What defines an autotroph in comparison to a heterotroph?

An autotroph is defined by its ability to produce its own energy source, primarily through processes like photosynthesis or chemosynthesis. This means that autotrophs convert inorganic substances, such as carbon dioxide and water, into organic compounds, using energy from sunlight or chemical reactions. This production of their own energy is a fundamental characteristic that distinguishes them from heterotrophs, which cannot synthesize their own food and instead rely on consuming organic material produced by other organisms. Therefore, the correct answer emphasizes the self-sufficiency of autotrophs in energy production.