What is the most important part of a food chain?

Decomposers are an important part of a food chain because they break down dead plants and animals and also the waste of other organisms, thus, keeping up a continuous flow of nutrients for the primary producers. Without the decomposers the plants would be unable to source their energy as well as the environment would be filled with dead matter and waste.

Further Readings – 

1. Energy Flow in Ecosystem
2. Biodiversity – Species, Genetics & Ecosystem