Which organism uses organic material as a carbon source?

Which organism uses organic material as a carbon source?

• A. Autotroph
• B. Heterotroph
• C. Lithotroph
• D. Phototroph

Answer: (B)

Using organic material as a carbon source means the organism relies on preformed organic molecules from other organisms to build its own biomass. This is the defining trait of heterotrophs. Autotrophs, by contrast, fix inorganic carbon (typically carbon dioxide) to form organic matter. Lithotrophs describe the energy source—derived from inorganic compounds—not the carbon source. Phototrophs describe how they gain energy (from light) and can have either CO2 or organic carbon as their carbon source, but the clear match to “organic material as a carbon source” is heterotroph. So the organism is a heterotroph.

Using organic material as a carbon source means the organism relies on preformed organic molecules from other organisms to build its own biomass. This is the defining trait of heterotrophs. Autotrophs, by contrast, fix inorganic carbon (typically carbon dioxide) to form organic matter. Lithotrophs describe the energy source—derived from inorganic compounds—not the carbon source. Phototrophs describe how they gain energy (from light) and can have either CO2 or organic carbon as their carbon source, but the clear match to “organic material as a carbon source” is heterotroph. So the organism is a heterotroph.