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.
April 2017 - Like screws, wedges are really a kind of inclined plane, but they are so useful that people give them their own category. A wedge is two inclined planes back to back against each other. Wedges evolved on their own long before people. Sharp teeth are a kind of wedge that cuts through meat and vegetables when fish or crocodiles eat something. People have been using wedges in Africa since the earliest Stone Age, about 2.6 million years ago.