<span>Both photoautotrophs and chemoautotrophs synthesize organic compounds from (inorganic) carbon dioxide, a process known as carbon fixation. Photoautotrophs get the energy to perform these reactions from light. Chemoautotrophs get it from electron donors such as hydrogen sulfide and ammonia. Cyanobacteria, by contrast, convert nitrogen from the atmosphere into ammonia, a process known as nitrogen fixation.</span>
B . to supply energy for splitting the water molecules
I would say the nucleotides
Cytosine
Guanine
Adenine
Thymine
