Microorganisms are classified under kingdom "Protista" as it was found unsatisfactory to place them under plant and animal kingdom. Based on the differences in cellular organization and biochemical characteristics kingdom Protista is divided into two groups: prokaryotes and eukaryotes.
Bacteria are unicellular organism and doesn't show true branching except the group of higher bacteria called actinomycetales. Bacteria of medical importance usually measures about 0.2-1.5 μm in diameter and 3-5 μm in length. Bacteria and blue green algae are classified under prokaryotic groups while fungi, other algae(except blue green algae), slime molds and protozoa are placed under eukaryotic groups.
Apart from few similarities eukaryotes and prokaryotes shows vast range of differences. Nucleus of eukaryotic cells contains nuclear membrane and contains nucleolus and deoxyribonucleoprotein while these are absent in prokaryotic cell. Number of chromosome in eukaryotic cells are usually more than one and linear in shape while it's single in number and circular in shape in prokaryotic cells. Mitotic cell division is present in eukaryotes while it's absent in prokaryotic cell.
Cytoplasm of eukaryotic cell shows cytoplasmic streaming, pinocytosis while prokaryotic cytoplasm doesn't exhibit such characteristics. Mitochondria, lysosomes, golgi apparatus and endoplasmic reticulum are present in the cytoplasm of eukaryotic cells but those are absent in prokaryotic cytoplasm. Sterols is only present in eukaryotic cell while muramic acid is found only in prokaryotic cells.