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The Fungi "myco" = fungus; Mycology = study of fungi Your text does not have a section devoted to fungi, so it is important to jump around to various contextual references. As you do, make sure you are aware of the context of the section you are reading. I've put together some information from my own vast knowledge, and referenced page numbers in your text to supplement my own information. The fungi are mostly multicellular (exception = yeasts) life forms that have cell walls made of chitin. Chitin is also found in the exoskeletons of arthropods. It is generally considered to be a polysaccharide carbohydrate, except that the monomer is glucosamine (there is an amine group (NH2) on the #2 carbon of an otherwise normal-looking glucose unit). The Kingdom is most commonly divided into 4 Phyla, but this is changing. Three of the Phyla are locked in. They are grouped based on their sexual reproductive (spore-bearing) structures (p 478, 486). The three major phyla are: Zygomycota (Zygomycetes): Common Molds. The spore bearing structure is a zygosporanium. The common black mold Rhizopus nigricans is found in soil all over the world. Ascomycota (Ascomycetes): The Sac Fungi. Ascus = sac. Examples include yeasts (the only unicellular fungi), cup fungi, morels, and truffles (the latter 2 considered delicacies among connoisseurs). Basidiomycota (Basidiomycetes): The Club Fungi. Basidium = club. Include mushrooms, bracket or shelf fungi, and puffballs, among many other less-conspicuous species. Traditionally, a fourth group of fungi - The Deuteromycetes (Imperfect Fungi) were classified as such because they have evolved beyond sex (no sexual structures for placement in other groups), utilizing other means to exchange genetic material. This group is dwindling to nothing as scientists using genetic technology assign them to (mostly) Ascomycetes or (less- commonly) Basidiomycetes. Penicillin is a very common member of this group, but has now been reassigned to the Ascomycetes. Same for Tenia pedis, the pathogen of athletes foot. The Chytridomycota are a strange group of fungi that have been in and out of the kingdom, but currently they are back in. The Chytrids are gaining attention these days with the discovery that they are important pathogens of amphibians and are involved with the global decline in frogs. Chytrids live in water (often), and have flagellated spores. Feeding: All fungi are heterotrophic and feed in a manner very similar to bacteria (p 68). They produce and secrete enzymes onto the food upon which they live (their substrate). They are important decomposers (p 637). Some are parasites of plants and animals. Those that feed on dead stuff are called saprobes. There are obligate saprobes, obligate parasites, and others can go either way. A few fungi parasitize humans, but their virulence is low, skin infections caused by fungi are more common in tropical areas. Ecology: The fungi play many vital roles in ecosystems. In addition to being significant decomposers, most fungi have co-evolved with land plants, forming mutualistic symbiotic relationships. The most important of these relationships involve the Mycorrhizal fungi. Mycorrhizae "fungus root" take their nourishment from secretions from plant roots, and in exchange they provide the plant with water and minerals using their unsurpassed powers of absorption (p 188). Lichens are intimate relationships between a fungus and a photosynthetic alga or cyanobacterium (p 479). The partners in these lichen relationships are incapable of living apart from one another and many scientists have suggested that they be given their own place in the tree of life and a single species name, instead of the species of both members of the partnership. Morphology: Most fungi grow in long filaments called hyphae. The hyphae of Ascomycetes and Basidiomycetes is divided into distinct cells by crosswalls called septa (septate hyphae). The Zygomycetes lack these septa, and their hyphae is therefore coenocytic (without septa), resulting in multinucleate hypha. Mycelium is the name given to the body of most fungi. It consists of lots and lots of hyphae. A hypha is to mycelium as a tree is to a forest. The extremely important yeasts do not produce hyphae or mycelium, but they do have sexy time occasionally, and the resulting spore structure is an ascus. Yeast are unicellular, and reproduce asexually by the process of budding. They are also the only organisms capable of alcoholic fermentation which produces ethyl alcohol and CO2, important throughout the history of our species. Reproduction: All fungi reproduce asexually, and all but the Deuteromycetes can reproduce sexually. Sex in the fungi is beneficial for maintaining genetic diversity, but from a reproductive standpoint it is very inefficient in terms of energy consumption. The life cycles of the three groups include the sexual stage that defines them, as well as their very unique sexual activities. Fungi are prodigious producers of reproductive spores, which can be of either sexual or asexual origin.
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