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.
Dictionary entry overview: What does hub mean? â¢ HUB (noun) The noun HUB has 2 senses: 1. the central part of a car wheel (or fan or propeller etc) through which the shaft or axle passes 2. a center of activity or interest or commerce or transportation; a focal point around which events revolve Familiarity information: HUB used as a noun is rare.