Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 21
21.1
1. Fungi are important in ecosystems as decomposers that break down dead organic matter. This
releases inorganic nutrients, allowing them to be recycled. They are also parasites of plants and
animals.
2. Fungi are heterotrophic, have cell walls made of chitin, store carbohydrates as glycogen, and
have diploid zygotes that divide meiotically to produce haploid nuclei that then divide mitotically
as the fungus grows.
3. Fungi and animals produce chitin, are heterotrophs, and use glycogen as a storage
carbohydrate. Molecular data support the close relationship between fungi and animals.
4. Hyphae are filamentous structures that make up a fungal body. Mycelium is a visible mass of
hyphae. Spores are the reproductive structures of fungi, and the fruiting body produces the
spores.
5. Chytridiomycetes, Zygomycetes, Ascomycetes, and Basidiomycetes are the four main groups
of fungi. Deuteromycetes form an informal group containing the fungi for which a sexual phase
has not been observed.
21.2
1. Zoospores are motile spores that swim in a film of water, allowing chytrids to spread in moist or
wet environments.
2. Chytrids are decomposers that eat cellulose, chitin, and keratin.
21.3
1. Zygomycetes occur in decaying organic matter in soil (and often decay spoiled food as well).
2. A zygospore is formed by the union of two haploid hyphae. Inside the zygospore, two nuclei
fuse into a zygote. The zygote then undergoes meiosis and germinates into a spore sac that
releases haploid fungal spores.
21.4
1. Ascomycetes that are important to humans include the fungi that cause Dutch elm disease,
chestnut blight, athlete’s foot, and other diseases. Penicillium notatum produces antibiotics and
other Penicillium species flavor cheeses. Morels and truffles are ascomycetes. Yeasts are used in
baking, brewing, winemaking, and production of soy sauce. The drug cyclosporine comes from
ascomycetes.
2. Dikaryotic cells form when two hyphae fuse but the nuclei remain separate. Inside the fruiting
body, the nuclei fuse to form a diploid zygote. Meiosis follows, and the haploid spores that are
formed are held within asci.
3. An ascus comes to contain eight ascospores after a diploid nucleus within an ascus undergoes
meiosis. The result is four haploid nuclei, which each immediately undergo mitosis to produce
eight nuclei (that mature into eight ascospores).
21.5
1. Familiar basidiomycetes include mushrooms, toadstools, puffballs, stinkhorns, shelf fungi, and
bird’s nest fungi.
2. Club-shaped cells called basidia are characteristic of basidiomycetes.
3. In the basidiomycete life cycle, the zygote occurs within a basidium after the fusion of haploid
nuclei. In a mushroom, the basidia are produced on gills.
4. A “fairy ring” forms as hyphae grow outward from a food source, producing mushrooms near
the outer edge of the ring.
21.6
1. A plant gains water and minerals from its mycorrhizal partners, whereas the fungus gains
carbohydrates that the plant produces in photosynthesis.
2. In leaf-cutter ant colonies, the ants harvest plant materials and transport them into their
underground nests. There, they process the leaves into a paste and inoculate the paste with
fungal spores. The fungi develop into structures that the ants eat. Bacteria on the ants’ cuticles
secrete a potent antibiotic that kills an ascomycete that attacks the cultivated fungus.
3. The fungal hyphae are wrapped tightly around the algal cells.
4. Pollution kills lichens, which absorb toxins from surrounding air and water. When lichens
disappear from an environment, is an indicator of polluted air.