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Fungi

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					Fungi
   Fungi are eukaryotic heterotrophs
    that digest food externally and
    absorb the the digested materials
    through their body walls.

   Most fungi, including molds and
    mushrooms, are multicellular and
    macroscopic. Yeasts, though, are
    unicellular and microscopic.
   Like plants, fungal cells have
    walls, but these walls are made of
    chitin, not cellulose.

   Fungi are classified by the
    way they produce sexual
    spores.
   Hyphae are the basic structure of
    threadlike filaments that grow
    from a fungal spore.


   Hyphae grow into a mycelium – a
    cottony mass covering and
    distributed within whatever the
    fungus is feeding on.
   Inside the hyphae are cross walls
    called septa. Within the septa
    there can be one to many nuclei
    depending on the species.


   Cytoplasm flows through pores in
    the septa
This is a cross-section of
hyphae. It shows septa,
pore and cytoplasm.
   Fungi are heterotrophs.


   Most are saprobes,
    decomposing dead organisms.
   Some fungi have symbiotic
    relationships with other
    organisms.


   Parasitic fungi absorb nutrients
    from their host through
    specialized hyphae called
    haustoria.
   Lichens are among the most
    fascinating organisms on this
    planet. Their very structure is
    unique: a symbioses of two
    organisms -- a fungus and algae --
    so complete that they behave and
    look like an entirely new being. A
    lichen can literally eat stones,
    survive severe cold, and remain
    dormant for long periods without
    harm. What type of relationship is
    this?
   Mycorrhiza is another symbiotic
    association in which a fungus
    lives in close contact with roots
    of a plant partner. What type of
    symbiosis is this?
   Fungi use extra cellular
    digestion – breaking down their
    food outside the cell then
    absorbing the nutrients.
   Fungi may reproduce sexually or
    asexually.

   Most produce spores which grow
    when they encounter favorable
    conditions.
   Budding is a form of asexual reproduction
    in which mitosis takes place and a new
    organism grows out and eventually
    separates from the parent cell.
   A sporangium
    is a sac or case
    in which spores
    are produced.



   This is a
    Rhizopus
    sporangium.
   The four phyla of fungi are
    identified by the shape and
    presence of their sporangium.
   Phylum Zygomycota’s common
    names are “bread molds” and “pin
    molds.”

   Why do they carry these names?
Two views of a Zygomycota’s
sporangium.
   Phylum Zygomycota has stolons
    which grow horizontally across
    the surface of the food source and
    produce

   Rhiziods which grow down to
    anchor the mycelium to the food
    source.

   This is the site of most
    extracellular digestion and
    absorbtion.
   Phylum Zygomycota is
    characterized by zygospores –
    thick walled spores capable of
    withstanding unfavorable
    conditions.
   Phylum Ascomycota are
    commonly called “sac fungi.”
   Phylum
    Ascomycota is
    characterized
    by ascospores –
    sexual spores
    produced
    inside an

   Ascus – a
    saclike
    structure in
    which
    ascospores are
    produced.
   This phylum
    also has
    conidiaspores
    asexual spores
    produced in
    conidia.
   Phylum Basidiomycota is also the
    “Club Fungi”.


   It is characterized by basidia –
    club shaped hyphae that produce
    basidiaspores during sexual
    reproduction.

				
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posted:10/16/2011
language:English
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