What are the characteristics of prokaryotic cells?

Prokaryotes are exclusively unicellular organisms. All prokaryotic cells are encased by a cell wall that helps maintain the shape of the cell and keeps it hydrated. These cells do not have a true (membrane-bound) nucleus. Instead they have an irregularly-shaped nucleoid in the central part of the cell. It is poorly defined because of the lack of a nuclear membrane. Most prokaryotic cells have a single circular DNA, which is found in the nucleoid area. In addition to the genomic DNA, these cells may also have plasmids, which are smaller pieces of circular DNA. Membrane-bound cell organelles such as endoplasmic reticulum, and mitochondria are absent in prokaryotic cells. Prokaryotic cells are typically smaller in size, ranging from 0.1 to 5.0 μm in diameter. The small size facilitates quicker entry and diffusion of ions and molecules across the cell as well as quicker removal of waste products out of the cell. These cells often have different types of protrusions or appendages on their surface. Fimbriae help the cell adhere to a surface. Flagella along with some pili enable movement. Sex pili facilitate the exchange of DNA.