What is the primary carbon source for autotrophs?

Autotrophs are organisms that can produce their own food using inorganic substances. The primary carbon source for autotrophs is carbon dioxide (CO2), which they incorporate into organic compounds through processes such as photosynthesis or chemosynthesis.

In photosynthetic autotrophs, like plants and certain bacteria, CO2 is fixed into glucose and other carbohydrates during the Calvin cycle. This process not only provides energy and carbon skeletons for growth but also sustains the broader ecosystem by serving as a fundamental source of organic matter for other organisms.

Other options, such as glucose and organic molecules, represent sources of carbon for heterotrophs—organisms that obtain organic compounds by consuming other organisms. Ammonia, on the other hand, is primarily connected to nitrogen metabolism rather than carbon fixation. This understanding showcases the unique capability of autotrophs to utilize CO2, highlighting their essential role in the biosphere.