materials from a cell, diffusion refers to the passive movement of molecules from an area of higher concentration to lower concentration without the use of energy, and filtration typically involves the movement of water and solutes through a semipermeable membrane driven by hydrostatic pressure and does not involve active transport of larger substances into the cell. These distinctions highlight why endocytosis is the correct process for the active transport of large substances into cells.