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FUNGI Chapter 31 The Little Known Fungi 100,000 species known, 1.5 million unknown (estimate) Some are single-celled (yeast), but most multicelled (mushrooms) Found in every habitat Diverse, widespread, and essential for well-being Formerly classified as plants Molecular data says more closely related to animals Mycologists are the scientists that study fungi Nutrition Heterotrophs, but absorb food instead of digest Secrete enzymes into environment to break complex molecules into something more manageable Enzymes also disrupt walls of plant cells for nourishment Live as decomposers, parasites, or mutualisms' Fit into multiple niches Can digest wide range of food sources Body Structure Most grow as filaments and yeasts Yeast only growth is rare Bodies form filamentous networks called hyphae Form a mycelium to increase SA/volume ratio Proteins synthesized to rapidly extend (not grow) hyphae Concentratie of energy and resources to accomplish Not motile, but can move hyphae Specialized Hyphae Some allow predation of living animals Haustoria allow nutrient extraction or exchange Mycorrhizae are mutually beneficial relationships between fungi and plants Improve mineral delivery to plants in exchange for carbs Ectomycorrhizal fungi: form a sheath of hyphae over plant roots and between plant cells Arbuscular mycorrhizal fungi: extend hyphae through root cell walls and into plant Sexual Reproduction Hyphae release pheromones Different mating types attract Heterokaryon, nuclei don’t fuse right away Dikaryotic, nuclei pair off and divide without fusing Time to karyogamy varies Usually only 2n stage Final steps generate genetic variation Asexual Reproduction Varies widely among fungi (like sexual) Produce haploid spores by mitosis Informally known as molds if mycelia is visible Grow rapidly and reproduce sexually if contacted by species of different mating type Yeasts produce budding cells or spores via mitosis Deuteromycetes reproduce asexually only 5 phyla recognized currently, but chytrids are likely paraphyletic Study cycle diagrams for reproductive differences Fungi Functional Groups Chytridium globular fruiting bodies, one of the earliest to diverge Mucor, grow into fruits and breads; may act as decomposers, parasites, or symbionts Ecologically important; form mycorrhizal associations with plants Sac fungi, common to water and land Aleuria aurantia Decomposers and ectomycorrhizal fungi; fruiting bodies commonly called mushrooms Phylum Chytridiomycota Called chytrids and found in lakes and soil Decomposers and pararsites of protists, other fungi, plants, or animals Live in sheep GI tracts to help process plants Some form colonies with hyphae, others as single cells Only phyla with flagellated spores called zoospores Phylum Zygomycetes Reproduce by zygospores Sexually, formed in zygosporagium Asexually, formed atop sporangiophores Rhizopus stolonifer is black bread mold Know the life cycle Philobolus ‘aim’ and shoot sporangium Resistant to freezing and drying Phylum Glomeromycetes Form arbuscular mycorrhizae Tips of hyphae push into plant root cells and branch into treelike structures Minerals to plant and organic compounds to fungi Mutualistic partnership with 90% of all plant species Phylum Ascomycetes Reproduce sexually by spores in asci (sacs) and bear stages in ascocarps (fruiting bodies) Reproduce asexually by conidiospores, spores formed at tips of hyphae called conidiophores Include: morels and truffles Yeasts used in beer industry Phylum Basidiomycetes Includes mutualists that form mycorrhizae and plant parasites Reproduce sexually by producing fruiting bodies called basidiocarps Produces 4 haploid nuclei Asexual reproduction is rare Fungal Phylum Review Decomposers Any carbon containing substance can be consumed by some fungi Important use in bioremediation Maintain essential inorganic nutrients for plant growth Return nutrients to the soil Mutualists Fungus-Plant Ascomycetes benefit by producing toxins to deter prey Fungus-Animal Decomposers convert otherwise indigestible plant material Lichens: symbiotic association with algae Algae contribute carbon compounds and fix nitrogen Fungi contribute suitable environments for growth Reproduce separately Lichen: asexually via soredia, clusters of hyphae with algae Pathogens Mostly on or in plants Ascomycete Cryphonectria parasitica attacks chestnuts Basidiomycete Puccinia graminis causes black stem rust on wheat Ascomycete Aspergillus contaminates improperly stored grains and peanuts by secreting carcinogenic aflatoxins Mycosis are those that parasitize humans Ascomycetes cause ringworm and athlete’s foot Coccidioidomycosis produces tuberculosis like symptoms in lungs Candida albicans normal on moist epithelia, grow to rapidly causes vaginal infections, diaper rash, and thrush Practical Uses Food Flavors of cheese Aspergillus used for citric acid in cola Yeasts for breads, beer, and wine Medicine Antibiotic treatments Penicillium used to produce penicillin Saccharomyces used to study Parkinson’s and Huntington’s disease
