31
Fungi
PowerPoint Chapter Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Mighty Mushrooms
Fungi
Are diverse and widespread
Are essential for the well-being of most terrestrial
ecosystems because they break down organic
material and recycle vital nutrients
Figure 31.1
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Concept 31.1: Fungi are heterotrophs that feed
by absorption
Despite their diversity
Fungi share some key traits
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Nutrition and Fungal Lifestyles
Fungi are heterotrophs
But do not ingest their food
Fungi secrete into their surroundings
exoenzymes that break down complex
molecules
And then absorb the remaining smaller
compounds
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Fungi exhibit diverse lifestyles
Decomposers
Parasites
Mutualistic symbionts
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Body Structure
The morphology of multicellular fungi
Enhances their ability to absorb nutrients from
their surroundings
Reproductive structure.
The mushroom produces
tiny cells called spores.
Hyphae. The mushroom and its
subterranean mycelium are a continuous
network of hyphae.
Spore-producing
structures
20 m
Figure 31.2
Mycelium
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Fungi consist of
Mycelia, networks of branched hyphae
adapted for absorption
Most fungi
Have cell walls made of chitin
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Some fungi
Have hyphae divided into cells by septa, with
pores allowing cell-to-cell movement of
materials
Coenocytic fungi
Lack septa
Cell wall
Cell wall
Nuclei
Pore
Septum
Figure 31.3a, b
(a) Septate hypha
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Nuclei
(b) Coenocytic hypha
Some unique fungi
Have specialized hyphae that allow them to
penetrate the tissues of their host
Nematode
Hyphae
25 m
(a) Hyphae adapted for trapping and killing prey
Plant
cell
wall
Fungal hypha
(b) Haustoria
Haustorium
Figure 31.4a, b
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Plant cell
Plant cell
plasma
membrane
Mycorrhizae
Are mutually beneficial relationships between
fungi and plant roots
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Concept 31.2: Fungi produce spores through
sexual or asexual life cycles
Fungi propagate themselves
By producing vast numbers of spores, either
sexually or asexually
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The generalized life cycle of fungi
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
PLASMOGAMY
(fusion of cytoplasm)
Diploid (2n)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Spores
ASEXUAL
REPRODUCTION
SEXUAL
REPRODUCTION
Zygote
Mycelium
MEIOSIS
GERMINATION
GERMINATION
Spore-producing
structures
Figure 31.5
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Spores
Sexual Reproduction
The sexual life cycle involves
Cell fusion, plasmogamy
Nuclear fusion, karyogamy
An intervening heterokaryotic stage
Occurs between plasmogamy and karyogamy
in which cells have haploid nuclei from two
parents
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The diploid phase following karyogamy
Is short-lived and undergoes meiosis,
producing haploid spores
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Asexual Reproduction
Many fungi can reproduce asexually
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Many fungi that can reproduce asexually
Grow as mold, sometimes on fruit, bread, and
other foods
2.5 m
Figure 31.6
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Other asexual fungi are yeasts
That inhabit moist environments
Which produce by simple cell division
10 m
Parent cell
Bud
Figure 31.7
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Many molds and yeasts have no known sexual
stage
Mycologists have traditionally called these
deuteromycetes, or imperfect fungi
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Concept 31.3: Fungi descended from an
aquatic, single-celled, flagellated protist
Systematists now recognize Fungi and
Animalia as sister kingdoms
Because fungi and animals are more closely
related to each other than they are to plants or
other eukaryotes
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The Origin of Fungi
Molecular evidence
Supports the hypothesis that fungi and animals
diverged from a common ancestor that was
unicellular and bore flagella
Fungi probably evolved
Before the colonization of land by multicellular
organisms
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The oldest undisputed fossils of fungi
Are only about 460 million years old
Figure 31.8
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50 m
The Move to Land
Fungi were among the earliest colonizers of
land
Probably as symbionts with early land plants
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Concept 31.4: Fungi have radiated into a
diverse set of lineages
The phylogeny of fungi
Is currently the subject of much research
Molecular analysis
Has helped clarify the evolutionary
relationships between fungal groups, although
there are still areas of uncertainty
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Arbuscular
mycorrhizal
fungi
Sac
fungi
Club
fungi
Ascomycota
Basidiomycota
Zygomycota
Chytridiomycota
Zygote
fungi
Chytrids
Glomeromycota
The phylogeny of fungi
Figure 31.9
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A review of fungal phyla
Table 31.1
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Chytrids
Fungi classified in the phylum Chytridiomycota,
or chytrids
Are found in freshwater and terrestrial habitats
Can be saprobic or parasitic
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Chytrids are unique among fungi
In having flagellated spores, called zoospores
Hyphae
25 m
Flagellum
4 m
Figure 31.10
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Until recently, systematists thought that
Fungi lost flagella only once in their history
Molecular data
Indicate that some chytrids are actually more
closely related to another fungal group, the
zygomycetes
Glomeromycetes,
Zygomycetes and other chytrids
Some
ascomycetes, and
basidiomycetes
chytrids
Key
Figure
31.11
Common ancestor
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Loss of
flagella
Zygomycetes
Fungi in the phylum Zygomycota, the
zygomycetes
Exhibit a considerable diversity of life histories
Include fast-growing molds, parasites, and
commensal symbionts
Are named for their sexually produced
zygosporangia
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The life cycle of Rhizopus stolonifer
Is fairly typical of zygomycetes
M ycelia have
1
various mating types
2
Neighboring mycelia of different
Key
(here designated +,
mating types form hyphal extensions
with red nuclei, and ,
called gametangia, each walled off
with blue nuclei).
around several haploid nuclei by a septum.
Haploid (n)
Heterokaryotic (n + n)
Diploid
A heterokaryotic
3
zygosporangium
forms, containing
multiple haploid
nuclei from the two
PLASMOGAMY
Rhizopus
Mating
growing
t ype (+)
on bread
parents.
Gametangia with
Mating
haploid nuclei
t ype ()
100 m
Mycelia can also reproduce
asexually by forming sporangia
grow into new
t hat produce genetically identical haploid spores.
9
The spores
8
germinate and
mycelia.
Young
zygosporangium
(heterokaryotic)
SEXUAL
REPRODUCTION
Dispersal and
Sporangia
germination
7
The sporangium
Zygosporangium
KARYOGAMY
disperses genetically
(heterokaryotic)
diverse, haploid spores.
Diploid
Sporangium
ASEXUAL
nuclei
MEIOSIS
REPRODUCTION
This cell develops a
4
rough, thick-walled
coating that can resist
dry environments and
Dispersal and
other harsh conditions
germination
50 m
for months.
Mycelium
5
When conditions are favourable,
karyogamy occurs, followed by
Figure 31.12
The zygosporangium
6
t hen breaks dormancy,
germinating into a
short sporangium.
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meiosis.
Some zygomycetes, such as Pilobolus
Can actually aim their sporangia toward
conditions associated with good food sources
Figure 31.13
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Cummings
0.5 Zygosporangia, which are resistant to freezing
and drying
Are capable of persisting through unfavorable
conditions
Can undergo meiosis when conditions improve
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Microsporidia
Microsporidia
Are unicellular parasites of animals and
protists
10 m
Are now classified as zygomycetes
Host cell
nucleus
Developing
microsporidian
Spore
Figure 31.14
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Glomeromycetes
Fungi assigned to the phylum Glomeromycota
Were once considered zygomycetes
Are now classified in a separate clade
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All glomeromycetes
Form a distinct type of endomycorrhizae called
arbuscular mycorrhizae
2.5 m
Figure 31.15
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Ascomycetes
Fungi in the phylum Ascomycota
Are found in a variety of marine, freshwater,
and terrestrial habitats
Are defined by the production of sexual spores
in saclike asci, which are usually contained in
fruiting bodies called ascocarps
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Ascomycetes
Vary in size and complexity from unicellular
yeasts to elaborate cup fungi and morels
(a) The cup-shaped ascocarps (fruiting bodies)
of Aleuria aurantia give this species its
common name: orange peel fungus.
(b) The edible ascocarp of
Morchella esculenta, the
succulent morel, is often
found under trees in orchards.
10 m
Figure 31.16ad
(c) Tuber melanosporum is a truffle, an ascocarp that grows
underground and emits strong odors. These ascocarps
have been dug up and the middle one sliced open.
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(d) Neurospora crassa feeds as
a mold on bread and other
food (SEM).
Ascomycetes reproduce
Asexually by producing enormous numbers of
asexual spores called conidia
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The life cycle of Neurospora crassa, an
ascomycete
7 Ascomycete mycelia
can also reproduce
asexually by producing
haploid conidia.
Conidia;
mating type ()
Key
1 Neurospora can reproduce
sexually by producing specialized
hyphae. Conidia of the opposite
mating type fuse to these hyphae.
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
Dispersal
Germination
ASEXUAL
REPRODUCTION
Mating
type (+ )
Mycelium
PLASMOGAMY
Ascogonium
Mycelia
Conidiophore
2 A dikaryotic
ascus develops.
Ascus
(dikaryotic)
Dikaryotic
hyphae
SEXUAL
REPRODUCTION
Germination
Dispersal
6 The developing asci
are contained in an
ascocarp. The ascospores
are discharged forcibly
from the asci through an
opening in the ascocarp.
Germinating ascospores
give rise to new mycelia.
Asci
KARYOGAMY
Diploid nucleus
(zygote)
Eight
ascospores
Four
haploid
nuclei
3 Karyogamy
occurs within the
ascus, producing a
diploid nucleus.
MEIOSIS
Ascocarp
Figure 31.17
5 Each haploid nucleus divides
once by mitosis, yielding eight
nuclei. Cell walls develop around
the nuclei, forming ascospores (LM).
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4 The diploid nucleus
divides by meiosis, yielding
four haploid nuclei.
Basidiomycetes
Fungi in the phylum Basidiomycota
Include mushrooms and shelf fungi
Are defined by a clublike structure called a
basidium, a transient diploid stage in the life
cycle
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Basidiomycetes
(b) Maiden veil fungus (Dictyphora),
a fungus with an odor like rotting
meat
(a) Fly agaric (Amanita muscaria), a
common species in conifer forests in
the northern hemisphere
(d) Puffballs emitting spores
Figure 31.18ad
(c) Shelf fungi, important decomposers of
wood
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The life cycle of a basidiomycete
Usually includes a long-lived dikaryotic
mycelium, which can erect its fruiting structure,
a mushroom, in just a few hours
Figure 31.19
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The life cycle of a mushroom-forming
basidiomycete
2 A dikaryotic mycelium forms,
growing faster then, and ultimately
crowding out, the haploid parental mycelia.
1 Two haploid mycelia
of different mating types
undergo plasmogamy.
8 In a suitable
environment, the
basidiospores
germinate and
grow into
short-lived
haploid mycelia.
3 Environmental
cues such as rain or
temperature changes
induce the dikaryotic
mycelium to form
compact masses that
develop into
basidiocarps
(mushrooms, in this
case).
Dikaryotic
mycelium
PLASMOGAMY
Mating
type ()
Mating
type (+ )
Haploid
mycelia
SEXUAL
REPRODUCTION
Gills lined
with basidia
Basidiocarp
(dikaryotic)
Dispersal
and
germination
7 When mature,
the basidiospores
are ejected, fall
from the cap, and
are dispersed by
the wind.
Basidiospores
Basidia
(dikaryotic)
Basidium with
four appendages
Basidium containing
four haploid nuclei
Basidium
4 The basidiocarp
gills are lined with
terminal dikaryotic
cells called basidia.
KARYOGAMY
MEIOSIS
Figure 31.20
1 m
Basidiospore
6 Each diploid nucleus
yields four haploid
nuclei. Each basidium
grows four appendages,
and one haploid nucleus
enters each appendage
and develops into a
basidiospore (SEM).
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Diploid
nuclei
Key
5 Karyogamy in the
basidia produces diploid
nuclei, which then
undergo meiosis.
Haploid (n)
Dikaryotic (n + n)
Diploid (2n)
Concept 31.5: Fungi have a powerful impact on
ecosystems and human welfare
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Decomposers
Fungi are well adapted as decomposers of
organic material
Performing essential recycling of chemical
elements between the living and nonliving
world
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Symbionts
Fungi form symbiotic relationships with
Plants, algae, and animals
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Mycorrhizae
Mycorrhizae
Are enormously important in natural
ecosystems and agriculture
Increase plant productivity
EXPERIMENT Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to
prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed
mycorrhizae in the soybean plants roots.
RESULTS
The soybean plant on the left is typical of the experimental group. Its
RESULTS
stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on
the right is typical of the control group and has mycorrhizae.
Figure 31.21
CONCLUSION
These results indicate that the presence of mycorrhizae benefits a
soybean plant and support the hypothesis that mycorrhizae enhance the plants ability to take
up phosphate and other needed minerals.
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Fungus-Animal Symbiosis
Some fungi share their digestive services with
animals
Helping break down plant material in the guts
of cows and other grazing mammals
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Many species of ants and termites
Take advantage of the digestive power of fungi
by raising them in farms
Figure 31.22
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Lichens
Lichens
Are a symbiotic association of millions of
photosynthetic microorganisms held in a mass
of fungal hyphae
(a) A fruticose (shrub-like) lichen
Figure 31.23ac
(b) A foliose (leaf-like) lichen
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(c) Crustose (crust-like) lichens
The fungal component of a lichen
Is most often an ascomycete
Algae or cyanobacteria
Occupy an inner layer below the lichen surface
Ascocarp of fungus
Soredia
Fungal
hyphae
Algal
layer
Algal cell
Figure 31.24
1 0 m
Fungal hyphae
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Pathogens
About 30% of known fungal species
Are parasites, mostly on or in plants
Figure 31.25ac
(a) Corn smut on corn
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(b) Tar spot fungus on maple leaves
(c) Ergots on rye
Some of the fungi that attack food crops
Are toxic to humans
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Practical Uses of Fungi
Humans eat many fungi
And use others to make cheeses, alcoholic
beverages, and bread
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Antibiotics produced by fungi
Treat bacterial infections
Staphylococcus
Penicillium
Zone of
inhibited
growth
Figure 31.26
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Genetic research on fungi
Is leading to applications in biotechnology
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