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 structure of the lipid bilayer explains its function as a barrier. Lipids are fats, like oil, that are insoluble in water because of its long hydrophobic tails. The hydrophobic interactions among several phospholipids and glycolipids, a certain structure called lipid bilayer or bimolecular sheet is favored.he function of the lipid bilayer membrane is mediated by the specific protein that is embedded in it. The proteins of the lipid bilayer function as pumps, channels, energy transducers, receptors, and enzymes.