Detailed Notes on Fungi for Exam Preparation

Lecture Overview

• Exam 2 Review
• Focus on the following topics regarding fungi:
  1. Introduction to fungi
  2. Fungal nutrition and life cycle
  3. Fungal diversity
  4. Ecological roles of fungi
• Key Reminder: Lecture Exam 2 occurring Thursday!

Introduction to Fungi

• Opisthokonts: Fungi's origins trace back to a unicellular flagellated ancestor shared with animals and nucleariids.
• Timeline: Fungi were among the earliest organisms on land (~500 million years ago) forming mutualistic relationships with early plants.
• Species Count: Approximately 145,000 known species of fungi; estimates suggest total species number between 2.2 million - 3.8 million.

Characteristics of Fungi

• Eukaryotic Heterotrophs: Feed by absorption; primarily multicellular with cell walls made from chitin.
• Hyphae: Bodies constructed of networks called hyphae. They extend into surroundings and facilitate nutrient absorption through absorptive feeding.
• Reproduction: Fungi reproduce through spores (asexually and sexually); spores are typically haploid with short diploid stages during sexual life cycles.

Fungal Nutrition

• Heterotrophic Strategies:
  • Saprophytes/Saprobes: Decomposers feeding on dead organic matter.
  • Symbionts: Fungi in mutually beneficial relationships with organisms.
  • Parasites: Feed on living tissues of host organisms.
• Absorptive Feeding Process:
  • Hyphal tips release enzymes, breaking down substrates; products diffuse back into hyphae for nourishment.
• Nutrient Breakdown: Capable of digesting various organic molecules, making fungi vital decomposers.

Fungal Life Cycle

• Sexual Reproduction: Involves hyphal fusion and pheromones for mating type communication:
  • Plasmogamy: Fusion of parental hyphae.
  • Heterokaryon Formation: Contains unfused nuclei; Dikaryotic Mycelium contains paired haploid nuclei.
  • Karyogamy: Fusion of nuclei forms diploid zygote.

Fungal Diversity

• Major Fungal Phyla:
  • Chytridiomycetes: Simple fungi with motile spores. Can be decomposers, mutualists, or parasites.
  • Mucoromycetes: Fast-growing molds; include zygosporangium for sexual reproduction and common asexual reproduction.
  • Ascomycetes: Known as “sac fungi”; ~75% of known fungi, with diverse reproductive strategies and significant roles in ecosystems.
  • Basidiomycetes: Club fungi with unique basidiocarps; sexual reproduction through basidia, includes edible fungi as well as pathogens like rusts and smuts.

Ecological Roles of Fungi

• As Decomposers: Capable of breaking down complex compounds like cellulose and lignin.
• Mutualistic Relationships:
  • Mycorrhizae: Symbiotic relationships with plant roots, enhancing nutrient absorption while receiving carbohydrates in return.
  • Endophytes: Fungi living within plant tissues to aid in their health, while anti-pathogen effects may occur.
• Lichens: Symbiotic associations between fungi and photosynthetic organisms, beneficial for both parties.

Importance of Mycorrhizal Fungi

• Found on approximately 90% of vascular plant species; vital for enhancing absorption of water and nutrients.
• Two Types:
  • Arbuscular Mycorrhizal Fungi (AMF): Most common; penetrate root cells, forming arbuscules.
  • Ectomycorrhizal Fungi: Surrounds plant roots without penetration, often associated with forest trees.

Fungi as Pathogens

• Fungi may cause diseases in crops and humans, however, active immune systems in animals provide some defense against fungal infections.