These organisms are classified as a kingdom, Fungi, which is separate from the other life kingdoms of plants, animals, protists, and bacteria. One difference that places fungi in a different kingdom is that its cell walls contain chitin, unlike the cell walls of plants, bacteria and some protists.ungi are the principal decomposers in ecological systems. These and other differences place fungi in a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (is a monophyletic group).