The cell membrane has a fluid mosaic structure, comprising a phospholipid bilayer with embedded proteins. The phospholipid tails face each other at the center of the bilayer to be protected from the watery environments inside and outside the cell, while the phosphate heads face outwards. Transmembrane and peripheral proteins embedded in the bilayer form channels to regulate what passes in and out of the cell. Cholesterol maintains the fluidity and stability of the membrane. The membrane acts as a selectively permeable barrier and facilitates cell structure, communication, recognition, mobility, and chemical reactions.