Prokaryotes superkingdom is usually divided by two kingdoms (domains): Archaea (from Greek ldquo;arheosrdquo; - ldquo;oldrdquo;) and Bacteria, o

Prokaryotes (Archaea and Bacteria)

Prokaryotes superkingdom is usually divided by two kingdoms (domains): Archaea (from Greek “arheos” — “old”) and Bacteria, or Eubacteria (from Greek “Eus” — “true”).

Archaea

The first group includes quite primitive and small even in comparison with Bacteria microscopic single-celled creatures. By to their molecular structure and chemical composition of cells, they differ from all other organisms. Perhaps that is why they are referred to extremophiles (from Latin “extremum” — “extreme” and Greek “phileo” — “love”), i.e. organisms which naturally exist in the environment, marginal for other living organisms. Different types of Archaea do not just can withstand, but can easily live in the water with temperature of +45 … + 113 °C; in an acidic medium (pH 1-5); 25-30% solutions of NaCl; in a minimum moisture conditions and permanent water scarcity. Furthermore, among members of this kingdom are those which multiply at a temperature below zero and when the pressure is maintained at 700 atm.

It is believed that the Archaea are very old, appeared on Earth 3.5 billion years ago. Most species of Archaea are autotrophs that have chemosynthesis. There are practically no parasites and pathogens among them. Some scientists believe that the Archaea — are the most massive organisms that have ever existed on Earth.

Bacteria

Bacteria kingdom is often divided into two groups: actual Bacteria and Cyanobacteria (from Greek “cyano” — “blue”).

Actual Bacteria — are heterotrophic organisms or chemotrophic. Taken from http://worldofschool.org

Cyanobacteria are photosynthetic prokaryotes, which cells contain pigments homologous to plant pigments, including chlorophyll. Photosynthesis occurs with oxygen production. For this feature cyanobacteria are also called blue-green algae. It is believed that the oxygen atmosphere on Earth was originated about 2 billion years ago due to multiplied cyanobacteria. Individual cells of blue-green algae are microscopic — not more than 10 microns, but they are able to form colonies of a few meters. Cyanobacteria form a blue-green mass in the thickness and dense film on the surface of the water during the “bloom” of ponds in the summer heat.

Questions:
  • How prokaryotes are divided?