Pinocytosis is best described as which of the following?

• A. Receptor-mediated uptake
• B. Cell drinking
• C. Exocytosis
• D. Cell eating

Answer: (B)

Pinocytosis is a form of endocytosis focused on taking in extracellular fluid and dissolved solutes, so it’s often called “cell drinking.” This uptake involves small vesicles formed from the plasma membrane, capturing fluid rather than large particles. Exocytosis is the opposite process, exporting material from the cell, not taking it in. Phagocytosis, or “cell eating,” handles large particles like bacteria by engulfing them with membrane extensions. There is also receptor-mediated endocytosis, which is a selective form of pinocytosis where specific ligands bind receptors before uptake; it’s a specialized case, not the general description of pinocytosis. So describing pinocytosis as cell drinking best captures its non-specific intake of fluid and solutes.