Phylum Cyanobacteria
Cyanobacteria are prokaryotes, but they are not like bacteria in the usual sense of the word. The cyanobacteria lack chloroplasts, and their light capturing pigment is scattered over, highly folded inner membrane lamellae. However, their photosynthetic mechanism differ from that of other bacteria. Like plants, they derive their required electrons by breaking apart water molecules. The blue-greens have an important ability to 'fix' nitrogen,
1) Unicellular or filamentous, some of the filamentous forms bear branches.
2) Autotrophic, the photosynthesis is carried out on membranes round the periphery of the cells.
3) Photosynthetic pigments include chlorophyll plus red pigment (phycoerythin) and blue pigmerlt (phycocyanin). Some examples Chroococcus, Arlabaena