A fungus is any member of the group ofeukaryotic organisms that includes unicellular microorganisms such as yeasts and molds, as well as multicellular fungi that produce familiar fruiting forms known as mushrooms. 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. Similar to animals, fungi areheterotrophs, that is, they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. Growth is their means of mobility, except for spores, which may travel through the air or water (a few of which are flagellated). Fungi 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). This fungal group is distinct from the structurally similar myxomycetes (slime molds) andoomycetes (water molds). The discipline of biology devoted to the study of fungi is known as mycology (from the Greek μύκης, mukēs, meaning “fungus”). In the past, mycology was regarded as a branch of botany; today it is a separate kingdom in biologicaltaxonomy. Fungi are genetically more closely related to animals than to plants.
Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and their cryptic lifestyles in soil, on dead matter. They are both symbionts of plants, animals, or other fungi and also parasites. They may become noticeable whenfruiting, either as mushrooms or as molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment. They have long been used as a direct source of food, in the form of mushrooms and truffles, as a leavening agent for bread, in the fermentation of various food products, such as wine, beer, and soy sauce. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymesproduced by fungi are used industrially and in detergents. Fungi are also used asbiological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals including humans. The fruiting structures of a few species containpsychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g., rice blast disease) or food spoilage can have a large impact on humanfood supplies and local economies.