<P> Bacteria and archaea also can use chemiosmosis to generate ATP . Cyanobacteria, green sulfur bacteria, and purple bacteria synthesize ATP by a process called photophosphorylation . These bacteria use the energy of light to create a proton gradient using a photosynthetic electron transport chain . Non-photosynthetic bacteria such as E. coli also contain ATP synthase . In fact, mitochondria and chloroplasts are believed to have been formed when early eukaryotic cells ingested bacteria that could transfer energy using chemiosmosis . This is called the endosymbiotic theory . </P> <P> Chemiosmotic phosphorylation is the third pathway that produces ATP from inorganic phosphate and an ADP molecule . This process is part of oxidative phosphorylation . </P>

The chemiosmotic gradient of cellular respiration is an