Anoxygenic photosynthesis is a process used by certain bacteria, such as purple bacteria and green sulfur bacteria, to convert light energy into chemical energy. Unlike oxygenic photosynthesis, which produces oxygen as a byproduct, anoxygenic photosynthesis does not release oxygen. Instead, these bacteria use other molecules, like hydrogen sulfide or organic compounds, as electron donors. This type of photosynthesis occurs in environments where light is available but oxygen is limited, such as in deep-sea hydrothermal vents or anoxic lakes. Anoxygenic photosynthesis plays a crucial role in the global carbon cycle and helps sustain ecosystems that rely on these unique bacteria for energy.