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.
They found the lipid surface area was twice that of the red blood cells, and concluded that the lipids must be arranged in a layer two lipid molecules thick. Lipid bilayer is a double layer membrane formed from phospholipids. Phospholipids are composed of a polar head group and non-polar fatty acid tails.The arrangement of the phospholipids makes the cell membrane permeable.his is the so called lipid bilayer. Lipid bilayer is permeable to water molecules and other small, uncharged molecules like oxygen, carbon dioxide. A bimolecular sheet formed by amphipathic molecules in which the hydrophobic moieties are on the inside of the sheet and the hydrophilic ones are on the aqueous outside.