Biological Systems - Fungi Module

Learning Objectives

  • Describe the main characteristics of fungi, including specialized structures.
  • Describe how fungi obtain food.
  • Explain how fungi reproduce.
  • Describe some of the important ecological roles of fungi.
  • Discuss the mutualisms between fungi and other organisms.
  • Describe various uses of fungi by humans.

Introduction to Fungi

  • Fungi Characteristics:
    • Eukaryotic organisms, primarily multicellular (few unicellular).
    • Possess a cell wall made of chitin.
    • Estimated 100,000 described species, with a total of about 1.5 million estimated species.
    • Diverse reproductive cycles and ecological roles.
    • All fungi are heterotrophs; they obtain nutrients through absorption.
    • Ecological roles include breaking down organic material and nutrient recycling.

Nutrition in Fungi

  • Feeding Mechanism:

    • Fungi are heterotrophic like animals but acquire nutrients through absorption rather than ingestion.
    • They secrete digestive enzymes outside their bodies to breakdown large food particles.
    • Enzyme versatility contributes to their ecological success.

  • Feeding Types:

    • Decomposers (saprobes): Feed on dead organic material.
    • Parasites: Extract nutrients from living hosts.
    • Predators: Capture and digest other organisms.
    • Mutualists: Engage in beneficial interactions with host organisms while obtaining nutrients.

Fungal Structures

  • Hyphae & Mycelium:

    • Multicellular fungi consist of networks of hyphae, which are thread-like filaments.
    • Mycelium is the mass of hyphae, capable of vast expansions underground.
    • Fungi produce spores in various structures, which are essential for reproduction.

  • Reproductive Structures:

    • Reproductive structures vary between species and environments (e.g., mushrooms, puffballs).

Reproduction in Fungi

  • Spore Production:

    • Fungi can produce massive amounts of spores, with puffballs releasing trillions.

  • Reproductive Types:

    • Asexual Reproduction: Involves spores produced via mitosis.
    • Sexual Reproduction: More complex and includes the fusion of hyphae, followed by the fusion of nuclei (plasmogamy and karyogamy). The diploid state is temporary, followed by meiosis restoring haploidy.

  • General Life Cycle:

    • Haploid (n) and diploid (2n) stages alternate, with various structures involved in both asexual and sexual reproduction.

Fungal Phylogeny

  • Current Phyla Classification (5 main phyla):
    1. Phylum Chytridiomycota: Chytrids with flagellated zoospores.
    2. Phylum Zygomycota: Known for sexually produced zygosporangia.
    3. Phylum Glomeromycota: Important for arbuscular mycorrhizae with plants.
    4. Phylum Ascomycota: Includes diverse forms producing spores in sac-like asci.
    5. Phylum Basidiomycota: Known for club-shaped basidia and various ecological roles.

Phylum Descriptions:

  • Chytridiomycota: Exhibit zoospores, significant in diverse ecological roles (e.g., chytrid fungus affecting frogs).
  • Zygomycota: Include fast-growing moulds, exhibit diversity in life histories, resistant zygosporangia.
  • Glomeromycota: Form mutualistic relationships with about 80% of plant species, enhancing nutrient absorption.
  • Ascomycota: Sac fungi characterized by ascocarps and common yeast, known for varied habitats and reproductive methods.
  • Basidiomycota: Significant decomposers of plant material, producing fruiting bodies (mushrooms) and spores.

Ecological Roles of Fungi

  • Importance of Decomposers:

    • Essential for breaking down organic material, contributing to nutrient cycling (C, N).
    • Fungi can degrade challenging compounds; utilized in biotechnology (e.g., wastewater treatment).

  • Mutualistic Relationships:

    • Fungi form symbiotic relationships with plants (mycorrhizae) and animals for nutrient exchange.
    • Mycorrhizal Benefits: Increases water/nutrient absorption dramatically; key for plant evolution on land.
    • Animal associations (e.g., leaf-cutter ants) utilize fungi for digestion of plant materials.
    • Lichens: Composite organisms formed by fungi and algae, essential for many ecosystems.

  • Pathogenic Relationships:

    • Approximately 30% of fungal species are pathogenic, notably impacting crops (10% - 50% loss annually).
    • Some fungi produce mycotoxins harmful to humans.

Beneficial Uses of Fungi in Human Activities

  • Food Production: Truffles, cheese, beer, and bread (yeast).
  • Medicinal Uses: Antibiotics like penicillin, statins, and immune suppressants derived from fungi.
  • Research Uses: Models like Saccharomyces cerevisiae facilitate genetic studies.
  • Bioremediation: Utilization of fungal enzymes to remediate environmental issues.

Summary of Key Points

  • Fungi are heterotrophic eukaryotes that play vital ecological roles as decomposers, mutualists, and pathogens.
  • They exhibit diverse reproductive methods and life cycles across five recognized phyla, with significant implications for ecosystems and human use.