Light micrograph of a unicellular cyanobacteria (blue-green algae), Chroococcus, commonly found in an aquatic environment. Cyanobacteria have a different internal structure to the algae & are regarded as closer to bacteria. They are prokaryotic organisms with no membrane-bound nucleus. Instead their nuclear material is dispersed through the cell like that of the bacteria. Their chloroplasts are not restricted by a membrane, but lie free in the cell. In addition to a cell wall, Chroococcus cells are surrounded by a colloidal sheath. Several cells may cohere after cell division, forming incipient colonies as here. Magnification: x250 at 35mm size.