Fungi: The Decomposers and Mutualists in Terrestrial Ecosystems, Slides of Biology

Download Fungi: The Decomposers and Mutualists in Terrestrial Ecosystems and more Slides Biology in PDF only on Docsity! CHAPTER 29 FUNGI docsity.com Introduction • Fungi are the master decomposers and recyclers in terrestrial ecosystems – Saprophytes: – make their living by digesting dead plant material • The vast majority of fungi that live in association with other organisms benefit their hosts and are mutualists. • Some fungi absorb nutrients from their hosts…act as parasites • More closely related to animals than land plants docsity.com Analyzing Morphological Traits • Fungi have very simple bodies. Two growth forms exist: (1) single-celled forms—yeasts (2) multicellular, filamentous forms—mycelia • Some fungi adopt both forms. Single-celled fungi are called yeasts. Multicellular fungi have weblike bodies called mycelia. docsity.com Fungal Mycelium • All mycelia are dynamic – constantly grow in the direction of food sources and die back in areas where food is running out. • The filaments that make up a mycelium are called hyphae. • Most hyphae are haploid, although some are heterokaryotic: – each cell contains two haploid nuclei • Each filament is separated into cell-like compartments by cross- walls called septa – some fungi are coenocytic, meaning they lack septa entirely docsity.com Multicellular Fungi Have Unusual Bodies Hyphae are usually broken into compartments by septa. Both the reproductive structure and mycelium are composed of hyphae. Cell wall Septum Pore Hyphae Hyphae Mycelium Reproductive structure docsity.com Reproductive Structures • Chytridiomycota (chytrids): – live primarily in water. – the only fungi with motile cells: – produce spores and gametes with flagella • Zygomycota: – have haploid hyphae – the cells of the hyphae fuse to form a spore-producing structure: – called a zygosporangium docsity.com Reproductive Structures • Basidiomycota (club fungi): – have basidia that form at the ends of hyphae and produce spores – mushrooms, bracket fungi, and puffballs are among the complex reproductive structures this group produces. • Ascomycota (sac fungi): – produce complex reproductive structures – the tips of hyphae inside these structures produce distinctive saclike cells, called asci – generate spores docsity.com Four Distinct Reproductive Structures Are Observed in Fungi Spore Spores Chytridiomycota make swimming gametes and spores. Gametes Ascus Hyphae Hyphae Basidia Spores Zygosporangium Hyphae Ascomycota form spores in asci (sacs). Flagella Zygomycota hyphae yoke together and form a zygosporangium. Basidiomycota form spores on basidia (little pedestals). docsity.com Arbuscular Mycorrhizal Fungi • Arbuscular mycorrhizal fungi (AMF): – grow into the cells of root tissue and directly contact the plasma membrane of the plant cell. • provide phosphorus to the plants, but they do not provide nitrogen. • found in 80% of land plant species docsity.com Mutualistic Fungi Interact with the Roots of Plants in Two Ways Arbuscular mycorrhizal fungi (AMF) contact the plasma membranes of root cells. Ectomycorrhizal fungi (EMF) form sheaths around roots and penetrate between root cells. EMF AMF Cross section of plant root Cross section of plant root Hyphae extend outward into the soil Hyphae form a dense, continuous sheath around root Hyphae extend inward, between cells Hyphae extend outward into the soil Hyphae extend inward, penetrate cell wall, and contact plasma membrane docsity.com What Adaptations Make Fungi Effective Decomposers? • Fungi and a few bacterial species are the only organisms that can digest wood completely • Saprophytic fungi: – seek out large, complex molecules such as starch, cellulose, lignin, and proteins – breaks them down into many smaller compounds docsity.com Cellulose Digestion • Fungi break down cellulose, which they can live on – use enzymes called cellulases • Fungi secrete these enzymes – into the extracellular environment – these cellulases together convert cellulose into glucose docsity.com Variation in Life Cycles • The spore is the most fundamental reproductive cell in fungi. – spores are the dispersal stage in fungal life cycle – produced during both asexual and sexual reproduction • If a spore falls on a food source and is able to germinate, a mycelium begins to form – as the fungus expands… – hyphae grow in the direction where food is most abundant • If food begins to run out, the mycelium responds by making spores – dispersed by wind or animals docsity.com Unique Aspects of Fungal Life Cycles • The process of sexual reproduction begins when hyphae from two individuals fuse to form a hybrid hypha. • Fertilization occurs in two steps in many fungi: (1) fusion of cells and (2) fusion of nuclei from the fused cells. – Plasmogamy: – occurs when the cytoplasms fuse – if the nuclei remain independent, the mycelium becomes heterokaryotic. – Karyogamy occurs when the nuclei fuse docsity.com Neocallimastix species Chytridiomycota (Chytrids) • Chytrids are largely aquatic – common in freshwater environments • only fungi that can produce motile cells • produce spores that swim to new habitats via a flagellum docsity.com Nosema tractabile Spore case Polar tube Sporoplasm Microsporidia • All microsporidia: – are single celled and parasitic – a polar tube – allows them to enter the interior of the cells they parasitize • have a dramatically reduced genome and lack functioning mitochondria. docsity.com Arthrobotrys oligospora Roundworm Hyphae Zygomycota • Zygomycota: – primarily soil dwellers • Many are saprophytes – some are parasitic – some are predatory docsity.com Ascomycota (Sac Fungi) • Over half of all known fungi belong to the Ascomycota • The group is extremely large and diverse docsity.com Ascoymcota: Lichen Formers • The lichen-forming ascomycetes grow in association with cyanobacteria or green algae to form lichens Cross section of a lichen, showing three layers Soredia Asci produced by fungus Algal layer Fungal layer Fungal layer Substrate Top view of lichens on a rock Asexual reproduction occurs when “mini-lichens” are produced docsity.com Ascomycota: Non-Lichen Formers • The non–lichen-forming ascomycetes are sometimes called cup fungi: – because of their ascus-bearing cup- or saucer-shaped reproductive structure – called an ascocarp Sarcoscypha coccinea docsity.com