Pinocytosis is best described as?

• A. Uptake of extracellular fluid in tiny vesicles
• B. Uptake of large particles
• C. Non-selective diffusion through the plasma membrane
• D. Release of vesicles to the exterior

Answer: (A)

Pinocytosis is the cell’s way of sampling its surrounding fluid by forming small vesicles from the plasma membrane, a process often called cellular drinking. This makes the uptake of extracellular fluid in tiny vesicles the best description, since it focuses on fluid-phase uptake rather than solids. It is distinct from phagocytosis, which ingests large particles, and from diffusion, which is a passive, non-vesicle movement across the membrane. Exocytosis, in contrast, is the release of vesicles to the exterior, not their uptake.