Semi Micropara

• Topics covered


  • The characteristics of fungi
  • The evolution of the fungi
  • Fungal classification
  • Fungal life cycles
• Body form of fungi


  • Unicellular
  • Filamentous (tube-like strands called hypha (singular) or hyphae (plural))
  • Mycelium = aggregate of hyphae
  • Sclerotium = hardened mass of mycelium that generally serves as an overwintering stage
  • Multicellular, such as mycelial cords, rhizomorphs, and fruit bodies (mushrooms)
• Mycelium and fruiting bodies are both composed of hyphae
• Heterotrophy


  Feeding on 'other food'
• Types of heterotrophy in fungi

  • Saprophytes or saprobes - feed on dead tissues or organic waste (decomposers)
  • Symbionts - mutually beneficial relationship between a fungus and another organism
  • Parasites - feeding on living tissue of a host
• Pathogens


  Parasitic fungi that cause disease
• Heterotrophic by absorption


  1. Hyphal tips release enzymes

  2. Enzymatic breakdown of substrate

  3. Products diffuse back into hyphae
• Hyphae


  • Tubular
  • Hard wall of chitin
  • Crosswalls may form compartments (± cells)
  • Multinucleate
  • Grow at tips
• Fungi have an extremely important ecological role as saprobes and decomposers
• Mycorrhizae


  • Mutualism between fungus (nutrient & water uptake for plant) and plant (carbohydrate for fungus)
  • Several kinds: Zygomycota - hyphae invade root cells, Ascomycota & Basidiomycota - hyphae invade root but don't penetrate cells
• Types of lichens


  • Crustose lichens - flat crusty plates
  • Foliose lichens - leafy in appearance, although lobed or branched structures are not true leaves
  • Fruticose lichens - finely branched and may hang down like beards from branches or grow up from the ground like tiny shrubs

  
• Fungi are parasites and pathogens
• Spores


  • Asexual (product of mitosis) or sexual (product of meiosis) reproductive cells
  • Allow the fungus to move to new food source
  • Resistant stage that allows fungus to survive periods of adversity
  • Means of introducing new genetic combinations into a population
• Fungal reproduction by spores

  1. Spores formed directly on hyphae

  2. Spores formed inside sporangia

  3. Spores formed in fruiting bodies
• Mycelia have a huge surface area
• The fungus is often hidden from view, growing through its food source (substratum), excreting extracellular digestive enzymes, and absorbing dissolved food
• Fungus has indeterminate clonal growth and a generally sedentary vegetative phase
• Characteristics of fungi


  • Cell wall present, composed of cellulose and/or chitin
  • Food storage generally in the form of lipids and glycogen
  • Eukaryotes - true nucleus and other organelles present
  • All fungi require water and oxygen (no obligate anaerobes)
  • Grow in almost every habitat imaginable, as long as there is some type of organic matter present and the environment is not too extreme
  • Diverse group, number of described species is somewhere between 69,000 to 100,000 (estimated 1.5 million species total)
• Fungal phyla


  • Chytridiomycota - "chytrids"
  • Zygomycota - "zygote fungi"
  • Ascomycota - "sac fungi"
  • Basidiomycota - "club fungi"
• Chytridiomycota


  • Simple fungi
  • Produce motile spores - zoospores
  • Mostly saprobes and parasites in aquatic habitats
  • Could just as well be Protists
• Zygomycota


  • Sexual Reproduction - zygosporangia
  • Asexual reproduction - common (sporangia - bags of asexual spores)
  • Hyphae have no cross walls
  • Grow rapidly
  • Decomposers, pathogens, and some form mycorrhizal associations with plants
• Life cycle of Rhizopus (Zygomycota)

  1. Asexual sporangium with spores inside

  2. Sexual zygsporangium with one zygospore
• Ascomycota


  • Sexual Reproduction - asci (sing. = ascus)
  • Asexual Reproduction - common
  • Cup fungi, morels, truffles
  • Important plant parasites & saprobes
  • Yeast - Saccharomyces
  • Decomposers, pathogens, and found in most lichens
• Basidiomycota


  • Sexual Reproduction - basidia
  • Asexual reproduction - not so common
  • Long-lived dikaryotic mycelia
  • Rusts & smuts - plant parasites
  • Mushrooms, polypores, puffballs, boletes, bird's nest fungi
  • Enzymes decompose wood, leaves, and other organic materials
  • Decomposers, pathogens, and some form mycorrhizal associations with plants
• Basidiomycota life cycle


  1. Nuclear fusion in basidium

  2. Meiosis

  3. Hyphal fusion of haploid mycelia

  4. Mycelium and fruiting body are dikaryotic
• Some fungi, like Mycena, are bioluminescent
• Yeasts


  Single celled fungi adapted to liquids like plant saps, water films, and moist animal tissues
• Yeasts


  • Candida
  • Saccharomyces
• Molds


  • Rapidly growing fungi that produce many asexual spores
  • Have many human importances like food spoilage, food production, and antibiotics
• Noble rot, caused by the fungus Botrytis, is important in wine production
• Beneficial effects of fungi

  • Decomposition - nutrient and carbon recycling
  • Biosynthetic factories - can be used to produce drugs, antibiotics, alcohol, acids, food (e.g., fermented products, mushrooms)
  • Model organisms for biochemical and genetic studies
• Harmful effects of fungi

  • Destruction of food, lumber, paper, and cloth
  • Animal and human diseases, including allergies
  • Toxins produced by poisonous mushrooms and within food (e.g., grain, cheese)
  • Plant diseases