Chapter 12: The Eukaryotes – Fungi, Algae, Protozoa, and Helminths

Fungi

Defining Characteristics of Fungi

Fungi are a diverse group of eukaryotic organisms that play essential roles in ecosystems and human society. They are distinct from plants, animals, and bacteria in several key ways.

• Eukaryotic cells: Fungi possess membrane-bound organelles and a true nucleus.

• Cell walls: Composed primarily of chitin, glucans, and mannans (not peptidoglycan as in bacteria).

• Nutrition: Fungi are chemoheterotrophs, obtaining nutrients by absorbing dissolved organic matter.

• Growth forms: Can be unicellular (yeasts) or multicellular (molds, mushrooms).

• Reproduction: Both sexual and asexual reproductive spores are produced.

• Metabolism: Most are aerobic or facultative anaerobes.

Types of Fungal Reproduction

Fungi reproduce by forming spores, which can be produced sexually or asexually.

• Asexual reproduction: Involves mitotic division to produce genetically identical spores.

• Sexual reproduction: Involves the fusion of nuclei from two mating types, followed by meiosis to generate genetic diversity.

Ecological and Economic Roles of Fungi

Fungi have both beneficial and harmful effects on humans, animals, and plants.

• Beneficial effects:

  • Decomposition: Fungi decompose dead organic matter, recycling essential elements.

  • Symbiosis: Mycorrhizae form mutualistic relationships with plant roots, enhancing water and nutrient absorption.

  • Industrial uses: Fungi are used in the production of food (e.g., bread, wine) and antibiotics (e.g., penicillin).

• Harmful effects:

  • Pathogenicity: Many fungi cause diseases (mycoses) in humans, animals, and plants.

  • Food spoilage: Fungi can spoil stored food products.

Mycology and Fungal Nutrition

Mycology is the study of fungi. Fungi are chemoheterotrophs, meaning they obtain energy and carbon from organic compounds. They decompose organic matter and can be aerobic or facultative anaerobic.

Comparison of Fungi and Bacteria

The following table summarizes key differences between fungi and bacteria:

Feature	Fungi	Bacteria
Cell Type	Eukaryotic	Prokaryotic
Cell Membrane	Sterols present	Sterols absent (except Mycoplasma)
Cell Wall	Glucans; mannans; chitin (no peptidoglycan)	Peptidoglycan
Reproduction	Sexual and asexual reproductive spores	Endospores (not for reproduction); some asexual reproductive spores
Metabolism	Limited to heterotrophic; aerobic, facultatively anaerobic	Heterotrophic, autotrophic, aerobic, facultatively anaerobic, anaerobic

Vegetative Structures of Fungi

Fungi exhibit a variety of vegetative structures that are important for their growth and reproduction.

• Thallus: The body of a fungus, composed of long filaments called hyphae.

• Mycelium: A mass of hyphae that forms the main vegetative structure.

• Hyphae types:

  • Septate hyphae: Contain cross-walls (septa) dividing the hyphae into distinct, uninucleate cell-like units.

  • Coenocytic hyphae: Lack septa and consist of a continuous cytoplasmic mass with many nuclei.

• Vegetative hyphae: Obtain nutrients from the environment.

• Aerial hyphae: Involved in reproduction, often bearing spores.

Illustration: Fungal Hyphae

The diagram (Figure 12-2) shows the structure of septate and coenocytic hyphae, as well as the growth of a hypha from a spore. Septate hyphae have cross-walls, while coenocytic hyphae do not. Spores germinate to form new hyphae, which then grow and branch to form a mycelium.

Summary Table: Key Features of Fungi

Structure	Description
Thallus	Body of the fungus, composed of hyphae
Hyphae	Filamentous structures; can be septate or coenocytic
Mycelium	Mass of hyphae forming the main vegetative part
Vegetative hyphae	Involved in nutrient absorption
Aerial hyphae	Involved in reproduction (spore formation)

Additional info: Later sections of this chapter (not shown in these slides) would cover further details on fungal reproduction, medically important fungi, and the roles of fungi in disease and industry.