 Some lithotrophs produce organic compounds from carbon dioxide in a process called chemosynthesis, much as plants do in photosynthesis.Plants use energy from sunlight to drive carbon dioxide fixation, since both water and carbon dioxide are low in energy.By contrast, the hydrogen compounds used in chemosynthesis are higher in energy, so chemosynthesis can take place in the absence of sunlight (e.g., around a hydrothermal vent).