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 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.Cell membranes are fluid in the sense that the molecules in the membrane are in constant motion. The mosaic part refers to the proteins embedded in the phospholipids.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.