keep a civil tongue in one's head. Speak politely, as in The teacher won't allow swearing; she says we must keep a civil tongue in our heads. This expression uses tongue in the sense of a manner of speaking, a usage dating from the 1400s. An early cautionary version was Keep a good tongue in your head, lest it hurt your teeth (1595). See also: civil, head, keep, tongue. n. a civil servant.
Phospholipids serve a major function in the cells of all organisms: they form the phospholipid membranes that surround the cell and intracellular organelles such as the mitochondria. The cell membrane is a fluid, semi-permeable bilayer that separates the cell's contents from the environment, see animation below.hospholipids serve a major function in the cells of all organisms: they form the phospholipid membranes that surround the cell and intracellular organelles such as the mitochondria. The cell membrane is a fluid, semi-permeable bilayer that separates the cell's contents from the environment, see animation below.
Remember these key points: 1  Cell membranes or plasma membranes consist of a phospholipid bilayer with proteins embedded in the membrane. 2  Most of the functions of plasma membranes are handled by the proteins. 3  This arrangement of proteins and phospholipids is often called the fluid mosaic model for a cell membrane.he Actual Cell membrane has proteins embedded in the lipid bilayer. Embedded in the phospholipid bi-layer are a diverse set of proteins which do most of the important functions of the cell membrane. This idea is called the fluid mosaic model of the cell membrane.