Which statement correctly describes a chemoautotroph?

• A. Energy from chemicals; Carbon from CO2
• B. Energy from light; Carbon from CO2
• C. Energy from chemicals; Carbon from organic compounds
• D. Energy from light; Carbon from organic compounds

Answer: (A)

Chemoautotrophs get their energy from chemical reactions that involve inorganic substances, not from light, and they fix carbon from inorganic CO2 into biomass. That pairing—energy from inorganic chemicals and carbon from CO2—best describes them. So this statement matches the idea that metabolism is driven by chemical energy and growth uses carbon dioxide as the carbon source.

Think of examples like nitrifying bacteria, which oxidize ammonia for energy and then fix CO2 to build cellular material, or sulfur-oxidizing bacteria that derive energy from oxidizing reduced sulfur compounds while assimilating CO2. In contrast, using light as the energy source would describe photoautotrophs, and using organic carbon as the carbon source would describe chemoheterotrophs (or photoheterotrophs if energy came from light).