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
conidiaspore
s 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.