Which type of organism requires an external source of food for energy?

The organism that requires an external source of food for energy is a consumer. Consumers are organisms that cannot produce their own food and must rely on other living things for their nourishment. They typically fall into categories based on their feeding habits, such as herbivores, carnivores, and omnivores. These organisms obtain energy by consuming plants, animals, or other organic matter, utilizing the energy stored in the chemical bonds of the food they ingest.

In contrast, producers, such as plants and some algae, generate their own energy through photosynthesis or chemosynthesis, converting sunlight or chemicals into usable energy forms. Decomposers break down dead organic material, returning nutrients to the environment, but they also obtain energy from external sources, albeit indirectly. Autotrophs, like producers, synthesize their own food and do not require external sources for energy. This distinction highlights why consumers are the organisms that specifically rely on external food sources to meet their energy needs.