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Terms in this set (48)

1) Decomposers
1. Fungi are the principal decomposers of cellulose, lignin, and keratin on earth. This decomposition:
a. Gets rid of carcasses of other organisms
b. Aids in the formation of soil
c. Recycles mineral and other nutrients (e.g. fungi return carbon to the atmosphere as respired CO2, available for photosynthesis by plants (without them, it would be buried))
2) Parasites
1. Absorptive heterotrophs who get their nutrition from living hosts
2. Some parasitic fungi cause noticeable disease; these are classified as pathogenic
3. Parasites can be:
a. Obligate: grow only as a parasite, in association with a host
b. Facultative: can grow as a parasite, but can also grow as "free-living" organism, without a host fungal
4. Plant parasites
a. hyphae are well-suited to invade plant tissues, through stomata, wounds, or penetrating epidermal cell walls
b. Some hyphae produce haustoria, projections that press into plant cells without breaking through the plasma membranes
5. Animal parasites
a. Recent worldwide decline in amphibian population has been linked to a chytrid fungus endemic to South Africa, and possibly spread around the world with exports of the African clawed frog Xenopus laevis
b. Ophiocordyceps infects caterpillars, digests them from the inside out, then sends out a fruiting body, the fruiting bodies are collected by humans as an herbal medicine
c. Affects humans
i. Athlete's foot
ii. Ringworm
iii. Life-threatening diseases in humans with compromised immune systems: e.g., candidemia (severe infection with Candida), pneumocytosis (pneumonia caused by infection with Pneumocystis)
3) Mutualistic fungi
a. Mycorhizae
b. Endophytic fungi
c. lichens
4) Predatory fungi
• capture and kill animals
Most commonly, hyphae secrete sticky material that traps tiny animals
• some fungi make rings in their hyphae; when soil nematodes (roundworms) move through them, the rings constrict and trap the worm
• includes ~65,000 species: lots! They include marine, freshwater, and terrestrial species. Half of al lascomycete species participate in lichen symbioses
• most are multicellular, with septate hyphae, but some have evolved unicellularity
• they are also known as "sac fungi", since they form small sacs (asci: singular ascus) in which meiosis occurs to produce ascospores
• asexual reproduction
- Takes place by formation of mitotically produced haploid spores formed at the tips of hyphae - these spores are called conidia
Conidia give some "molds" their characteristic colors
• sexual reproduction
- Haploid hyphae fuse (plasmogamy)
- Dikaryotic hyphae form; these can be very long lived
- Eventually, the dikaryotic hyphae from a fruiting body (an ascocarp), which bears many asci
- In the asci, karyogamy occurs, making a single diploid nucleus in each ascus; this undergoes meiosis, making 4 haploid cells.
- These each undergo 1 round of meiosis, resulting in 8 haploid ascospores.
• the fruiting bodies (ascocarps) of some multicellular ascomycetes are familiar (and very delicious)
• Other important multicellular ascomycetes
- Many plant parasites, such as chestnut blight and dutch elm disease, and "powdery mildews" that infect cereal grains, roses
- Brown mold Aspergillus
○ Grows on grains and nuts and produce carcinogenic aflatoxin
- Green mold Penicillum
• unicellular (aka yeasts)
- Saccharomyces cerevisiae is baker's yeast. It metabolizes glucose to ethanol and CO2 by fermentation
- Yeasts reproduce asexually by budding
- In sexual reproduction, cells of different mating types fuse, the zygote nucleus undergoes meiosis to form ascospores, and the whole cell is the ascus
- Yeasts have lost the dikaryon stage!