Cyanobacteria

Cyanobacteria are a group of bacteria believed to be the first organisms on Earth to evolve the ability to use solar energy to produce sugars. This process — photosynthesis — is now common among all green plants. Photosynthesis by cyanobacteria also contributed to the abundance of oxygen in the atmosphere, which is essential for most life forms. The cyanobacterial cell is structurally simpler than that of plants, as it is a prokaryotic cell with no internal compartments. Like other bacteria, a cyanobacterial cell is surrounded by a plasma membrane and a cell wall. Inside the cell is the cytoplasm, which contains structures such as ribosomes and cellular DNA. Unlike most bacteria, cyanobacteria have a highly complex cell membrane with numerous internal folds known as thylakoids. Photosynthesis occurs on these thylakoids, specifically at structures called phycobilisomes.