Chapter 28: Fungi

1. Chapter 28: Fungi 28-1 Overview of Fungi 28-2 Classification 28-3 Fungi and Humans

2. 28-1 Overview of Fungi I. Characteristics of Kingdom Fungi (i.e., Mycology) • Differ from bacteria and protists in structure, reproduction (haploid for most of their life cycle), and in obtaining nutrition. (i.e., eukaryotic, multicellular heterotrophs) (1) Molds (saprophytic) • Tangled masses of filaments of cells that grow on bread and fruit (2) Yeasts • Unicellular fungi whose colonies resemble bacteria

4. (3) Hyphae (hypha) • Filaments of fungal cells (4) Chitin • Polysaccharide component of fungal cell walls NOT found in bacteria, protists, or plants, but found in the exoskeleton of insects.

5. Critical Thinking (1) The cell walls of fungi and the exoskeletons of insects and crustaceans contain chitin. Would this phenomenon be of phylogenetic significance or not?

6. (A) Structure of Fungi (vegetative and reproductive) • Multicellular and designed for extracellular digestion, making fungi excellent recyclers of organic material in nature. (1) Mycelium • An interwoven mat of hyphae visible to the unaided eye (2) Septa (Basidiomycota and Ascomycota) • Cross-sections that divide hyphae (called “septate hyphae”) (3) Coenocytic (Zygomycota and Ascomycota) • Hyphae that lack septa.

8. (4) Dimorphism (e.g., human disease, histoplasmosis) • When a fungus can change its form in response to changes in their environment (i.e., Histoplasma capsulatum grows as a mycelium in the soil, but inside a human host, grows unicellularly as a yeast.)

9. (B) Asexual Reproduction • Fungi produce thousands of genetically identical haploid spores, usually on modified cells of the hyphae. (NOTE: A variety of asexual spores are formed by different fungi) (1) Sporangiophores (Zygomycota) • Specialized hyphae that appear as upright stalks (2) Sporangium • Enclosed sac that sits on top of the sporangiophore (3) Sporangiospores (haploid) • Spores manufactured through meiosis in the sporangia

19. (4) Conidia (haploid) • Spores that lack the protection of an enclosing sac (5) Conidiophore (Ascomycota) • Stalk-like structure that produces conidia (e.g., Penicillium)

22. Critical Thinking (2) Fungi such as Penicillium engage in a kind of biochemical warfare against other microorganisms by producing chemicals that diffuse outward and kill nearby organisms. Suggest how producing antibiotics could be an adaptive advantage for fungi?

23. Critical Thinking (3) Long before antibiotics were discovered by Alexander Fleming, it was common practice to place a piece of moldy bread on wounds. Suggest a reason as to why this practice may have helped the wounds to heal.

24. (6) Fragmentation (another form of fungal asexual reproduction) • A septate dries and shatters, releasing individual cells that act as spores (e.g., Tinea pedis, Athlete foot fungus)

25. Critical Thinking (4)Most fungi grow best at temperatures between 50 and 68 degrees F. Aspergillus fumigatus, however, grows well between 96 and 100 degrees F. Knowing this, where would you expect A. fumigatus to grow?

26. (7) Budding (e.g., yeast cells) • Asexual process in which part of a yeast cell pinches itself off to produce a small offspring cell (able to be repeated many times)

29. (C) Sexual Reproduction (mating strains of all three phyla) • Ensures genetic recombination among offspring, assisting evolution of some fungal species (also called “conjugation”) • When 2 different mating types of the same species encounter each other, the opposing hyphae fuse together, producing a diploid cell (zygospore, basidiospore, ascospore—depending on the phylum).

32. (D) Evolution (~300 m.y.a, around the same time as early land plants) • Fungi, like other eukaryotes, arose from prokaryotes (endosymbiosis) • Possibly evolved as unicellular organisms that may have clung together after mitosis to form a long filament of cells.

33. 28-2 Classification (~100,000 species of fungi) I. Phylum Zygomycota (~600 species) • Terrestrial, rich soil fungi that have coenocytic hyphae (e.g., Rhizopus stolonifer—bread mold)

34. (1) Rhizoids • Specialized hyphae that anchor the fungus to the food source and secrete digestive enzymes to break down the source into absorbable nutrients.

39. (2) Stolons • Specialized hyphae that grow across the surface of the bread (3) Gametangium (occurs during fungal conjugation) • Sexual reproductive structure that contains a nucleus of each mating type of hyphae. (4) Zygosporangium (diploid) • Fused gametangia forms a thick wall and becomes dormant until environmental conditions promote germination. (this will grow into a new sporangiophore upon germination)

41. II. Phylum Basidiomycota (~25,000 species, sexual reproduction) • Club Fungi, noted for their basidia or gill-bearing caps. (e.g., portabellas and white-button mushrooms) (1) Basidia (the “clubs”) • Small, club-like structures that line the gills and are produced during sexual reproduction. (2) Basidiocarp (stalk (a.k.a. stipe) and mushroom cap) • Underside of cap are rows of gills that are each lined with thousands of dikaryotic (diploid) basidia.

42. (3) Dikaryotic • Basidia cells contain TWO nuclei and fuse to form a diploid zygote; zygote undergoes meiosis to form FOUR haploid basidiospores. (4) Basidiospores • Released into the air and will germinate to produce haploid mycelia that grow underground (when mating strains fuse, a basdiocarp emerges above ground)