FUNGI
I.
CHARACTERISTICS OF FUNGI
A. Fungi are eukaryotes
B. Nearly all are multi-cellular
1. Although yeast are unicellular
C. Nutrition
1. Fungi are heterotrophs that acquire food by absorption
a) Secrete hydrolytic enzymes and acids to decompose complex molecules into
simpler ones that can be absorbed
D. Motility
1. Fungi are non-motile and have no flagellated stages in their life cycle
II. FUNGAL STRUCTURE
A. Cell walls
1. Composed of the polysaccharide chitin
B. Hyphae
1. Filaments forming the fungal body
a) The network is collectively known as a mycelium
2. Hyphae may be divided into cells by septa
a) Coenocytic fungi have aseptate hyphae
(1) A continuos cytoplasmic mass with hundreds of nuclei
3. In parasitic fungi, some hyphae are modified as haustoria that penetrate tissues of the
host
C. Nuclei
1. Most nuclei are haploid, though diploid and dikaryotic stages occur in most
a) Dikaryons have two separate, genetically dissimilar, haploid nuclei in each cell
III. REPRODUCTION
A. Asexual
1. Spores are produced asexually when conditions are habitable
a) Spores are dispersed by wind or water and germinate in favorable conditions
B. Sexual
1. Haploid condition predominates
2. Form spores sexually when stressed
a) Conjugation occurs between hyphae of opposite mating strains join
(1) Conjugation refers to cell fusion
b) Syngamy may follow conjugation or may be delayed
(1) Syngamy refers to nuclei fusion
(2) If syngamy is delayed, cells are dikaryotic
c) Diploid spores formed by syngamy divide by meiosis to form new haploid spores
(1) Spores are dispersed by wind or water and germinate in favorable conditions to from
haploid mycelia
IV. DIVERSITY OF FUNGI
A. Division Zygomycota
1. Asexual spores develop in sporangia at tips of aerial hyphae
a) Spores may be dispersed by air currents (as in Rhizopus; bread mold)
2. When stressed, Zygomycetes undergo sexual reproduction
a) Hyphal extensions fuse to become a thick-walled resistant zygosporangium
(1) Dikaryotic stage
b) Under favorable conditions, haploid nuclei with in zygosporangia of two parents
fuse
(1) Diploid stage
c) The diploid cell then undergoes meiosis to form new haploid spores
B. Division Ascomycota
1. Ascomycetes include unicellular yeast and complex multicellular cup fungi
2. In asexual reproduction, the tips of specialized hyphae form conidia, which are chains
of haploid, asexual spores that are usually win dispersed
3. In sexual reproduction, haploid mycelia of opposite mating strains fuse
a) One acts as "female" and produces an ascogonium which receives haploid nuclei
from the antheridium of the "male"
b) The ascogonium grows hyphae with dikaryotic cells
(1) Syngamy is delayed
c) In terminal cells of dikaryotic hyphae, syngamy occurs
(1) Diploid stage
d) Meiosis forms 4 haploid nuclei which undergo mitotic division to yield eight haploid
nuclei
e) The nuclei form walls and become ascospores with in an ascus, the sac of
sexually produced spores
4. Unicellular yeast appear dissimilar, but produce the equivalent of an ascus during
sexual reproduction and bud during asexual reproduction in a manner similar to the
formation of conidia
a) Thus, they are classified as ascomycetes
5. Include important decomposers and both mutualistic and parasitic symbionts
a) Many live symbiotically with phototrophs as lichens
C. Division Basidiomycota
1. The division Basidiomycota includes mushrooms, shelf fungi, puffballs, and stinkhorns
a) Agaricus is the genus of the common store bought mushroom
2. Sexual reproduction
a) Opposite mating strands fuse to form dikaryotic hyphae
(1) Syngamy is delayed
b) Hyphae form basidiocarps
(1) A dikaryotic reproductive structure supported by a subterranean mycelium
(2) Commonly called a mushroom
c) The nuclei fuse and the cell swells to form a basidium
d) The diploid nucleus undergoes meiosis to form 4 haploid nuclei
e) The basidium grows 4 basidiospores
(1) Appendages containing a haploid nucleus
f)
Spores are dispersed by wind
3. A "fairy ring" is an expanding ring of living mycelium that produces mushrooms above
it
D. Division Deuteromycota
1. Sometimes called imperfect fungi, deuteromycetes are a diverse group of fungi that
reproduce asexually (have no observable sex life)
a) An example is Penicillium which produces the antibiotic penicillin
2. Many are probably related to Ascomycetes, suggested by their asexual formation of
conidia
V. ECOLOGICAL IMPORTANCE OF FUNGI
A. Lichens
1. Mutualism
a) Symbiotic association of algal cells (usually green algae or cyanobacter) with
fungal hyphae (usually ascomycetes)
(1) The algae provides fungus with food
(2) Fungi provides algae with water, minerals and protection
2. Lichen shape
a) Foliose
(1) Leafy
b) Fructicose
(1) Fruity
c) Crustose
(1) Crusty
3. Importance
a) Lichens are important pioneers, breaking down rock and allowing for colonization
by other plants
b) Food source for reindeer and caribou
c) Lichens are sensitive to air pollution due to their mode of mineral uptake
B. Fungi as decomposers
1. Fungi and bacteria are the principle demineralizers
a) Decomposers that reduce complex organic polysaccharides and proteins to
simples organic compounds that plants can assimilate as raw material for
photosynthesis
C. Mycorrhizae
1. Mycorrhizae are mutualistic associations of plant roots and fungi
a) Mycorrhizae are seen in 90% of trees and the majority of vascular plants
(1) Fungus is usually basidiomycete
2. Are necessary for optimal plant growth
a) The fungi increase the absorptive surface of roots and exchanges soil minerals
3. Plants and fungi moved from water to land together
VI. COMMERCIAL IMPORTANCE OF FUNGI
1. Food
a) Mushrooms, truffles and mycorrhizal on tree roots are edible
b) Penicillium species are used to make blue cheese and Roquefort
c) The metabolism of yeast Saccharomyces cerevisiae produces CO2 that makes
bread rise and ferments sugar to alcohol (beer and wine)
2. Antibiotics
a) In 1928, Alexander Fleming discovered that Penicillium strains produced an
antibacterial chemical
B. Spoilage
1. Fungi decompose food, wood, and even certain plastics
C. Pathogenicity
1. Some fungi are human pathogens
a) Athletes foot, ringworm, and vaginal yeast infections
2. Plant pathogen
a) For example, Dutch elm disease, caused by ascomycetes, drastically changed the
landscape of northeastern U.S.
3. Ergots = Purple structure on rye caused by an ascomycete
a) Produces lysergic acid from which LSD is made
b) Causes hallucinations and burning sensations