Transcript Fungi
Fungi AP Biology Spring 2011 Describe the various types of fungal body plans, patterns of reproduction, and natural history Discuss economic impact of fungi on humans Provide at least one example of each of the major groups of fungi Provide the two examples of symbiotic relationships with fungi Fungal Characteristics and Classification Fungi: spore producing heterotrophs with chitin cell walls that utilize organic matter Saprobes: get nutrients from the nonliving matter and cause its decay Parasites: thrive on tissues in living hosts All rely on extracellular enzymatic digestion and absorption Valuable decomposers in all environments Most multicellular Mycelium: the food-absorbing part of fungus, mesh of branching filaments Each tubular filament is a hypha with chitinous walls Interconnections and perforations allow cytoplasmic flow necessary for transport to nonabsorptive parts of the body Either a haploid or dikaryotic (2 haploid nuclei in one cell) stage dominantes fungal life cycle Like most protists Fungi disperse by means of spores Asexual reproduction is mostly by spores produced in sporangia Sexual reproduction proceeds through the formation of gametes in gametangia as well as by spores Gene comparisons show that fungi are more closely related to animals than plants Several major groups that make up the fungal kingdom Chytids, zygote fungi, and glomermycetes are small groups that are not monophyletic 1. Lack a dikaryotic stage and have hypha with few or no cross walls (septae) Chytids: ancient fungal lineage, flagellates spores and gametes that swim in water, wet soil, and in soil animal digestive systems ▪ ▪ Feed on organic wastes and remains helping to recycle nutrients Some aid herbivores in the digestion of cellulose, others pathogens Sac and Club Fungi: 2 large monophyletic groups 2. Both make dikaryotic mycelium and the cells of their hyphae are separated by septae Are successful because the dikaryotic mycelium increase genetic diversity of sexually produced spores Zygomycetes Zygomycetes: form a zygospore during reproduction Have haploid mycelium, no dikaryotic hyphae, most are saprobes, some are parasites, and a few have mutual relationships with plant roots Sexual reproduction: begins when 2 hyphae (different mating strains) grow toward each other and fuse Gametangia forms and makes haploid nuclei, which later fuse to form a diploid zygospore Zygospore later release haploid spores, which form in sacs at the tips of the hyphae Microsporidians: intracellular parasites of animals Have no mitochondria and rely on host for ATP Spore has long polar tube hat it uses to connect with a host cell and inject the contents of the spore into the host Glomeromycetes: associate with plant roots and do not reproduce sexually Their association with plant cell walls helps nutrients enter plant cell roots Basidiomycetes: Club Fungi Club fungi: have club-shaped sexual spores that form on the gills of mushrooms Which are the spore-producing structures of this group The aboveground part of the fungal body is the common mushroom consisting of a stalk and cap Basidiospores are produced in club-shaped structures on the outer surface of the cap When spores land on a suitable site, they germinate to produce extensive underground mycelia that then reproduce sexually Resulting in a dikaryotic stage Sexual reproduction is accomplished when two compatible mating strains make contact Cytoplasmic fusion results in a dikaryotic mycelium Eventually, the nuclei will fuse to form a zygote, which undergoes meiosis to form haploid spores dispersed in the wind Ascomycetes Sac Fungi Sac Fungi: form sexual spores called ascospores inside sac-shaped cells called asci Asci enclosed in reproductive structures of interwoven hyphae Types of Sac Fungi: Multicelled sac fungi include: Edible morels and truffles Most of food-spoiling molds Single celled yeasts Septae in the ascomycet hyphae prevents damage from causing the organism to dry out Making ascomycetes (and basidomycetes) more successful than fungi without septae Spores form from inside a sac-like cell (ascus) Sexual reproduction starts when 2 compatible hyphae meet and form a dikaryotic hyphae Nuclear fission, followed by meiosis in the asci at the tips of the hyphae Some ascomycetes can reproduce asexually by the process of budding or by producing haploid spores called condida Genetic research: neurospora Food: truffles and morels Fermentation: Saccharomyes cervisiae helps bread rise and produces beer and wine; Aspergilus makes soy sauce and citric acid for soda; Penicillium roquefortii helps produce blue cheese Medicine: Penicillium chrysogenum is used for antibiotics; Aspergillus lowers cholesterol, and Trichoderma prevents organ rejection Agriculture: a sac fungi species may help control roundworm populations in agricultural settings Fungal Symbionts Lichens: mutualistic associations between fungi and cyanobacteria, green algae, or both The fungus is the mycobiont and the photosynthetic part is the photobiont The tip of a fungal hypha binds with a suitable host cell Both lose their cell wall and their cytoplasm fuses as both organisms grow together The fungus recieves a long-term source of nutrients, which it absorbs from the photobiont cells Lichen helps to shelter the photobiont and anchor it to the substrate Live in inhospitable places Bare rock, tree trunks By their metabolic activities, lichens can change the composition of their substrate Usually sensitive to air pollution Endophytic fungi: symbionts that live inside the leaves and stems of many plants Fungi living in the tissues of fescue grass produce an alkaloid that deters grazers The fungus-roots Mycorrhiza: is a symbiotic relationship in which fungi hyphae surround roots of shrubs and trees Because of extensive surface area, fungus can absorb mineral ions and facilitate their entry into the plant