pg - Fungi How they are constructed How they make their...

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1 Fungi How they are constructed How they make their living Their unusual life cycles Three major groups Their ecological importance Construction Cell walls of chitin Single celled fungi are called yeasts These may be from any of the major phyla Multi-celled fungi grow filaments known as hyphae. Cells of hyphae usually separated by septa, walls with pores. The hyphae form dense networks called mycelia (singular mycelium) Some hyphae form haustoria, branching projections that push into living cells, usually of plants. The “mushroom” is the fruiting body, usually representing a small fraction of the total mass of the fungus. Body Structure The morphology of multicellular fungi – Enhances their ability to absorb nutrients from their surroundings Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae. Reproductive structure. The mushroom produces tiny cells called spores. Spore-producing structures 20 μ m Mycelium Figure 31.2
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2 The “Humungous Fungus” Armillaria bulbosa • 10,000kg 15 hectares 1500 years old Bigger/older clones exist If you rent a U-haul truck in Michigan, this may be painted on it. Some fungi – Have specialized hyphae that allow them to penetrate the tissues of their host (b) Haustoria Fungal hypha Plant cell wall Haustorium Plant cell plasma membrane Plant cell Figure 31.4a, b
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3 Some fungi – Have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of materials Coenocytic fungi – Lack septa Nuclei Cell wall Septum Pore (a) Septate hypha (b) Coenocytic hypha Cell wall Nuclei Figure 31.3a, b Nutrition Heterotrophs that feed by absorbtion Excrete exoenzymes that break down complex organic molecules. Smaller molecules then absorbed into hyphae. Fungi may be: Decomposers (saprobes) Parasites (pathogens of plants and animals) Mutualistic (get some nutrition from host, provide some nutrition to host) Generalized Fungal life cycle The generalized life cycle of fungi Key Haploid ( n ) Heterokaryotic (unfused nuclei from different parents) Diploid (2 n ) PLASMOGAMY (fusion of cytoplasm) Heterokaryotic stage KARYOGAMY (fusion of nuclei) SEXUAL REPRODUCTION Spore-producing structures Spores ASEXUAL REPRODUCTION Zygote Mycelium GERMINATION GERMINATION MEIOSIS Spore-producing structures Spores Figure 31.5
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4 The phylogeny of fungi Chytrids Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota Figure 31.9 Ascomycetes Fungi in the phylum Ascomycota – Are defined by the production of sexual spores in saclike asci, which are usually contained in fruiting bodies called ascocarps • Ascomycetes – Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels (a) The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus.
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