Unformatted text preview: Fungi Mushrooms, Molds, and Yeasts Learning Objective 1 What are the distinguishing characteristics of kingdom Fungi? Singular = fungus Fungi Eukaryotic heterotrophs Secrete digestive enzymes onto food then absorb predigested food Cell walls made of chitin General Characteristics Eukaryotic Heterotrophs Feed by Absorption Fungi cannot make their own food like plants. They depend upon other organisms for their carbon source. Secrete digestive enzymes onto food then absorb predigested food Saprotrophs: organisms that feed on dead organic matter Heterotrophic by Absorption
Fungi get carbon from organic sources Hyphal tips release enzymes Enzymatic breakdown of substrate Products diffuse back into hyphae Nucleus hangs back and "directs" Product diffuses back into hypha and is used KEY CONCEPTS Fungi are eukaryotic heterotrophs that absorb nutrients from their surroundings Learning Objective 2 What is the body plan of a fungus? General Characteristics Multicellular (except for yeasts) Have cell walls made of chitin Body made up of long, threadlike filaments called hyphae Hyphae branch and form a tangled mass called the mycelium Hyphae Mycelium 25 m Hyphae In most fungi perforated septa (cross walls) divide hyphae into individual cells In some fungi hyphae are coenocytic (form elongated, multinuclear cell) zygomycetes and glomeromycetes Hyphae septate coenocytic Hyphae There is cytoplasmic flow between cells of septate hyphae Movement of nutrients throughout mycelium Septate Dikaryotic Coenocytic Fig. 26-1 (c-e), p. 557 KEY CONCEPTS A fungus may be a unicellular yeast or a filamentous, multicellular mold consisting of long, branched hyphae that form a mycelium Learning Objective 3 What is the life cycle of a typical fungus, including sexual and asexual reproduction? Reproduction Most fungi reproduce sexually and asexually by spores Spores produced on aerial hyphae land in suitable spot and germinate Germination of a Spore Asexual Reproduction Budding yeast nucleus divides; new cell buds off of mother cell Life Cycles of Fungi Reproduction Fungi reproduce by means of spores Asexual spores Sexual spores Spores Produced by Divisions Mitosis forms new mycelia when spores germinate Meiosis produces 4 different haploid (n) nuclei each nucleus becomes part of a spore Asexual Spores Can be produced by mitosis genetically similar Spore germination Hyphal thread grows out of spore As it grows and branches, it develops into a mass of hyphae called a mycelium. Sexual Spores Plasmogamy Karyogamy Fungi of two different mating types meet, hyphae fuse Cytoplasm fuses but nuclei remain separate Fungi enter dikaryotic (n + n) stage each new cell has one nucleus of each type Fusion of nuclei takes place in hyphal tip results in diploid (2n) zygote nucleus produces 4 different haploid (n) spores Meiosis 7 Large numbers of haploid (n) spores are produced by mitosis. Asexual reproduction 8 Spore germinates and forms mycelium by mitosis. Spores germinate 1 and form mycelia by mitosis. 6 Spores are released. Mycelia Mycelia of two different mating types fuse at their 2 tips, and plasmogamy (fusion of cytoplasm) occurs. Spores Sexual reproduction Haploid stage (n) Dikaryotic stage (n + n) Diploid stage (2n) Zygote nucleus (2n) Plasmogamy 5 Meiosis results in four genetically different haploid ( n ) nuclei. Spores develop around nuclei. 3 Dikaryotic (n + n) mycelium develops. Dikaryotic mycelium Meiosis Karyogamy 4 Karyogamy (fusion of nuclei) occurs, forming a diploid (2 n ) zygote nucleus. Fig. 26-4, p. 559 KEY CONCEPTS Most fungi reproduce both asexually and sexually by means of spores Learning Objective 4 Support the hypothesis that fungi are opisthokonts, more closely related to animals than to plants Opisthokonts Fungi are opisthokonts along with animals and choanoflagellates based on chemical and structural characters Flagellate Cells Animals and chytrids have flagellate cells Example: chytrid gametes and spores Example: animal sperm Flagellate cells propel themselves with single posterior flagellum Platelike Cristae Like animal cells, fungal cells have platelike cristae in their mitochondria Flatties asci zygosporangia motile spores basidia Classification & Phylogeny Glomeromycetes Ascomycetes Evolution of ascospores Evolution of basidiospores Evolution of dikaryotic stage Motile gametes and spores Loss of flagellum Common flagellate ancestor Basidiomycetes Zygomycetes Chytrids Fig. 26-5, p. 560 Fungal Evolution 5 phyla Chytrids (Chytridiomycetes) Ascomycota: sexual and asexual reproduction; spores in ascus (sac) Zygomycota: sexual and asexual reproduction; form zygospore Glomeromycota: arbuscular mycorrhizaelive on plants and absorb nutrients Basidiomycota: sexual reproduction only; spores form on basidium Learning Objective 5 Support the hypothesis that chytrids may have been the earliest fungal group to evolve from the most recent common ancestor of fungi Chytrids (Chytridiomycetes) Produce flagellated cells during life cycle no other fungi have flagella Probably earliest fungi to evolve from flagellate protist common ancestor of all fungi Learning Objective 6 List distinguishing characteristics, describe a typical life cycle, and give examples of each of these fungal phyla: Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota Chytridiomycota "chytrids" Simple fungi Produce motile spores Mostly saprobes and parasites in aquatic habitats Could just as well be Protists Chytrids Reproduce both asexually and sexually Gametes and zoospores are flagellated Allomyces part of life is multicellular haploid thallus part is multicellular diploid thallus 1 6
Haploid zoospore Mature haploid thallus gametangium gametangium 2 Gamete Gamete Resting sporangium SEXUAL REPRODUCTION HAPLOID (n) GENERATION DIPLOID (2n) GENERATION Resting sporangium Zoosporangium 4 Zygote germinates and develops into diploid thallus.
ASEXUAL REPRODUCTION (by mitosis) 3 Meiosis 5 Plasmogamy and karyogamy Motile zygote 7 Diploid zoospore Zygomycota "zygote fungi" Sex zygosporangia Asexual common Hyphae have no cross wallscoenocytic Grow rapidly Mycorrhizae
Rhizopus on strawberries Zygomycetes Rhizopus (black bread mold) forms haploid thallus produces asexual spores and sexual spores Asexual spores germinate form new thalli Zygomycetes 2 In sexual reproduction hyphae of 2 different haploid mating types form gametangia Plasmogamy occurs as gametangia fuse Zygomycetes 3 Karyogamy occurs diploid zygote forms from which zygospore develops Meiosis produces recombinant haploid zygospores Zygomycetes 4 When zygospores germinate each hypha develops a sporangium at its tip Spores are released develop into new hyphae Zygospore and suspensors Fig. 26-9b, p. 564 Glomeromycetes 1 Phylum Glomeromycota symbionts that form intracellular associations (mycorrhizae) with plant roots Endomycorrhizal fungi extend hyphae into root cells Glomeromycetes 2 Arbuscular mycorrhizae most common endomycorrhizae hyphae inside root cells form branched, tree shaped structures (arbuscules) Glomeromycetes have coenocytic hyphae reproduce asexually with large, multinucleate spores (blastospores) Arbuscular Mycorrhizae Ascomycota "sac fungi" Sexual asci Asex. common Cup fungi, morels, truffles Important plant parasites & saprobes Yeast Saccharomyces Most lichens A cluster of asci with spores inside Ascomycetes 1 Produce asexual spores (conidia) Produce sexual spores (ascospores) in asci Asci line a fruiting body (ascocarp) Conidia Ascocarp Asci Ascomycetes 2 Haploid mycelia of opposite mating types produce septate hyphae Plasmogamy occurs, nuclei exchanged Dikaryotic n + n stage occurs hyphae form, produce asci and ascocarp Ascomycetes 3 Karyogamy occurs followed by meiosis Recombinant nuclei divide by mitosis produce 8 haploid nuclei that develop into ascospores When ascospores germinate can form new mycelia Ascomycetes 4 Ascomycetes include yeasts cup fungi morels truffles pink, brown, and bluegreen molds Some ascomycetes form mycorrhizae others form lichens Ascomycete Life Cycle Chytrids Zygomycetes Common flagellate ancestor
Fig. 26-13a, p. 567 Glomeromycetes Ascomycetes Basidiomycetes In asexual reproduction,10 hyphae produce haploid conidia that can develop into new mycelia. Conidiophore When released, 9 ascospores germinate and form new haploid mycelia. 8 Each nucleus becomes incorporated into an ascospore. Mature ascus has eight haploid ascospores Second meiotic division (+) mating type () mating type Conidia Haploid (n) Germinating conidium ASEXUAL REPRODUCTION (by conidia) Haploid mycelia of 1 opposite mating types both produce coenocytic sexual hyphae. 2 Plasmogamy occurs as hyphae of the two mating SEXUAL types fuse and nuclei are REPRODUCTION exchanged. 3 HAPLOID ( n ) STAGE Mitosis DIKARYOTIC produces eight STAGE Hyphae 7 haploid nuclei. (n + n) form an First meiotic division
DIPLOID (2n) STAGE Nuclei Zygote fuse Plasmogamy Nuclei migrate 4 ascocarp. Dikaryotic hyphae form and produce asci. Developing ascus with n+n nuclei Meiosis 6 Meiosis occurs, forming four haploid nuclei. Ascocarp Karyogamy 5 Mycelium Karyogamy occurs in each ascus. Two haploid nuclei fuse, forming a diploid zygote nucleus. Fig. 26-13b, p. 567 Basidiomycota "club fungi"
Sex basidia Asex rare Longlived dikaryotic mycelia Rusts & smuts primitive plant parasites Mushrooms, polypores, puffballs Enzymes decompose wood Mycorrhizas SEM of basidia and spores Basidiomycetes 1 Produce sexual spores (basidiospores) on outside of basidium Basidia develop on surface of gills in mushrooms a type of basidiocarp (fruiting body) Hyphae in this phylum have septa Basidiomycete Fruiting Bodies Basidiomycetes 2 Plasmogamy occurs fusion of 2 hyphae of different mating types Dikaryotic secondary mycelium forms Basidiocarp develops basidia form Basidiomycetes 3 Karyogamy occurs producing diploid zygote nucleus Meiosis produces 4 haploid nuclei become basidiospores When basidiospores germinate form haploid primary mycelia Plasmogamy haploid mycelium mycelium and fruiting Plasmogamy body are dikaryotic of haploid mycelia Mushroom Life Cycle
N Meiosis 2N N+N Karyogamy in basidium young basidia - the only diploid cells Basidiospore Basidium 5 m
Fig. 26-16, p. 570 Basidiomycetes 4 Basidiomycetes include mushrooms puffballs bracket fungi rusts smuts Yeasts
Single celled fungi Adapted to liquids Plant saps Water films Moist animal tissues Saccharomyces Candida Fungal Ecology Saprobes Parasites Decomposers Mostly of plants, some animals Harm host Mostly on plants, some animals Lichens Mycorrhizas Others Mutualists Importance of Fungi Decomposers and nutrient recyclers Importance of Fungi Mutualists: organisms that are associated with each other to their mutual benefit Most trees and prairie plants have fungi called mycorrhizae associated with their roots. help the plants gather nutrients Lichens Dual organisms Composed of a fungus and an alga Fungus gathers water, minerals, and provides a home for the algae sugars for the fungus Algae provides Commercial Uses for Fungi Beer and wine are produced by fermentation using single celled fungi called yeasts Produce alcohol and carbon dioxide Carbon dioxide from fermentation by yeast causes bread dough to rise Foods Mushrooms, corn smut (a favorite in Mexico) Corn smut Chanterelles Problem Fungi Some fungi are parasites of plants and animals Athletes foot Vaginal yeast infections Rust on wheat plants Ergot grows on rye seeds produces LSD May have been the culprit behind the accusations of witchcraft in 1620 Salem Mildew in your shower (not a disease producer just gross!) Heterotrophic by Absorption Fungi get carbon from organic sources Hyphal tips release enzymes Enzymatic breakdown of substrate Products diffuse back into hyphae Nucleus hangs back and "directs" Product diffuses back into hypha and is used Hyphae are the threadlike fibers that make up the mycelium. Hyphae are composed of partially separated cellslike compartments Cellular components can move between cells of hyphae. Most of the mycelium is hidden in the substrate (the ground, piece of fruit, etc). Reproductive structures are visible above ground ...
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