Food chain describes a single pathway that energy and nutrients may follow in an ecosystem. There is one organism per trophic level, and trophic levels are therefore easily defined. They usually start with a primary producer and end with a top predator. Here is an instance of a food chain: phytoplankton-zooplankton-fish-squid-seal-Orca (killer whale). Producers plants, algae and certain types of bacteria called cyanobacteria are producers, Producers use radiant energy (sunlight) to synthesize chemical energy (sugar), and in other words, plants perform a complex set of chemical reactions called photosynthesis. Producers are also called autotrophs which means self-feeders, because they make their own food. The Primary Consumers-organisms that eat plants are called primary consumers, including primary consumers are herbivores, and the only eat plant material.