Organisms that use hydrogen sulfide or other chemicals as an energy source instead of light are called what?

• A. Chemoautotrophs
• B. Lithoautotrophs
• C. Photoautotrophs
• D. Chemoheterotrophs

Answer: (A)

The main idea is how organisms obtain energy and carbon. If an organism uses chemical reactions for its energy instead of light, that’s chemotrophy. If it also uses carbon dioxide as its carbon source, it’s an autotroph. Put those together and organisms that run on chemical energy and fix CO2 are chemoautotrophs. Hydrogen sulfide is a classic chemical energy source for this type of metabolism, so they’re categorized as chemoautotrophs. Lithoautotrophs are a related, more specific group that uses inorganic electron donors like H2S, but chemoautotrophs is the broader and most inclusive term for organisms using chemical energy to build biomass from CO2.