What is endocytosis?

Endocytosis is a cellular process that involves the uptake of substances into the cell. This mechanism allows cells to engulf large molecules, particles, or even other cells by folding their plasma membrane inward to form a vesicle that contains the material being internalized. This process is critical for various cellular functions, including nutrient uptake, receptor-mediated signaling, and the removal of pathogens.

In contrast to endocytosis, the discharge of substances out of the cell refers to exocytosis, where vesicles within the cell fuse with the plasma membrane to release their contents. The movement of substances around the cell pertains to intracellular transport mechanisms, which involve cytoskeletal structures and motor proteins rather than the influx of materials from the external environment. Absorption of nutrients into the blood typically occurs in the digestive system and involves specialized transport mechanisms but is not directly a function of endocytosis itself. Thus, the correct answer accurately reflects the definition and function of endocytosis.