Chapter 24: Fungi Flashcards
What are the defining characteristics of fungi?
Eukaryotic, heterotrophic organisms (absorb nutrients via external digestion). Cell walls contain chitin (unlike plants, which have cellulose). Body structure: Composed of hyphae (filaments) forming a network called mycelium. Reproduce via spores (sexually or asexually). Ecological roles: Decomposers, mutualists (e.g., mycorrhizae), or parasites.
Name and describe the major phyla of fungi with examples.
Chytridiomycota (Chytrids): Aquatic, flagellated spores (zoospores). Example: Batrachochytrium dendrobatidis (causes amphibian chytridiomycosis). Zygomycota (Zygote fungi): Form zygospores during sexual reproduction. Example: Rhizopus stolonifer (black bread mold). Ascomycota (Sac fungi): Produce spores in asci (sac-like structures). Example: Penicillium (antibiotics), Morchella (morel mushrooms). Basidiomycota (Club fungi): Produce spores on basidia (club-shaped structures). Example: Amanita (toxic mushrooms), Agaricus (button mushrooms). Glomeromycota: Form arbuscular mycorrhizae with plant roots (mutualistic). No known sexual reproduction.
Explain the structure and function of hyphae and mycelium.
Hyphae: Thread-like filaments made of tubular cells. Septate hyphae: Divided by cross-walls (septa). Coenocytic hyphae: Lack septa; multinucleate. Mycelium: Mass of hyphae that absorbs nutrients from the environment. Maximizes surface area for efficient digestion/absorption.
How do fungi reproduce sexually and asexually?
Asexual reproduction: Fragmentation: Hyphae break off and grow into new mycelium. Spores: Produced via mitosis in sporangia (e.g., Rhizopus) or conidia (e.g., Aspergillus). Sexual reproduction: Plasmogamy: Fusion of cytoplasm from two mating types. Karyogamy: Fusion of nuclei, forming diploid zygote. Meiosis: Produces haploid spores (e.g., basidiospores in mushrooms).
What are mycorrhizae, and why are they ecologically important?
Mycorrhizae: Symbiotic associations between fungi and plant roots. Types: Ectomycorrhizae: Hyphae surround root cells (common in trees). Arbuscular mycorrhizae: Hyphae penetrate root cells (Glomeromycota). Importance: Fungi provide plants with phosphorus/nutrients; plants supply sugars. Critical for plant growth in nutrient-poor soils.
Describe the role of fungi as decomposers.
Fungi break down organic matter (e.g., dead plants, wood) using enzymes (e.g., lignin peroxidase). Release carbon, nitrogen, and phosphorus back into ecosystems. Without fungi, dead material would accumulate, and nutrient cycles would stall.
What are lichens? Describe their structure and ecological roles.
Lichens: Symbiotic organisms of fungi (usually Ascomycota) + photosynthetic partner (algae or cyanobacteria). Structure: Crustose (crust-like), foliose (leaf-like), fruticose (shrub-like). Roles: Pioneer species in barren environments (e.g., rocks). Bioindicators of air quality (sensitive to pollution).
How do fungi impact human health and agriculture?
Negative impacts: Crop diseases: Puccinia (wheat rust), Magnaporthe oryzae (rice blast). Human diseases: Candida (yeast infections), Aspergillus (respiratory illness). Positive impacts: Food: Edible mushrooms, blue cheese (Penicillium), soy sauce fermentation. Medicine: Penicillin (antibiotic), cyclosporine (immunosuppressant).
What is ergotism, and which fungus causes it?
Ergotism: Poisoning from consuming grains contaminated with Claviceps purpurea (Ascomycota). Symptoms: Hallucinations, convulsions, gangrene. Historical note: Linked to the Salem witch trials and LSD discovery.
Compare saprophytic, parasitic, and mutualistic fungi.
Saprophytic: Decompose dead organic matter (e.g., Mucor). Parasitic: Harm hosts (e.g., Cordyceps infects insects). Mutualistic: Benefit both partners (e.g., mycorrhizae, lichens).
How do fungal spores differ from bacterial endospores?
Fungal spores: Reproductive structures (haploid or diploid). Produced sexually or asexually. Bacterial endospores: Dormant structures for survival (not for reproduction). Resistant to extreme conditions (e.g., Bacillus anthracis).
What is the fungus-plant partnership in lichens and mycorrhizae?
Lichens: Fungus provides structure/protection; algae/cyanobacteria provide sugars via photosynthesis. Mycorrhizae: Fungus enhances nutrient/water absorption; plant provides carbohydrates.
Why are fungi critical to biotechnology?
Enzymes: Cellulases (biofuel production), proteases (detergents). Fermentation: Yeast (Saccharomyces cerevisiae) for bread, beer, and wine. Medicine: Statins (cholesterol-lowering drugs from Aspergillus).
Explain the life cycle of a basidiomycete (e.g., mushroom).
Haploid spores germinate into mycelia. Plasmogamy: Fusion of two mycelia → dikaryotic (n + n) mycelium. Fruiting body (mushroom) forms; karyogamy occurs in basidia → diploid zygote. Meiosis produces haploid basidiospores, released to restart cycle.
What is yeast, and how is it used by humans?
Yeast: Unicellular fungi (Ascomycota or Basidiomycota). Uses: Fermentation: Saccharomyces cerevisiae for bread, beer, and wine. Research: Model organism for genetics/cell biology.
