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Chapter 14
Kingdom Fungi
Chapter Outlines
Introduction
Life Cycle of Fungi
Characteristics of Fungi
Economic Importance of Fungi
Classification of Fungi
Introduction
The kingdom Fungi includes multicellular eukaryotic heterotrophs. Fungi store reserve
energy in the form of glycogen and do not have flagella at any stage in their life cycle. They are
very diverse, but they share several characteristics: they are heterotrophs and obtain their food by
absorption, the adult is haploid (n), they follow the haplontic life cycle, and have cell walls made
of chitin. Recent molecular analysis indicates that fungi are more closely related to animals than
to plants.
Fungi obtain their food by digesting dead organic matter and absorbing nutrients through
the cell wall and plasma membrane. They secrete powerful hydrolytic enzymes, called
exoenzymes, into their immediate environment, digest dead organic matter, and absorb nutrients.
This mode of feeding makes fungi important decomposers that break down dead matter and
recycle inorganic and organic molecules in ecosystems. The scientific study of fungi is called
mycology.
The body of a fungus, called mycelium, is composed of thin strands or filaments called
hyphae (singular, hypha). Hyphae often interweave to form aboveground reproductive or
fruiting bodies. Some fungi have cross walls in their hyphae called septa that separate the
cytoplasm into cells with one or more nuclei. These hyphae are called septate. The septa,
however, have pores that allow cytoplasm to pass freely from one cell to another. The septa that
separate reproductive cells are complete in all fungal groups. Other hyphae have no septa (i.e.,
aseptate) and therefore are coenocytic (multinucleated). Fungi store reserve energy in the
polysaccharide glycogen.
Reproduction in most fungi is by nonmotile spores and can be either asexual or sexual.
Asexual reproduction includes mycelial fragmentation, budding, and the mitotic production of
spores either within specialized sporangia (singular, sporangium) or in rows at the tips of
specialized hyphae.
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Life Cycle
Sexual reproduction in fungi begins when hyphae from two different mycelia release
sexual signaling molecules called pheromones. When the hyphae meet, they fuse. The union of
the cytoplasm of the two parent mycelia is known as plasmogamy. In many fungi, the haploid
nuclei do not fuse right away. Instead, parts of the mycelia contain coexisting, genetically
different nuclei. Such a mycelium is said to be heterokaryotic. In some fungi, the haploid nuclei
pair off two to a cell, one from each parent. Such a mycelium is said to be dikaryotic (n + n).
During karyogamy, the two nuclei fuse producing diploid (2n) zygote. The zygote immediately
divides by zygotic meiosis to produce haploid spores. The wind-blown spores germinate into
haploid hyphae. Because the haploid phase is dominant, the life cycle of most fungi is called
haplontic life cycle.
When fungi reproduce sexually, distinctive spore-producing structures form. The
kingdom Fungi is divided into different phyla based on the shape of these structures. These
sexual structures are called zygosporangium (phylum Zygomycota), ascus (phylum Ascomycota)
and basidium (phylum Basidiomycota). Fungi that don’t reproduce sexually are called imperfect
fungi and are included in the phylum Deuteromycota. All fungi also reproduce asexually in a
structure called sporangium.
Economic Importance
Fungi are of economic importance to humans. We depend on the ecological services of
fungi as decomposers and recyclers of organic matter. Without mycorrhizae, our agriculture
would be far less productive. About 30 species of mushrooms are edible. Mushrooms, such as
Agaricus campestris, are a popular food. Other edible fungi include morels and truffles. The
distinctive flavors of certain kinds of cheeses, including Roquefort and blue cheese, come from
the fungi used to ripen them. The soft drink industry uses a species of Aspergillus to produce
citric acid for colas. Humans have used yeast (Saccharomyces cerevisiae) to produce alcoholic
beverages and to bake bread for thousands of years.
Many fungi have great medical value as well. Some fungi, such as the mold Penicillium
chrysogenum, produce antibiotics, such as penicillin, that are essential in treating bacterial
infection. A new fungal chemical known as fumagillin strongly inhibits growth of blood vessels
and thus shows promise for the treatment of cancer and rheumatoid arthritis. Fumagillin is an
angiogenesis inhibitor produced by the fungus Aspergillus fumigatus. The chemical also is used
against the infections of the parasitic fungus Nosema apis in the honeybee. Nosema apis has
recently been implicated as a potential culprit for the symptoms of colony collapse disorder
(CCD) of the honeybee. Cyclosporin, a product isolated from the fungus Tolypocladium
inflatum, is prescribed for recipients of transplanted organs to suppress their autoimmune system
and prevent organ rejection. Transplant operations became more successful after the discovery of
cyclosporin in 1971. A compound extracted from ergots (Claviceps purpurea) is used to reduce
high blood pressure and to stop maternal bleeding after childbirth. Some fungi are used to
produce hallucinogenic compounds such as psilocybin.
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Fungi also figure prominently in research in molecular biology and biotechnology.
Researchers use yeast (Saccharomyces cerevisiae) to study the molecular genetics of eukaryotes
because its cells are easy to culture and manipulate. Scientists are gaining insight into the genes
involved in human diseases such as Parkinson’s disease and Huntington’s disease. In 2003,
scientists succeeded in engineering a strain of Saccharomyces cerevisiae that produces human
glycoproteins, such as insulin. Fungi are also used in bioremediation to rid water or soils of
environmental contamination.
Some mushrooms are poisonous, such as Amanita phalloides, others produce
carcinogenic compounds such as aflatoxin produced by Aspergillus flavus, and still others
produce hallucinogenic compounds such as psilocybin and psilocin produced by Psilocybe
cubensis and P. semilanceata. Amanita muscaria produces the hallucinogens muscimol and
ibotenic acid.
Red yeast rice is rice cultivated with the fungus Monascus purpureus (Phylum
Ascomycota). It’s a food preparation tradition going back to 300 BC. In addition to its culinary
(dietary) use, red yeast rice is also used in Chinese herbology and traditional Chinese medicine.
Its use has been documented as far back as 800 AD. It is taken internally to invigorate the body,
aid in digestion, and revitalize the blood. In Chinese medicine, red yeast rice is used to lower
cholesterol, promote blood circulation, and aid digestive problems. It contains substances similar
to statin prescription medications. Red yeast rice has been used with diet, exercise, and medical
care to lower cholesterol and triglyceride levels. It may reduce levels of LDL and increase HDL
in blood. Red yeast rice supplements are manufactured by culturing the fungus Monascus
purpureus on rice at carefully controlled temperatures and growing conditions to increase the
concentrations of chemicals that lower cholesterol and triglycerides. Discoveries of cholesterollowering statins produced by Monascus purpureus have prompted research into its possible
medical uses. It produces a number of statins. Some cholesterol-lowering medications can result
in the breakdown of skeletal muscles, leading to kidney failure.
Many fungi cause serious diseases in humans, animals, and plants. Fungi cause many
plant diseases, and they are responsible for billions of dollars in agricultural losses every year.
Fungi also spoil food products that have been harvested and stored. In addition, fungi often
secrete substances into the foods they are attacking that make these foods unpalatable,
carcinogenic, or poisonous. Some fungi cause animal and human diseases such as ringworm,
athlete’s foot, and lung infection (Pneumocystis jiroveci) in mammals, including humans.
Some fungi form beneficial symbiotic associations with green algae or cyanobacteria,
called lichens; and with roots of most trees, called mycorrhiza. Mycorrhiza is a symbiotic
association between a club fungus and roots of most trees. The mycorrhizal fungus increases the
surface area of the root system and allows more absorption of water and minerals. Pine trees
absorb adequate levels of nitrogen, phosphorus, and water from the soil only when their root
system is infected by mycorrhizal fungi.
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Lichen is a symbiotic association between sac fungi and green algae or cyanobacteria.
Lichens are classified based on shape and growth form into crustose, foliose, and fruticose. In
crustose lichens, growth form resembles encrustation. In foliose lichens, growth form resembles
flat and prostate leaves. Fruticose lichens have shrub-like, branching growth form. In lichens,
green algae or cyanobacteria receive minerals and protective substrates for growth, and the
fungus receives carbohydrates.
Classification of Fungi
Phylum Zygomycota
The Phylum Zygomycota includes the zygomycetes or zygospore fungi (665 species).
These are mainly saprotrophs living off plant and animal remains. The black bread mold,
Rhizopus stolonifer, is a common example. The body of this fungus is composed of hyphae with
no septa (aseptate, and therefore coenocytic or multinucleate hyphae). In Rhizopus, stolons are
horizontal connecting hyphae that exist on the surface of the bread; rhizoids grow into the bread,
anchor the mycelium, and carry out digestion; and sporangiophores are stalks that bear
sporangia. A sporangium is a capsule that produces spores. During asexual reproduction, all
structures involved are haploid.
During sexual reproduction, two different strains of hyphae (denoted + and –) unite by
conjugation and produce progametangia which develop into gametangia. The gametangia
produce isogametes which fuse together to form a diploid zygote. A thick-walled zygospore
forms around the zygote. When the zygospore germinates, it produces a sporangium. Meiosis
occurs during germination, and two strains of spores are produced. Spores germinate into two
mating strains of hyphae. In the bread mold Rhizopus, stolons are horizontal connecting hyphae
that exist on the surface of the bread; rhizoids grow into the bread to anchor the mycelium and
carry out digestion; sporangiophores are stalks that bear sporangia.
Phylum Ascomycota
The phylum Ascomycota includes the ascomycetes or sac fungi (30,000 species). The
defining feature of ascomycetes (phylum Ascomycota) is the production of sexual spores in
saclike structures called asci (singular, ascus). The spore-forming asci are found in cup-shaped
fruiting bodies called ascocarps. Most of these fungi are saprotrophs that play an essential
ecological role by digesting resistant materials containing cellulose, lignin, or collagen. Yeast
(Saccharomyces), some species of Aspergillus and Penicillium, red bread molds (e.g.,
Neurospora), cup fungi (e.g., Sarcoscypha, Peziza), morels (Morchella), and truffles (Trufella),
are ascomycetes. Most ascomycetes are composed of septate hyphae. They usually reproduce
asexually by conidiospores. During sexual reproduction, each ascus within an ascocarp
(fruiting body) produces eight ascospores. Dikaryotic hyphae terminate in the ascocarp and
develop asci where meiosis follows nuclear fusion and spore formation takes place. During the
life cycle of an ascomycete, the fruiting body (ascocarp) is dikaryotic and often cup-shaped. It is
lined by the hymenium layer that produces asci. Nuclei from two different strains fuse within an
ascus to form a zygote (2n). The zygote divides by meiosis to form four haploid nuclei. Each
haploid nucleus divides once by mitosis. The resulting eight ascospores are released from each
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ascus and germinate into hyphae. Sporangia are not formed during asexual reproduction. Instead,
spores called conidia are pinched off in neat rows at the tips of the exposed hyphae called
conidiophores.
Phylum Basidiomycota
The phylum Basidiomycota includes basidiomycetes or club fungi (16,000 species).
These fungi are so named because they form spores (basidiospores) on club-shaped structures
called basidia (singular, basidium). The fruiting body of a basidiomycete is called basidiocarp,
the edible part of mushroom typically found in supermarkets. This group of fungi includes
mushrooms, shelf fungi, puffballs, and many parasitic and gourmet fungi. The mycelium is
composed of septate hyphae with single nuclei (monokaryotic). When these hyphae touch each
other under the soil, they exchange nuclei and give rise to hyphae with dikaryotic nuclei. These
hyphae form the secondary mycelium. Dikaryotic hyphae grow and form the aboveground
basidiocarp. The gills of the basidiocarp are lined with basidia. Each basidium produces four
basidiospores by meiosis. The windblown basidiospores germinate into monokaryotic hyphae
that form the primary mycelium. Occasionally club fungi reproduce asexually by conidiospores.
Phylum Deuteromycota
The phylum Deuteromycota includes deuteromycetes or imperfect fungi. These are the
fungi in which sexual reproduction has not yet been observed. Whenever a sexual stage of a socalled deuteromycete is discovered, the species is reclassified in a particular phylum, depending
on the type of sexual structures it forms. Deuteromycetes always reproduce asexually by
conidiospores. Conidiospores are produced at the tips of modified hyphae called conidiophores,
and not in sporangia. Although some species of both Penicillium and Aspergillus form ascocarps,
and therefore should be classified as ascomycetes, the genera are still classified primarily as
deuteromycetes because the ascocarps are found rarely in only a few species. Candida albicans
is a deuteromycete that causes infection of the vagina and thrush, an inflammation of the mouth
and throat. Many deuteromycetes are economically important:
a.
Some species of Penicillium are used to produce the antibiotic penicillin. Other
species of Penicillium give the characteristic flavors and aromas to cheeses such
as Roquefort and Camembert.
b.
The fungus Tolypocladium inflatum is one of the sources of cyclosporin, a drug
that suppresses immune reactions and thus assists in making human organ grafts
possible. Cyclosporin was put on the market in 1979.
c.
A species of Aspergillus is used to produce soy sauce and soy paste by
fermentation of soybeans. A Japanese food called miso is made by fermenting
soybeans and rice with Aspergillus. Aspergillus oryzae is used to brew Japanese
saki and to enrich food for livestock. In the U.S., Aspergillus is used to produce
citric and gallic acids, which serve as additives during the manufacture of a wide
variety of products, including foods. Aspergillus also causes several human
diseases such as aspergillosis, ringworm, and athlete’s foot. Aflatoxins, among the
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most carcinogenic compounds known, are produced by some Aspergillus flavus
strains growing on moist seeds such as corn, peanuts, etc. Most developed
countries have legal limits on the concentration of aflatoxin permitted in different
foods.
d.
Candida albicans is a deuteromycete that causes infections of the vagina. This
organism also causes thrush, an inflammation of the mouth and throat.
e.
Fusarium species growing on spoiled food produce highly toxic substances such
as trichothecenes.
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Review Questions
Multiple Choice Questions: Select the most appropriate answer or statement.
1.
Although fungi are nonmotile and have cell walls as plants do, recent paleontological and
molecular data suggest that fungi are more closely related to animals than they are to
plants. The cell walls of fungi are made of chitin and the cell walls of plant are made of
cellulose. Also, plants obtain their food by photosynthesis while fungi obtain their food
by extracellular digestion and then absorption of nutrients. While plants store their
reserve energy in the form of starch, fungi store their reserve energy in the form of
glycogen like animals. Because of these reasons and because fungi are unique in their
structure and function, they are now included in a kingdom of their own. Which of the
following statements justifies the inclusion of fungi in a kingdom of their own?
A.
fungi obtain their food by extracellular digestion and then absorption of nutrients
B.
molecular data suggest that fungi are more closely related to animals than plants
C.
fungi store their reserve energy as glycogen rather than as starch
D.
fungi have cell walls made of chitin rather than cellulose
E.
all of these are correct
Answer: E
2.
Honey mushroom (Armillaria ostoyae) is the largest living organism. Its subterranean
network of filaments spreads through 890 hectares (2,200 acres), more than the area of
1,600 football fields. This giant fungus is found in the Malheur National Forest in eastern
Oregon. Based on its current growth rate, scientists estimate that this mushroom, which
weighs hundreds of tons, has been growing for 2,600 years. Honey mushrooms are a
fitting symbol of the neglected grandeur of the kingdom fungi. Although 100,000 species
have been described so far, mycologists (scientists that study fungi) expect this number of
species to increase to 1.5 million in the future. The scientific study of fungi is called
A.
phylogeny
B.
phycology
C.
mycology
D.
zoology
E.
botany
Answer: C
3.
Which of the following is not correct about fungi?
A.
all fungi are heterotrophic
B.
all fungi have cellulose cell walls
C.
some fungi have a dikaryotic stage (n + n)
D.
all fungi lack flagella with the exception of the chytrids
E.
some fungi form mutualistic symbiosis with other organisms
Answer: B
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4.
Fungi are heterotrophs that digest their food while it is still in the environment by
secreting powerful hydrolytic enzymes, called exoenzymes, into their surroundings.
Exoenzymes break down waste products and dead remains of plants and animals to
smaller organic compounds (nutrients) that the fungi can absorb into their bodies and use.
What is the difference between the nutritional mode of a fungus and your own nutritional
mode?
A.
fungi digest their food externally by secreting exoenzymes into the food and then
absorb nutrients; humans ingest relatively large pieces of food and digest food
within their bodies
B.
a fungus could have a saprobic, mutualistic, or parasitic mode of nutrition,
humans are parasitic
C.
fungi have extracellular digestion and humans have intracellular digestion
D.
fungi are heterotrophs and humans are autotrophs
E.
both A and B are correct
Answer: A
5.
The body of a fungus, called mycelium, is composed of thin strands or filaments called
hyphae. Hyphae often interweave to form aboveground reproductive or fruiting bodies.
Some fungi have cross walls in their hyphae called septa that separate the cytoplasm into
cells with one or more nuclei. These hyphae are called septate. The septa, however, have
pores that allow cytoplasm to pass freely from one cell to another. The septa that separate
reproductive cells are complete in all fungal groups. Other hyphae have no septa and
therefore are coenocytic. What is the primary role of the underground mycelium of fungi?
A.
secretion of exoenzymes and absorption of nutrients
B.
asexual reproduction
C.
sexual reproduction
D.
anchorage
E.
protection
Answer: A
6.
The functional significance of porous septa in certain fungal hyphae is most similar to
that represented by the gap junctions in certain animal cells, and by the plasmodesmata of
certain plant cells. In septate fungi, what structures allow cytoplasmic streaming to
distribute needed nutrients throughout the mycelium?
A.
gap junctions that form in septal walls between cells
B.
complex microtubular cytoskeletons
C.
pores in septal walls
D.
plasmodesmata
E.
haploid nuclei
Answer: C
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7.
Which of the following is not a characteristic of hyphate fungi (fungi featuring hyphae)?
A.
their body plan, called a mycelium, is a netlike mass of filaments called hyphae
B.
they may be saprobes, parasites, or mutualistic symbionts
C.
their cell walls contain a polysaccharide called cellulose
D.
the nuclei of their cells are typically haploid
E.
they acquire their nutrients by absorption
Answer: C
8.
The vast majority of fungi are multicellular and their body, called a mycelium, is a
network of filaments called hyphae. Hyphae give the mycelium quite a large surface area
per volume of cytoplasm, and this facilitates absorption of nutrients into the body of a
fungus. The adaptive advantage associated with the filamentous nature of fungal mycelia
is primarily related to
A.
an extensive surface area well suited for absorptive nutrition
B.
the ability to form haustoria and parasitize other organisms
C.
the potential to inhabit extreme terrestrial environments
D.
the production of gametes
E.
the production of spores
Answer: A
9.
Mutually beneficial relationships between some fungi and plant roots are called
mycorrhizae. Plants whose roots are invaded by mycorrhizae grow more successfully in
poor soils and absorb more phosphorus and other minerals from the soil. In exchange, the
plant supplies the fungus with organic nutrients. Ectomycorrhizal fungi form sheaths of
hyphae over the surface of a root and also grow into the extracellular spaces of the root
cortex. Endomycorrhizal fungi extend their hyphae through the root cell wall and into
tubes formed by invaginations of the root cell membrane. What will happen to plants that
grow in soils that lack mycorrhizae?
A.
stunted growth
B.
symptoms of phosphorus deficiency
C.
failure of sexual reproduction
D.
both A and B are correct
E.
both A and C are correct
Answer: D
10.
Lichens are a mutualistic symbiosis between a fungus, usually a sac fungus, and a
cyanobacterium or a green alga. Three types of lichens are recognized: crustose,
fruticose, and foliose. Lichens can live in areas of extreme conditions and contribute to
the formation of soils. Which of the following statements about lichens is not correct?
A.
lichens are symbiotic associations between sac fungi and green algae
B.
the three types of lichens are crustose, fruticose, and foliose
C.
lichens are able to live in extreme environments
D.
lichens contribute to the formation of soils
E.
lichens cannot reproduce
Answer: E
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11.
How are the vascular plants that are involved in mycorrhizae and the photosynthetic algal
cells that are involved in lichens alike?
A.
they secrete acids that keep the fungal partner from growing too quickly
B.
they are digested by fungal exoenzymes while still alive
C.
they both provide organic nutrients to fungal partners
D.
they contain endosymbiotic fungi
E.
both A and C are correct
Answer: C
12.
Fungi propagate themselves by producing spores, either sexually or asexually. Asexual
reproduction includes mycelial fragmentation, budding, and the mitotic production of
spores either within specialized sporangia (singular, sporangium) or in rows at the tips of
specialized hyphae. Ascomycetes produce naked asexual spores, called conidia, at the
ends of specialized hyphae called conidiophores. Sexual reproduction begins when
hyphae from two different mycelia release sexual signaling molecules called
pheromones. When the hyphae meet, they fuse. The union of the cytoplasm of the two
parent mycelia is known as plasmogamy. In many fungi, the haploid nuclei do not fuse
right away. Instead, parts of the mycelia contain coexisting, genetically different nuclei.
Such a mycelium is said to be heterokaryotic. In some fungi, the haploid nuclei pair off
two to a cell, one from each parent. Such a mycelium is said to be dikaryotic (n + n).
During karyogamy, the two nuclei fuse producing diploid (2n) zygote. The zygote
immediately divides by meiosis to produce haploid spores. Spores are nonmotile and can
be carried by wind or water, and when they land in a moist place where there is food,
they germinate, producing new hyphae and mycelia. Because the haploid phase is
dominant, the life cycle of most fungi is called haplontic life cycle. Which of the
following processes or conditions is associated with only sexual reproduction in fungi?
A.
karyogamy
B.
plasmogamy
C.
heterokaryon
D.
zygotic meiosis
E.
all of these are correct
Answer: E
13.
Which of the following statements is correct about asexual reproduction in fungi?
A.
mycelial fragmentation and budding
B.
mitotic production of spores within sporangia
C.
mitotic production of spores in rows at the tips of specialized hyphae
D.
production of naked spores (conidia) at the ends of hyphae called conidiophores
E.
all of these are correct
Answer: E
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14.
The group of fungi that have, at present, no known sexual stage is the
A.
deuteromycetes
B.
basidiomycetes
C.
zygomycetes
D.
ascomycetes
E.
chytrids
Answer: A
15.
A chemical secreted by female Bombyx moths helps the male of the species locate
females, at which time sexual reproduction may occur. This chemical is most similar in
function to which chemicals used by certain fungi during sexual reproduction?
A.
aflatoxins
B.
antibiotics
C.
exoenzymes
D.
pheromones
E.
sex hormones
Answer: D
16.
A mycologist is trying to classify a new fungus on the basis of the following
characteristics: fungus-like in appearance, reproduces by conidia, has no apparent sexual
phase, and parasitizes woody plants. To which phylum of the kingdom Fungi should the
mycologist assign this new species?
A.
Glomeromycota
B.
Deuteromycota
C.
Basidiomycota
D.
Zygomycota
E.
Ascomycota
Answer: B
17.
When fungi reproduce sexually, distinctive spore-producing structures form. The
kingdom Fungi is divided into 6 phyla based on the shape of the structure in which sexual
spores are produced. These phyla include Chytridiomycota (chytrids), Zygomycota
(zygomycetes), Glomeromycota (glomeromycetes), Ascomycota (sac fungi),
Basidiomycota (club fungi), and Deuteromycota (imperfect fungi). Which of the
following is a mis-match between a fungus and its sexual spore-producing structure?
A.
ascomycete – ascus
B.
chytrid – sporangium
C.
basidiomycete – basidium
D.
zygomycete – conidiophore
E.
deuteromycete – no sexual structure
Answer: D
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18.
An example of a parasitic fungal-animal symbiosis is chytridiomycosis, first identified in
1998 as an emerging infectious disease of amphibians. Amphibian populations have been
declining worldwide for three decades. The decline correlates with the presence of the
chytrid Batrachochytrium dendrobatidis. Sick and dead frogs have flasklike structures
encased in their skin. The connection with B. dendrobatidis has been supported by DNA
sequence data, by isolating and culturing the chytrid, and by infecting healthy frogs with
the organism and replicating disease symptoms. The fungi that cause the frog disease
chytridiomycosis are included in the species
A.
Neurospora crassa
B.
Armillaria ostoyae
C.
Rhizopus stolonifer
D.
Saccharomyces cerevisiae
E.
Batrachochytrium dendrobatidis
Answer: E
19.
The Phylum Zygomycota includes the zygomycetes or zygospore fungi. These are mainly
saprotrophs living off plant and animal remains. The black bread mold, Rhizopus
stolonifer, is a common example. The body of this fungus is composed of hyphae with no
septa. In Rhizopus, stolons are horizontal connecting hyphae that exist on the surface of
the bread; rhizoids grow into the bread to anchor the mycelium and carry out digestion
and absorption; and sporangiophores are stalks that bear sporangia. A sporangium is a
capsule that produces spores. During asexual reproduction, all structures involved are
haploid. During sexual reproduction, two different strains of hyphae (denoted + and –)
unite by conjugation and form hyphal extensions called gametangia, each with several
haploid nuclei. After plasmogamy, a thick-walled zygosporangium forms, containing
multiple haploid nuclei from the two strains. When conditions are favorable, karyogamy
occurs producing zygotes with diploid nuclei. Meiosis follows producing haploid spores.
The zygosporangium then breaks dormancy, germinating into a short sporangium. The
sporangium disperses genetically diverse spores that germinate and grow into new
mycelia. Which of the following is not correct about zygomycetes?
A.
they include fast-growing molds responsible for rotting produce such as peaches,
strawberries and sweet potatoes during storage
B.
the mycelium is composed of hyphae with no septa
C.
horizontal hyphae spread out over food, penetrate it, digest it, and absorb nutrients
D.
sporangia, carried on sporangiophores, are sexual structures that produce
genetically identical haploid spores
E.
during sexual reproduction, plasmogamy produces a thick-walled
zygosporangium, in which karyogamy and then meiosis occur
Answer: D
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20.
The defining feature of ascomycetes (phylum Ascomycota) is the production of sexual
spores in saclike structures called asci (singular, ascus). The spore-forming asci are found
in fruiting bodies called ascocarps. Most of these fungi are saprotrophs that play an
essential ecological role by digesting resistant materials containing cellulose, lignin, or
collagen. Yeast (Saccharomyces), some species of Aspergillus and Penicillium, red bread
molds (Neurospora), cup fungi (Sarcoscypha and Peziza), morels (Morchella), and
truffles (Trufella), are examples of ascomycetes. Most of these fungi are composed of
septate hyphae. They usually reproduce asexually by conidiospores. During sexual
reproduction, plasmogamy produces dikaryotic asci. Karyogamy occurs within the ascus,
producing a diploid nucleus. Each ascus produces eight ascospores by meiosis followed
by mitosis. When spores are dispersed, they germinate and grow into new mycelia. You
are given a fungus to identify. It has a cup-shaped fruiting body that contains many
saclike structures each with eight haploid spores lined up in a row. In which phylum will
you classify this fungus?
A.
Chytridiomycota
B.
Glomeromycota
C.
Basidiomycota
D.
Zygomycota
E.
Ascomycota
Answer: E
21.
Club fungi or basidiomycetes (phylum Basidiomycota) are so named because they form
spores (basidiospores) on club-shaped structures called basidia (singular, basidium). The
fruiting body of a basidiomycete is called basidiocarp. This group of fungi includes
mushrooms, shelf fungi, puffballs, and many parasitic and gourmet fungi. The mycelium
is composed of septate hyphae with single nuclei (monokaryotic). When these hyphae
touch each other under the soil, they exchange nuclei and give rise to hyphae with
dikaryotic nuclei. These hyphae form the secondary mycelium. Dikaryotic hyphae grow
and form the aboveground basidiocarp. The gills of the basidiocarp are lined with basidia.
Each basidium produces four basidiospores by meiosis. The windblown basidiospores
germinate into monokaryotic hyphae that form the primary mycelium. Mushrooms with
gills, typically available in supermarkets, have basidiospores located on basidia and
belong to the phylum
A.
Chytridiomycota
B.
Glomeromycota
C.
Basidiomycota
D.
Zygomycota
E.
Ascomycota
Answer: C
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22.
The phylum Deuteromycota includes deuteromycetes or imperfect fungi. These are the
fungi in which sexual reproduction has not yet been observed. Whenever a sexual stage
of a so-called deuteromycete is discovered, the species is reclassified in a particular
phylum, depending on the type of sexual structures it forms. Deuteromycetes always
reproduce asexually by conidiospores. Conidiospores are produced at the tips of modified
hyphae called conidiophores, and not in sporangia. Although some species of both
Penicillium and Aspergillus form ascocarps, and therefore should be classified as
ascomycetes, the genera are still classified primarily as deuteromycetes because the
ascocarps are found rarely in only a few species. Candida albicans is a deuteromycete
that causes infection of the vagina and thrush, an inflammation of the mouth and throat.
Fungi in which sexual reproduction has not yet been observed are classified in the
phylum
A.
Chytridiomycota
B.
Basidiomycota
C.
Zygomycota
D.
Ascomycota
E.
None of these
Answer: E
23.
We depend on the ecological services of fungi as decomposers of organic matter and
recyclers of nutrients. Without mycorrhizae, our agriculture would be far less productive.
Mushrooms, such as Agaricus campestris, are a popular food. Other edible fungi include
morels and truffles. The distinctive flavors of certain kinds of cheeses, including
Roquefort and blue cheese, come from the fungi used to ripen them. The soft drink
industry uses a species of Aspergillus to produce citric acid for colas. Humans have used
yeast (Saccharomyces cerevisiae) to produce alcoholic beverages and to bake bread for
thousands of years. Many fungi have great medical value as well. For example, a
compound extracted from ergots (Claviceps purpurea) is used to reduce high blood
pressure and to stop maternal bleeding after childbirth. The immunosuppressive drug
cyclosporin is isolated from the fungus Tolypocladium inflatum. Transplant operations
became more successful after the discovery of cyclosporin in 1971. Some fungi, such as
the mold Penicillium chrysogenum, produce antibiotics that are essential in treating
bacterial infection. Fungi also figure prominently in research in molecular biology and
biotechnology. Which of the following fungi produces the immunosuppressive drug
cyclosporin?
A.
Aspergillus flavus
B.
Psilocybe mexicana
C.
Tolypocladium inflatum
D.
Penicillium chrysogenum
E.
Saccharomyces cerevisiae
Answer: C
14
24.
Fungi have a strong impact on human health and economy. Some mushrooms are
poisonous, such as the death angel Amanita phalloides. Other fungi produce carcinogenic
compounds such as aflatoxin produced by some Aspergillus flavus strains, and still others
produce hallucinogenic compounds such as psilocybin produced by Psilocybe mexicana.
Amanita muscaria produces the hallucinogens muscimol and ibotenic acid. Many fungi
cause serious diseases in humans, animals, and plants. Many fungi cause plant diseases,
and they are responsible for billions of dollars in agricultural losses every year. Some
fungi spoil food products that have been harvested and stored. In addition, fungi often
secrete substances into the foods they are attacking that make these foods unpalatable,
carcinogenic, or poisonous. Some fungi cause human diseases such as ringworm,
athlete’s foot, and lung infection, and many more. Which of the following fungus –
product associations are correct?
A.
Penicillium chrysogenum – antibiotics
B.
Tolypocladium inflatum – cyclosporin
C.
Psilocype mexicana – psilocybin
D.
Aspergillus flavus – afflatoxin
E.
all of these are correct
Answer: E
25.
Recent paleontological and molecular data suggest that fungi are more closely related to
animals than they are to plants and algae. Both animals and fungi are heterotrophic and
store their food in the form of glycogen. However, animals ingest and then digest their
food, while fungi digest their food externally and then absorb the nutrients. The life cycle
of fungi is the haplontic life cycle which is different from the diplontic life cycle of
animals and the alternation of generations life cycle of plants. In this way, fungi are
unique and deserve their own kingdom. In which of the following ways do fungi
resemble animals?
A. both fungi and animals are non-photosynthetic heterotrophs
B. both fungi and animals store their excess food as glycogen
C. both fungi and animals obtain their food by absorption
D. both A and B are correct
E. A, B, and C are correct
Answer: D
Although fungi are very diverse, they share several characteristics. Most fungi are
multicellular and have filamentous feeding bodies called mycelia. A mycelium is made of
slender filaments called hyphae. Adult fungi are haploid (n) and have the haplontic life
cycle. Some fungi have a dikaryotic (n + n) stage. Fungi have cell walls made of chitin
and they store their food reserves as glycogen. With the exception of the chytrids
(phylum Chytridiomycota), fungi lack flagella at any stage of their life cycle. Which of
the following is NOT a characteristic of fungi?
A. lack of flagella with the exception of the chytrids
B. mutualistic symbiosis with other organisms
C. some fungi have a dikaryotic stage (n + n)
D. cell wall made of cellulose
E. both A and B are correct
Answer: D
15
26.
27.
Fungi are heterotrophic organisms that feed on preformed organic matter. The majority of
them are saprotrophic decomposers that feed on dead remains of plants and animals.
Some fungi are parasitic, living off the tissues of living plants and animals. Other fungi
have mutualistic relationships with the roots of seed plants called mycorrhiza. The fungus
acquires inorganic nutrients for plants, and in return it receives organic nutrients. Other
fungi form associations with green algae or cyanobacteria called lichens. Lichens can live
on rocks and are important soil formers. Which of the following is NOT a correct mode
by which fungi obtain food?
A. saprotrophic decomposers that feed on dead remains of plants and animals
B. mutualistic relationship with green algae and cyanobacteria
C. parasitic, living off the tissues of living plants and animals
D. mutualistic relationship with the roots of some seed plants
E. ingestion of food followed by intracellular digestion
Answer: E
28.
Fungi are heterotrophs that digest their food while it is still in the environment by
secreting powerful hydrolytic enzymes, called exoenzymes, into their surroundings.
Exoenzymes break down waste products and dead remains of plants and animals to
smaller organic compounds (nutrients) that the fungi can absorb into their bodies and use.
What is the difference between the nutritional mode of a fungus and your own nutritional
mode?
A.
fungi digest their food externally by secreting exoenzymes into the food and then
absorb nutrients; humans ingest relatively large pieces of food and digest food
within their bodies
B.
a fungus could have a saprobic, mutualistic, or parasitic mode of nutrition,
humans are parasitic
C.
fungi have intracellular digestion and humans have extracellular digestion
D.
fungi are heterotrophs and humans are autotrophs
E.
both A and B are correct
Answer: A
29.
The feeding body of a fungus, called mycelium, is composed of thin strands or filaments
called hyphae. Hyphae give the mycelium quite a large surface area per volume of
cytoplasm, and this facilitates absorption of nutrients into the body of the fungus. What is
the advantage of hyphae in the mycelia of fungi?
A.
hyphae give mycelium large surface area which facilitates absorption
B.
hyphae are used for both asexual and sexual reproduction
C.
hyphae have pores for gas exchange
D.
both A and B are correct
E.
A, B, and C are correct
Answer: A
16
30.
Lichens are a mutualistic symbiosis between a fungus, usually a sac fungus, and a
cyanobacterium or a green alga. Three types of lichens are recognized: crustose,
fruticose, and foliose. Lichens can live in areas of extreme conditions and contribute to
the formation of soils. Which of the following statements about lichens is not correct?
A.
lichens are symbiotic associations between sac fungi and green algae
B.
the three types of lichens are crustose, fruticose, and foliose
C.
lichens are able to live in extreme environments
D.
lichens contribute to the formation of soils
E.
lichens cannot reproduce
Answer: E
31.
The defining feature of ascomycetes (phylum Ascomycota) is the production of sexual
spores in saclike structures called asci (singular, ascus). The spore-forming asci are found
in cup-shaped fruiting bodies called ascocarps. Most of these fungi are saprotrophs that
play an essential ecological role by digesting resistant materials containing cellulose,
lignin, or collagen. Yeast (Saccharomyces), some species of Aspergillus and Penicillium,
red bread molds (Neurospora), cup fungi (Sarcoscypha and Peziza), morels (Morchella),
and truffles (Trufella), are examples of ascomycetes. Most of these fungi are composed
of septate hyphae. They usually reproduce asexually by conidiospores. During sexual
reproduction, plasmogamy produces dikaryotic asci (n + n). Karyogamy occurs within
the ascus, producing a diploid nucleus. Each ascus produces eight ascospores by meiosis
followed by mitosis. When spores are dispersed, they germinate and grow into new
mycelia. Which of the following is NOT a correct statement about ascomycetes?
A.
they play an essential ecological role by digesting resistant materials containing
lignin, collagen and cellulose
B.
ascomycetes reproduce asexually by conidiospores
C.
sexual reproduction involves both plasmogamy and karyogamy
D.
the mycelia of ascomycetes are composed of non-septate hyphae
E.
each ascus produces eight ascospores by meiosis followed by mitosis
Answer: D
32.
Fungi in the phylum Ascomycota are commonly known as ascomycetes. Why are these
fungi also known as cup fungi and sac fungi?
A.
because their ascospores are produced in asci that look like sacs
B.
because their fruiting body, the ascocarp, looks like a cup
C.
because they produce ascospores that look like sacs
D.
both A and B are correct
E.
A, B, and C are correct
Answer: B
17
33.
Club fungi or basidiomycetes (phylum Basidiomycota) are so named because they form
spores (basidiospores) on club-shaped structures called basidia (singular, basidium). The
fruiting body of a basidiomycete is called basidiocarp. This group of fungi includes
mushrooms, shelf fungi, puffballs, and many parasitic and gourmet fungi. The mycelium
is composed of septate hyphae with single nuclei (monokaryotic). When these hyphae
touch each other under the soil, they exchange nuclei and give rise to hyphae with
dikaryotic nuclei. These hyphae form the secondary mycelium. Dikaryotic hyphae grow
and form the aboveground basidiocarp. The gills of the basidiocarp are lined with basidia.
Each basidium produces four basidiospores by meiosis. The windblown basidiospores
germinate into monokaryotic hyphae that form the primary mycelium. Which of the
following is a correct statement about basidiocarb?
A.
basidiocarb is the edible part of mushroom typically found in supermarkets
B.
basidiocarb is produced by dikaryotic hyphae of the secondary mycelium
C.
basidiocarb has gills lined with basidiospores
D.
only A and B are correct
E.
A, B, and C are correct
Answer: A
34.
The phylum Deuteromycota includes deuteromycetes or imperfect fungi. These are the
fungi in which sexual reproduction has not yet been observed. Whenever a sexual stage
of a so-called deuteromycete is discovered, the species is reclassified in a particular
phylum, depending on the type of sexual structures it forms. Deuteromycetes always
reproduce asexually by conidiospores. Conidiospores are produced at the tips of modified
hyphae called conidiophores, and not in sporangia. Although some species of both
Penicillium and Aspergillus form ascocarps, and therefore should be classified as
ascomycetes, the genera are still classified primarily as deuteromycetes because the
ascocarps are found rarely in only a few species. Candida albicans is a deuteromycete
that causes infection of the vagina and thrush, an inflammation of the mouth and throat.
Deuteromycetes are characterized by all of the following except
A.
conidiospores are produced inside heads of modified hyphae called sporangia
B.
conidiospores are produced at tips of modified hyphae called conidiophores
C.
some of them cause thrush and vaginal infection
D.
always reproduce asexually by conidiospores
E.
both A and B are correct
Answer: A
18
35.
A new fungal chemical known as fumagillin strongly inhibits growth of blood vessels
and thus shows promise for the treatment of cancer and rheumatoid arthritis. Fumagillin
is an angiogenesis inhibitor produced by the fungus Aspergillus fumigatus. The chemical
also is used against the infections of the parasitic fungus Nosema apis in the honeybee.
Nosema apis has recently been implicated as a potential culprit for the symptoms of
colony collapse disorder (CCD) of the honeybee. The fungal chemical fumagillin has
promise to treat
A. cancer
B. rheumatoid arthritis
C. colony collapse disorder (CCD) of the honeybee
D. only A and B are correct
E. A, B, and C are correct
Answer: E
36.
Fungi are of economic importance to humans. About 30 species of mushrooms are edible.
Truffles are gourmet delights that flourish in France. The unique flavors of many cheeses,
such as Roquefort and Camembert, are the result of fungal metabolism. The fungus yeast
is used in the bakery and alcohol industries. Some fungi are used to produce antibiotics
such as penicillin. The fungal product fumagillin has promise as an anticancer agent.
Cyclosporin, another fungal product, is prescribed for recipients of transplanted organs to
suppress their autoimmune system and prevent organ rejection. Some fungi are used to
produce hallucinogenic compounds such as psilocybin. Which of the following is a mismatch?
A. cyclosporin – used by recipients of transplanted organs
B. antibiotics – used to treat human mycoses
C. psilocybin – hallucinogenic compounds
D. fumagillin – anticancer agent
E. yeast – beer making
Answer: B
19
True/False Questions. If the answer is “True,” learn the scientific fact presented in the
question. If the answer is “False,” find why it is false, and learn the correct scientific fact
presented in the question.
37.
The phylum Zygomycota formerly included the members of the new phylum
Glomeromycota, and may also contain the Microsporidia.
Answer: True
38.
The body of a fungus is a mycelium made up of hyphae
Answer: True
39.
Fungi produce windblown spores during asexual reproduction and seeds during sexual
reproduction.
Answer: False
40.
Fungal cells are normally nonmotile and have a cell wall that contains chitin.
Answer: True
41.
Nonseptate fungal hyphae are multinucleated.
Answer: True
42.
Sac fungi reproduce sexually by forming conidia and asexually by forming ascospores.
Answer: False
43.
The dikaryotic stage in club fungi periodically produces fruiting bodies, where
basidiospores are produced in a zygosporangium.
Answer: False
44.
The mushroom Psilocybe mexicana produces a hallucinogenic chemical called psilocybin
that is a structural analogue of LSD and mescaline.
Answer: True
45.
The only reliable way to tell a nonpoisonous mushroom from a poisonous one is to be
able to correctly identify the species.
Answer: True
46.
Because the toxic alkaloids that cause the human disease ergotism stimulate smooth
muscle and selectively block the sympathetic nervous system, they can be used in
medicine to cause uterine contractions and to treat certain circulatory disorders, including
migraine headaches.
Answer: True
47.
All fungi are characterized by extracellular digestion using exoenzymes and absorption of
nutrients.
Answer: True
20
48.
The extremely fast growth of a fungal mycelium accounts for the rapid distribution of
synthesized proteins by cytoplasmic streaming.
Answer: True
49.
The vegetative (nutritionally active) body of most fungi is composed of hyphae, referred
to as a mycelium, and is usually underground.
Answer: True
50.
The fungal process during which the cytoplasm of cells from two individuals fuse,
without the fusion of nuclei is called karyogamy.
Answer: False
51.
Deuteromycetes are the group of fungi that have, at present, no known sexual stage.
Answer: True
52.
All fungi follow the haplontic life cycle with zygotic meiosis.
Answer: True
53.
A conidium is a fungal structure associated with sexual reproduction.
Answer: False
54.
Both Penicillium and Aspergullus produce asexual spores, called conidia, at tips of
specialized hyphae called conidiophores.
Answer: True
55.
If there were no mycorrhizae in soil, most vascular plants would be stunted in their
growth.
Answer: True
56.
Both fungus-derived antibiotics and hallucinogens used by humans probably evolved in
certain fungi as a means to reduce competition for nutrients.
Answer: True
21
Concept Questions and their Answers
57.
Compare and contrast the nutritional mode of a fungus with your own nutritional
mode.
Both a fungus and a human are heterotrophs. A fungus digests its food externally
(extracellular digestion) by secreting digestive enzymes into the food (dead organic
matter) and then absorb the nutrients that result from digestion. In contrast, humans
ingest relatively large pieces of food and digest the food within their bodies (intracellular
digestion).
58.
Describe how the structure of a fungus is adapted to its nutritional mode.
The extensive network of hyphae that make up a fungus body (mycelium) puts a large
surface area in contact with the food source, and rapid growth of the mycelium extends
hyphae into new territory.
59.
Explain the evolutionary significance of the presence of mycorrhizae in the earliest
vascular plants.
This indicates that fungi had already established symbiotic relationships with plants by
the time the first vascular plants evolved.
60.
Why are glomeromycetes (phylum Glomeromycota) so ecologically significant?
Glomeromycetes were formerly considered zygomycetes. All glomeromycetes form a
distinct type of endomycorrhizae called arbuscular mycorrhizae. The tips of the hyphae
that push into the plant root cells branch into tiny treelike structures known as arbuscules.
About 90% of all pants have such symbiotic partnerships with glomeromycetes. The
fungal hyphae increase the plant root surface area allowing for more absorption of
minerals and water. The fungus also breaks down organic compounds and makes the
minerals in them more available to the plant roots. Without the fungus, the plants will be
poorly nourished.
61.
Give different examples of how form fits function in zygomycetes, ascomycetes, and
basidiomycetes.
In zygomycetes, the sturdy, thick-walled zygosporangium can withstand harsh conditions
and then undergo karyogamy and meiosis when the environment is favorable for
reproduction. In ascomycetes, the asexual spores (conidia) are produced in chains or
clusters at the tips of conidiophores, where they are easily dispersed by wind. The often
cup-shaped ascocarps house the sexual spore-forming asci. In basidiomycetes, the
Basidiocarp supports and protects a large surface area of basidia, from which spores are
dispersed.
22
62.
What are some of the benefits that algae in lichens can derive from their
relationship with fungi?
A suitable environment for growth, retention of water and minerals, protection from
sunlight, and protection from being eaten.
63.
Discuss some practical uses of fungi.
We depend on the ecological services of fungi as decomposers and recyclers of organic
matter. Without mycorrhizae, our agriculture would be far less productive. Mushrooms,
such as Agaricus campestris, are a popular food. Other edible fungi include morels and
truffles. The distinctive flavors of certain kinds of cheeses, including Roquefort and blue
cheese, come from the fungi used to ripen them. The soft drink industry uses a species of
Aspergillus to produce citric acid for colas. Humans have used yeast (Saccharomyces
cerevisiae) to produce alcoholic beverages and to bake bread for thousands of years.
Many fungi have great medical value as well. For example, a compound extracted from
ergots (Claviceps purpurea) is used to reduce high blood pressure and to stop maternal
bleeding after childbirth. The immunosuppressive drug cyclosporin is isolated from the
fungus Tolypocladium inflatum. Transplant operations became more successful after the
discovery of cyclosporin in 1971. Some fungi, such as the mold Penicillium
chrysogenum, produce antibiotics that are essential in treating bacterial infection. Fungi
also figure prominently in research in molecular biology and biotechnology. Researchers
use yeast (Saccharomyces cerevisiae) to study the molecular genetics of eukaryotes
because its cells are easy to culture and manipulate. Scientists are gaining insight into the
genes involved in human diseases such as Parkinson’s disease and Huntington’s disease.
In 2003, scientists succeeded in engineering a strain of Saccharomyces cerevisiae that
produces human glycoproteins, such as insulin. Fungi are also used in bioremediation to
rid water or soils of environmental contamination.
23