Prokaryotes have only one lipid bilayer- the cell membrane (also known as the plasma membrane). Many prokaryotes also have a cell wall, but the cell wall is composed of proteins or long chain carbohydrates, not lipids.
3. countable noun. A wedge is an object with one pointed edge and one thick edge, which you put under a door to keep it firmly in position. 4. countable noun. A wedge is a piece of metal with a pointed edge which is used for splitting a material such as stone or wood, by being hammered into a crack in the material.
The Wedge. The wedge is one of the so-called  simple machines  from which many more complex machines are derived. The wedge embodies the same principles as the incline in the sense that a smaller force working over a longer distance can produce a larger force acting through a small distance.