WEEK 13 - FUNGI.docx

**1. Characteristics of Fungi** - **Eukaryotic Nature**: - Fungi are eukaryotes, meaning they possess a true nucleus and other organelles. - **Cell Wall Composition**: - Fungi have cell walls composed of **cellulose** and/or **chitin**. - **Food Storage**:...

**1. Characteristics of Fungi** - **Eukaryotic Nature**: - Fungi are eukaryotes, meaning they possess a true nucleus and other organelles. - **Cell Wall Composition**: - Fungi have cell walls composed of **cellulose** and/or **chitin**. - **Food Storage**: - They store food in the form of **lipids** and **glycogen**. - **Environmental Requirements**: - Fungi require **water** and **oxygen**. No obligate anaerobes are known among fungi. - They can grow in almost every habitat that contains organic matter, provided the environment is not extreme. - **Diversity**: - The number of described fungal species ranges between **69,000** to **100,000**, but it is estimated that there could be as many as **1.5 million species**. **Body Structure** - **Hyphae**: - Fungi are composed of tubular structures called **hyphae** (singular: hypha). - Hyphae are multinucleate, have a hard wall made of **chitin**, and grow at their tips. - **Crosswalls** (septae) may form, creating compartments within the hyphae. - **Mycelium**: - An aggregate of hyphae forms a **mycelium**, which is the vegetative, ecologically active part of the fungus. - **Sclerotium**: - A hardened mass of mycelium that typically serves as an overwintering stage. - **Multicellular Forms**: - Fungi can be multicellular, forming **mycelial cords**, **rhizomorphs**, and **fruiting bodies** (e.g., mushrooms). **2. Fungal Growth and Nutrition** - **Heterotrophy**: - Fungi are heterotrophic, meaning they obtain their food by absorbing nutrients from other organic sources. - **Types of Heterotrophs**: - **Saprophytes/Saprobes**: Feed on dead tissues or organic waste (decomposers). - **Symbionts**: Form mutually beneficial relationships with other organisms (e.g., mycorrhizae with plants). - **Parasites**: Feed on living tissue; those causing disease are known as **pathogens**. - **Hyphal Growth**: - Hyphal tips release **enzymes** that break down the substrate, allowing the fungus to absorb the resulting nutrients. - The **nucleus** of the hypha directs growth, while the hyphal tip stretches and grows. **3. Fungal Reproduction** - **Spores**: - Fungi reproduce via spores, which can be either **asexual** (mitotic) or **sexual** (meiotic) in origin. - **Purpose of Spores**: - **Dispersal**: Allow the fungus to spread to new food sources. - **Resistance**: Enable the fungus to survive adverse conditions. - **Genetic Variation**: Introduce new genetic combinations within populations. - **Methods of Spore Formation**: - **Directly on Hyphae**: Spores can form directly on hyphae. - **Inside Sporangia**: A sporangium is a structure where spores are produced. - **Fruiting Bodies**: Complex structures like mushrooms that produce spores. **4. Fungal Classification and Phylogeny** - **Chytridiomycota (\"Chytrids\")**: - **Characteristics**: Simple fungi that produce **motile spores** called zoospores. - **Habitat**: Mostly aquatic, with many saprobes and parasites. - **Notable Species**: - **Synchytrium endobioticum**: Pathogen of potatoes. - **Batrachochytrium dendrobatidis**: Pathogen that affects amphibians. - **Ecological Role**: Degrade **chitin** and **keratin**. - **Zygomycota (\"Zygote Fungi\")**: - **Sexual Reproduction**: Occurs via the formation of **zygosporangia**. - **Asexual Reproduction**: Commonly occurs via **sporangia** (bags of asexual spores). - **Hyphal Structure**: Hyphae lack cross walls. - **Ecological Role**: Includes decomposers, pathogens, and species that form mycorrhizal associations. - **Notable Genera**: - **Mucor** and **Rhizopus** (e.g., Rhizopus commonly grows on bread and strawberries). - **Ascomycota (\"Sac Fungi\")**: - **Sexual Reproduction**: Occurs in sac-like structures called **asci** (singular: ascus). - **Asexual Reproduction**: Also common among sac fungi. - **Ecological Role**: Includes decomposers, pathogens, and many species that form lichens. - **Notable Members**: - **Cup fungi**, **morels**, **truffles**. - **Plant Parasites**: Many are important plant pathogens. - **Basidiomycota (\"Club Fungi\")**: - **Sexual Reproduction**: Occurs in structures called **basidia**. - **Asexual Reproduction**: Less common compared to other groups. - **Long-lived Mycelia**: These fungi often have long-lived dikaryotic mycelia (n+n). - **Ecological Role**: Important decomposers and plant parasites. - **Notable Members**: - **Mushrooms**, **polypores**, **puffballs**, **rusts**, and **smuts**. - **Deuteromycota (\"Imperfect Fungi\")**: - **Characteristics**: Fungi that seldom or never reproduce sexually. - **Reproduction**: Predominantly by **asexual spores**. **5. Specialized Fungal Relationships** - **Mycorrhizae (\"Fungus Roots\")**: - **Mutualistic Relationship**: Between fungi and plant roots. - **Types**: - **Zygomycota**: Hyphae invade root cells. - **Ascomycota & Basidiomycota**: Hyphae invade roots but do not penetrate the cells. - **Ecological Importance**: Mycorrhizae play a crucial role in nutrient and water uptake for plants. - **Lichens**: - **Mutualism**: Between a fungus and an alga or cyanobacterium. - **Types**: - **Crustose**: Crust-like, tightly bound to the substrate. - **Foliose**: Leaf-like, flat sheets not tightly bound. - **Fruticose**: Finely branched, free-standing, or hanging structures. - **Pollution Indicators**: Lichens are sensitive to air pollution and can be used to monitor environmental quality. **6. Human-Fungi Interactions** - **Beneficial Effects**: - **Decomposition**: Recycling of nutrients and carbon. - **Biosynthesis**: Production of drugs, antibiotics, alcohol, acids, and fermented foods. - **Model Organisms**: Used in genetic and biochemical research. - **Harmful Effects**: - **Destruction**: Damage to food, lumber, paper, and cloth. - **Diseases**: Human and animal diseases, including fungal infections and allergies. - **Toxins**: Production of toxins in food (e.g., aflatoxins in grains). - **Plant Diseases**: Many fungi are responsible for serious plant diseases. **7. Fungal Life Cycles** - **General Life Cycle**: - **Chytridiomycota**: Motile spores that swim using flagella. - **Zygomycota**: Includes the formation of a **zygospore** after the fusion of hyphae from two different mating types. - **Ascomycota**: Involves the formation of **ascospores** within an ascus after sexual reproduction. - **Basidiomycota**: Produces **basidiospores** on club-shaped structures called basidia.