In this model, a fungus grows on a fallen dead tree trunk and absorbs substances from the decaying wood. It does not use sunlight to make food. What role does it have in the web?

Explication

The fungus obtains its energy from dead, decaying material rather than from sunlight or from living tissue, which is what defines a decomposer. Primary consumer fails because that role means feeding on living plants, and the wood in this scenario is already dead.