What has been described above are the noncyclic energy-fixing reactions. Certain microorganisms are also known to participate in cyclic energy-fixing reactions. Excited electrons leave the chlorophyll molecules, pass through coenzymes of the electron transport system, and then follow a special pathway back to the chlorophyll molecules. Each electron powers the proton pump and encourages the transport of a proton across the membrane. This process enriches the proton gradient and eventually leads to the generation of ATP. ATP production in the energy-fixing reactions of photosynthesis occurs by the process of chemiosmosis. Essentially, it consists of a rush of proteins across a membrane (the microbial membrane, in this case) accompanied by the synthesis of ATP molecules. It has been calculated that
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