A fungus is a member of eukaryotic organisms which includes microorganisms such as yeasts and moulds, as well as the more familiar mushrooms. These organisms are classified as a kingdom: Fungi, which is separate from plants, animals, protists, and bacteria. One major difference is that fungal cell walls contain chitin, unlike the cell walls of plants and some protists, which contain cellulose, and unlike the cell walls of bacteria. Fungi cannot photosynthesize like plants and mode of nutrition is either saprophytic (live on dead decaying organic matter) or parasitic. These and other differences show that the fungi form a single group of related organisms, named the Eumycota (true fungi), that share a common ancestor (is a monophyletic group). Study of fingi: mycology has developed in to an independent branch. Mycology has often been regarded as a branch of botany, even though it is a separate kingdom in biological taxonomy. Genetic studies revealed that fungi are more closely related to animals than plants.