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Introduction
Molds, mushrooms, yeast, rusts and smuts are all members of a diverse group of haploid eukaryotic organisms called fungi. Most members of this group are multicellular and macroscopic, whereas some are single-celled and microscopic. Most fungal cells are enclosed by a cell wall containing the polysaccharide chitin. Fungi begin their life cycle as spores that divide rapidly to form threadlike structures called hyphae. These spores are single cells and quite often are dispersed by the wind or air currents.
Hyphae grow in several directions and form a mass called mycelium. The hyphal strand of most fungi is composed of individual cells separated by cross walls called septa. A few fungi, including Rhizopus , have hyphae that lack septa and are a continuous mass of cytoplasm with multiple nuclei. Hyphae with cross walls are termed septate hyphae and those lacking septa are coenocytic. Most fungi reproduce by spores produced on specialized hyphae termed fruiting bodies.
As saprophytes , the heterotrophic fungi release enzymes that break down organic compounds in the environment which are subsequently absorbed. Most fungi live on dead and decaying organic matter; thus, they play an important role in nutrient recycling and are known as decomposers in food webs.
Some fungi are parasitic , especially on plants. Rusts, smuts and blights are common plant diseases caused by fungi. Animals may also have fungal diseases, including athlete’s foot, ringworm and vaginal yeast infections. Spores of certain fungi are known allergens while penicillin (which is isolated from a fungus) is an important antibiotic.
Earlier classification of fungi was based mainly on sexual reproductive structures; however, recent molecular data, such as comparative DNA and RNA sequencing, have also begun to play a role in fungal classification. This lab will consider three phyla of Kingdom Fungi:
Kingdom Fungi Phylum Zygomycota Phylum Ascomycota Phylum Basidiomycota
Study tip: You should be familiar with the characteristics of fungi and the terms in bold above.
Fungi Laboratory
STATION 1: Phylum Zygomycota
Fungi belonging to this phylum are terrestrial and thrive in damp places. A representative zygomycete, Rhizopus stolonifer (black bread mold), colonizes the moist interior of bread. In asexual reproduction, aerial hyphae called sporangiophores terminate in spore-bearing sporangia. The thousands of dark spores within the sporangium account for the common name of black bread mold.
Sexual reproduction is triggered when there is scarcity of food. Two hyphae of different mating strains (+/–) develop suspensors on which gametangia form. The gametangia fuse to form a diploid zygospore with a rough outer coat. The zygospore is a dormant structure composed of a zygote enclosed by a thick protective wall. Under appropriate conditions, zygospores undergo meiosis to produce haploid spores that begin the next generation. A. Using the model, label the life cycle of black bread mold, Rhizopus : hyphae, mycelium, sporangiophore, sporangium, spores, suspensor, gametangia and zygospore.
STATION 2: Phylum Ascomycota
Sac fungi Peziza , also commonly known as a type of cup fungus, sexually reproduces by fusion of two different strains (+/–) of hyphae. After fusion of the hyphae, the nuclei remain separate until after the fruiting body, an ascocarp , is formed. The ascocarp contains long thin cells called asci (ascus - singular). Within each ascus , meiosis followed by mitosis results in eight ascospores.
A. Label sexual reproductive structures of Peziza : mycelium, ascocarp, ascus, asospores
B. View the demo slide of Peziza - observe all structures labeled above.
Questions: Are the ascospores inside or outside of the ascus?
How many ascospores are in each ascus?
What structure is referenced when using the common name 'cup fungus'?
Fill out the following chart:
Common name Genus Kingdom Phylum
Peziza
STATION 3: Phylum Basidiomycota The common grey mushroom Coprinus, sexually reproduces by fusion of two different strains of hyphae. After fusion of the hyphae, the haploid nuclei remain separate until after the fruiting body, a basidiocarp , is formed. The basidiocarp consists of a cap , stalk (stipe) and gills. Spore formation occurs within the gills on club-shaped basidia. As the basidiocarp open to expose the gills, a ring of scar-tissue ( annulus ) is sometimes left behind on the stipe.
A. Label sexual reproductives structures of Coprinus : mycelium, basidiocarp, cap, stalk, annulus, gills, basidium, basidiospores
B. Examine a basidiocarp, identify the cap, stalk, gills and annulus.
C. View the demo slide of Coprinus - observe structures listed above.
Questions:
Are the basidiospores inside or outside of the basidium?
What happens to the basidiospores after they are released?
What cellular division process forms the four basidiospores each basidium produces?
Fill out the following chart:
Common name Genus Kingdom Phylum
Common grey mushroom
