Fungi absorb food after digesting it outside their
bodies
ƒ Fungi
– are absorptive heterotrophic eukaryotes,
– secrete powerful enzymes to digest their food externally,
and
– acquire their nutrients by absorption.
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Fungi absorb food after digesting it outside their
bodies
ƒ Most fungi consist of a mass of threadlike hyphae
(菌絲) making up a mycelium (菌絲體).
ƒ Hyphal cells
– are separated by cross-walls with pores large enough for
ribosomes, mitochondria, and nuclei to cross,
– are sometimes multinucleate without cross-walls, and
– have a huge surface area to secrete digestive enzymes
and absorb food.
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Figure 17.14B
Reproductive
structure
Hyphae
Spore-producing
structures (tips of hyphae)
Animation: Fungal Reproduction and Nutrition
Mycelium
Right click on animation / Click play
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1
Fungi absorb food after digesting it outside their
bodies
Fungi absorb food after digesting it outside their
bodies
ƒ Fungal hyphae
ƒ Mycorrhizae (plural)
– are surrounded by a cell wall made of chitin instead of
cellulose (纖維素).
ƒ Some fungi
– are parasites and
– obtain their nutrients at the expense of living plants or
animals.
– represent a symbiotic relationship between fungi and
plant root cells and
– are present in nearly all vascular plants.
ƒ Mycorrhizal fungi absorb phosphorus and other
essential materials from the soil and make them
available to the plant.
ƒ Sugars produced by the plant through
photosynthesis nourish the mycorrhizal fungi.
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© 2012 Pearson Education, Inc.
Fungi produce spores in both asexual and sexual
life cycles
Fungi produce spores in both asexual and sexual
life cycles
ƒ Fungi produce huge numbers of asexual spores,
ƒ In many fungi, sexual fusion of haploid hyphae
leads to a heterokaryotic stage, in which cells
contain two genetically distinct haploid nuclei.
each of which can germinate to form a new fungus.
– Hours or centuries may pass before parental nuclei fuse
to form a short-lived diploid phase.
– Zygotes undergo meiosis to produce haploid spores.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Fungi produce spores in both asexual and sexual
life cycles
ƒ In asexual reproduction, spore-producing structures
arise from haploid mycelia that have undergone
neither a heterokaryotic stage or meiosis.
Key
Haploid (n)
Heterokaryotic (n + n)
(unfused nuclei)
Diploid (2n)
ƒ Many fungi that reproduce sexually can also
produce spores asexually.
Heterokaryotic
stage
Fusion of nuclei
1
Fusion of cytoplasm
Spore-producing
structures
Spores
(n)
Sexual
reproduction
Asexual Mycelium
reproduction
4
2
Zygote
(2n)
Meiosis
Spore-producing
structures
Germination
3
Germination
Spores (n)
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Fungi produce spores in both asexual and sexual
life cycles
Fungi are classified into five groups
ƒ Molds (黴) are any rapidly growing fungus that
reproduces asexually by producing spores.
ƒ There are over 100,000 described fungi species.
ƒ Suspected but as yet undescribed species may
number as many as 1.5 million.
ƒ Sexual reproductive structures are often used to
classify fungi.
ƒ Fungi and animals may have diverged
ƒ Yeasts are single-celled fungi that reproduce
asexually by cell division or budding.
– from a flagellated unikont ancestor
– more than 1 billion years ago.
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© 2012 Pearson Education, Inc.
Fungi are classified into five groups
ƒ Chytrids (壺菌) are the
– only fungi with flagellated spores and
– earliest lineage of fungi.
ƒ Chytrid fungi are
– common in lakes, ponds, and soil and
– linked to the widespread decline of amphibian species.
Chytrids
(壺菌)
Zygomycetes
(zygote fungi)
(接合菌)
Glomeromycetes
(arbuscular
mycorrhizal fungi)
(球囊菌)
Ascomycetes
(sac fungi)
(原囊菌)
Basidiomycetes
(club fungi)
(擔子菌)
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Fungi are classified into five groups
ƒ Zygomycetes, or zygote fungi (接合菌)
– are characterized by their protective zygosporangium
(接合孢子囊), where zygotes produce haploid spores
by meiosis.
– This diverse group includes fast-growing molds that
attack
– bread
– peaches,
– strawberries,
– sweet potatoes, and
– some animals.
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Fungi are classified into five groups
Figure 17.16C
ƒ Glomeromycetes (球囊菌)
– form a distinct type of mycorrhizae, in which hyphae that
invade plant roots branch into treelike structures known
as arbuscules (叢枝體).
– About 90% of all plants have symbiotic partnerships with
glomeromycetes.
Glomeromycete: an arbuscule in a root cell
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Fungi are classified into five groups
Ascomycetes
ƒ Ascomycetes (原囊菌), or sac fungi
– form saclike structures called asci (菌囊), which
produce spores in sexual reproduction,
– live in marine, freshwater, and terrestrial habitats, and
– range in size from unicellular years to elaborate (綿密)
morels (羊肚菌) and cup fungi.
– Some ascomycetes live with green algae or
cyanobacteria in symbiotic associations called lichens.
Edible morels
Cup fungus
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Fungi are classified into five groups
ƒ Basidiomycetes, or club fungi (擔子菌),
– include common mushrooms, puffballs (馬勃), and
shelf fungi (托架真菌) and
– are named for their club-shaped, spore-producing
structure called a basidium (擔子).
ƒ These fungi include
– important forest decomposers and
– particularly destructive plant parasites called rusts (銹
斑菌) and smuts (黑穗菌).
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Figure 17.16E
Basidiomycetes
Mushrooms
A puffball
Shelf fungi
Fungal groups differ in their life cycles and
reproductive structures
Fungal groups differ in their life cycles and
reproductive structures
ƒ The life cycle of a black bread mold is typical of
zygomycetes.
ƒ When food is depleted (耗盡), the fungus reproduces
sexually.
– Mycelia of different mating types join and produce a
zygosporangium, a cell containing multiple nuclei from
two parents.
ƒ Hyphae reproduce asexually by producing spores
in sporangia at the tips of upright hyphae.
– The zygosporangium develops into a thick-walled
structure that can tolerate dry, harsh conditions.
– When conditions are favorable, the parental nuclei fuse
to form diploid zygotes, which undergo meiosis
producing haploid spores.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Fungal groups differ in their life cycles and
reproductive structures
Zygosporangium (n + n)
Hyphae of
different
mating types
Cells
fuse
2
ƒ The life cycle of a mushroom is typical of
basidiomycetes.
3
ƒ The heterokaryotic stage
Fusion of
nuclei
1
Young zygosporangium
(heterokaryotic)
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
Meiosis
Sporangium
(on stalk arising
from the
zygosporangium)
4
– begins when mycelia of two different mating types fuse,
– forming a heterokaryotic mycelium,
Spores
(n)
– which grows and produces the mushroom.
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Fungal groups differ in their life cycles and
reproductive structures
ƒ In the club-shaped cells called basidia, which line
the gills of the mushroom, the haploid nuclei fuse,
forming diploid nuclei.
ƒ Each diploid nucleus produces haploid spores by
meiosis.
Hyphae of two
different mating types
ƒ A mushroom can release as many as a billion
spores.
ƒ If spores land on moist matter that can serve as
food, they germinate and grown into haploid
mycelia.
1
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
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3
Fusion of
nuclei
Mushroom
Diploid nuclei
Mushroom
Basidia
Hyphae of two
different mating types
2
Heterokaryotic
mycelium
1
Hyphae of two
different mating types
2
Heterokaryotic
mycelium
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
1
3
Fusion of
nuclei
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
3
Fusion of
nuclei
Diploid nuclei
Diploid nuclei
Meiosis
Meiosis
Mushroom
Mushroom
Basidia
Haploid
nuclei
Basidia
4
Haploid
nuclei
Spore
(n)
Hyphae of two
different mating types
2
Heterokaryotic
mycelium
1
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
4
Spore
(n)
Hyphae of two
different mating types
2
Heterokaryotic
mycelium
1
5
Haploid
mycelia
Key
Haploid (n)
Heterokaryotic (n + n)
Diploid (2n)
6
Parasitic fungi harm plants and animals
Figure 17.18A
Order
ƒ Of the 100,000 known species of fungi, about 30%
are either parasites or pathogens in or on plants.
ƒ About 80% of plant diseases are caused by fungi.
– Between 10 and 50% of the world’s fruit harvest is lost
each year to fungal attack.
– A variety of fungi, including smuts and rusts, infect grain
crops.
Stately (挺拔) English elms (榆樹) in Australia,
unaffected by Dutch elm disease
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Ergots
Corn smut
Ergots (麥角菌) on rye (黑麥)
Parasitic fungi harm plants and animals
Fungi have enormous ecological benefits
ƒ Only about 50 species of fungi are parasitic on
animals.
ƒ The general term for a fungal infection is mycosis
(真菌病).
ƒ Fungi
ƒ Skin mycoses include
– ringworm (錢癬), named because it appears as
circular red areas on the skin,
– athlete (運動員)’s foot, also caused by the ringworm
fungus,
– vaginal yeast infections, and
– supply essential nutrients to plants through symbiotic
mycorrhyizae and
– are essential decomposers in ecosystems, breaking
down decomposing leaves, logs, and feces (糞便) and
dead animals.
ƒ Fungi may also be used to digest petroleum (石油)
products to clean up oil spills, such as the 2010 BP
(British Petroleum) spill in the Gulf of Mexico.
– deadly lung diseases.
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Fungi have many practical uses
ƒ Fungi have many practical uses for humans.
– We eat mushrooms and cheeses modified by fungi.
– Yeasts produce alcohol and cause bread to rise.
– Some fungi provide antibiotics that are used to treat
bacterial disease.
– Fungi figure prominently (突出) in molecular biology and
in biotechnology. Yeasts, for example, are often used to
study molecular genetics of eukaryotes.
– Fungi may play a major role in the future production of
biofuels from plants.
A fungal mycelium
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Blue cheese
Penicillium
(mold)
Staphylococcus
aureus (bacteria)
Zone of
inhibited
growth
Blue cheese
Lichens are symbiotic associations of fungi and
photosynthetic organisms
ƒ Lichens consist of algae or cyanobacteria within a
mass of fungal hyphae.
– Many lichen associations are mutualistic.
– The fungus receives food from its photosynthetic partner.
– The fungal mycelium helps the alga absorb and retain
water and minerals.
White rot fungus (白腐菌)
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Lichens are symbiotic associations of fungi and
photosynthetic organisms
ƒ Lichens are important pioneers on new land, where
they help to form soil.
ƒ Lichens are sensitive to air pollution, because they
obtain minerals from the air.
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Algal cell
Fungal hyphae
Reindeer moss, a lichen
(a) Pine tree, a gymnosperm
(b) Puffball,
a club fungus
9