(c) Costin Stoica
Prokaryotes: unicellular microorganisms of 0.1 to 15 μm,
presenting rod or coccus shape, sometimes occurring filamentous or
mycelial forms. They are widely distributed in nature (soil, water, foods,
plants, animals, rarely in hot springs or radioactive environment).
Cells have a single circular DNA chromosome, contained within
a region called the nucleoid and may also have various small
circular pieces of DNA (plasmids) inside the cell. The nucleoplasm
is not separated from the cytoplasm by a nuclear membrane.
Reproduction is most often asexual, through binary fission,
occasionally by budding. Cells may remain attached after division
resulting specific arrangements: strepto-, staphylo- etc.
The organisms are surrounded by a rigid peptidoglicans based
wall with the exception of the Mollicutes. The plasma membrane
forms vesicular, lamellar or tubular intrusions into the cytoplasm.
Respiratory and photosyntetic functions are associated with the
plasma membrane system (where available). Ribosomes of the 70S
type are dispersed in the cytoplasm.
Kingdom Prokaryotae includes Cyanobacteria (blue-green algae)
and Bacteria. The last makes the object of our pages.