heterotrofy

Heterotrophy is a nutritional strategy in which organisms obtain carbon from organic compounds produced by other organisms. In contrast to autotrophy, where CO2 is fixed into organic matter, heterotrophs acquire carbon from existing organic molecules. Their energy source can be light (in some cases) or chemical energy derived from organic compounds, depending on the organism.

Heterotrophs are commonly divided into subgroups such as chemoheterotrophs, which obtain both energy and carbon from organic molecules, and photoheterotrophs, which use light to generate energy while assimilating organic carbon. In practice, heterotrophy includes various feeding modes: absorptive heterotrophy (such as in fungi and many microbes that take up dissolved organics), phagotrophy (ingestion of solid particles, as in many protists and some animals), saprotrophy (decomposition of dead organic matter), parasitism, and predation.

The most familiar heterotrophs are animals, fungi, and many bacteria and protists. Animals typically ingest and digest food; fungi absorb dissolved organic compounds through their body surface. Bacteria and protists display diverse strategies, ranging from saprotrophy to parasitism and predation. Some organisms exhibit mixotrophy, combining heterotrophic and autotrophic metabolism under different conditions.

Ecological and evolutionary roles of heterotrophy include recycling of organic matter, nutrient cycling, and energy transfer through ecosystems. Heterotrophy is a fundamental and ancient nutritional strategy; in many evolutionary scenarios, heterotrophic metabolism preceded widespread autotrophy, with autotrophy evolving later in some lineages to exploit inorganic energy and carbon sources such as light or carbon dioxide.