Which best describes an autotroph's role in an ecosystem?

An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. This ability primarily comes from processes like photosynthesis or chemosynthesis, wherein they convert inorganic substances into organic matter. By producing energy-rich organic compounds, autotrophs serve as the foundational source of energy in an ecosystem, feeding themselves as well as supporting other organisms, such as herbivores and higher trophic levels.

This role is essential for maintaining the flow of energy through an ecosystem, which makes the identification of autotrophs as producers critically important for understanding ecological dynamics. In contrast, the other options describe roles that do not align with the defining characteristics of autotrophs. For instance, primary consumers are herbivores that rely on autotrophs for food, decomposers break down organic materials but do not produce energy, and organisms that rely on others for nutrients are classified as heterotrophs.