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.