The transfer of energy from one trophic level to another is called the food chain or the process of eating and being eaten.
In any food chain, the producers transfer energy to primary consumers, which in turn transfer to secondary consumers which in turn transfer energy to tertiary consumers.
Decomposers :
The organisms which break down or decompose complex organic matter(dead remains of living organisms) into inorganic matter.
Decomposers such as bacteria and fungi degrade or break down the complex organic dead and decaying matter by secreting enzymes that break down the decaying matter into inorganic matter.
In a food chain, decomposers occupy the last trophic level.