Lipid bilayer sheets, also known as unit membranes, are large, two-dimensional structures formed by two opposing rows of phospholipids. In these sheets, the hydrophobic tails are oriented inward, congregated tail-to-tail, while the hydrophilic polar heads face outward. These assemblies serve as the structural foundation of cellular membranes in almost all organisms, as well as the membranes of various internal cell components.