Morphology and Physiology of Bacteria
All living beings can be classified into three kingdoms: Plant,Animal, and Protista. Microorganisms are a heterogeneousgroup of several distinct living structures of microscopic size, classified under the kingdom Protista. The kingdom Protista includes unicellular organisms, such as bacteria, fungi, proto-zoa, and algae. Based on the differences in cellular organization and biochemistry, the kingdom Protista has been divided into three groups: prokaryotes, eukaryotes, and the most recently described archaebacteria.
Prokaryotes: Bacteria and blue green algae are prokary-otes. Bacteria are unicellular free living organisms having both DNA and RNA. They are capable of performing all essential processes of life, e.g., growth, reproduction, and metabolism. They do not show any true branching except Actinomycetales, the higher bacteria. Bacteria lack chloro-phyll unlike blue green algae, which contain chlorophyll.
Eukaryotes: Fungi, algae other than blue green, protozoa,and slime moulds are eukaryotes.
Archaebacteria: These are more closely related to eukary-otes than prokaryotes. They however do not include any human pathogens.
Differences between prokaryotes and eukaryotes have been summarized in Table 2-1.