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Fungus

2007 Schools Wikipedia Selection. Related subjects: Organisms

   iFungi

                    Fossil range: Early Silurian - Recent

   Amanita muscaria, a basidiomycete
   Amanita muscaria, a basidiomycete
                 Scientific classification

   Domain:  Eukaryota
   Kingdom: Fungi
            L., 1753

                                  Divisions

   Chytridiomycota
   Zygomycota
   Glomeromycota
   Ascomycota
   Basidiomycota
   Deuteromycota

   The fungi (singular fungus) are a kingdom of eukaryotic organisms. They
   are heterotrophic and digest their food externally, absorbing nutrient
   molecules into their cells. Yeasts, molds, and mushrooms are examples
   of fungi. The branch of biology involving the study of fungi is known
   as mycology.

   Fungi often have important symbiotic relationships with other
   organisms. Mycorrhizal symbiosis between plants and fungi is
   particularly important; over 90% of all plant species engage in some
   kind of mycorrhizal relationship with fungi and are dependent upon this
   relationship for survival. Fungi are also used extensively by humans:
   yeasts are responsible for fermentation of beer and bread, and mushroom
   farming and gathering is a large industry in many countries.

   Fungi and bacteria are the primary decomposers of organic matter in
   most terrestrial ecosystems.

Phylogeny and classification of fungi

   Fungi were originally classified as plants, however they have since
   been separated as they are heterotrophs. This means they do not fix
   their own carbon through photosynthesis, but use carbon fixed by other
   organisms for metabolism. Fungi are now thought to be more closely
   related to animals than to plants, and are placed with animals in the
   monophyletic group of opisthokonts. For much of the Paleozoic Era, the
   fungi appear to have been aquatic. The first land fungi probably
   appeared in the Silurian, right after the first land plants appeared,
   even though their fossils are fragmentary. Fungi absorb their food
   while animals ingest it; also unlike animals, the cells of fungi have
   cell walls. For these reasons, these organisms are placed in their own
   kingdom, Fungi.

   The Fungi are a monophyletic group, meaning all varieties of fungi come
   from a common ancestor. The monophyly of the fungi has been confirmed
   through repeated tests of molecular phylogenetics; shared ancestral
   traits include chitinous cell walls and heterotrophy by absorption,
   along with other shared characteristics.

   The taxonomy of the Fungi is in a state of rapid flux at present,
   especially due to recent papers based on DNA comparisons, which often
   overturn the assumptions of the older systems of classification. There
   is no unique generally accepted system at the higher taxonomic levels
   and there are constant name changes at every level, from species
   upwards. Web sites such as Index Fungorum, ITIS and Wikispecies define
   preferred up-to-date names (with cross-references to older synonyms),
   but do not always agree with each other or with names in Wikipedia in
   its various language variants.

Types of fungi

   The major divisions ( phyla) of fungi are mainly classified based on
   their sexual reproductive structures. Currently, five divisions are
   recognized:
     * The Chytridiomycota are commonly known as chytrids. These fungi
       produce zoospores that are capable of moving on their own through
       liquid menstrua by simple flagella.
     * The Zygomycota are known as zygomycetes and reproduce sexually with
       meiospores called zygospores and asexually with sporangiospores.
       Black bread mold (Rhizopus stolonifer) is a common species that
       belongs to this group; another is Pilobolus, which shoots
       specialized structures through the air for several meters.
       Medically relevant genera include Mucor, Rhizomucor, and Rhizopus.
       Molecular phylogenetic investigation has shown the zygomycota to be
       a polyphyletic group.
     * Members of the Glomeromycota are also known as the arbuscular
       mycorrhizal fungi. Only one species has been observed forming
       zygospores; all other species only reproduce asexually. This is an
       ancient association, with evidence dating to 350 million years ago.
     * The Ascomycota, commonly known as sac fungi or ascomycetes, form
       meiotic spores called ascospores, which are enclosed in a special
       sac-like structure called an ascus. This division includes morels,
       some mushrooms and truffles, as well as single-celled yeasts and
       many species that have only been observed undergoing asexual
       reproduction. Because the products of meiosis are retained within
       the sac-like ascus, several ascomyctes have been used for
       elucidating principles of genetics and heredity (e.g. Neurospora
       crassa).
     * Members of the Basidiomycota, commonly known as the club fungi or
       basidiomycetes, produce meiospores called basidiospores on
       club-like stalks called basidia. Most common mushrooms belong to
       this group, as well as rust (fungus) and smut fungi, which are
       major pathogens of grains.

   Although the water moulds and slime moulds have traditionally been
   placed in the kingdom Fungi and those who study them are still called
   mycologists, they are not true fungi. Unlike true fungi, the water
   moulds and slime moulds do not have cell walls made of chitin. In the
   5-kingdom system, they are currently placed in the kingdom Protista.
   Water moulds are descended from algae, and are placed within the phylum
   Oomycota, within the Kingdom Protista.

Structure

   Hyphae as seen under a log
   Enlarge
   Hyphae as seen under a log

   Fungi may be single-celled or multicellular. Multicellular fungi are
   composed of networks of long hollow tubes called hyphae. The hyphae
   often aggregate in a dense network known as a mycelium. The mycelium
   grows through the medium on which the fungus feeds. Because fungi are
   embedded in the medium in which they grow, they are often not visible
   to the naked eye.
   Fungi growing in axenic culture (ascomycetes)
   Enlarge
   Fungi growing in axenic culture (ascomycetes)

   Although fungi lack true organs, the mycelia of ascomycetes and
   basidiomycetes may become organized into more complex reproductive
   structures called fruiting bodies, or sporocarps, when conditions are
   right. " Mushroom" is the common name given to the above-ground
   fruiting bodies of many fungal species. Although these above-ground
   structures are the most conspicuous to humans, they make up only a
   small portion of the entire fungal body. Some fungi form rhizoids,
   which are underground root-like structures that provide support and
   transport nutrients from the soil to the rest of the mycelium.

   A fungus of the species Armillaria ostoyae may be the largest organism
   on the planet. It was discovered in the Malheur National Forest in
   Oregon, and its underground mycelial network covers an area of 8.9 km²
   (2200 acres). Whether or not this is an actual individual organism is
   disputed: some tests have indicated that they have the same genetic
   makeup, but this does not exclude its being a clonal colony of numerous
   smaller individuals.

Reproduction

   Fungi on a fence post near Orosí, Costa Rica.
   Enlarge
   Fungi on a fence post near Orosí, Costa Rica.

   Fungi may reproduce sexually or asexually. In asexual reproduction, the
   offspring are genetically identical to the “parent” organism (they are
   clones). During sexual reproduction, a mixing of genetic material
   occurs so that the offspring exhibit traits of both parents. Many
   species can use both strategies at different times, while others are
   apparently strictly sexual or strictly asexual. Sexual reproduction has
   not been observed in some fungi of the Glomeromycota and Ascomycota.
   These are commonly referred to as Fungi imperfecti or Deuteromycota.

   Yeasts and other unicellular fungi can reproduce simply by budding, or
   “pinching off” a new cell. Many multicellular species produce a variety
   of different asexual spores that are easily dispersed and resistant to
   harsh environmental conditions. When the conditions are right, these
   spores will germinate and colonize new habitats.

   Sexual reproduction in fungi is somewhat different from that of animals
   or plants, and each fungal division reproduces using different
   strategies. Fungi that are known to reproduce sexually all have a
   haploid stage and a diploid stage in their life cycles. Ascomycetes and
   basidiomycetes also go through a dikaryotic stage, in which the nuclei
   inherited by the two parents do not fuse right away, but remain
   separate in the hyphal cells (see heterokaryosis).

   In zygomycetes, the haploid hyphae of two compatible individuals fuse,
   forming a zygote, which becomes a resistant zygospore. When this
   zygospore germinates, it quickly undergoes meiosis, generating new
   haploid hyphae and asexual sporangiospores. These sporangiospores may
   then be distributed and germinate into new genetically-identical
   individuals, each producing their own haploid hyphae. When the hyphae
   of two compatible individuals come into contact with one another, they
   will fuse and generate new zygospores, thus completing the cycle.

   In ascomycetes, when compatible haploid hyphae fuse with one another,
   their nuclei do not immediately fuse. The dikaryotic hyphae form
   structures called asci (sing. ascus), in which karyogamy (nuclear
   fusion) occurs. These asci are embedded in an ascocarp, or fruiting
   body, of the fungus. Karyogamy in the asci is followed immediately by
   meiosis and the production of ascospores. The ascospores are
   disseminated and germinate to form new haploid mycelium. Asexual
   conidia may be produced by the haploid mycelium. Many ascomycetes
   appear to have lost the ability to reproduce sexually and reproduce
   only via conidia.

   Sexual reproduction in basidiomycetes is similar to that of
   ascomycetes. Sexually compatible haploid hyphae fuse to produce a
   dikaryotic mycelium. This leads to the production of a basidiocarp. The
   most commonly-known basidiocarps are mushrooms, but they may also take
   many other forms. Club-like structures known as basidia generate
   haploid basidiospores following karyogamy and meiosis. These
   basidiospores then germinate to produce new haploid mycelia.

Ecological role

   Polypores growing on a tree in Borneo
   Enlarge
   Polypores growing on a tree in Borneo

   Although often inconspicuous, fungi occur in every environment on Earth
   and play very important roles in most ecosystems. Along with bacteria,
   fungi are the major decomposers in most terrestrial (and some aquatic)
   ecosystems, and therefore play a critical role in biogeochemical cycles
   and in many food webs.

   Many fungi are important as partners in symbiotic relationships with
   other organisms, as mutualists, parasites, or commensalists, as well as
   in symbiotic relationships that do not fall neatly into any of these
   categories. One of the most important of these relationships are
   various types of mycorrhiza, which is a kind of mutualistic
   relationship between fungi and plants, in which the plant's roots are
   closely associated with fungal hyphae and other structures. The plant
   donates to the fungus sugars and other carbohydrates that it
   manufactures from photosynthesis, while the fungus donates water and
   mineral nutrients that the hyphal network is able to find much more
   efficiently than the plant roots alone can, particularly phosphorus.
   The fungi also protect against diseases and pathogens and provide other
   benefits to the plant. Recently, plants have been found to use
   mycorrhizas to deliver carbohydrates and other nutrients to other
   plants in the same community and in some cases can make plant species
   that would normally exclude each other able to coexist in the same
   plant community. Such mycorrhizal communities are called "common
   mycorrhizal networks". Over 90% of the plant species on Earth are
   dependent on mycorrhizae of one type or another in order to survive,
   and it is hypothesized that the presence of terrestrial fungi may have
   been necessary in order for the first plants to colonize land.

   Lichens are formed by a symbiotic relationship between algae or
   cyanobacteria (referred to in lichens as " photobionts") and fungi
   (mostly ascomycetes of various kinds and a few basidiomycetes), in
   which individual photobiont cells are embedded in a complex of fungal
   tissue. As in mycorrhizas, the photobiont provides sugars and other
   carbohydrates while the fungus provides minerals and water. The
   functions of both symbiotic organisms are so closely intertwined that
   they function almost as a single organism.

   Certain insects also engage in mutualistic relationships with various
   types of fungi. Several groups of ants cultivate various fungi in the
   Agaricales as their primary food source, while ambrosia beetles
   cultivate various kinds of fungi in the bark of trees that they infest.

   Some fungi are parasites on plants, animals (including humans), and
   even other fungi. Pathogenic fungi are responsible for numerous
   diseases, such as athlete’s foot and ringworm in humans and Dutch elm
   disease in plants. Some fungi are predators of nematodes, which they
   capture using an array of devices such as constricting rings or
   adhesive nets .

Human uses of fungi

   Fungi have a long history of use by humans. Many types of mushrooms and
   other fungi are eaten, including button mushrooms, shiitake mushrooms,
   and oyster mushrooms. Of course, many species of mushrooms are
   poisonous and are responsible for numerous cases of sickness and death
   every year. A type of single-celled fungus called yeast is used in
   baking bread and fermenting alcoholic beverages, while mycelial fungus
   is used to make Shoyu ( soy sauce) and tempeh. Fungi are also used to
   produce industrial chemicals like lactic acid, antibiotics and even to
   make stonewashed jeans. Some types of fungi are ingested for their
   psychedelic properties, both recreationally and religiously (see main
   article, Psychedelic mushroom).

Edible and poisonous fungi

   Some of the most well-known types of fungi are the edible and poisonous
   mushrooms. Many species are commercially raised, but others must be
   harvested from the wild. Button mushrooms (Agaricus bisporus) are the
   most commonly eaten species, used in salads, soups, and many other
   dishes. Portobello mushrooms are the same species, but are allowed to
   grow to a much larger size. Other commercially-grown mushrooms that
   have gained in popularity in the West and are often available fresh in
   grocery stores include straw mushrooms (Volvariella volvacea), oyster
   mushrooms (Pleurotus ostreatus), shiitakes (Lentinula edodes), and
   enokitake (Flammulina spp.).
   Stilton cheese veined with Penicillium roqueforti
   Enlarge
   Stilton cheese veined with Penicillium roqueforti

   There are many more mushroom species that are harvested from the wild
   for personal consumption or commercial sale. Milk mushrooms, morels,
   chanterelles, truffles, black trumpets, and porcini mushrooms (also
   known as king boletes) all command a high price on the market. They are
   often used in gourmet dishes.

   It is also a common practice to permit the growth of specific species
   of mold in certain types of cheeses that give them their unique flavor.
   This mold is non-toxic and is safe for human consumption. This accounts
   for the blue colour in cheeses such as Roquefort or Stilton.
   Death cap, Amanita phalloides
   Enlarge
   Death cap, Amanita phalloides

   Hundreds of mushroom species are toxic to humans, causing anything from
   upset stomachs to hallucinations to death. Some of the most deadly
   belong to the genus Amanita, including A. virosa (the "destroying
   angel") and A. phalloides (the "death cap"). Stomach cramps, vomiting,
   and diarrhea usually occur within 6-24 hours after ingestion of these
   mushrooms, followed by a brief period of remission (usually 1-2 days).
   Patients often fail to present themselves for treatment at this time,
   assuming that they have recovered. However, within 2-4 weeks liver and
   kidney failure leads to death if untreated. There is no antidote for
   the toxins in these mushrooms, but kidney dialysis and administration
   of corticosteroids may help. In severe cases, a liver transplant may be
   necessary (Kaminstein 2002). It is difficult to identify a "safe"
   mushroom without proper training and knowledge, thus it is often
   advised to assume that a mushroom in the wild is poisonous and leave it
   alone.

   Fly agaric mushrooms (A. muscaria) are also responsible for a large
   number of poisonings, but these cases rarely result in death. The most
   common symptoms are nausea and vomiting, drowsiness, and
   hallucinations. In fact, this species is used ritually and
   recreationally for its hallucinogenic properties. However, if it is
   taken in over a long period of time (regularly over more than six
   months), this species might cause a temporary loss of sight, which can
   last from several minutes to an hour.

Fungi in the biological control of pests

   Many fungi compete with other organisms, or directly infect them. Some
   of these fungi are considered beneficial because they can restrict, and
   sometimes eliminate, the populations of noxious organisms like pest
   insects, mites, weeds, nematodes and other fungi, such as those that
   kill plants. There is much interest on the manipulation of these
   beneficial fungi for the biological control of pests. Some of these
   fungi can be used as biopesticides, like the ones that kill insects (
   entomopathogenic fungi). Specific examples of fungi that have been
   developed as bioinsecticides are Beauveria bassiana, Metarhizium
   anisopliae, Hirsutella, Paecilomyces fumosoroseus, and Verticillium
   lecanii (= Lecanicillium lecanii ).
   Retrieved from " http://en.wikipedia.org/wiki/Fungus"
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   with only minor checks and changes (see www.wikipedia.org for details
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