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.
The lipid bilayer (phospholipid bilayer/cell membrane) is a structural component of the cell that isolates the cell components (organelles, cytoplasm) from the extracellular environment. Functions of the lipid bilayer.