Prokaryotic Organisms
Prokaryotic organisms do not have a cell nucleus, or any other membrane bound organelles. Most prokaryotic organisms are unicellular, though in certain rare cases they are multicellular. The structural difference between prokaryotic and eukaryotic organisms (which do have nucleus and membranous organelles) is so profound it is considered the primary division between groups of organisms. Most prokaryotes are bacteria, but some are archaebacteria.
In addition to the missing cell nucleus, prokaryotes do not have structures like mitochondria, chloroplasts, vacuoles, and the endoplasmic reticulum. Prokaryotes, since so many of the organelles found in eukaryotic cells are absent, are much smaller than eukaryotes. The single circular chromosome of a prokaryote is found in the nucleoid region, and small circular pieces of DNA called plasmids are often spread throughout the cell. Reproduction is exclusively asexual through binary fission. There are parasexual processes, however, in which DNA may be recombined.
Prokaryotic organisms may form groups of cells called colonies. These colonies are often bound together through a secreted slime layer. Prokaryotic organisms also have a higher metabolic and growth rate than eukaryotic organisms, and therefore they reproduce more quickly. They're found in most environments on earth, from human skin to volcanoes to the depths of the ocean and even far down in the dense frozen muck at the bottom. Prokaryotic organisms may photosynthesize or use organic materials, but they may also use inorganic chemicals like hydrogen sulfide to produce energy.
Web Resources On Prokaryotic Organisms
Prokaryotic Cell Diagrams
Prokaryotic Cellular Components
Book Resources On Prokaryotic OrganismsProkaryotic Genomics by Michel Blot (Ed)
Prokaryotic Structure and Function : A New Perspective by S. Mohan (Ed), et al
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