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Biology 102 Week 4
Plant Diversity II: The
Evolution of Seed Plants
Fungi
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Feeding the World
• Seeds changed the course of plant evolution,
enabling their bearers to become the dominant
producers in most terrestrial ecosystems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 30.1: The reduced gametophytes of seed
plants are protected in ovules and pollen grains
• In addition to seeds, the following are common to
all seed plants:
– Reduced gametophytes
– Heterospory
– Ovules
– Pollen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Advantages of Reduced Gametophytes
• The gametophytes of seed plants develop within
the walls of spores retained within tissues of the
parent sporophyte
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-2
Sporophyte
(2n)
Sporophyte
(2n)
Gametophyte
(n)
Sporophyte dependent on
gametophyte (mosses
and other bryophytes)
Microscopic female
gametophytes (n) in
ovulate cones
(dependent)
Gametophyte
(n)
Large sporophyte and
small, independent gametophyte (ferns and other
seedless vascular plants)
Sporophyte (2n),
the flowering plant
(independent)
Microscopic male
gametophytes (n) in
inside these parts
of flowers
(dependent)
Microscopic male
gametophytes (n)
in pollen cones
(dependent)
Sporophyte (2n),
(independent)
Microscopic female
gametophytes (n) in
inside these parts
of flowers
(dependent)
Reduced gametophyte dependent on sporophyte (seed
plants: gymnosperms and angiosperms)
Heterospory: The Rule Among Seed Plants
• Seed plants evolved from plants with
megasporangia, which produce megaspores that
give rise to female gametophytes
• Seed plants evolved from plants with
microsporangia, which produce microspores that
give rise to male gametophytes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ovules and Production of Eggs
• An ovule consists of a megasporangium,
megaspore, and one or more protective
integuments
• Gymnosperm megaspores have one integument
• Angiosperm megaspores usually have two
integuments
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-3
Integument
Female
gametophyte (n)
Seed coat
(derived from
integument)
Spore wall
Egg nucleus (n)
Megasporangium
(2n)
Megaspore (n)
Unfertilized ovule
Male gametophyte
(within germinating
pollen grain) (n)
Micropyle
Fertilized ovule
Discharged
sperm nucleus (n)
Pollen grain (n)
Food supply
(female
gametophyte
tissue) (n)
Embryo (2n)
(new sporophyte)
Gymnosperm seed
Pollen and Production of Sperm
• Microspores develop into pollen grains, which
contain the male gametophytes
• Pollination is the transfer of pollen to the part of a
seed plant containing the ovules
• Pollen can be dispersed by air or animals,
eliminating the water requirement for fertilization
• If a pollen grain germinates, it gives rise to a
pollen tube that discharges two sperm into the
female gametophyte within the ovule
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Evolutionary Advantage of Seeds
• A seed develops from the whole ovule
• A seed is a sporophyte embryo, along with its food
supply, packaged in a protective coat
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 30.2: Gymnosperms bear “naked” seeds,
typically on cones
• The gymnosperms include four phyla:
– Cycadophyta (cycads)
– Gingkophyta (one living species: Ginkgo
biloba)
– Gnetophyta (three genera: Gnetum, Ephedra,
Welwitschia)
– Coniferophyta (conifers, such as pine, fir, and
redwood)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-4aa
Cycas revoluta
LE 30-4ab
LE 30-4ac
LE 30-4ad
Gnetum. This genus
includes about 35
species of tropical
trees, shrubs, and
vines, mainly native
to Africa and Asia.
Their leaves look
similar to those of
flowering plants,
and their seeds look
somewhat like fruits.
LE 30-4ae
Ephedra. This genus includes about 40 species that inhabit arid
regions throughout the world. Known in North America as
“Mormon tea,” these desert shrubs produce the compound
ephedrine, commonly used as a decongestant.
LE 30-4af
Welwitschia. This genus
consists of one species
Welwitschia mirabilis, a
plant that lives only in the
deserts of southwestern
Africa. Its strap like
leaves are among the
largest known.
LE 30-4ag
Ovulate
cones
LE 30-4ba
Douglas fir. “Doug fir”
(Pseudotsuga menziesii)
provides more timber
than any other North
American tree species.
Some uses include
house framing, plywood,
pulpwood for paper,
railroad ties, and boxes
and crates.
LE 30-4bb
Pacific yew. The
bark of Pacific yew
(Taxa brevifolia) is a
source of taxol, a
compound used to
treat women with
ovarian cancer. The
leaves of a
European yew
species produce a
similar compound,
which can be
harvested without
destroying the plants. Pharmaceutical companies are now refining
techniques for synthesizing drugs with taxol-like properties.
LE 30-4bc
Bristlecone pine.
This species (Pinus
longaeva), which is
found in the White
Mountains of
California, includes
some of the oldest
living organisms,
reaching ages of
more than 4,600
years. One tree (not
shown here) is
called Methuselah
because it may be
the world’s oldest
living tree. In order
to protect the tree,
scientists keep its
location a secret.
LE 30-4bd
Sequoia. This giant
sequoia (Sequoiadendron
giganteum), in California’s
Sequoia National Park
weighs about 2,500 metric
tons, equivalent to about
24 blue whales (the
largest animals), or 40,000
people. Giant sequoias
are the largest living
organisms and also some
of the most ancient, with
some estimated to be
between 1,800 and 2,700
years old. Their cousins,
the coast redwoods
(Sequoia sempervirens),
grow to heights of more
than 110 meters (taller
than the Statue of Liberty)
and are found only in a
narrow coastal strip of
northern California.
LE 30-4be
Common juniper.
The “berries” of
the common
juniper (Juniperus
communis), are
actually ovuleproducing cones
consisting of
fleshy sporophylls.
LE 30-4bf
Wollemia pine. Survivors of a confer group
once known only from fossils, living Wollemia
pines (Wollemia nobilis), were discovered in
1994 in a national park
only 150 kilometers
from Sydney, Australia.
The species consists of
just 40 known
individuals two small
groves. The inset photo
compares the leaves of
this “living fossil” with
actual fossils.
Gymnosperm Evolution
• Fossil evidence reveals that by the late Devonian
period some plants, called progymnosperms, had
begun to acquire some adaptations that
characterize seed plants
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Gymnosperms appear early in the fossil record
and dominated the Mesozoic terrestrial
ecosystems
• Living seed plants can be divided into two clades:
gymnosperms and angiosperms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
A Closer Look at the Life Cycle of a Pine
• Key features of the gymnosperm life cycle:
– Dominance of the sporophyte generation
– Development of seeds from fertilized ovules
– The transfer of sperm to ovules by pollen
• The life cycle of a pine is an example
Animation: Pine Life Cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-6_3
Key
Haploid (n)
Diploid (2n)
Ovule
Ovulate
cone
Pollen
cone
Megasporocyte (2n)
Integument
Longitudinal
Micropyle
section of
ovulate cone
Megasporangium
Mature
sporophyte
(2n)
Microsporocytes
(2n)
MEIOSIS
Longitudinal
section of
pollen cone
Sporophyll
Microsporangium
Germinating
Pollen pollen grain
grains (n)
MEIOSIS
(containing male
gametophytes)
Surviving
megaspore (n)
Seedling
Germinating
pollen grain
Archegonium
Egg (n)
Seeds on surface
of ovulate scale
Female
gametophyte
Germinating
pollen grain (n)
Food reserves Seed coat
(gametophyte (derived from
Discharged
tissue) (n)
sperm nucleus (n)
parent
sporophyte) (2n)
Pollen
tube
Embryo
(new sporophyte)
(2n)
FERTILIZATION
Egg nucleus (n)
Integument
Concept 30.3: The reproductive adaptations of
angiosperms include flowers and fruits
• Angiosperms are flowering plants
• These seed plants have reproductive structures
called flowers and fruits
• They are the most widespread and diverse of all
plants
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Characteristics of Angiosperms
• All angiosperms are classified in a single phylum,
Anthophyta
• The name comes from the Greek anthos, flower
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Flowers
• The flower is an angiosperm structure specialized
for sexual reproduction
• A flower is a specialized shoot with up to four
types of modified leaves:
– Sepals, which enclose the flower
– Petals, which are brightly colored and attract
pollinators
– Stamens, which produce pollen
– Carpels, which produce ovules
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-7
Stigma
Stamen
Anther
Carpel
Style
Filament
Ovary
Petal
Sepal
Ovule
Receptacle
Video: Flower Blooming (time lapse)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fruits
• A fruit typically consists of a mature ovary but can
also include other flower parts
• Fruits protect seeds and aid in their dispersal
• Mature fruits can be either fleshy or dry
Animation: Fruit Development
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-8
Tomato, a fleshy fruit with soft
outer and inner layers of pericarp
Ruby grapefruit, a fleshy fruit
with a hard outer layer and soft
inner layer of pericarp
Nectarine, a fleshy
fruit with a soft outer
layer and hard inner
layer (pit) of pericarp
Milkweed, a dry fruit that splits
open at maturity
Walnut, a dry fruit that remains
closed at maturity
• Various fruit adaptations help disperse seeds
• Seeds can be carried by wind, water, or animals to
new locations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-9
Wings enable maple
fruits to be easily
carried by the wind.
Seeds within berries
and other edible fruits
are often dispersed in
animal feces.
The barbs of cockleburs
facilitate seed dispersal
by allowing these fruits to
hitchhike on animals.
The Angiosperm Life Cycle
• In the angiosperm life cycle, double fertilization
occurs when a pollen tube discharges two sperm
into the female gametophyte within an ovule
• One sperm fertilizes the egg, while the other
combines with two nuclei in the central cell of the
female gametophyte and initiates development of
food-storing endosperm
• The endosperm nourishes the developing embryo
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-10a
Key
Haploid (n)
Diploid (2n)
Microsporangium
Microsporocytes (2n)
Anther
Mature flower on
Sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Ovule with
megasporangium (2n) Male
gametophyte
(in pollen
grain)
Ovary
MEIOSIS
Megasporangium
(n)
Surviving
megaspore
(n)
Female gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
Synergids
Eggs (n)
Pollen
tube
Sperm
(n)
Generative cell
Tube cell
LE 30-10b
Key
Haploid (n)
Diploid (2n)
Microsporangium
Microsporocytes (2n)
Anther
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Ovule with
megasporangium (2n) Male
gametophyte
(in pollen
grain)
Ovary
Generative cell
Pollen
grains
MEIOSIS
Stigma
Pollen
Megasporangium tube
(n)
Sperm
Surviving
megaspore
(n)
Pollen
tube
Style
Antipodal cells
Female gametophyte
Polar nuclei
(embryo sac)
Synergids
Eggs (n)
Pollen
tube
Sperm
(n)
Eggs
nucleus (n)
Discharged
sperm nuclei (n)
Tube cell
LE 30-10c
Key
Haploid (n)
Diploid (2n)
Microsporangium
Microsporocytes (2n)
Anther
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore (n)
Ovule with
megasporangium (2n) Male
gametophyte
(in pollen
grain)
Ovary
Germinating
seed
Generative cell
Pollen
grains
MEIOSIS
Stigma
Pollen
Megasporangium tube
(n)
Sperm
Surviving
megaspore
(n)
Embryo (2n)
Endosperm
(food
supply) (3n)
Seed
Pollen
tube
Seed coat (2n)
Style
Antipodal cells
Female gametophyte
Polar nuclei
(embryo sac)
Synergids
Eggs (n)
Pollen
tube
Sperm
(n)
Zygote (2n)
Nucleus of
developing
endosperm
(3n)
Eggs
nucleus (n)
FERTILIZATION
Discharged
sperm nuclei (n)
Tube cell
Animation: Plant Fertilization
Animation: Seed Development
Video: Flowering Plant Life Cycle (time lapse)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Angiosperm Evolution
• Clarifying the origin and diversification of
angiosperms poses fascinating challenges to
evolutionary biologists
• Angiosperms originated at least 140 million years
ago
• During the late Mesozoic, the major branches of
the clade diverged from their common ancestor
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fossil Angiosperms
• Primitive fossils of 125-million-year-old
angiosperms display derived and primitive traits
• Archaefructus sinensis, for example, has anthers
and seeds but lacks petals and sepals
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-11
Carpel
Stamen
5 cm
Archaefructus sinensis, a
125-million-year-old fossil
Artist’s reconstruction of
Archaefructus sinensis
An “Evo-Devo” Hypothesis of Flower Origins
• Scientist Michael Frohlich hypothesized how
pollen-producing and ovule-producing structures
were combined into a single flower
• He proposed that the ancestor of angiosperms
had separate pollen-producing and ovuleproducing structures
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Angiosperm Diversity
• The two main groups of angiosperms are
monocots and eudicots
• Basal angiosperms are less derived and include
the flowering plants belonging to the oldest
lineages
• Magnoliids share some traits with basal
angiosperms but are more closely related to
monocots and eudicots
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 30-12aa
BASAL ANGIOSPERMS
Amborella trichopoda
Water lily (Nymphaea
“Rene Gerald”)
Star anise (Illicium
floridanum)
LE 30-12ab
MAGNOLIIDS
Southern magnolia
(Magnolia
grandiflora)
Eudicots
Monocots
Magnoliids
Star anise
and relatives
Water lilies
Amborella
HYPOTHETICAL TREE OF FLOWERING PLANTS
LE 30-12ba
MONOCOTS
EUDICOTS
Orchid
Monocot
(Lemboglossum
Characteristics
rossii)
Eudicot
Characteristics
Embryos
One cotyledon
Two cotyledons
California
poppy
(Eschscholzia
california)
LE 30-12bb
MONOCOTS
EUDICOTS
Pyrenean oak
(Quercus
pyrenaica)
Leaf
venation
Veins usually
netlike
Veins usually
parallel
Stems
Pygmy date palm (Phoenix roebelenii)
Vascular tissue
scattered
Vascular tissue
usually arranged
in ring
LE 30-12bc
MONOCOTS
EUDICOTS
Lily (Lilium
“Enchantment”)
Roots
Dog rose (Rosa canina), a wild rose
Root system
usually fibrous
(no main root)
Taproot (main root)
usually present
LE 30-12bd
MONOCOTS
EUDICOTS
Barley (Hordeum vulgare), a grass
Pea
(Lathyrusner
vosus, Lord
Anson’s
blue pea),
a legume
Pollen
Pollen grain with
one opening
Pollen grain with
three openings
Flowers
Anther
Stigma
Filament
Ovary
Floral organs
usually in
multiples of three
Floral organs usually
in multiples of
four or five
Zucchini
(Cucurbita
Pepo), female
(left), and
male flowers
Evolutionary Links Between Angiosperms and Animals
• Pollination of flowers by animals and transport of
seeds by animals are two important relationships
in terrestrial ecosystems
Video: Bee Pollinating
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Video: Bat Pollinating
LE 30-13
A flower pollinated by
honeybees.
A flower pollinated by
hummingbirds.
A flower pollinated by nocturnal animals.
Concept 30.4: Human welfare depends greatly on
seed plants
• No group of plants is more important to human
survival than seed plants
• Plants are key sources of food, fuel, wood
products, and medicine
• Our reliance on seed plants makes preservation of
plant diversity critical
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Products from Seed Plants
• Most of our food comes from angiosperms
• Six crops (wheat, rice, maize, potatoes, cassava,
and sweet potatoes) yield 80% of the calories
consumed by humans
• Modern crops are products of relatively recent
genetic change resulting from artificial selection
• Many seed plants provide wood
• Secondary compounds of seed plants are used in
medicines
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Threats to Plant Diversity
• Destruction of habitat is causing extinction of
many plant species
• Loss of plant habitat is often accompanied by loss
of the animal species that plants support
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 31
Fungi
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 31.1: Fungi are heterotrophs that feed by
absorption
• Despite their diversity, fungi share key traits, most
importantly the way in which they derive nutrition
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Nutrition and Fungal Lifestyles
• Fungi are heterotrophs but do not ingest their food
• They secrete exoenzymes that break down
complex molecules, and then they absorb the
smaller compounds
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• Fungi exhibit diverse lifestyles:
– Decomposers
– Parasites
– Mutualistic symbionts
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Body Structure
• 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
Animation: Fungal Reproduction and Nutrition
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-2
Reproductive structure
Hyphae
Spore-producing
structures
20 µm
Mycelium
• Some fungi have hyphae divided into cells by
septa, with pores allowing cell-to-cell movement
• Coenocytic fungi lack septa
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-3
Cell wall
Cell wall
Nuclei
Pore
Septum
Septate hypha
Nuclei
Coenocytic hypha
• Some unique fungi have specialized hyphae that
allow them to penetrate the tissues of their host
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-4
Nematode
Hyphae
25 µm
Hyphae adapted for trapping and killing prey
Plant
cell
wall
Fungal hypha
Plant cell
Haustorium
Haustoria
Plant cell
plasma
membrane
• Mycorrhizae are mutually beneficial 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
• Endomycorrhizal fungi extend hyphae through the
cell walls of root cells and into tubes formed by
invagination of the root cell membrane
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-5–3
Key
Heterokaryotic
stage
Haploid (n)
Heterokaryotic
(unfused nuclei from
different parents)
PLASMOGAMY
(fusion of cytoplasm)
Diploid (2n)
KARYOGAMY
(fusion of nuclei)
Spore-producing
structures
Zygote
Spores
ASEXUAL
REPRODUCTION
Mycelium
SEXUAL
REPRODUCTION
MEIOSIS
GERMINATION
GERMINATION
Spore-producing
structures
Spores
Sexual Reproduction
• Plasomogamy is the union of two parent mycelia
• In many fungi, the haploid nuclei from each parent
do not fuse right away; they coexist in the
mycelium, called a heterokaryon
• In some fungi, the haploid nuclei pair off two to a
cell; such a mycelium is said to be dikaryotic
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Hours, days, or even centuries may pass before
the occurrence of karyogamy, nuclear fusion
• During karyogamy, the haploid nuclei fuse,
producing diploid cells
• 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
• Many of these species grow as mold, sometimes
on fruit, bread, and other foods
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-6
2.5 µm
• Other fungi that can reproduce asexually are
yeasts, which inhabit moist environments
• Instead of producing spores, yeasts reproduce
asexually by simple cell division
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-7
10 m
Parent
cell
Bud
• Many molds and yeasts have no known sexual
stage
• Mycologists have traditionally called these
deuteromycetes, or imperfect fungi
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 31.3: Fungi descended from an aquatic,
single-celled, flagellated protist
• Systematists now recognize Fungi and Animalia
as sister kingdoms
• In other words, fungi and animals are more closely
related to each other than they are to plants or
other eukaryotes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Origin of Fungi
• Molecular evidence supports the hypothesis that
fungi and animals diverged from a common
unicellular, flagellated ancestor
• Fungi probably evolved before the colonization of
land by multicellular organisms
• The oldest undisputed fossils of fungi are only
about 460 million years old
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LE 31-8
50 µm
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
• Fungi phylogeny is the subject of much research
• Molecular analysis has helped clarify evolutionary
relationships between fungal groups, although
areas of uncertainty remain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Arbuscular
mycorrhizal
fungi
Sac
fungi
Club
fungi
Glomeromycota
Ascomycota
Basidiomycota
Chytridiomycota
Chytrids
Zygote
fungi
Zygomycota
LE 31-9
Chytrids
• Chytrids (phylum Chytridiomycota) are found in
freshwater and terrestrial habitats
• They can be saprobic or parasitic
• Molecular evidence supports the hypothesis that
chytrids diverged earliest in fungal evolution
• Chytrids are unique among fungi in having
flagellated spores, called zoospores
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LE 31-10
Hyphae
25 µm
Flagellum
4 µm
Video: Allomyces Zoospore Release
Video: Phlyctochytrium Zoospore Release
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Until recently, systematists thought that fungi lost
flagella only once in their evolutionary history
• Molecular data indicate that some “chytrids” are
actually more closely related to another fungal
group, the zygomycetes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-11
Some
chytrids
Zygomycetes and other chytrids
Glomeromycetes,
ascomycetes, and
basidiomycetes
Key
Common ancestor
Loss of
flagella
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
• The life cycle of black bread mold (Rhizopus
stolonifer) is fairly typical of the phylum
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-12
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
PLASMOGAMY
Rhizopus
growing
on bread
Mating
type (+)
Gametangia with
Mating haploid nuclei
type (–)
100 µm
Young
zygosporangium
(heterokaryotic)
SEXUAL
REPRODUCTION
Dispersal and
germination
Sporangia
Sporangium
ASEXUAL
REPRODUCTION
MEIOSIS
Dispersal and
germination
50 µm
Mycelium
KARYOGAMY
Diploid
nuclei
Zygosporangium
(heterokaryotic)
• Zygosporangia, which are resistant to freezing and
drying, can survive unfavorable conditions
• Some zygomycetes, such as Pilobolus, can
actually “aim” their sporangia toward conditions
associated with good food sources
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LE 31-13
0.5 mm
Microsporidia
• Microsporidia are unicellular parasites of animals
and protists
• They are now classified as zygomycetes
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10 µm
LE 31-14
Host cell
nucleus
Developing
microsporidian
Spore
Glomeromycetes
• The glomeromycetes (phylum Glomeromycota)
were once considered zygomycetes
• They are now classified in a separate clade
• Glomeromycetes form a distinct type of
endomycorrhizae called arbuscular mycorrhizae
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LE 31-15
2.5 µm
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 vary in size and complexity, from
unicellular yeasts to elaborate cup fungi and
morels
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LE 31-16
The cup-shaped ascocarps (fruiting bodies) of
Aleuria aurantia give this species its common
name: orange peel fungus.
The edible ascocarp of
Morchella esculenta, the
succulent morel is often
found under trees in
orchards.
10 µm
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.
Neurospora crassa feeds as
a mold on bread and other
food (SEM).
• 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
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LE 31-17
Key
Haploid (n)
Dikaryotic (n + n)
Conidia;
mating type (–)
Diploid (2n)
Dispersal
Germination
ASEXUAL
REPRODUCTION
Mating
type (+)
Mycelium
PLASMOGAMY
Ascus
(dikaryotic)
Mycelia
Conidiophore
Dikaryotic hyphae
extended from
ascogonium
SEXUAL
REPRODUCTION
Germination
Dispersal
Asci
Diploid nucleus
(zygote)
Eight
ascospores
Four
haploid
nuclei
Ascocarp
KARYOGAMY
MEIOSIS
Basidiomycetes
• Basidomycetes (phylum Basidiomycota) include
mushrooms and shelf fungi
• The phylum is defined by a clublike structure
called a basidium, a transient diploid stage in the
life cycle
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LE 31-18
Maiden veil fungus (Dictyphora), a fungus
with an odor like rotting meat
Fly agaric (Amanita muscoria), a
common species in conifer forests
in the northern hemisphere
Puffballs emitting spores
Shelf fungi, important decomposers of wood
• The life cycle of a basidiomycete usually includes
a long-lived dikaryotic mycelium
• In response to environmental stimuli, the
mycelium reproduces sexually by producing
elaborate fruiting bodies call basidiocarps
• Mushrooms are examples of basidiocarps
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The numerous basidia in a basidiocarp are
sources of sexual spores called basidiospores
• Asexual reproduction is much less common in
basidiomycetes than in ascomycetes
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LE 31-20
Dikaryotic
mycelium
PLASMOGAMY
Mating
type (–)
Haploid
mycelia
Mating
type (+)
SEXUAL
REPRODUCTION
Gills lined
with
basidia
Basidiocarp
(dikaryotic)
Dispersal and
germination
Basidiospores
Basidium with
four appendages
Basidium
Basidia
(dikaryotic)
Basidium containing
four haploid nuclei
KARYOGAMY
MEIOSIS
Key
Diploid
nuclei
1 µm
Basidiospore
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 efficient decomposers
• They perform 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
• All of these relationships have profound ecological
effects
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mycorrhizae
• Mycorrhizae are enormously important in natural
ecosystems and agriculture
• They increase plant productivity
RESULTS
RESULTS
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fungus-Animal Symbiosis
• 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”
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Lichens
• Lichens are a symbiotic association of millions of
photosynthetic microorganisms held in a mass of
fungal hyphae
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 31-23
A fruticose (shrub-like) lichen
A foliose (leaf-like) lichen
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
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LE 31-24
Ascocarp of fungus
Soredia
Fungal
hyphae
Algal
layer
Algal cell
10 µm
Fungal hyphae
Pathogens
• About 30% of known fungal species are parasites,
mostly on or in plants
• 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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LE 31-25
Corn smut on corn
Tar spot fungus of sycamore leaves
Ergots on rye
Practical Uses of Fungi
• Humans eat many fungi and use others to make
cheeses, alcoholic beverages, and bread
• Genetic research on fungi is leading to
applications in biotechnology
• Antibiotics produced by fungi treat bacterial
infections
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LE 31-26
Staphylococcus
Penicillium
Zone of
inhibited
growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings