Answer 1- Earthworms are decomposers. They decompose the organic matter and convert the complex substances into simpler digested molecules. These molecules are released into the soil by the feces of earthworms. This way earthworms replenish the soil fertility and return the nutrients back to the ecosystem.
Answer 2- Food chain is a series in which organisms are placed in a systematic order of flow of energy and nutrients. An example of food chain with earthworm is shown in image shared below.