Which organisms obtain energy by oxidizing inorganic compounds to synthesize organic matter?

• A. Chemosynthetic Bacteria
• B. Photoautotrophic Bacteria
• C. Heterotrophic Bacteria
• D. Saprotrophic Fungi

Answer: (A)

Chemoautotrophy is when organisms obtain energy by oxidizing inorganic compounds and use that energy to convert carbon dioxide into organic matter. Chemolithoautotrophic bacteria do exactly this: they oxidize inorganic substrates such as ammonia, nitrite, hydrogen sulfide, or ferrous iron to release energy and power CO2 fixation into organic compounds. This allows them to thrive in environments without light.

In contrast, photoautotrophs use light energy to drive photosynthesis, though they still fix CO2 into organic matter. Heterotrophs rely on preformed organic matter for both energy and carbon, and saprotrophic fungi decompose dead organic material rather than deriving energy from inorganic oxidation.