This document defines key vocabulary terms related to cell functions, including concentration gradient, diffusion, osmosis, endocytosis, exocytosis, plasmolysis, cytolysis, turgor pressure, tonicity, hypertonic, hypotonic, isotonic, permeability, selectively permeable, permeable, and impermeable. It provides short descriptions of each term to explain concepts like the movement of molecules and water across membranes under different concentration conditions.