cells must be in osmotic equilibrium with their surrounding environments, because if they swell or shrink their membranes will rupture. A) Animal B) Bacterial C) Fungal D) Plant About two-thirds of a cell is composed of water. What is the name of the process in which water moves into or out of the cell membrane to maintain homeostasis? A) regulation B) endocytosis C) exocytosis D) osmosis