Chapter 22
The Diversity of Fungi
Chapter 22 Learning Goals




What Are the Key Features of Fungi?
What Are the Major Groups of Fungi?
How Do Fungi Interact with Other Species?
How Do Fungi Affect Humans?
22.1 What Are the Key Features of Fungi?
 Fungal bodies consist of slender threads
– Most fungi are multicellular
– Cells are surrounded by cell walls composed of
chitin, a nitrogen-containing polysaccharide
– The body of almost all fungi is a mycelium, an
interwoven mass of threadlike filaments called
hyphae (singular, hypha)
Edible Chanterelle
Morrel
22.1 What Are the Key Features of Fungi?
 Fungal bodies consist of slender threads
(continued)
– Hyphae of most species are divided into many
cells by partitions called septa (singular,
septum); each cell possesses one or more nuclei
–Fungi cannot move, but grow rapidly in any
direction within a suitable environment
The Filamentous Body of a Fungus
cell wall
cytoplasm
pore
septum
hyphae
(a) Mycelium
(b) Hyphae
(c) Hypha cross-section
Fig. 22-1
22.1 What Are the Key Features of Fungi?
 Fungi obtain their nutrients from other
organisms
– Fungi secrete enzymes outside their bodies and
absorb the digested nutrients
– Fungal decomposers feed on dead organic
material and wastes
– Fungal parasites absorb nutrients from cells of
living hosts and may cause disease
22.1 What Are the Key Features of Fungi?
 Fungi propagate by spores
– Spores are tiny reproductive packages capable
of developing into adult fungi
–They are often produced in large numbers,
and are dispersed by animals or air currents
Some Fungi Can Eject Spores
Fig. 22-3
22.1 What Are the Key Features of Fungi?
 Most fungi can reproduce both asexually and
sexually
– During asexual reproduction:
–For the most part, asexual reproduction
occurs under stable conditions
–A haploid mycelium produces haploid asexual
spores by mitosis
–Spores germinate and develop into a new
mycelium by mitosis
–This results in the rapid production of
genetically identical clones
22.1 What Are the Key Features of Fungi?
 During sexual reproduction:
– Neighboring haploid mycelia of different, but compatible,
mating types come into contact with each other
– The two different hyphae fuse so that the nuclei share a
common cell
– The different haploid nuclei fuse to form a diploid zygote
– The zygote undergoes meiosis to form haploid sexual
spores
– The spores germinate and develop into a new mycelium
by mitosis
– This results in the production of fungal bodies that are
genetically distinct from either parent
Evolutionary Tree of the Major Groups of Fungi
Fig. 22-4
22.2 What Are the Major Groups of Fungi?
 Fungus species are classified into five phyla
– Chytridiomycota (chytrids)
– Zygomycota (zygomycetes)
– Glomeromycota (glomeromycetes)
– Basidiomycota (basidiomycetes)
– Ascomycota (ascomycetes)
Evolutionary Tree of the Major Groups of Fungi
Fig. 22-4
Table 22-1
22.2 What Are the Major Groups of Fungi?
 The chytrids
– Most chytrids are aquatic
–They are distinguished from other fungi by
forming flagellated spores that require water
for dispersal
–They reproduce both asexually and sexually
Chytrid Filaments
flagellum
eyespot
contractile
vacuole
stored food
nucleus
nucleolus
chloroplasts
Fig. 22-5
22.2 What Are the Major Groups of Fungi?
 The chytrids (continued)
– Most feed on dead aquatic material
– Some species are parasites of plants and
animals
–One chytrid species is a frog pathogen
believed to be a major cause of the current
worldwide die-off of frogs
– Primitive chytrids are believed to have given rise
to the other groups of modern fungi
Table 22-1
22.2 What Are the Major Groups of Fungi?
 The zygomycetes
– Most zygomycetes live in soil or on decaying
plant or animal material
–The group includes the black bread mold
Rhizopus
–They reproduce both asexually and sexually
The Life Cycle of a Zygomycete
1 In asexual reproduction, mycelia give rise
to sporangia that produce haploid spores
sporangia
spores
hypha
7 If spores
formed by sexual
or asexual
reproduction land
on a suitable
substrate, they
develop into
hyphae
ASEXUAL
REPRODUCTION
hypha, (–)
mating type
sporangia
hypha, (+)
mating type
hypha
spores
sporangia
6 Haploid spores
disperse from the
sporangia
2 Sexual reproduction
begins when hyphae of
opposite mating types meet
SEXUAL
REPRODUCTION
3 The two hyphae fuse,
forming a zygosporangium
that contains haploid nuclei
from the two parents
5 The diploid nuclei in the
zygosporangium undergo meiosis
and give rise to stalked sporangia
FUSION
OF NUCLEI
4 The haploid nuclei
in the zygosporangium
fuse to form diploid
nuclei
MEIOSIS
haploid (n)
zygosporangium
diploid (2n)
Fig. 22-6
22.2 What Are the Major Groups of Fungi?
 The zygomycetes (continued)
– During asexual reproduction:
–Haploid spores are produced in black spore
cases called sporangia
–The spores disperse through the air and
germinate to form new haploid hyphae
22.2 What Are the Major Groups of Fungi?
 The zygomycetes (continued)
– During sexual reproduction:
– Two hyphae of different mating types come into
contact and fuse to form a zygosporangium that
contains multiple haploid nuclei
– Haploid nuclei fuse within the zygosporangium to form
diploid nuclei
– Diploid nuclei give rise to stalked sporangia that
produce haploid spores that disperse, germinate, and
develop into new haploid hyphae
Evolutionary Tree of the Major Groups of Fungi
Fig. 22-4
22.2 What Are the Major Groups of Fungi?
 The glomeromycetes
– Glomeromycetes live in intimate contact with
the roots of plants
– Their hyphae penetrate root cells and form
microscopic branching structures inside the cell
– The interaction forms a beneficial relationship
called a mycorrhiza
Glomeromycete in a Plant Cell
Fig. 22-7
22.2 What Are the Major Groups of Fungi?
 The glomeromycetes (continued)
– Reproduction in the glomeromycetes:
–Sexual reproduction has not been observed
–During asexual reproduction, clusters of
spores are produced by mitosis and remain
outside the host plant cell at the tips of hyphae
–When the spores germinate, hyphae grow
into the surrounding soil and penetrate new
plant roots
Evolutionary Tree of the Major Groups of Fungi
Fig. 22-4
22.2 What Are the Major Groups of Fungi?
 The basidiomycetes
– The basidiomycetes are called the club fungi because
they produce club-shaped reproductive structures
– These fungi typically reproduce sexually
– During reproduction, two hyphae of different mating
types come into contact and fuse, resulting in the
formation of a fruiting body
– Each fruiting body contains numerous club-shaped
structures called basidia (singular, basidium)
– Nuclei within each basidium fuse, forming a diploid
nucleus
22.2 What Are the Major Groups of Fungi?
 The basidiomycetes (continued)
–The diploid nucleus divides by meiosis
producing four haploid basidiospores
–Basidiomycete fruiting bodies are the familiar
mushrooms, puffballs, shelf fungi, and
stinkhorns
–Basidiospores are released from the fruiting
bodies, and disperse and germinate to form
new haploid hyphae that enter the sexual
cycle
The Life Cycle of a Typical Basidiomycete
2 The fused hyphae grow into a
mycelium in which each cell contains
a haploid nucleus from each parent
1 Sexual reproduction
begins when hyphae of
opposite mating types
meet and fuse
hypha, (–) mating type
hypha, (+) mating type
3 Hyphae from
the mycelium
aggregate to form
a mushroom
7 After dispersal, the
basidiospores germinate
and develop into hyphae
6 The diploid nuclei divide by
meiosis and give rise to haploid
basidiospores that are ejected
4 Reproductive cells
called basidia form on
the mushroom's gills
5 The two haploid nuclei
in each basidium fuse to
form a diploid nucleus
MEIOSIS
FUSION
OF NUCLEI
haploid (n)
diploid (2n)
Fig. 22-8
Diverse Basidiomycetes
Fig. 22-9
A Mushroom Fairy Ring
Fig. 22-10
Evolutionary Tree of the Major Groups of Fungi
Fig. 22-4
22.2 What Are the Major Groups of Fungi?
 The ascomycetes
– The ascomycetes are called sac fungi and
reproduce both asexually and sexually
– During asexual reproduction:
–Haploid spores are produced at the tips of
specialized hyphae
–Spores disperse and germinate to form new
haploid hyphae
22.2 What Are the Major Groups of Fungi?
 The ascomycetes (continued)
– Better known examples include:
–Most food-spoiling molds
–Morels and truffles (edible delicacies)
–Penicillium, the mold that produces penicillin
(the first antibiotic)
–Yeasts (unicellular fungi)
Diverse Ascomycetes
Fig. 22-12
22.3 How Do Fungi Interact with Other Species?
 Symbiotic relationships
– A symbiotic relationship is a close interaction
between organisms of different species over an
extended period of time
– The fungal member of a symbiotic relationship
may be harmful or beneficial
22.3 How Do Fungi Interact with Other Species?
 Lichens are formed by fungi that live with
photosynthetic algae or bacteria
– The fungus provides its photosynthetic partner
with shelter and protection
– The photosynthetic partner in turn provides the
fungus with food (sugar)
22.3 How Do Fungi Interact with Other Species?
 Lichens are formed by fungi that live with
photosynthetic algae or bacteria (continued)
– Lichens grow on a wide variety of materials
(soils, tree trunks and branches, rocks, fences,
roofs, and walls)
– They are able to survive environmental extremes
(newly formed volcanic islands, deserts)
– They are very diverse in form
Diverse Lichens
Fig. 22-14
22.3 How Do Fungi Interact with Other Species?
 Mycorrhizae (singular, mycorrhiza) are symbiotic
associations between fungi and plant roots
– The fungi digest and absorb minerals and organic
nutrients from the soil, passing some of them directly into
the plant root cells
– The plant provides the fungi with energy-rich sugar
molecules produced photosynthetically by the plant
– Plants without mycorrhizal fungi tend to be smaller and
less vigorous than are plants with mycorrhizal partners
Micorrhizae Enhance Plant Growth
Fig. 22-15
22.3 How Do Fungi Interact with Other Species?
 Mycorrhizae may have helped plants invade land
– The relationship between an aquatic fungus and a green
alga could have helped the alga acquire the water and
mineral nutrients it needed to survive out of water
– Fossils formed just after the invasion to land show that
fully developed mycorrhizae were present very early in
the evolution of land plants
– This suggests that a simpler plant-fungus association
might have been present even earlier
22.3 How Do Fungi Interact with Other Species?
 Endophytes are fungi that live inside plant
stems and leaves
– Some are parasites that cause plant diseases
– Some are beneficial to the host plant
–Some ascomycete species live inside grasses
and produce substances that are distasteful or
toxic to insects and grazing mammals,
protecting the grasses from predation
22.3 How Do Fungi Interact with Other Species?
 Some fungi are important decomposers
– Fungi are Earth’s undertakers, feeding on the
dead of all kingdoms
– Fungal saprophytes (which feed on dead
organisms) release extracellular substances that
digest the tissues of the dead and liberate
carbon, nitrogen, and phosphorus compounds,
as well as minerals that can be reused by plants
22.4 How Do Fungi Affect Humans?
 Fungi attack plants that are important to people
– Fungal parasites cause the majority of plant
diseases
–Ascomycete parasites cause Dutch elm
disease and chestnut blight
–Rusts and smuts are basidiomycete parasites
that cause considerable damage to grain
crops
Corn Smut
Fig. 22-16
22.4 How Do Fungi Affect Humans?
 Fungi attack plants that are important to people
(continued)
– Fungi can destroy plant material that has been
harvested for human use
–They cause wooden structures to rot
–Some ascomycete molds secrete enzymes
that damage cotton and wool fabrics
22.4 How Do Fungi Affect Humans?
 Fungi attack plants that are important to people
(continued)
– Some fungi benefit agriculture
–Some fungal parasites are used to control
insect pests such as termites, rice weevils,
tent caterpillars, aphids, citrus mites, and
other pests
– Certain fungi attack mosquitoes, which transmit
malaria
Helpful Fungal Parasites
Fig. 22-17
22.4 How Do Fungi Affect Humans?
 Fungi cause human diseases
– Athlete’s foot, jock itch, and ringworm are caused
by fungi that attack the skin
– Most vaginal infections are caused by the yeast
Candida albicans
– Valley fever and histoplasmosis are caused by
fungi that attack the lungs
–Infection occurs when the victim inhales
spores
The Unusual Yeast (Candida)
Fig. 22-18
22.4 How Do Fungi Affect Humans?
 Fungi can produce toxins
– Molds of the genus Aspergillus produce aflatoxins that
are highly toxic, carcinogenic compounds
– They infect foods such as peanuts
– Claviceps purpurea (an ascomycete) produces several
toxins
– It infects rye plants and causes a disease called ergot
– Symptoms of ergot poisoning include vasoconstriction
of blood vessels, vomiting, convulsive twitching,
hallucinations, and death (Witches in New England?)
22.4 How Do Fungi Affect Humans?
 Many antibiotics are derived from fungi
– Penicillin is produced by an ascomycete mold
–It was the first antibiotic to be discovered and
is used to combat bacterial diseases
– Cyclosporin
–Used to suppress the immune response after
organ transplants
Penicillium
Fig. 22-19
22.4 How Do Fungi Affect Humans?
 Fungi make important contributions to
gastronomy
– Wild and cultivated basidomycete mushrooms,
such as morels and truffles, are highly prized
– Certain ascomycete molds impart flavor to some
of the world’s most famous cheeses
–Roquefort
–Camembert
–Stilton
–Gorgonzola
The Truffle
Fig. 22-20
22.4 How Do Fungi Affect Humans?
 Fungi make important contributions to
gastronomy (continued)
– Yeasts are used in the production of wine, beer,
and bread
– Wine is produced when yeasts ferment fruit
sugars; ethyl alcohol is retained, while CO2 is
released
22.4 How Do Fungi Affect Humans?
 Fungi make important contributions to
gastronomy (continued)
– Beer is derived when yeasts ferment sugars in
germinating grains (usually barley); ethyl alcohol
and CO2 are retained
– Bread rises when yeasts ferment sugar that has
been added to bread dough; both ethyl alcohol
and CO2 escape during baking