Fungi are heterotrophs that obtain nutrition from their environment by extracellular digestion

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• Fungi are heterotrophs that obtain nutrition from
  their environment by extracellular digestion
• have cell walls
• spend their lives fixed in place
• disperse by producing spores
• most are free-living saprobes
• others live on or in other organisms
• fungi are heterotrophs 2 min video

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Ecology of Fungi

• decomposers of organic wastes and remains
• helps recycle nutrients in ecosystems
• symbionts form beneficial partnerships with
• plants ? mychorrizae
• photosynthetic protists ? lichens
• herbivores
• parasites or pathogens

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Structure of Fungi

• yeasts unicellular
• molds mushrooms multicellular
• mycelium a mesh of branching filaments
• hypha each filament

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Hyphae in a Mycelium
one cell (part of one hypha of the mycelium)
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Hyphae

• In the oldest fungal lineages chytrids,
  zygomycetes, and glomeromycetes hyphae do not
  have cross-walls
• Hyphae divided into compartments by cross-walls
  septae evolved in the common ancestor of sac
  fungi and club fungi
• Cross-walls made hyphae stronger, allowing the
  evolution of larger, more elaborate
  spore-producing bodies
• Septate hyphae also are more resistant to
  desiccation than nonseptate hyphae

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Fungi Life Cycles

• Asexual reproduction
• spores form by mitosis in sporangia located at
  the tips of specialized haploid hyphae
• Sexual reproduction
• begins with cytoplasmic fusion of haploid hyphae
  to produce a dikaryotic stage ? having two
  genetically distinct types of nuclei (nn) in
  each cell
• fusion of the two haploid nuclei produces a
  diploid zygote that will undergo meiosis,
  restoring the haploid state

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Fungi Phylogeny and Classification

• Chytrids, Zygomycetes Glomeromycetes
• have few or no septae between cells of hyphae
• Ascomycetes sac fungi Basidiomycetes club fungi
  
• have regular cross walls septae between
  cells of hyphae

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What are the main characteristics of fungi?

• heterotrophs that absorb nutrients from their
  environment
• some live as single cells
• others live as a multicellular mycelium
• disperse by producing spores
• can be decomposers, symbionts, parasites or
  pathogens

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• Chytrids flagellated fungi
• the only fungi with a life cycle that includes
  flagellated cells
• some feed on organic wastes and remains
• some live in guts of herbivores digest
  cellulose
• some are parasites

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• Frog populations are threatened by
  Batrachochytrium dendrobatidis, a parasitic
  chytrid that causes chytridiomycosis
• mycosis a fungus caused disease
• Outbreaks of B. dendrobatididis have far-reaching
  ecological effects because frogs help control
  populations of insects and are food for many
  other animals

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What are chytrids?

• Chytrids are fungi with flagellated cells
• most are decomposers in soil
• some live in the animal gut
• some are parasites
• A parasitic chytrid species that kills amphibians
  is a matter of ecological concern

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• Zygomycetes zygote fungi
• produce a thick-walled diploid spore zygospore
  during sexual reproduction
• form a branching haploid mycelium on organic
  material, or inside living plants and animals
• Rhizopus species include
• black bread mold Rhizopus eating your bagel 38
  sec.
• other food spoiling molds Rhizopus eating your
  fruit! 37 sec.
• zygomycosis causing fungus
• Pilobolus Pilobolus spore discharge 2 min
• produces specialized spore-bearing hyphae with
  fluid-filled sacs that blast spores up to 2 m

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Spore Bearing Structures of Pilobolus
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• Glomeromycetes
• take part in plant rootfungus partnerships
  mycorrhizae
• glomeromycete hyphae grow into a root and
  branches inside the wall of a root cell
• the fungus shares nutrients from the soil with
  its plant host

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sporangium
plant root
hypha branching inside a plant cell wall
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• Mycorrhizae
• partnership between fungi and plant roots
• some hyphae form a dense net around roots but do
  not penetrate the plant cells (ascomycetes and
  basidiomycetes)
• some hyphae penetrate root cells (glomeromycetes)
• Hyphae increase the absorptive surface area of
  the plant
• Both partners benefit
• Fungus concentrates nutrients for plant
• Plant supplies sugars to the fungus

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without fungus
with fungus
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What are zygote fungi and their relatives?

• Zygomycetes form a thick-walled diploid spore
  when they reproduce sexually
• Some spoil food or cause disease
• Microsporidia are single-celled parasites that
  invade an animal cell
• Glomeromycetes are mycorrhizal fungi, they form
  beneficial symbiotic relationships with plants

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• Ascomycetes sac fungi
• are the most diverse fungal group
• some are single cells yeasts
• in most a haploid mycelium dominates the life
  cycle
• the hyphae have cross-walls at regular intervals
  and often form elaborate spore-producing bodies
• the group that most often causes diseases in
  humans
• commonly reproduce by asexual mechanisms
• yeasts reproduce asexually by binary fission or
  budding
• multicellular sac fungi grow as a haploid
  mycelium that produces spores by mitosis at the
  tips of specialized hyphae

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Asexual Reproduction in Sac Fungi
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Economical uses of Ascomycetes

• Food and beverages
• Morels Morel mushrooms an American delicacy
• Truffles Truffles The Most Expensive Food in
  the World
• Saccharomyces Aspergillus ? baking and
  fermentation
• Penicillium ? blue cheese
• Drugs
• Penicillium, Cephalosporium ? Antibiotics
• Aspergillus ? Statins
• Natural herbicides and pesticides
• Arthrobotrys

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What are Ascomycetes?

• Ascomycetes are the most diverse group of fungi
• some are unicellular yeasts, the others have a
  haploid mycelium that dominates their life cycles
• reproduce sexually by forming spores inside an
  ascus
• yeasts reproduce asexually by budding
• used for food and beverages, drugs, and as
  control agents for pests

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• Basidiomycetes club fungi
• make the largest most elaborate fruiting
  bodies of all fungi
• multicellular fungi in which a dikaryotic
  mycelium dominates the life cycle
• form sexual spores inside club-shaped cells that
  develop on a fruiting body basidiocarp composed
  of interwoven dikaryotic hyphae

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Diploid (2n) stage
Meiosis
Nuclear fusion
Dikaryotic (nn) stage
Haploid (n) stage
spore (n)
gill
cap
stalk
Cytoplasmic fusion
Hyphae of mycelium
Sexual spore (n) at gill margin
Figure 23-13 p386
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Ecology Diversity of Basidiomycetes

• Basidiomycetes
• the only decomposers capable of breaking down
  lignin in plants and trees (e.g. shelf fungus,
  honey mushroom)
• Jelly fungi form a parasitic gelatinous fruiting
  body that taps into the mycelia of other fungi
  that feed on wood
• Basidiomycetes include
• edible mushrooms (e.g. chanterelles, puffballs)
• poisonous mushrooms (e.g. death cap)
• hallucinogenic psilocybin-containing mushrooms

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What are Basidiomycetes?

• mostly multicellular fungi
• spend most of their life cycle as a dikaryotic
  mycelium
• largest, most complex spore-bearing structures of
  all fungi
• the only fungi that can break down lignin
• important in forests both as
• decomposers
• pathogens of trees

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• Lichens
• composite organisms consisting of an ascomycete
  fungus and a photosynthetic cyanobacteria or
  green algae
• may be a mutualism that benefits both partners
• or the fungus may be parasitically exploiting
  captive cells!
• disperse by fragmentation
• or the fungus alone can release spores
• break down rock by releasing acids
• colonize uninhabitable places such as bedrock

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Lichen Structure
dispersal fragment (cells of fungus and
of photosynthetic species)
outer layer of fungal cells
photosynthetic species
inner layer of loosely woven hyphae
outer layer of fungal cells
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• Plant pathogens
• Wheat stem rust
• Powdery mildew
• Claviceps Ergot ? ergotism (alkaloid poisoning)
• Human pathogens
• Athletes foot
• Ringworm
• Candida ? yeast infection

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• Puccinia graminis is the fungal pathogen that
  causes wheat stem rust, a disease that destroys
  food crops worldwide
• dust carries spores of fungi long distances (even
  across oceans)
• Plant breeding programs have developed
  rust-resistant wheat but a mutant form of the
  fungus is now infecting rust-resistant wheat

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Fungi relationships with other species?

• Fungi form mutually beneficial partnerships with
  plants, cyanobacteria, and green algae
• Some ants, termites, beetles farm fungus and
  rely on them for food
• Some fungi are pathogens that invade the tissues
  of plants and animals