Cyanobacteria. Blue-green scytonema (false branching) alga Pseudanabaena sp. Blue-green algae maybe the first oxygen-producing organisms to evolve, thereby being responsible for the Earth's atmosphere. They are related to bacteria (prokaryotes) containing no membrane-bound nucleus; instead nuclear material is dispersed throughout the cell. Photosynthetic lamellae (layered structures green) are the primitive chloroplasts.