Fungi Outline David Fan I.
Fungi A. Introduction 1. Eukaryotic 2. Unique and diverse 3. Mostly multicellular, some are unicellular 4. Molds, mushrooms, yeasts, rusts, smuts, blights, morels and truffles B. Food 1. Chemoheterotrophic 2. Can’t synthesize organic molecules from inorganic substances. Obtain energy and nourishment from organic substances present in the environment. 3. Cannot engulf food. Obtain their nutrition by secreting, into the environment, enzymes that digest organic matter 4. After the enzymes break down the organic matter into smaller components, the fungi absorb the organic molecules into their cells. 5. Saprophytic -obtain nourishment from decaying matter, dead organisms, or organic material from other organisms 1. Animal carcasses, leaf litter 6. Parasitic fungi absorb nutrients from living hosts, including both plants and animals, and can cause infectious diseases. 7. C. Bodies 1. Long slender filaments 2. Yeast are nonfilamentous 3. Molds and fleshy fungi consist of filaments called hyphae 4. Mostly multicellular, though yeasts are unicellular 5. Cell walls are made of chitin 6. Haploid (single set of chromosomes) 7. Exist as diploids during a brief phase of reproduction 8. Cannot undergo photosynthesis or engulf food D. Habitats 1. Fungi can also grow on foods such as bread or fruit and even in substances such as house paint. 2. Slightly acidic conditions (pH of about 5) that are unfavorable for most bacteria favor fungal growth 3. Fungi are also more resistant to low-moisture and high-salt environments. E. Reproduction 1. Reproduce by forming spores from the end of their hyphae 2. Since fungal spores are so small, they can travel long distances with the wind.
3. Fungal spores are different from bacterial spores 1. Fungal spores are true reproductive structures. Each one gives rise to a new organism, therefore the overall population increases 2. Bacterial endospores allow cells to survive harsh or unfavorable conditions but do not increase the number of bacterial cells. 4. In asexual reproduction, the offspring are genetically identical to the parent 5. Filamentous fungi can reproduce asexually by fragmentation, when a separated piece of mycelium develops into an entire new colony. 6. Asexual fungal spores reproduce by mitosis and cell division 7. In sexual reproduction, two different mating types ( a donor cell “+” and a recipient cell “-“ of hyphae join together, fuse, and develop into a new organism that forms spores containing genetic information from both parents 8. Formation of sexual spores occurs in three main stages: plasmogamy, karyogamy, and meiosis 9. During plasmogamy, the haploid nucleus from a “+” mating type invades the cytoplasm of a “-“ mating type. 10. The two haploid nuclei fuse in a process called karyogamy, resulting in a diploid nucleus. 11. Meoisis occurs, forming nuclei of sexual spores. F. Classification of Fungi by Reproduction 1. Since sexual spores develop in a variety of diverse ways, one means of classifying fungi is by their mode of sexual reproduction. 2. Three of the most common divisions are Zygomycota, Ascomycota, and Basidiomycota. 3. Members of the phylum Zygomycota usually reproduce asexually, but when opposite mating types fuse, sexual spores called zygospores form 4. The zygospores are large, thick-walled spores that undergo meiosis and germination. The resulting mycelium gives rise to haploid sporangia that resemble the asexual sporangium, except that it contains nuclei with genetic information from both parents. 5. Zygomycetes distribute spores more accurately than letting them drift aimlessly in the air 6. Hyphae of zygomycetes usually have no cell walls. Black bread molds such as Rhizopus stolonifer belong to the phylum Zygomycota.
7. Members of the phylum Ascomycota generally produce ascospores inside a tubelike sac called an ascus that forms when two mating types join to form a diploid nucleus. 8. Subsequent meiosis and germination result in the formation of haploid ascospores that disperse when the ascus breaks open. G. Generalized Lifespan of a Zygomycota
H. The Imperfect Fungi 1. Two less well-known phylum are Deuteromycota and Chytridiomycota. 2. Deuteromycota, commonly called the imperfect fungi, includes various fungi that are incapable of sexual reproduction or organisms for which the means of sexual reproduction is not yet known. 3. The organisms that cause athlete's foot and that give Camembert and Roquefort cheeses their unique flavors belongs to Deuteromycota 4. Members of the phylum Chytridiomycota are usually unicellular and aquatic and produce flagellated, motile gametes and spores 5. Slime molds and water molds were once classified as fungi because they appeared to share similar life cycles and under certain conditions form structures resembling sporangia. Biologists now believe they are unrelated to fungi. I. Ecological Importance and Symbiotic Relationships
1. Fungi closely interact with other organisms in many different ways. 2. A mycorrhiza is a mutualistic relationship formed between a fungi and a plant 3. The fungi grows inside or wraps around the roots of the plant, and the mycelia branch out to increase the surface area through which absorption of water and nutrients such as phosphorus and minerals occurs. 4. The fungus benefits from carbohydrates synthesized by the plant during photosynthesis 5. Plants with mycorrhizae can inhabit soil that is less fertile or live in environments that are drier than plants without them. 6. Lichens are symbiotic associations formed by a fungus with a photosynthetic organism such as a photosynthetic bacterium or an alga. 7. The photosynthetic organism provides a food source for the fungus, while in return the fungus protects its partner from the environment, allowing it to live in habitats that would normally be too harsh, such as on the surface of a rock, in an arid desert, or on a tree trunk 8. The mycelia absorb moisture and carbon dioxide from the atmosphere for use in photosynthesis. 9. . Lichens play an important role in ecological succession, the replacement of one type of community by another at a single location over time, such as after a forest burns down. 10. Lichens help prepare the previously barren terrain for other species by secreting an acid that breaks down rocks into soil and liberates nutrients. 11. Over time, the organic material from dead lichens nourishes future inhabitants. 12. Lichens also serve an important role monitoring the air for pollutants such as sulfur dioxide. Because they are sensitive to such manufactured pollutants, their growth is a good indicator of air quality. 13. Because most fungi are saprophytes and obtain their nutrition from decomposing organic material of other species, they play a crucial role in the food chain. 14. Plants contain cell walls made of cellulose, a carbohydrate that animals are incapable of digesting. Fungi break down the decaying leaf litter on the forest floors, recycling the nutrients back into the environment in a form that other organisms can utilize. 15. Without fungi, many nutrients would become depleted as they became incorporated into forms unusable to other organisms. Fungi are essential to maintaining conditions that support other life-forms.
J. Impact of Fungi 1. The ecological role played by fungi translates into important economic consequences. 2. The maintenance of soil conditions that support many crops depends on relationships that fungi engage in with plants and other microorganisms 3. However, some fungi inflict devastating damage to crops by causing diseases such as potato blight, black stem rust of wheat, covered smut of barley, powdery mildew, fruit rots, and Dutch elm disease. 4. Other fungi are used in the biological control of costly plant diseases. a. They prevent the growth of mold, and enhance plant growth, degrade pesticides, and prevent the synthesis of toxins produced by other fungi 5. The production of many types of foods depends on fungi. Food and beverage manufacturers exploit the ability of yeasts to produce ethanol and carbon dioxide, two end products of fermentation. 6. Different fungi impart unique flavors and textures to cheeses, and edible fungi such as mushrooms are a food source themselves. Other fungi cause fruit to rot or bread and cheese to mold 7. Acidic conditions, as in jams and jellies and inside fruit, inhibit bacterial growth but encourage fungal growth. Fungi can also withstand high solute concentrations used to preserve many foods. 8. Antibiotics are chemicals produced by one organism that kill or inhibit the growth of another. Many antibiotics are produced by fungi or are derivatives of fungal products 9. Less than 1 percent of fungal species are pathogenic to humans and animals are systemic and affect a number of organs. 10. Many mycoses are superficial or penetrate to just below the surface of the skin, but some are systemic and affect a number of organs