Biology Chapter 31

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  1. How do fungi acquire nutrients from their environment?
    • Fungi are heterotrophs and absorb nutrients from outside of their body
    • Fungi use enzymes to break down a large variety of complex molecules into smaller organic compounds
    • The versatility of these enzymes contributes to fungi's ecological success
    • Fungi exhibit diverse lifestyles-decomposers, parasites, mutualists
    • The morphology of mulitcellular fungi enhances their ability to abosrb nutrients
    • Fungi consist of mycelia, networks of branched hypae adapted for absorption
    • Most fungi have cell walls made of chitin
  2. Describe and compare the sexual and asexual life cycles of fungi
    • Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually
    • Fungi can produce spores from different types of life cycles
    • Fungal nuclei are normally haploid, with the exception of transient diploid stages formed during the sexual life cycles
    • Sexual reproduction requires the fusion of hyphae from different mating types
    • Fungi use sexual signaling molecules called pheromones to communicate their mating type
    • In addition to sexual reproduction, many fungi can reproduce asexually
    • Molds produce haploid spores by mitosis and form visible mycelia
    • Instead of producing spores, yeasts reproduce asexually by simple cell division and the pinching of "bud cells" from a parent cell
  3. What is the role of a mushroom?
    • The life cycle of a basidiomycete usually includes a long-lived dikaryotic mycelium
    • In response to environmental stimuli, the mycelium reproduces sexually by producing elaborate fruiting bodies called basidiocarps
    • Mushrooms are examples of basidiocarps
    • The numerous basidia in a basidiocarp are sources of sexual spores called basidiospores
  4. Describe the structure and characteristics of lichens.What sort of relationships do they embody?
    • A lichen is a symbiotic association between a photsynthetic microorganism and a fungus in which millions of photsynthetic cells are held in a mass of fungal hyphae
    • The fungal component of a lichen is most often an ascomycete
    • Algae or cyanobacteria occupy an inner layer below the lichen surface
    • The algae provide carbon compounds, cyanobacteria provide organic nitrogen, and fungi provide the environment for growth
    • The fungi of lichens can reproduce sexually and asexually
    • Asexual reproduction is by fragmentation or the formation of soredia, small clusters of hyphae with embedded algae
    • Lichens are important pioneers on new rock and soil surfaces
    • Lichens are sensitive to pollution, and their death can be a warning that air quality is deteriorating
  5. Describe some positive ecological and practical roles of fungi
    • Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread
    • Some fungi are used to produce antibiotics for the treatment of bacterial infections, for example the ascomycete Penicillium
    • Genetic research on fungi is leading to applications in biotechnolgy
    • For examples, insulin-like growth factor that can be produced in the fingus Saccharomyces cerevisiae
  6. Describe mycorrhizae and the role they may have played in plant evolution
    • Mycorrhizae are mutually beneficial relationships between fungi and plant roots
    • Ectomycorrhizal fungi from sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex
    • Arbuscular mycorrhizal fungi extend hyphae through the cell walls of root cells and into tubes formed by invagination of the root cell membrane
  7. Describe plasmogamy, karyogamy, and the heterokaryotic stage in a mushrooms life cycle
    • Plasmogamy is the union of two parent mycelia
    • In most fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon
    • In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic
    • Hours, days, or even centuries may pass before the occurence of karyogamy, nuclear fusion
    • During karyogamy, the haploid nuclei fuse, producing diploid cells
    • The diploid phase is short-lived and undergoes meiosis, producing haploid spores
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Biology Chapter 31
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