Fungi Invade the Land
17.1 Complex Multicellularity Complex multicellular organisms Individuals are composed of many highly specialized cells that c...
17.1 Complex Multicellularity Complex multicellular organisms Individuals are composed of many highly specialized cells that coordinate their activities Three kingdoms exhibit multicellularity Plants Animals Fungi
17.1 Complex Multicellularity Two key characteristics distinguish between complex multicellular and simple multicellular organisms Cell specialization Different cells use different genes They therefore develop in different ways Intercell coordination Cells adjust their activity in response to what other cells are doing
17.2 A Fungus Is Not a Plant The study of fungi is called mycology Fungi have traditionally been included in the plant kingdom However, there are significant differences between fungi and plants Fungi are heterotrophs Fungi have filamentous bodies Fungi have nonmotile sperm Fungi have cell walls made up of chitin Fungi have nuclear mitosis
17.3 Reproduction and Nutrition of Fungi Fungi have three types of reproductive structures Fig. 17.3 Gametangia Form haploid gametes that fuse to form zygote
Sporangia Produce haploid spores that are dispersed
Puffball spores
Conidiophores Produce asexual spores
Spores are a common means of fungal reproduction
17.3 Reproduction and Nutrition of Fungi Fungi obtain nutrients by external digestion They secrete digestive enzymes into their surroundings and absorb the resulting organic molecules
Some fungi are active predators Immobilizes nematodes then eats them!
Fig. 17.4 The oyster mushroom
17.4 Kinds of Fungi 73,000 species of fungi have been named so far There are divided into four phyla Zygomycota Distinguished primarily Ascomycota by their mode of Basidiomycota sexual reproduction Chitrydiomycota A fifth group, the imperfect fungi, is artificial It’s a “catch-all” grouping of fungi in which sexual reproduction has not been observed yet!
17.5 Zygomycetes Zygomycetes make up < 1% of named fungi They include Bread molds Some pathogens Candida Rhizopus
Zygomycetes typically undergo asexual reproduction
17.6 Ascomycetes Phylum Ascomycota, the ascomycetes, is the largest of the four phyla Yeasts, morels and truffles Many plant fungal pathogens Dutch elm disease and chestnut blight
Reproduction is usually asexual
Morel
17.7 Basidiomycetes Phylum Basidiomycota contains the most familiar of the fungi Mushrooms, toadstools, puffballs Many plant fungal pathogens
Asexual reproduction is rare
Amanita
17.8 Chytridiomycetes, Imperfect Fungi, and Yeasts Chytridiomycetes Aquatic, flagellated fungi Most closely related to ancestral fungi Include Plant pathogens A frog pathogen
Fig. 17.8 The pathogenic chytrid, Batrachochytrium dendrobatidis
17.8 Chytridiomycetes, Imperfect Fungi, and Yeasts Imperfect fungi Fungi where sexual reproduction has not been observed Fungi that cause ringworm infections
Fig. 17.9 The imperfect fungus, Verticillium alboatrum A pathogen of alfalfa
17.8 Chytridiomycetes, Imperfect Fungi, and Yeasts Yeasts Generic name given to unicellular fungi
Baker’s yeast
~ 250 named species
Reproduction is mostly asexual Fig. 17.10 Budding in the yeast Saccharomyces cerevisiae
17.9 Ecological Roles of Fungi Fungi, together with bacteria, are the principal decomposers in the biosphere Fungi are virtually the only organisms that can break down lignin
Fungi cause animal diseases Fungi are the most harmful pests of living plants Fig. 17.11 Armillaria: World’s largest organism?
Coniferous forest
8 hectares
17.9 Ecological Roles of Fungi Many commercial products are dependent on the biochemical activities of fungi Bread Beer Cheese Soy sauce Penicillin
Fungal Associations Mutualism is a form of symbiosis in which each partner benefits Two kinds of mutualistic associations between fungi and autotrophic organisms are ecologically important 1. Mycorrhizae 2. Lichens
Mycorrhizae Symbiotic association between a fungus and the roots of plants Fungus helps plant absorb minerals and nutrients Plant provides fungus with food (organic molecules) No mycorrhizae
Fig. 17.12 Mycorrhizae on the roots of pines
Fig. 17.13 How mutualism aids plant growth
Mycorrhizae Endomycorrhizae vs. Ectomycorrhizae
Far more common type
Hyphae penetrate root cells
Fig. 17.14
Hyphae do not penetrate root cells
Lichens Symbiotic association between a fungus and a green algae or cyanobacterium Lichens are found in the harshest of habitats They are often the first colonists in such harsh areas
