Phagocytosis involves which event?

• A. Exocytosis
• B. Endocytosis of fluids
• C. Diffusion of molecules
• D. Molecules or entire cells are engulfed; a food vacuole forms, which fuses with a lysosome

Answer: (D)

Phagocytosis is a form of endocytosis that focuses on taking in large particles or whole cells. The cell wraps its membrane around the target, pulling it inside to form a membrane-bound vesicle known as a food vacuole (phagosome). This vesicle then fuses with a lysosome, whose enzymes digest the ingested material inside the phagolysosome. This sequence—engulfing the object to form a vacuole, followed by fusion with a lysosome for digestion—is what phagocytosis involves. Exocytosis involves expelling material, pinocytosis is uptake of fluids, and diffusion is passive movement without vesicle formation, so they don’t capture the defining process of phagocytosis.