Chapter 31A-Fungi Classification

Chapter 31: Fungi

Overview

  • Fungi contribute significantly to the ecosystem as decomposers and symbionts.

  • Structure and function in fungi are intrinsic to their ecological roles.

  • Fungi can be single-celled or multicellular, showcasing diversity.

Concept 31.1: Fungi as Heterotrophs

  • Fungi are heterotrophs that feed by absorption, with distinct nutritional strategies.

  • Nutrition:

    • Hydrolytic Enzymes: Fungi secrete these enzymes to break down complex molecules into smaller organic compounds.

    • Source Variety: Can digest from both living organisms and nonliving organic material.

Roles in Ecosystem

  • Decomposers: Feed on dead organic matter, recycling nutrients back into the ecosystem.

  • Parasitic Fungi: Draw nutrients from living hosts, potentially harming them.

  • Mutualistic Fungi: Create beneficial relationships with hosts, providing nutrients in return for sustenance.

Body Structure

  • Fungi typically exhibit two main body forms: multicellular filaments and single-celled yeasts.

  • Hyphae:

    • Filaments that comprise the fungal body.

    • Chitin: A polymer in the cell walls that provides structural support and prevents cell lysis during nutrient absorption.

  • Septa: Cross-walls in hyphae that allow organelle movement, while some fungi are coenocytic and lack septa.

  • Mycelium: An extensive network of hyphae that maximizes nutrient absorption by increasing surface area.

Specialized Hyphae

  • Certain fungi develop specialized hyphae, such as:

    • Haustoria: Extract nutrients from plants.

    • Arbuscules: Facilitate nutrient exchange in mycorrhizal relationships with plant roots.

  • Mycorrhizae: A critical symbiotic relationship between fungi and plant roots that enhances nutrient exchange, particularly phosphorus.

Types of Mycorrhizal Fungi

  • Two key types:

    • Ectomycorrhizal Fungi: Form sheaths over roots; penetrate root cortex.

    • Arbuscular Mycorrhizal Fungi: Extend into root cell walls to facilitate nutrient exchange.

Concept 31.2: Fungal Reproduction

  • Fungi reproduce via spores, which can be produced sexually or asexually.

  • Life Cycle:

    • Begin with spore formation, then germination and mycelium production.

    • Spores can disperse via wind or water to new environments.

Sexual Reproduction

  • Involves the fusion of hyphae from different mating types.

  • Karyogamy: Fusion of nuclei after plasmogamy, lasting hours to centuries in some species.

  • Genetic variation is increased through meiosis from the diploid zygote.

Asexual Reproduction

  • Typically through mitosis, producing haploid spores, and can occur via budding in yeasts.

  • Some species develop a visible mycelium (e.g., molds).

Evolutionary Aspects

  • Fungi and animals share a common ancestry with a unicellular, flagellated protist, making them closer relatives to each other than to plants.

  • Fungi played a critical role as early land colonizers and developed mutualistic associations with plants.

Fungal Diversity

  • Cryptomycetes & Microsporidians: Early branching lineages of fungi, predominantly unicellular with unique life cycles.

  • Chytrids: Flagellated spores present in a wide range of habitats; both decomposers and parasites.

  • Zoopagomycetes & Mucoromycetes: Include intestinal and environmental species, with life cycles involving zygosporangium.

  • Ascomycetes: Known for their sac-like structures in which spores develop; prominent in various habitats.

  • Basidiomycetes: Encompass mushrooms and key decomposers; crucial in wood decomposition with characteristic fruiting bodies.