Fungi are heterotrophs, meaning they can't produce their own food like plants do. Instead, they obtain their nutrients from other organisms, including:

1. Dead organic matter: Many fungi are saprotrophs and break down dead plants, animals, and their waste products. This plays a vital role in decomposition and recycling nutrients in ecosystems. Think of mushrooms growing on decaying wood!

2. Living organisms: Some fungi are parasites and obtain nutrients from living hosts, often causing harm to them. These can be plant parasites (like rusts and smuts) or animal parasites (like ringworm or athlete's foot).

3. Symbiosis: Some fungi live in mutually beneficial relationships with other organisms. This is called symbiosis. Examples include:

* Mycorrhizae: Fungi form a symbiotic relationship with plant roots, providing them with water and nutrients in exchange for sugars.

* Lichens: Fungi live in a symbiotic relationship with algae or cyanobacteria, providing structure and protection in exchange for food produced by the algae.

4. Other Fungi: Some fungi are predators, capturing and feeding on other fungi.

So, in short, fungi feed on a wide variety of things, playing essential roles in decomposition, symbiosis, and even predation.