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.
Recall that membranes have two major components: phospholipids arranged in a bilayer, and membrane proteins. Click Here for a more elaborate picture of a cell membrane. One of the functions of membranes is to control what passes into and out of the cell.In this module you will review mechanisms of membrane transport.ecall that membranes have two major components: phospholipids arranged in a bilayer, and membrane proteins. Click Here for a more elaborate picture of a cell membrane. One of the functions of membranes is to control what passes into and out of the cell.