chapter 24 fungi

Structure & Function of Fungi

  • Fungi are primarily multicellular eukaryotes, with approximately 80,000 species.

  • They are absorptive heterotrophs that secrete hydrolytic enzymes, breaking down complex nutrients to absorb simpler molecules. Most are saprobes, decomposing dead organic material, while others are parasitic or form mutualistic relationships.

Processes of Reproduction in Fungi

  • Asexual Reproduction:

    • Involves the formation of haploid spores. Methods include budding and fragmentation.

    • Types of asexual spores:

      • Conidiospores: Formed on conidiophores.

      • Sporangiospores: Released from sporangia at the end of hyphae.

  • Sexual Reproduction:

    • Involves mating types instead of genders. Fungal life cycles can alternate between sexual and asexual stages.

    • Key steps include plasmogamy, formation of a heterokaryotic stage, and karyogamy to form diploid zygote, which then produces spores through meiosis.

Phylogenetic Origin of Kingdom Fungi

  • Evolved from a common ancestral protist shared with plants and animals. Molecular studies reveal a closer relationship between fungi and animals.

  • The common ancestor was likely a flagellated unicellular protist.

Five Phyla within Kingdom Fungi

  1. Chytridiomycota:

    • Primitive fungi with flagella in reproductive cells.

  2. Zygomycota:

    • Coenocytic hyphae, reproduce via zygosporangia (sexual) and sporangiospores (asexual).

  3. Glomeromycota:

    • Form mutualistic arbuscular mycorrhizae with plants.

  4. Ascomycota:

    • Sac fungi producing spores in asci and asexual spores via conidiophores.

  5. Basidiomycota:

    • Club fungi with spores formed in basidia, including familiar mushrooms.

Ecological Roles of Fungi

  • Decomposers:

    • Crucial for recycling nutrients in ecosystems, breaking down complex substances.

  • Mutualistic Relationships:

    • Fungi in mycorrhizal relationships enhance plant nutrient uptake.

  • Pathogenic Effects:

    • Some fungi can cause infections or diseases in plants and animals.

Beneficial and Harmful Roles of Fungi in Human Society

  • Beneficial Roles:

    • Source of antibiotics (e.g., penicillin), use in genetic studies, and essential in fermentation (e.g., bread, beer).

    • Play a role in creating certain food products (e.g., cheese).

  • Harmful Roles:

    • Can cause structural damage in properties (e.g., molding and rotting) and health issues such as mycoses and poisoning from toxic fungi.