Which process brings substances into the cell by engulfing with a membrane vesicle?

• A. Facilitated diffusion
• B. Exocytosis
• C. Osmosis
• D. Endocytosis

Answer: (D)

Endocytosis is the process by which the cell takes in materials by the plasma membrane wrapping around them and pinching off a vesicle into the cytoplasm. This vesicle then carries the substance inside, often fusing with an endosome or lysosome for processing. The mechanism can handle different types of cargo: phagocytosis for large particles, pinocytosis for fluids, or receptor‑mediated endocytosis for specific molecules. This energy‑dependent uptake via membrane vesicle formation distinguishes it from other processes: exocytosis exports material by vesicles fusing with the membrane, facilitated diffusion moves substances across the membrane with carrier proteins without forming vesicles, and osmosis is the passive movement of water across a membrane.