A cell membrane is a phospholipid bilayer that defines the external boundaries of cells and regulate the molecular traffic across the boundary.
Explanation: Cell membranes are flexible, self-sealing and selectively permeable bilayer of phospholipids with proteins embedded in the bilayer through hydrophobic interactions. Cell membranes are formed by the interactions of the hydrophobic tails of the phospholipids, the hydrophobic tails of the phospholipids face each other while their polar head groups face outward, thus forming a bilayer with a fluid hydrophobic core. The selective permeability of membranes makes them to retain certain compounds and ions within cells while excluding others. Cell membranes include an array of proteins specialized for promoting or catalyzing various cellular processes such as synthesis of lipids and certain proteins and the energy transductions in mitochondria and chloroplasts.
