Biology II Chapter 31

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Yasham
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85954
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Biology II Chapter 31
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2011-10-06 18:20:57
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Biology Campbell Fungi
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Chapter 31 of Campbell's Biology Textbook - Fungi
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  1. (T/F) Fungi are heterotrophs - they cannot make their own food as plants and algae can.
    True.
  2. (T/F) Unlike animals, fungi do not ingest their food.
    True.

    Instead, a fungus absorbs nutrients from the environment outside of its body.

    Many fungi accomplish this task by secreting powerful hydrolytic enzymes into their surrounds. These enzymes break down complex molecules to smaller organic compounds that the fungi can absorb into their bodies and use.

    Other fungi use enzymes to penetrate the walls of plant cells, enabling the fungi to absorb nutrients from the plant cell.
  3. (T/F) Many fungi accomplish the absorption of nutrients by secreting powerful hydrolytic enzymes into their surrounds. These enzymes break down complex molecules to smaller organic compounds that the fungi can absorb into their bodies and use.

    Other fungi use enzymes to penetrate the walls of plant cells, enabling the fungi to absorb nutrients from the plant cell.
    True.
  4. Fungi may take on many roles in ecological communities, with different species living as

    a) decomposers
    b) mutualists
    c) parasites
    d) all of the above
    D.
  5. What are yeasts?
    Single cells of fungi
  6. (T/F) Many species can grow as both filaments and yeasts, but even more grow only as filaments.
    True.
  7. (T/F) Yeasts often inhabit moist environments, including plant sap and animal tissues, where there is a ready supply of soluble nutrients, such as sugars and amino acids.
    True.
  8. What are are the networks of tiny filaments formed by fungi known as? What are they comprised of?
    The network of certain fungi form a network of tiny filaments which are called hyphae.

    Hyphae consist of tubular cell walls surrounding the plasma membrane and cytoplasm of the cells. Unlike plant cell walls, which contain cellulose, fungal cell walls are strengthed by chitin, a strong but flexible nitrogen-containing polysaccharide also found in the external skeletons of insects and other arthropods.
  9. Fungal hyphae form an interwoven mass called a _____________ that infiltrates the material on which the fungus feeds. A mycelium's structure maximizes its surface area-to-volume ratio making feeding more efficient.
    mycelium
  10. What is mycelium?
    The densely branched network of hypae in a fungus. The mycelium infiltrates the material in which the fungus feeds on.
  11. (T/F) Fungus concentrate its energy and resources on adding hyphal length, and thus overall surface area, rather than on increasing hyphal girth.
    True.

    Fungi are not motile in the typical sense of the word - they cannot run, swim, or fly in search of food or mates. However, as they grow, fungi can move into new places, swiftly extending the tips of their hyphae into previously unoccupied territory.
  12. In most fungi, the hyphae are divided into cells by cross walls, or ______. These cross-walls have pores large enough to allow ribosome, mitochondria, and even nuclei to flow from cell to cell.
    septa (singular, septum)
  13. (T/F) Some fungi lack septa and are known as coenocytic fungi, these consists of a continuous cytoplasmic mass having hundreds or thousands of nucli.

    The coenocytic condition results of repeated division of nucli without cytokinesis.
    True.

    Cytokinesis is the process in which the cytoplasm divides, which does not occur in this type of fungus. This leads to the division of nuclei within a continuous cytoplasmic mass.
  14. (T/F) Mycorrhizal fungi have specialized hyphae known as haustoria, which allow the fungi to extract nutrients from - or exchange nutrients with - their hosts.
    True.
  15. What are haustoria?
    Specialized hyphae which allow fungi to extract nutrients from - or exchange nutrients with - their hosts.

  16. What are two types of mycorrhizal fungi?
    Ectomycorrhizal fungi and arbuscular mycorrhizal fungi.

    Ectomycorrhizal fungi form sheaths of hyphae over the surface of a root and also grow into the extracellular spaces of the root cortex.

    Arbuscular mycorrhizal fungi extend their branching hyphae through the root cell wall and into tubes formed by invagination (pushing inward) of the root cell membrane.
  17. What are the differences between the two mycorrhizal fungi: ectomycorrhizal and arbuscular mycorrhizal fungi?
    Arbuscular mycorrhizal fungi extend the hyphae into the cells, past the cell walls while ectomycorrhizal fungi grow into the extracellular spaces of the root cortex but do not penetrate the cells.

    Ectomycorrhizal fungi form sheaths of hyphae over the surface of a root and also grow into the extracellular spaces of the root cortex.

    Arbuscular mycorrhizal fungi extend their branching hyphae through the root cell wall and into tubes formed by invagination (pushing inward) of the root cell membrane.
  18. Compare and contrast the nutritional mode of a fungus with your own nutritional mode.
    Both a fungus and a human are heterotrophs. Many fungi digest their food externally by secreting enzymes into the food and then absorbing the small molecules that result from digestion. Other fungi absorb such small molecules directly from their environment. In contrast, humans (and other animals) ingest relatively large pieces of food and digest the food within their bodies.
  19. Suppose a certain fungus is a mutualist that lives within its insect host, yet its ancestors were parasites that grew in and on the insect's body. What derived traits might you find it this mutualistic fungus?
    The ancestors of such a mutualist most likely secreted powerful enzymes to digest the body and/or cell walls of their insect host. Since such enzymes would harm a living host, it is likely that the mutualist would not produce such enzymes or would restrict their secretion and use.
  20. (T/F) Most fungi propagate themselves by producing vast numbers of spores, either sexually or asexually.
    True.
  21. (T/F) Many - but not all - fungi reproduce both sexually and asexually. Some reproduce only sexually, others only asexually.
    True.

  22. (T/F) The nuclei of fungal hyphae and the spores of most fungal species are haploid, although many fungi have transient diploid stages that form during sexual life cycles.
    True.

    The hyphae are haploids.....
  23. Sexual reproduction begins when hyphae from two mycelia release sexual signaling molecular called __________.
    Pheromones.
  24. If the mycelia are different mating types, the pheromones from each partner bind to the receptors on the other, and the hyphae extend toward the source of the pheromones. When the hyphae meet, they _______.

    The union of the cytoplasms of the two parent mycelia is known as ________.
    fuse.

    plasmogamy.

    In species with such a "compatibility test", this process contributes to genetic variation by preventing hyphae from fusing with other hyphae from the same mycelium or another genetically identical mycelium.

  25. What is the fusion of the cytoplasm known as?
    plasmogamy.

    In most fungi, the haploid nuclei contributed by each parent do not fuse right away. Instead parts of the fused mycelium contain coexisting, genetically different nucli.

    Such a mycelium is said to be a heterokaryon (meaning "different nuclei"). In some species, the different nuclei may even exchange chromosomes and genes in a process similar to crossing over. In other species, the haploid nuclei pair off two to a cell, one from each parent (known as dikaryotic - meaning two nuclei).
  26. What is heterokaryon?
    A fungal mycelium that contains two or more haploid nuclei per cell.

    In most fungi during the plasmogamy, the haploid nuclei contributed by each parent do not fuseright away. Instead parts of the fused mycelium contain coexisting, genetically different nucli.

    • Such a mycelium is said to be a heterokaryon
    • (meaning "different nuclei").

    In some species, the different nuclei may even exchange chromosomes and genes in a process similar to crossing over. In other species, the haploid nuclei pair off two to a cell, one from each parent (known as dikaryotic - meaning two nuclei).
  27. What is dikaryotic?
    Referring to a fungal mycelium with two haploid nuclei per cell, one from each parent.

    As a dikaryotic mycelium grows, the two nuclei in each cell divide in tandem without fusing. Because these cells retain two separate haploid nuclei, they differ from diploid cells, which have pairs of homologous chromosomes within a single nucleus.
  28. In sexual reproduction of a fungi, what stage follows the fusion of cytoplasm (plasmogamy)?
    karyogamy.

    Hours, days or (in some fungi) even centuries may pass between plasmogamy and the next stage in the sexual cycle - karyogamy.

  29. What occurs during karyogamy?
    The haploid nuclei contributed by the two parents fuse, producing diploid cells. Zygotes and other transient structures form during karyogamy, the only diploid stage in most fungi.

    Meiosis then restores the haploid condition, leading to the formation of spores that enable fungi to disperse.
  30. After the karyogamy phase, what occurs to restore the haploid condition and leads to the formation of spores that enable fungi to disperse?
    Meiosis.

    The heterokaryotic condition offers some of the advantages of diploidy, in that one haploid genome may compensate for harmful mutations in the other.
  31. What process do fungi reproduce asexually by growing filamentous fungi that produce (haploid) spores?
    They produce haploid spores by mitosis. These are also known as molds if they form visible mycelia.
  32. (T/F) Many yeasts and filamentous fungi have no known sexual stage.
    True.

    They reproduce asexually.

    Single-celled yeasts occur by ordinary cell division or by the pinching of small "bud cells" off a parent cell. Also, some fungi that grow as yeasts can also grow as filamentous mycelia.
  33. What are fungi deuteromycetes?
    Fungi without any known sexual stage. If one is discovered for a so-called deuteromycete, the species is reclassified in a particular phylum, depending on the type of sexual structures it forms.
  34. In terms of haploidy versus diploidy, how do the life cycles of humans and fungi differ?
    The majority of fungal life cycle consists of haploid stages, whereas the majority of the human life cycle consists of diploid stages.
  35. (T/F) The ancestor of fungi was an aquatic, single-celled flagellated protist.
    True...

    While the majority of fungi lack flagella, some of the earliest-diverging lineages of fungi (such as chytrids) do have flagella.
  36. What clade are fungi, animals and the protistan relatives categorized in?
    opisthokonts - a name that refers to the posterior (opistho-) location of the flagellum in these organisms.
  37. What does the nucleariids consist of? Why is this group of protists mentioned in this chapter?
    Nucleariids consist of amoebas that feed on algae and bacteria.

    • DNA indicates that fungi are more closely related to these protists than with other animals (and humans).
    • Also, DNA evidence indicates that animals are more closely related to a different group of protists (choanoflagellates) than they are with fungi or nucleariids.

    This indicates that multicellularity must have evolved in animals and fungi independely, from different single-celled ancestors.
  38. (T/F) Based on the molecular clock analysis, the ancestors of animals and fungi diverged into separate lineages about one billion years ago.
    True.
  39. Why are fungi classified as opisthokonts despite the fact that most fungi lack flagella?
    DNA evidence indicates that fungi, animals, and their protistan relatives form a clade, the opisthokonts.

    Furthermore, an early-diverging fungal lineage, the chytrids, have posterior flagella, as do most other opisthokonts. This suggests that other fungal lineages lost their flagella after diverging from chytrids, which have flagella.
  40. Explain the evolutionary significance of the presence of mycorrhizae in the earliest vascular plants.
    This indicates that fungi had already established a mutualistic relationships with plants by the date that fossils of the earliest vascular plants had formed.
  41. What fungi have flagella?
    Chytrids.
  42. What are the phylum lineages for fungi?
    • Chrtrids
    • Zygomycetes
    • Glomeromycetes
    • Ascomycetes
    • Basidiomycetes
  43. What a chytrids?
    Fungi that are ubiquitous in lakes and soil; some acting as decomposers or parasites of protists, other fungi, plants or animals. Also, some are important mutualists.

    Some chytrids form colonies with hyphae while others exist as single spherical cells.

    Chytrids are thought to be one of the earliest fungal groups to diverge from other fungi.

    Chytrids are unique among fungi in having flagellated spores called zoospores.
  44. What is a zoospore? What phyllum is it included in?
    A flagellated spore that exists under the phylum Chytrids.

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