Which statement correctly distinguishes autotrophs from heterotrophs?

• A. Autotrophs rely on organic material; Heterotrophs fix CO2
• B. Autotrophs use CO2 as a carbon source; Heterotrophs use organic material as a carbon source
• C. Autotrophs require sunlight exclusively; Heterotrophs do not require light
• D. Autotrophs cannot metabolize carbon; Heterotrophs can

Answer: (B)

The main idea being tested is how organisms obtain carbon to build their molecules. Autotrophs fix inorganic carbon from carbon dioxide into organic compounds, using energy from light or inorganic chemical reactions. Heterotrophs rely on organic molecules that were produced by other organisms as their carbon source.

That’s why the correct statement is that autotrophs use CO2 as a carbon source, while heterotrophs use organic material as a carbon source. The other options mix up these roles or make false claims: autotrophs don’t rely on organic material for their carbon, not all autotrophs require sunlight (some use chemical energy instead), and autotrophs do metabolize carbon rather than being unable to.