Unit 3: Fungi & Lichens

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General Characteristics of Fungi

Fungi are eukaryotic, achlorophyllous (non-photosynthetic), and heterotrophic organisms. They are characterized by several distinct features:

• Heterotrophy: Since they lack chlorophyll, they obtain nutrients as saprophytes (dead matter) or parasites (living hosts).
• Thallus Structure: The body is usually filamentous, composed of hyphae that collectively form a mycelium.
• Cell Wall: Composed primarily of chitin.
• Reproduction: They reproduce through vegetative, asexual, and sexual methods.

Classification and Economic Importance

Classification

Fungi are classified based on their morphology, type of spores produced, and life cycle patterns. Major groups include Phycomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetes.

Economic Importance

Fungi have significant impacts on human welfare and the environment:

• Beneficial Roles: Decomposition of organic matter, production of antibiotics (e.g., Penicillin), use in the food industry (baking and brewing), and consumption as food (edible mushrooms).
• Harmful Roles: Causing diseases in plants (e.g., rusts, smuts), spoilage of food, and human fungal infections.

Morphology and Life Cycle of Specific Genera

Detailed study of representative fungal genera is essential for understanding their diversity:

1. Rhizopus (Bread Mold)

• Morphology: Saprophytic fungus with a mycelium consisting of branched, coenocytic hyphae divided into rhizoids, stolons, and sporangiophores.
• Reproduction: Asexual reproduction via non-motile sporangiospores; sexual reproduction through gametangial copulation resulting in a zygospore.

2. Penicillium

• Morphology: Characterized by a branched mycelium with septate hyphae and distinctive brush-like conidiophores.
• Reproduction: Primarily reproduces asexually by the formation of conidia.
• Importance: Source of the antibiotic Penicillin and used in cheese ripening.

[Image of Penicillium conidiophore structure]

3. Puccinia (Wheat Rust)

• Morphology: An obligate parasite that causes black stem rust of wheat.
• Life Cycle: It is a heteroecious fungus, meaning it requires two different hosts (Wheat and Barberry) to complete its complex life cycle involving five different spore stages (Urediniospores, Teliospores, Basidiospores, Pycniospores, and Aeciospores).

Symbiotic Associations: Lichens

Lichens represent a classic example of a symbiotic association between a fungus (mycobiont) and an alga or cyanobacterium (phycobiont).

• Nature of Association: The fungus provides structure, protection, and water/minerals, while the alga provides photosynthetic food.
• Growth Forms: Crustose (flat), Foliose (leaf-like), and Fruticose (shrubby).
• Economic Importance: Indicator of air quality (pollution indicators), source of dyes (litmus), and food for certain animals (reindeer moss).

Mycorrhiza: Account and Significance

Mycorrhiza is a symbiotic association between fungi and the roots of higher plants.

• Types:
  • Ectomycorrhiza: Fungal hyphae grow around the root surface and between cortical cells without penetrating them.
  • Endomycorrhiza (VAM): Hyphae penetrate the cortical cells, forming specialized structures like arbuscules.
• Significance: Enhances nutrient uptake (especially Phosphorus), provides resistance to root-borne pathogens, and improves drought tolerance of the plant.

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