Chapter 30 Fungi Fungi are heterotrophs that Feed by Absorption Nutrition and ecology o Heterotrophs Don t eat but instead absorb nutrients from outside their body by secreting hydrolytic enzymes to break down complex molecules into smaller organics that can be absorbed and used o Decomposers saprophytes break down nonliving organic material o Parasites absorb from cells of living hosts o Mutualists absorb from host cells but also benefit the host ex termite gut fungi Body structure o Yeasts single celled fungi o Multicellular filaments o Multicellular fungi Hyphae tiny filaments that form a network Tubular cell walls of chitin Mycelium interwoven hyphae that goes into the material that the fungus feeds Septa cross walls dividing up the hyphae still allow organelles to flow through on Maximizes surface to volume ratio pores Coenocyte fungi fungi that lack septa Multinucleate o Mycorrhizae fungus roots mutually beneficial relationships between fungi and plant roots Can expand plant root networks because mycelial network are more efficient Haustoria specialized hyphae used to extract exchange nutrients with plant hosts 2 main types of mycorrhizae Ectomycorrhizal fungi form sheaths of hyphae over root surfaces and grow Arbuscular mycorrhizal fungi hyphae enter root cell walls and into tubes in between root cells outside cells made by root cell plasma membrane Almost all vascular plants have mycorrhizae and rely on them for essential nutrients Sexual reproduction Fungi Produce Spores through Sexual and Asexual Life Cycles o Most fungal hyphae and spores are haploid o Sexual reproduction usually starts when hyphae from 2 mycelia produce pheromones If they are of opposite mating types they are attracted and grow together o Plasmogamy fusion of 2 cytoplasms Heterokaryon mycelium with 2 different nuclei Dikaryotic n n o Karyogamy fusion of nuclei to make a diploid zygote Undergoes meiosis to make spores o Heterokaryotic condition might offer diploid like advantages by cancelling out harmful mutations Asexual reproduction o Many fungi reproduce both asexually and sexually o May grow as filamentous fungi that make haploid spores by mitosis Molds if they have visible mycelia Reproduce asexually but also sexually if they come in contact with a species of a different mating type Asexually as single celled yeasts bud cells pinch off Some can be filamentous or single celled based on nutrient availability o Deuteromycetes fungi lacking sexual reproduction Ancestor of Fungi was a Single Celled Flagellated Protist Origin of fungi o From flagellated protists o Some of the earliest diverging lineages chytrids have flagella o Most protists with flagella have a common ancestor with animals and fungi o Opisthokonts DNA indicates that fungi animals and protistan relatives formed a o Fungi are more closely related to protists than animals ancestor was unicellular Multicellularity evolved independently in fungi and animals o Hard to tell history because early fungi fossilized poorly The move to land o Most diversity in fungi came about when they moved to land o Moved with plants to land as mycorrhizal fungi clade Diverse Lineages of Fungi Chytridiomycetes chytrids o Lakes and soil o Decomposers o Parasites global amphibian decline o Mutualists in guts of herbivores break down cellulose o Diverged early o Colonial and single celled o Zoospores Unique flagellated spores Zygomycetes o Molds o Parasites o Commensal symbionts of animals o Rhizopus Stolonifer black bread mold Aseptate hyphae spread across and in bread Septa only at reproductive parts o Asexual phase sporangia develop at tips of upright hyphae Make spores through mitosis o Sexual when environmental conditions deteriorate Union of mycelia of different mating types Plasmogamy makes diploid zygosporangium Zygosporangium is resistant to freezing drying and are metabolically inactive Glomeromycetes Karyogamy and then meiosis makes spores o Almost all arbuscular mycorrhizae o Tips of hyphae make bundles called arbuscles in root cells Ascomycetes sac fungi o Saclike asci that make spores during sexual reproduction o Ascocarp fruiting body that contain asci o Conidia asexual spores produced in specialized hyphae called conidiophores Could also be sexual when hyphae of different mating types fuse and then asci develop from the tips Karyogamy within each ascus results in a diploid Meiosis then mitosis makes 8 ascospores Basidiomycetes club fungi o Mushrooms puffballs shelf fungi mutualists that form mycorrhizae and plant parasites 9rusts and smuts o Important decomposers of wood lignin o Long lived dikaryotic stage multiplies result of 1 making o Basidiocarp fruiting bodies Gills lined with basidia source of spores Nuclei fuse in basidium undergo meiosis to make 4 haploid nuclei 4 appendages grow and each haploid nucleus goes and makes a basidiospore o Basidium club shaped cell where karyogamy occurs Fungi play Key Roles in Nutrient recycling ecological interactions and human Welfare Fungi as decomposers o Break down almost any organic material Cellulose and lignin o Help keep ecosystems stocked with essential inorganic nutrients Carbon nitrogen and other elements Fungi as mutualists o Endophytes fungi that live inside leaves and other plant parts causing harm All plant species have them Mostly ascomycetes Benefit grasses by making toxins to deter herbivores Increase plant hardiness o Fungus animal mutualisms Digestive help Farmer ants grow fungi and feed it leaves Feed on specialized hyphae tips filled with protein and carbs Fungi can no longer exist without ants Lichens symbiotic associations between photosynthetic organisms and fungus in which photosynthetic cells are held in a mass of hyphae o Grow on logs trees and roots o Photosynthetic partners are cyanobacteria or green algae o Most common fungus is the ascomycete Some glomeromycetes and basidiomycetes o Fungus gives overall shape o Hyphae most of lichen mass o Asexual reproduction Fragmentation Soredia small clusters of hyphae with embedded algae o Fungi and algae can reproduce separately o Algae provide carbon compounds cyanobacteria fix nitrogen o Fungi provides suitable environment for growth Allow for gas exchange protects and retains water minerals o Important pioneers often the first to return to an area Break down surface Add organic nitrogen to soil o Don t stand up well to pollination good indicators of air pollution Fungi as pathogens o 30 of fungi are pathogens mostly plant o Some
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