Photosynthetic organisms are photoautotrophs, which means that they are able to synthesize food directly from and water using energy from light. However, not all organisms that use light as a source of energy carry out photosynthesis, since "photoheterotrophs" use organic compounds, rather than , as a source of carbon. In plants, algae and cyanobacteria, photosynthesis releases oxygen. This is called "oxygenic photosynthesis". Although there are some differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms. However, there are some types of bacteria that carry out anoxygenic photosynthesis, which consumes but does not release oxygen.