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Fungi
AP Biology
Spring 2011
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Describe the various types of fungal body
plans, patterns of reproduction, and natural
history
Discuss economic impact of fungi on humans
Provide at least one example of each of the
major groups of fungi
Provide the two examples of symbiotic
relationships with fungi
Fungal Characteristics and Classification
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Fungi: spore producing heterotrophs with
chitin cell walls that utilize organic matter
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Saprobes: get nutrients from the nonliving
matter and cause its decay
Parasites: thrive on tissues in living hosts
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All rely on extracellular enzymatic digestion
and absorption
Valuable decomposers in all environments
Most multicellular
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Mycelium: the food-absorbing part of
fungus, mesh of branching filaments
 Each tubular filament is a hypha with chitinous
walls
 Interconnections and perforations allow
cytoplasmic flow necessary for transport to
nonabsorptive parts of the body
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Either a haploid or dikaryotic (2 haploid
nuclei in one cell) stage dominantes fungal
life cycle
 Like most protists
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Fungi disperse by means of spores
 Asexual reproduction is mostly by spores
produced in sporangia
 Sexual reproduction proceeds through the
formation of gametes in gametangia as well as by
spores
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Gene comparisons show that fungi are more
closely related to animals than plants
Several major groups that make up the fungal
kingdom
Chytids, zygote fungi, and glomermycetes
are small groups that are not monophyletic
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Lack a dikaryotic stage and have hypha with few
or no cross walls (septae)
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Chytids: ancient fungal lineage, flagellates
spores and gametes that swim in water, wet soil,
and in soil animal digestive systems
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Feed on organic wastes and remains helping to recycle
nutrients
Some aid herbivores in the digestion of cellulose,
others pathogens
Sac and Club Fungi: 2 large monophyletic
groups
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Both make dikaryotic mycelium and the cells of
their hyphae are separated by septae
Are successful because the dikaryotic mycelium
increase genetic diversity of sexually produced
spores
Zygomycetes
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Zygomycetes: form a zygospore during
reproduction
 Have haploid mycelium, no dikaryotic hyphae,
most are saprobes, some are parasites, and a few
have mutual relationships with plant roots
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Sexual reproduction: begins when 2 hyphae
(different mating strains) grow toward each
other and fuse
 Gametangia forms and makes haploid nuclei,
which later fuse to form a diploid zygospore
 Zygospore later release haploid spores, which
form in sacs at the tips of the hyphae
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Microsporidians: intracellular parasites of
animals
 Have no mitochondria and rely on host for ATP
 Spore has long polar tube hat it uses to connect
with a host cell and inject the contents of the
spore into the host
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Glomeromycetes: associate with plant roots
and do not reproduce sexually
 Their association with plant cell walls helps
nutrients enter plant cell roots
Basidiomycetes: Club Fungi
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Club fungi: have club-shaped sexual spores
that form on the gills of mushrooms
 Which are the spore-producing structures of this
group
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The aboveground part of the fungal body is
the common mushroom consisting of a stalk
and cap
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Basidiospores are produced in club-shaped
structures on the outer surface of the cap
When spores land on a suitable site, they
germinate to produce extensive underground
mycelia that then reproduce sexually
 Resulting in a dikaryotic stage
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Sexual reproduction is accomplished when
two compatible mating strains make contact
 Cytoplasmic fusion results in a dikaryotic
mycelium
 Eventually, the nuclei will fuse to form a zygote,
which undergoes meiosis to form haploid spores
dispersed in the wind
Ascomycetes Sac Fungi
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Sac Fungi: form sexual spores called
ascospores inside sac-shaped cells called asci
 Asci enclosed in reproductive structures of
interwoven hyphae
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Types of Sac Fungi:
Multicelled sac fungi include:
 Edible morels and truffles
 Most of food-spoiling molds
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Single celled yeasts
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Septae in the ascomycet hyphae prevents
damage from causing the organism to dry
out
Making ascomycetes (and basidomycetes)
more successful than fungi without septae
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Spores form from inside a sac-like cell (ascus)
Sexual reproduction starts when 2
compatible hyphae meet and form a
dikaryotic hyphae
Nuclear fission, followed by meiosis in the
asci at the tips of the hyphae
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Some ascomycetes can reproduce asexually
by the process of budding or by producing
haploid spores called condida
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Genetic research: neurospora
Food: truffles and morels
Fermentation: Saccharomyes cervisiae helps
bread rise and produces beer and wine;
Aspergilus makes soy sauce and citric acid for
soda; Penicillium roquefortii helps produce
blue cheese
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Medicine: Penicillium chrysogenum is used for
antibiotics; Aspergillus lowers cholesterol,
and Trichoderma prevents organ rejection
Agriculture: a sac fungi species may help
control roundworm populations in
agricultural settings
Fungal Symbionts
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Lichens: mutualistic associations between
fungi and cyanobacteria, green algae, or both
 The fungus is the mycobiont and the
photosynthetic part is the photobiont
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The tip of a fungal hypha binds with a suitable
host cell
Both lose their cell wall and their cytoplasm
fuses as both organisms grow together
The fungus recieves a long-term source of
nutrients, which it absorbs from the
photobiont cells
Lichen helps to shelter the photobiont and
anchor it to the substrate
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Live in inhospitable places
 Bare rock, tree trunks
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By their metabolic activities, lichens can
change the composition of their substrate
Usually sensitive to air pollution
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Endophytic fungi: symbionts that live inside
the leaves and stems of many plants
Fungi living in the tissues of fescue grass
produce an alkaloid that deters grazers
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The fungus-roots
Mycorrhiza: is a symbiotic relationship in
which fungi hyphae surround roots of shrubs
and trees
Because of extensive surface area, fungus can
absorb mineral ions and facilitate their entry
into the plant