Fungi

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HappyJedi7
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139730
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Fungi
Updated:
2012-03-05 15:25:10
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Bio 244 lab
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Unit 15
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  1. fungi
    • decompose and break down dead organic matter, recycling scarce nutrients
    • form mutualistic associations
    • medical benefits
    • number of commercial foods
    • serious pathogens
    • agricultural pests
    • allergies
    • spoil stored food
    • Eumycota - "true fungi" number at least 200k different species
    • colonized land at the same time as plants
  2. common characteristics:
    • lack chlorophyll
    • multicellular (yeast are unicellular representatives)
    • heterotrophic (via saprobic nutrient acquisition or as symbionts)
    • cell walls strengthened with chitin; most body mass consists of the mycelium
    • possess a zygotic life cycle, or can reproduce asexually
  3. saprobic nutrient acquisition
    • secrete digestive enzymes out of their hyphae, and the enzymes digest the organic molecules extracellularly
    • then absorb the nutrients through the cell walls
  4. symbiotic nutrient acquisition
    • parasites - absorb host tissues and harm the host
    • mutualists - absorb nutrients from the host, but in return provide materials to the host
  5. hyphae
    • filaments that compose the mycelium
    • aseptate - coenocytic; no cross walls between individual cells
    • septate - one or two haploid nuclei in each distinct cell
  6. zygotic life cycle:
    • diploid phase is brief and unicellular
    • plasmogamy - fusion of the hyphae and cytoplasms of two genetically different mating strains
    • followed by the formation of coenocytic (dikaryotic) hyphae
    • karyogamy - the fusion of the two nuclei; happens a while after plasmogamy
    • followed immediated by meiosis
    • the haploid spores produced via meiosis are called meiospores
  7. asexual reproduction (general fungi)
    sporangiophores and conidiophores are two types of structures that arise from mitotic divisions of hyphae and give rise to asexual spores and conidiospores, which germinate and form hyphae of the same genetic composition
  8. Division: Zygomycota (zygomycetes)
    • most primitive
    • "algal-like fungi" or "zygote fungi"
    • coenocytic aseptate hyphae
    • both asexual and sexual reproduction
    • do not produce sporocarps - multicellular fruiting bodies
    • ex Rhizopus stolonifer (black bread mold)
  9. Zygomycota sexual life cycle
    • hyphae of two different mating strains come into close contact and produce hyphal extensions (gametangia) --> the gametangia fuse (plasmogamy) --> forming the heterokaryotic zygosporangium, containing a number of haploid nuclei from the two parental mycelia
    • formation of a unicellular resting stage, called the zygosporangium --> produces a thick wall that protects against desiccation --> karyogamy occurs --> quickly undergo meiosis
    • zygosporangium breaks open --> a sporangium on top of a stalk (sporangiophore) appears --> the haploid spores (meiospores) are released and dispersed via wind --> spores germinate, sproducing haploid hyphae that form a new mycelium
  10. Zygomycota asexual life cycle
    • generating many sporangiospores
    • germinate
    • hypha emerge from each spore
  11. Division Ascomycota (ascomycetes)
    • "sac fungi"
    • septate hyphae
    • some are unicellular yeasts
    • sexual and asexual reproduction
    • ex: Saccharomyces cerevisae (yeast), Peziza (cup fungus), Morchella (morel mushroom)
  12. Ascomycota asexual life cycle
    • asexual spores (conidia) are formed externally via mitosis at the ends of specialized hyphae called condiphores
    • dispersed via wind
    • germinate, forming new mycelia
  13. Ascomycota sexual life cycle
    hyphae of two mating strains come into close contact --> form two distinct kinds of gametangia, called ascogonia and antheridia --> plasmogamy of the two gametangia occurs --> nuclei of the antheridium travels across a cytoplasmic bridge into the ascogonium --> dikaryotic hyphae arise from the ascogonia and form a cup-like structure called the ascocarp --> as ascus forms --> karyogamy then occurs in the ascus --> diploid nucleus then undergoes meiosis --> total of eight haploid nuclei lined up inside the ascus --> form eight ascospores, which are then released out
  14. Division Basidiomycota (basidiomycetes)
    • "club fungi"
    • diverse
    • commonly referred to as mushrooms and toadstools
    • Agaricus campestris is edible, while Amanita muscaria is deadly
    • obligate parasites (wheat rust fungus and corn smut fungus)
    • wood-decaying organisms (bracket fungi)
    • primitive basidiomycete species, such as smuts and rusts, do not produce basidiocarps
    • may form "fairy rings"
  15. Basidiomycota life cycle
    • haploid hyphae of two mating strains come into close contact --> hyphae undergo plasmogamy --> forms a long-lived dikaryotic mycelium
    • special environmental cues (ex temp, rainfall) cause the dikaryotic mycelium to rapidly form large, extensive, aboveground structures, called basidiocarps ("mushroom")
    • the pileus (cap) sits on top of the stalk-like stipe; large number of gills on the pileus, where the terminal dikaryotic cells form club-shaped basidia
    • inside a basidium, karyogamy occurs --> the diploid nucleus then undergoes meiosis --> 4 haploid nuclei --> each haploid nucleus enters a cytoplasmic extension off of the basidium and forms a basidiospore --> basidiospores break away --> dispersed via wind, germinate into short-lived haploid mycelia, etc.
  16. Division Deuteromycota (fungi imperfecti, deuteromycetes)
    • many multicellular fungi that cannot be placed in any of the other divisions
    • their sexual phase is unknown
    • polyphyletic group
    • actually include very common species (ex Penicillium and Aspergillus; although both have recently been moved)
    • mold - rapidly growing asexual fungus
  17. yeasts
    • unicellular fungi that inhabit moise or aquatic habitats
    • live as commensals or parasites on many animals and plants
    • most are Ascomycetes
    • can also reproduce asexually by budding
    • Saccharomyces cervisiae (brewer's yeast, baker's yeast)
    • Candida (can be passed sexually)
    • Rhodotorula (on shower curtains)
  18. lichens
    • a composite organism consisting of a fungus (mycobiont) and an alga/cyanobacterium (phycobiont) that are mutually dependent on one another
    • phycobionts may produce organic material or fix nitrogen into forms the fungus can use
    • mycobiont protects the phycobiont and provides moisture and minerals
    • the mycobiont is typically an ascomycete or basidiomycete
    • phycobiont lives in a thin layer just below the lichen's upper surface
    • reproduce asexually by fragmentation
    • three basic growth forms
  19. lichen asexual reproduction
    • fragmentation
    • producing structures called soredia
    • consist of a few hyphae surrounding a number of the phycobiont cells
    • the soredia break away and disperse
  20. three basic growth forms of lichens:
    • crustose - flattened, crust-like thallus
    • foliose - leafy looking
    • fruticose - a collection of small branching cylinders or tubes creating a bushy appearance
  21. mycorrhizae
    • composed of a mutualistic association of plant roots and fungi
    • fungi greatly increase the surface area over which minerals can be absorbed by the roots
    • plants provide organic nutrients
    • most are vascular plants
    • basidiomycetes in particular form mycorrhizaes

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