Trophic Levels:
The trophic level of an organism is the position it holds in a food chain.
Primary producers (organisms that make their own food from sunlight and/or chemical energy from deep sea vents) are the base of every food chain - these organisms are called autotrophs.
Primary consumers are animals that eat primary producers; they are also called herbivores (plant-eaters).
Secondary consumers eat primary consumers. They are carnivores (meat-eaters) and omnivores (animals that eat both animals and plants).
Tertiary consumers eat secondary consumers.
Quaternary consumers eat tertiary consumers.
Food chains "end" with top predators, animals that have little or no natural enemies.
When any organism dies, it is eventually eaten by detrivores (like vultures, worms and crabs) and broken down by decomposers (mostly bacteria and fungi), and the exchange of energy continues.