Pinocytosis specifically involves the uptake of what?

• A. Small dissolved substances or fluids
• B. Uptake of large particles
• C. Release of intracellular vesicles
• D. Active transport of ions

Answer: (A)

Pinocytosis is a form of endocytosis where the cell ingests extracellular fluid and the dissolved substances within it by forming small vesicles from the plasma membrane. This fluid-phase uptake means it concentrates on small dissolved particles and water rather than whole, solid particles. In contrast, taking in large particles is phagocytosis, releasing vesicles from the cell is exocytosis, and moving ions across the membrane via transport proteins is active transport. So the uptake of small dissolved substances or fluids best describes pinocytosis.