Lecture Notes: Fungi (Chapter 24)

Introduction

• Focus: Basic characteristics of fungi
• Distinctive Trait: Cell walls made of chitin (distinct from bacteria's peptidoglycan and various protist cell walls)

Types of Fungi

• Single-celled Fungi (Yeasts):

  • Unicellular fungi collectively known as "yeasts"
  • Not a clade or evolutionary group
  • Important for study despite being a generalized term

• Multicellular Fungi:

  • Produce structures called hyphae
  • Hyphae: Fungal filament composed of one or more cells
  • Two types:
    • Septate Hyphae: Cells separated by walls (septa) with pores for nutrient flow
    • Coenocytic Hyphae: No septa, multinucleated continuous cell

Structure and Function

• Mycelium:

  • Mass of fungal hyphae
  • Increases surface area for nutrient absorption
  • Fungi primarily absorb nutrients from their environment

• Mushrooms:

  • Visible part used for reproduction
  • Majority of fungal mass (mycelium) underground

Nutrition

• Heterotrophic:
  • Derive energy and carbon from organic compounds
  • Types: Saprobic, parasitic, predatory

Oxygen Requirements

• Obligate Aerobes: Need oxygen (e.g., humans, common fungi)
• Obligate Anaerobes: Cannot survive with oxygen
• Facultative Anaerobes: Can survive with or without oxygen
• Example: Brewer's yeast is a facultative anaerobe

Reproduction

• Asexual Reproduction Methods: Fragmentation, Budding, Spore Formation

  • Fragmentation: New organism from hyphal fragment
  • Budding: Seen in yeasts
  • Spores: Released from sporangium

• Sexual Reproduction: Basic Life Cycle

  • Two mating strains fuse (plasmogamy)
  • Dikaryotic cells form
  • Karyogamy: Fusion of nuclei
  • Zygote undergoes meiosis

Classification and Phylogeny

• Five Major Groups:

  • Chytridiomycota:

    • Aquatic, flagellated spores
    • Notable parasite of amphibians causing chytridiomycosis

  • Zygomycota:

    • Coenocytic hyphae, form zygospores
    • Example: Black bread mold

  • Ascomycota:

    • Form sac-like ascocarps, produce ascospores
    • Includes penicillium (source of penicillin) and brewer's yeast

  • Basidiomycota:

    • Form basidia in mushrooms, produce basidiospores
    • Includes typical mushrooms, toadstools

  • Glomeromycota:

    • Only reproduce asexually
    • Associated with arbuscular mycorrhizae

Ecology of Fungi

• Role in Ecosystems:

  • Present in all ecosystems
  • Important decomposers in the carbon cycle

• Symbiotic Relationships:

  • Mutualism: Both species benefit
  • Parasitism: One benefits, other is harmed
  • Commensalism: One benefits, other unaffected

• Note: Further exploration of symbiotic relationships deferred to next lecture.