Cyanobacteria The cyanobacteria have typical prokaryotic cell structures and a normal gram-negative cell wall. They range in diameter from about 1 – 10 µm and may be unicellular or form filaments. They have chlorophyll and carry out oxygen￾producing photosynthesis, much as plants and the eukaryotic algae do.Cyanobacteria The cyanobacteria have typical prokaryotic cell structures and a normal gram-negative cell wall. They range in diameter from about 1 – 10 µm and may be unicellular or form filaments. They have chlorophyll and carry out oxygen￾producing photosynthesis, much as plants and the eukaryotic algae do