The document discusses the three categories in a food chain: producers, consumers, and decomposers. Producers, like plants, obtain energy from sunlight through photosynthesis. Consumers, like animals, eat producers or other consumers to obtain energy and include carnivores, herbivores, and omnivores. Decomposers, like mushrooms and worms, break down dead organisms and waste and return nutrients to the soil. All categories are interdependent in the food chain.