co23 - CHAPTER 23 EVOLUTION OF FUNGI Chapter Outline 23.1...

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CHAPTER 23 E VOLUTION OF F UNGI Chapter Outline 23.1 Characteristics of Fungi A. Fungi Are Multicellular Eukaryotes 1. Fungi are mostly multicellular eukaryotes that share a common mode of nutrition. 2. Similar to animals, they are heterotrophic and consume preformed organic matter. 3. However, animals are heterotrophic by ingestion while fungi are heterotrophic by absorption. 4. Fungal cells secrete digestive enzymes; following breakdown of molecules, the nutrients are absorbed. 5. Most fungi are saprotrophic decomposers, breaking down wastes or remains of plants and animals. 6. Some are parasitic, living off tissues of living plants and animals. a. Fungi enter leaves through stomates; plants are especially subject to fungal diseases. b. Fungal diseases account for millions of dollars in crop losses each year; fungal diseases also have decimated some tree species. c. Fungi also cause human diseases including ringworm, athlete’s foot, and yeast infections. 7. Several types of fungi are adapted to mutualistic relationships with other organisms. a. As symbionts of roots, they acquire inorganic nutrients for plants and receive organic nutrients. b. Others form an association with a green alga or cyanobacterium to form a lichen . B. Structure of Fungi 1. Fungi can be unicellular (e.g., yeasts). 2. Most fungi are multicellular in structure. a. The thallus (body) of most fungi is a mycelium . b. A mycelium is a network of hyphae comprising the vegetative body of a fungus. c. Hyphae are filaments that provide a large surface area and aid absorption of nutrients. d. When a fungus reproduces, a portion of the mycelium becomes reproductive structures. 3. Fungal cells lack chloroplasts and have a cell wall made of chitin, not cellulose. a. Chitin, like cellulose, is a polymer of glucose molecules organized into microfibrils. b. In chitin, unlike cellulose, each glucose has an attached nitrogen containing amino group. 4. The energy reserve of fungi is glycogen as in animals, and not starch. 5. Fungi are nonmotile; their cells lack basal bodies and do not have flagella at any stage in their life. 6. Fungi move to a food source by growing toward it; hyphae can grow up to a kilometer a day! 7. Nonseptate hyphae lack septa or cross walls; hyphae are multinucleated. 8. Septate fungi have cross walls in their hyphae; pores allow cytoplasm and organelles to pass freely. 9. The septa that separate reproductive cells, however, are complete in all fungal groups. C. Reproduction of Fungi 1. In general, fungal sexual reproduction involves the following: haploid hyphae dikaryotic stage diploid zygote --------------------- meiosis------------------ 2. During sexual reproduction, haploid hyphae from two different mating types fuse. 3.
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co23 - CHAPTER 23 EVOLUTION OF FUNGI Chapter Outline 23.1...

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