Kingdom Fungi

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Kingdom Fungi

• Natures
• decomposers

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• General Characteristics of Fungi. . .
• Fungi are eukaryotic organisms with cell walls
• They lack chlorophyll
• They are nonmotile
• They are heterotrophic absorbing their food
• Fungi reproduce sexually or asexually by means of
  spores
• Most are decomposers - specifically saprobes
• They absorb nutrients from wastes and dead
  organisms
• Digest food externally by secreting hydrolytic
  enzymes onto food
• In the process, carbon dioxide is released into
  the atmosphere and minerals are returned to the
  soil
• (Beer and wine production depend on saprobic
  fungi)

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• Symbiotic relationships formed by fungi. . .
• Some are parasites - absorbing their food from a
  host
• Parasitic fungi cause disease in humans and
  other animals
• Fungi are the most important disease-causing
  organisms in plants

• Some fungi form mutualistic relationships
• Mycorrhizae associate with roots of a plant they
  breakdown organic compounds in the soil,
  releasing mineral components which are then
  available to the plant
• Lichens - this is an intimate association between
  a fungus and an alga or cyanobacterium very
  important in soil formation

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• A fungus may be unicellular (the yeast form) or
  multicellular (the mold form)
• The cell walls contain chitin, which is highly
  resistant to microbial breakdown (rather than
  cellulose which is associated with cell walls in
  plants).
• Yeasts.
• Unicellular
• Reproduce asexually by fission and budding
• Reproduce sexually by spore formation
• Yeasts are larger than most bacteria some form
  colonies
• Most yeast occur in the Ascomycota

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Most fungi are filamentous molds.
Hyphae are singular filaments that compose the
mycelium of a fungus. Mycelium is a tangled
tissue-like aggregation of hyphae. An example to
think of is the cobweb-like mold sometimes seen
on bread. The thallus is the whole fungal body.
In some species, hyphae are divided by perforated
walls (septa) which allow cytoplasmic flow
between individual cells that contain one or more
nuclei. Other species are coenocytic
(multinucleate and not separated into separate
cells).
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• Fungi growth requirements...
• Fungi are found wherever organic material is
  available
• They grow best in the dark
• Moisture is required
• Fungi can survive dry periods by entering a
  resting stage or by producing spores
• Some can tolerate and grow in a wide range of pH
  and temperature
• Many can tolerate high osmotic pressure
• On an appropriate substrate, spore will germinate
• The hyphae emerges, forming a hyphal mat that
  infiltrates the substrate
• Other hyphae extend up into the air
• The hyphae secrete a digestive enzyme that
  degrades the substrate

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• Reproduction in Fungi
• Fungi reproduce asexually by fission, budding, or
  spore formation
• There are two types of structures associated with
  sexual reproduction
• Sporangia - produce spores
• Gametangia - produce gametes

• Spores are nonmotile cells that are produced on
  aerial hyphae
• Spores aid in distribution - they are spread by
  wind or animals
• The sporocarp is a large complex reproductive
  structure that produces spores it is the
  familiar part of a mushroom.
• Spores can be produced sexually or asexually
• Fungal cells contain haploid nuclei
• Only the zygote is diploid

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Division Zygomycota

• Defining characteristic is the presence of
  zygospores

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• Members of the Division Zygomycota produce sexual
  resting spores called zygospores.
• The hyphae are coenocytic septa separate hyphae
  from sporangia and gametangia
• Many live in soil on decaying plant or animal
  matter
• Some are parasites on plants and animals
• An example is black bread mold
• Stolons are hyphae that grow horizontally with
  amazing speed
• Rhizoids are hyphae that anchor stolons to the
  bread
• Sporangium is the spore sac at the tip of an
  aerial hyphae

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• Sexual reproduction in Zygomycota . . .
• Bread mold is heterothallic - an individual
  fungus mates with an individual of a different
  mating type (plus and minus strains)
• There is no morphological sex differentiation,
  only physiological
• Hyphae of opposite mating types meet, and
  hormones are produced that cause hyphal tips to
  join and form gametangia
• Plus and minus nuclei fuse, forming diploid
  nuclei (the zygotes)
• Zygospore forms around the zygote which may lie
  dormant for months - note the zygote is the only
  diploid structure
• Meiosis occurs, and all haploid nuclei but one
  degenerate
• Aerial hyphae forms with sporangia at the tip
• Haploid spores are produced, which eventually
  germinate
• The cycle repeats

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Division Ascomycota

• The Sac Fungi

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• General Information about Ascomycetes.
• They are a large group - about 30,000 known
  species
• Their spores are produced in sacs (asci)
• Hyphae usually have septa that permit cytoplasmic
  streaming
• This division includes some yeasts powdery
  mildews blue-green, red and brown molds edible
  morels and truffles
• Some cause serious plant diseases (Dutch Elm
  disease, Chestnut Blight)
• Vary in degree of complexity

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• Asexual reproduction in Ascomycota. . .
• This involves the production of spores (conidia)
  that are pinched off specialized hyphae called
  conidiophores
• Conidia are a means of rapidly propagating new
  mycelia
• They occur in various shapes, sizes, colors in
  different species

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• Sexual Reproduction in Ascomycota. . .
• Some are heterothallic others are homothallic
  (able to mate with self)
• Two hyphae join and their cytoplasm mingles
• Nuclei come together but do not fuse
• New hyphae develop and each is dikaryotic (has
  two nuclei)
• These dikaryotic hyphae form a fruiting body
  called an ascocarp
• Within a cell in the ascocarp, the two nuclei
  fuse, forming a diploid nucleus (zygote)
• Meiosis then occurs, forming four haploid nuclei
• Each nucleus then undergoes mitosis, resulting in
  eight nuclei
• The haploid nuclei then separate forming eight
  haploid ascospores within each ascus
• Ascospores are released with the ascus breaks

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Division Basidiomycota

• The Club Fungi

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• General Characteristics of Basidiomycota
• There are about 25,000 known species including
  the mushrooms, toadstools, bracket fungi, puff
  balls, rusts, smuts
• Acharacteristic feature is the development of
  basidiospores on the outside of a basidium (an
  enlarged, club-shaped, hyphal cell)
• A common example is the Agaricus campestris (the
  type of mushroom found in the grocery store)
• Structure consists of a mass of white, branching,
  threadlike hyphae occuring below the ground
• Compact masses of hyphae (buttons) develop along
  the mycelium
• The button grows into the familiar mushroom
  (sporocarp or basidiocarp) consisting of a stalk
  and cap
• The lower surface of the cap develops gills which
  contain basidia

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• The typical life cycle of Basidiomycetes. . .
• A basidiospore gives rise to new primary
  mycelium, consisting of monokaryotic cells
• Hyphae of different mating types fuse haploid
  nuclei do not, resulting in secondary mycelium
  with dikaryotic, heterokaryotic hyphae
• Heterokaryotic hyphae grow extensively, forming
  basidiocarps
• On the gills, the nuclei of the cells at the tips
  of the hyphae fuse, forming diploid zygotes
  (these are the only diploid cells)
• Meiosis occurs, forming four haploid nuclei
• Four basidiospores form, each containing one the
  haploid nuclei, on stalks
• When the stalk breaks, the basidiospores are
  released

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Division Deuteromycota

• The Imperfect Fungi

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• General information about the Deuteromycota. . .
• There are about 25,000 known species
• A sexual stage has not been observed
• Most reproduce by conidia
• One species is associated with the production of
  the antibiotic Penicillin
• Other species are responsible for the unique
  flavors of cheeses some are used to produce soy
  sauce from soy beans
• Some cause infectious diseases of humans
  (ringworm, athletes foot, thrush, systemic
  fungus infections)

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Lichens

• Lichens represent a symbiotic relationship
  between a phototroph and a fungus.
• The phototroph is usually a green alga or
  cyanobacterium fungus is usually an ascomycete

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Lichens

• The nature of the relationship is unclear
• Possibly mutualism, with phototroph receiving
  water and minerals from fungus
• Possibly parasitism of the phototroph by the
  fungus

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• General information about Lichens. . .
• There are about 20,000 known types of lichens
• Lichens grow wherever life can be supported
  except polluted cities (can be used as air
  pollution indicators)
• They are often the first organisms to inhabit
  bare rocky areas
• They play an important role in soil formation by
  etching rocks
• They serve as a food source for reindeer and
  caribou in arctic regions
• They grow slowly and can vary in size from almost
  invisible to ankle deep
• They may reproduce asexually by fragmentation
  some lichens have dipersal units containing cells
  of both partners in others the alga reproduces
  asexually by mitosis and the fungus produces
  ascospores

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Mycorrhizae

• Fungus-roots

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• General information about mycorrhizae. . .
• Mycorrhizae are fungi that form symbiotic
  relationships with roots of higher plants
• They occur in about 90 of all families of higher
  plants
• The fungus decomposes organic material in soil,
  making the minerals available to the plant
• The plant may supply nutrients to the fungus
• Many plants do not grow and will die without
  appropriate fungus

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Economic Importance of Fungi

• Fungi are of both positive and negative economic
  importance

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• I ? Fungi!
• Life would be impossible without fungi (as
  decomposers)
• There are 200 kinds of edible mushrooms
• Yeasts play an important role in brewing beer and
  in baking
• Fungi can be used for production of drugs such as
  antibiotics (Alexander Fleming) 1928 - discovered
  penicillin produced by the deuteromycete
  Penicillium notatum
• Cyclosporine, the drug used to suppress immune
  responses in patients receiving organ transplants
  is produced from fungi
• Some fungi can be used as biological control
  agents

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• Fungi have a negative impact also. . .
• Some fungi damage stored goods, lumber
• Some fungi are poisonous (cyclopeptides are toxic
  substances found in mushrooms)
• Ergot is a type of fungus (Claviceps pupurea)
  that has historic importance - it causes nervous
  spasms, convulsions, psychotic delusions,
  gangrene
• In 1722, Ergot was called St. Anthonys fire,
  and its outbreak caused many to be burned at the
  stake as witches
• Many fungi cause plant diseases (Chestnut blight,
  Dutch Elm disease, Apple scab, Brown rot) Many
  smuts and rusts attack cereals
• Many fungi cause human diseases (Ringworm,
  Athletes foot, Candidiasis, Histoplamosis (a
  systemic disease)