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Fungi Lecture Notes

Fungi - Chapter 29 Notes

Key Concepts

  • Evolution and Distinctive Features of Fungi

  • Overview of Asexual and Sexual Reproduction in Fungi

  • Fungal Ecology and Biotechnology

Evolution and Distinctive Features of Fungi

  • Taxonomy: Fungi belong to the eukaryote supergroup Opisthokonta, which includes certain protists, Kingdom Animalia, and Kingdom Fungi.

  • Origin: Fungi originated in aquatic habitats and evolved from protists related to Nuclearia, an amoeba that feeds by engulfing cells.

  • Early Divergence: The Cryptomycota represent the earliest-diverging modern fungi.

Relationship to Animals

  • Heterotrophic Nature: Fungi cannot produce their own food; they are heterotrophic and feed on various substrates.

  • Nutrition Method: They utilize absorptive nutrition by secreting enzymes and absorbing organic molecules.

  • Food Storage: Surplus food is stored as glycogen, similar to animals.

Unique Cellular Structure

  • Cell Walls: Composed of chitin, which prevents phagocytosis and enables resistance to high osmotic pressure due to osmotrophy.

  • Reproductive Cells: Some aquatic fungi have flagellated reproductive cells.

Fungal Body Structure

  • Mycelium: Most fungi form a mycelium made of hyphae.

  • Hyphae Types:

  • Aseptate Hyphae: Not divided into compartments; multinucleate, known as coenocytic.

  • Septate Hyphae: Contain cross walls (septa) dividing the cells of the mycelium.

  • Fruiting Bodies: Visible reproductive structures (e.g., mushrooms) arise from mating of hyphae and produce spores through meiosis.

Growth Process of Fungi

  • Rapid Growth: Mycelia can grow quickly in abundance of food; hyphae extend their tips into the substrate.

  • Absorption: Narrow dimensions and extensive branching of hyphae provide a high surface area for absorption due to osmosis and cytoplasmic streaming.

  • Mechanism of Hyphal Tip Growth:

  1. Vesicles carry digestive enzymes to the plasma membrane.

  2. Enzymes break down extracellular organic polymers.

  3. Resulting small organic molecules are absorbed into the hypha via transport proteins.

  4. Water enters by osmosis, aiding in cell enlargement and tip extension.

Reproductive Strategies

Asexual Reproduction

  • Mechanism: Asexual reproduction allows rapid spread without the need to find a mate or undergo meiosis.

  • Methods: Many fungi produce conidia at the tips of hyphae, and unicellular yeasts reproduce by budding.

  • Implications: Often associated with food spoilage and human diseases (e.g., athlete’s foot, Candida infections).

Sexual Reproduction

  • Process: Involves the fusion of gametes, zygote formation, and meiosis. Typical fungal life cycles are haploid-dominant.

  • Gametes: Formed from hyphal branches; mating types differ biochemically.

  • Fruiting Body Formation: A mated mycelium can produce fruiting bodies like mushrooms which generate haploid spores.

Types of Fungi

Dikaryotic Fungi

  • Characteristics: Two nuclei per cell during part of their life cycle.

  • Subkingdom Dikarya: Contains two main groups: Ascomycota and Basidiomycota.

Distinctive Features of Phyla

  1. Mucoromycota: Terrestrial; form beneficial associations with plants.

  2. Ascomycota: Mostly terrestrial; reproduce with ascocarps. Examples: yeast, truffles.

  3. Basidiomycota: Terrestrial; important decomposers and symbionts, reproduce with basidiocarps. Examples: mushrooms.

Fungal Ecology and Biotechnology

  • Role in Ecosystems: Major decomposers breaking down complex materials like cellulose and lignin, recycling nutrients.

  • Fungal Plant Pathogens: Over 5000 species causing crop diseases; management through fungicides and resistant crops.

  • Mycotoxins: Certain fungi produce harmful toxins affecting food safety (e.g., aflatoxins).

  • Biotechnology Applications: Used in fermentation (e.g., production of citric acid, alcohols) and as model organisms in research (e.g., Saccharomyces cerevisiae).

Key Examples of Pathogenic Fungi

  • Animal Pathogens: Include Geomyces destructans causing white nose syndrome in bats, and various dermatophytes in humans.

  • Dimorphic Fungi: Change forms from hyphal to yeast depending on environmental conditions, can cause respiratory diseases in humans.

These notes provide an in-depth understanding of the evolution, structure, reproduction, ecology, and significance of fungi. Adjust as necessary for different study focuses.