Endocytosis is the process of moving substances into a cell. Which best describes endocytosis?

• A. Release of substances out of a cell by vesicle fusion with the membrane
• B. Process of moving substances into a cell
• C. Movement of water across a membrane via pores
• D. Transport through transporter proteins in the membrane

Answer: (B)

Endocytosis is a vesicle-mediated process by which the cell takes in material from outside. The plasma membrane folds inward, engulfs extracellular substances, and then buds off to form an internal vesicle, often powered by cytoskeletal changes and energy use. This mechanism allows the cell to internalize large particles, fluids, or molecules bound to receptors, such as uptake of cholesterol via LDL or iron-bound transferrin. Because endocytosis describes bringing material into the cell through vesicle formation, it matches the description best.

Exocytosis is the opposite: substances are released from the cell by vesicle fusion with the plasma membrane. Movement of water across the membrane via pores corresponds to osmosis, not vesicle-based intake. Transport through transporter proteins in the membrane refers to carrier- or channel-mediated transport, which moves substances without forming vesicles.