The role of cellular membranes in maintaining homeostasis is vital as they regulate the transport of substances into and out of cells. Comprised of a phospholipid bilayer with embedded proteins, these membranes selectively permit the passage of ions, nutrients, and waste products. This selective permeability ensures that essential molecules enter the cell while harmful substances are kept out. Additionally, cellular membranes play a role in signaling and communication between cells, helping to maintain overall physiological balance and respond to environmental changes.