Chapter 31

Fungi

PowerPoint® Lecture
Presentations for

Biology
Eighth Edition
Neil Campbell and Jane
Reece
Lectures by Chris Romero, updated by Erin Barley with
contributions from Joan Sharp
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Overview: Mighty Mushrooms

Fungi are diverse and widespread.

They are essential for the well-being of most
terrestrial ecosystems because they break down
organic material and recycle vital nutrients.
Fungi are heterotrophs and absorb nutrients from
outside of their body.
Fungi use enzymes to break down a large variety
of complex molecules into smaller organic
compounds.
The versatility of these enzymes contributes to
fungi’s ecological success.

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 The most common body structures are
multicellular filaments and single cells
(yeasts).
Some species grow as either filaments or
yeasts; others grow as both.
Fungi exhibit diverse lifestyles:
Decomposers / saphrophytes
Parasites + -
Mutualists + +

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Fungal Morphology : hyphae

The morphology of multicellular fungi

enhances their ability to absorb nutrients.
Fungi consist of mycelia, networks of
branched hyphae adapted for absorption.
Most fungi have cell walls made of chitin.

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Multicellular Fungus:
hyphae …
Reproductive
structure

Hyph
ae

Spore-
producing
structures

20
µm

Myceli
um
 Septate fungi - Some fungi have
hyphae divided into cells by septa, with
pores allowing cell-to-cell movement of
organelles.
Coenocytic fungi lack septa.
Some unique fungi have specialized
hyphae called haustoria that allow
them to penetrate the tissues of their
host.

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 Two forms of hyphae

Cell
Nucle wall Cell
i wall
Po
re
Septu Nucle
m i

(a) Septate (b) Coenocytic

hypha hypha
Specialized Hyphae in Mycorrhizal Fungi + +

Mycorrhizae + + are mutually

beneficial symbiotic relationships
between fungi and plant roots.
Ectomycorrhizal fungi form sheaths of
hyphae over a root and also grow into
the extracellular spaces of the root
cortex.
Arbuscular mycorrhizal fungi extend
hyphae through the cell walls of root
cells and into tubes formed by
invagination of the root cell membrane.

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Fungus -
have Nemato
Hyphae
25
specialized de µm

hyphae

Hyphae adapted for trapping and killing

(a)
prey
Pl
Fungal an
hypha t
ce
ll
w
all

Plant
cell
Plant
cell
Haustori plasm
um a
(b) Haustoria - penetrate
memb cell walls of plants ++
rane
Fungi produce spores through sexual
or asexual life cycles
Fungi propagate themselves by
producing vast numbers of spores, either
sexually or asexually.
Fungal nuclei are normally haploid.
Sexual reproduction requires the fusion
of hyphae from different mating types.
Fungi use sexual signaling molecules
called pheromones to communicate
their mating type.

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 Life Cycle of Fungi
Key

Haploid Heterokaryo
(n)
Heterokaryotic tic
(unfused nuclei stage
PLASMOGAMY
from (fusion of
different
Diploid cytoplasm)
parents)
(2n) KARYOGAMY
Spore- (fusion of
producing nuclei)
structures Zyg
SEXUAL ote
Spor 2n
es REPRODUCTI
ASEXUAL Myceli
um ON
REPRODUCTI
ON

MEIOS
GERMINATIO IS
GERMINATIO
N
N

Spor
es
 Plasmogamy is the union of two parent
hyphae, mycelia.
In most fungi, the haploid nuclei from each
parent do not fuse right away; they coexist in
the hyphae, this mycelium is called a
heterokaryon.
In some fungi, the haploid nuclei pair off two to
a cell; such a mycelium is dikaryotic.
During karyogamy, the haploid nuclei fuse,
producing diploid cells: n + n = 2n.

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 Hours, days, or even centuries may pass
before the occurrence of karyogamy,
nuclear fusion.
The diploid phase is short-lived and
undergoes meiosis, producing haploid
spores.

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Asexual Reproduction

In addition to sexual reproduction, many

fungi can reproduce asexually.
Molds produce haploid spores by mitosis
and form visible mycelia.
Other fungi that can reproduce asexually
are yeasts, which inhabit moist
environments.
Instead of producing spores, yeasts
reproduce asexually by budding: simple
cell division and pinching of “bud cells”
from a parent cell.
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Penicillium: a mold that decomposes food.
Mold produce spores asexually
by mitosis.

2.5
µm
The yeast Saccharomyces cerevisiae in several
stages of asexual reproduction by budding.
10
µm

Pare
nt
cell

B
ud
Concept 31.3: The ancestor of fungi was an
aquatic, single-celled, flagellated protist

Fungi and animals are more closely related to

each other than they are to plants or other
eukaryotes.
DNA evidence suggests that fungi are most
closely related to unicellular nucleariids while
animals are most closely related to unicellular
choanoflagellates.
This suggests that fungi and animals evolved
from a common flagellated unicellular ancestor
and multicellularity arose separately in the two
groups.
The oldest undisputed fossils of fungi are only
about 460 million years old.
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 Fungi and their close relatives

Animals (and their

close
protistan relatives)
UNICELLUL O
AR, Nuclearii
ds p
FLAGELLAT i
ED s
ANCESTOR Chytrids t
h
F o
u k
n Other
fungi o
g n
i t
s
The Move to Land

Fungi were among the earliest colonizers

of land and probably formed mutualistic
++ relationships with early land plants.
Chytrids (phylum Chytridiomycota) are
found in freshwater and terrestrial
habitats.
They can be decomposers, parasites, or
mutualists.
Chytrids are unique among fungi in
having flagellated spores, called
zoospores.
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Fungus Hyp 25
Diversity Chytrids (1,000
hae µ
m
species)

Zygomycetes (1,000
species)

Fungal
hypha
Glomeromycetes (160
species)

Ascomycetes (65,000
species)

Basidiomycetes (30,000
species)
Zygomycetes

The zygomycetes (phylum

Zygomycota) exhibit great diversity of
life histories.
They include fast-growing molds,
parasites, and commensal symbionts.
The zygomycetes are named for their
sexually produced zygosporangia.
Zygosporangia, which are resistant to
freezing and drying, can survive
unfavorable conditions.
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 Life Cycle of the zygomycete
K
Rhizopus black bread mold e
Haploid
y
(n)
Heterokaryotic
(n + n)
Diploid
(2n)

PLASMOGA
MY
Mati Gametangia
ng Mati with
type ng haploid
(+) type nuclei 100
(–) Young µm
zygosporang
Rhizop ium
us (heterokaryo
SEXUAL tic)
growin REPRODUCTI
g
on ON
bread Dispersal Zygosporangi
and KARYOGAMY um
Sporan germinati
gia on Spo
res
Sporangiu Dipl
m oid
ASEXUAL nucl
MEIO
REPRODUCT SIS ei
ION
Dispersal
and
germinati
50 Myceliu
on
µm m
Some zygomycetes, such as Pilobolus, can actually “aim” their
sporangia toward conditions associated with good food sources.

0.5
mm
Ascomycetes

Ascomycetes (phylum Ascomycota) live in

marine, freshwater, and terrestrial habitats.
The phylum is defined by production of
sexual spores in saclike asci, usually
contained in fruiting bodies called
ascocarps.
Ascomycetes are commonly called sac
fungi.
Ascomycetes vary in size and complexity
from unicellular yeasts to elaborate cup
fungi and morels.
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 Ascomycetes - sac fungi

Morchella
esculenta,
the tasty morel

Tuber melanosporum, a
truffle
 Ascomycetes include plant pathogens,
decomposers, and symbionts
Ascomycetes reproduce asexually by
enormous numbers of asexual spores
called conidia.
Conidia are not formed inside sporangia;
they are produced asexually at the tips
of specialized hyphae called
conidiophores.
Neurospora is a model organism with a
well-studied genome.
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 Conidia;
mating
Haploid spores type (–) K
(conidia) e
Haploi
dy(n)
Dikaryotic (n
+ n)
Diploid
Dispersal Germinati Matin (2n)
on g
ASEXUA
Hyp type PLASMOG
L (+) AMY
REPRODUCT ha
ION
Ascus
Conidioph (dikaryo
ore tic)
Myce Dikary
Myceli lia otic
um hypha
Germinati SEXUAL e
on REPRODUCTI KARYOGA
MY
Dispersal
ON
Diploid
As Eight nucleus
Ascoc ci ascospo (zygote)
arp res

Four
hapl
oid MEIO
nucl SIS
ei

The life cycle of

Neurospora, an
ascomycete
Basidiomycetes

Basidomycetes (phylum Basidiomycota)

include mushrooms, puffballs, and shelf
fungi, mutualists, and plant parasites.
The phylum is defined by a clublike
structure called a basidium, a transient
diploid stage in the life cycle.
The basidiomycetes are also called club
fungi.

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 Maiden veil
fungus
(Dictyphora),
a
fungus with
an
Basidiomyce odor like
rotting
tes club meat

fungi

Puffballs
emitting
spores

Shelf fungi,
important
decomposers of
wood
Concept 31.5: Fungi play key roles in nutrient
cycling, ecological interactions, and human welfare

Fungi interact with other organisms in

many ways.
Fungi are efficient decomposers. They
perform essential recycling of chemical
elements between the living and
nonliving world.
Fungi form mutualistic relationships
with plants, algae, cyanobacteria, and
animals.
All of these relationships have profound
ecological effects.
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Fungus-Plant Mutualisms + +

Mycorrhizae live ++ symbiotically in

plant roots and are enormously important
in natural ecosystems and agriculture.
Plants harbor harmless symbiotic
endophytes that live inside leaves or
other plant parts ++
Endophytes make toxins that deter
herbivores and defend against pathogens.

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 Do endophytes benefit a woody plant?

RESULT
S
Endophyte not present; pathogen
present
Both (E–P+) and pathogen
endophyte
present (E+P+)
3 1
0 5

2 1
0 0

1 5
0
L 0 0
e L
a E– E+ E– E+
P+ P+ e P+ P+
f a
m f
Fungus-Animal Symbioses

Some fungi share their digestive services

with animals.
These fungi help break down plant
material in the guts of cows and other
grazing mammals.
Many species of ants and termites use
the digestive power of fungi by raising
them in “farms.”

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Fungus-gardening insects: Leaf-cutting ants depend on fungus to
digest plant material to a form the insects can use for their nutrition + +.
Lichens

A lichen is a ++ symbiotic association

between a photosynthetic microorganism
and a fungus in which millions of
photosynthetic cells are held in a mass of
fungal hyphae.
The fungal component of a lichen is most
often an ascomycete.
Algae or cyanobacteria occupy an inner
layer below the lichen surface.

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Variety of lichens + +

Crustos
e
A fruticose (shrublike) (encrusti
lichen ng)
lichens

A
foliose
(leaflik
e)
lichen
Anatomy of a common fungal ascomycete lichen

Ascocarp of
fungus Fung Sore
al dia
Alg
hyph al
ae lay
er

Algal
cell
Fungal
hyphae
2
0

µ
m
 Lichen ++

The algae provide carbon compounds,

cyanobacteria provide organic nitrogen, and
fungi provide the environment for growth.
The fungi of lichens can reproduce sexually and
asexually. Asexual reproduction is by
fragmentation or the formation of soredia,
small clusters of hyphae with embedded algae.
Lichens are important pioneers on new rock
and soil surfaces -- pioneer organisms in
ecological succession.
Lichens are sensitive to pollution, and their
death can be a warning that air quality is
deteriorating.

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Fungi as Pathogens + -

About 30% of known fungal species are

parasites or pathogens, mostly on or in
plants.
Some fungi that attack food crops are
toxic to humans.
Animals are much less susceptible to
parasitic fungi than are plants.
The general term for a fungal infection in
animals is mycosis.

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 Fungal Diseases in Plants

(a) Corn smut on (b) Tar spot (c) Ergots on

corn fungus on rye
maple leaves
Practical Uses of Fungi

Food: Humans eat many fungi and use

others to make cheeses, alcoholic
beverages, and bread.
Some fungi are used to produce
antibiotics for the treatment of bacterial
infections, for example the ascomycete
Penicillium.
Genetic research on fungi is leading to
applications in biotechnology:
For example, insulin-like growth factor can be produced in the
fungus Saccharomyces cerevisiae.

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Penicillium: Fungal production of an Antibiotic The mold
penicillium produces an antibiotic that inhibits bacteria growth
resulting in a clear area between the mold and the bacteria

Staphylococ Penicilli
cus um
Zone
of
inhibit
ed
growth
Review
You should now be able to:

1. List the characteristics that distinguish

fungi from other multicellular kingdoms.
2. Discuss mycorrhizal fungi.
3. Describe the processes of plasmogamy
and karyogamy.
4. Describe the evidence that
multicellularity evolved independently in
fungi and animals.

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1. Describe the life cycles of Rhizopus
stolonifer and Neurospora crassa.
2. Distinguish among zygomycetes,
ascomycetes, and basidiomycetes.
3. Describe some of the roles of fungi in
ecosystems, lichens, animal-fungi
mutualistic symbioses, food production,
and medicine and as pathogens.

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