Diversity of The World of Life
etc. (Division Chytridiomycota)
Bread Molds etc.
Baker's Yeast, Candida, etc.
Morel, Truffle, Penicillium, etc. (Euascomycetes)
Rusts etc. (Urediniomycetes)
Smuts etc. (Ustilaginomycetes)
Mushrooms, Bracket Fungi, Puffballs, etc. (Homobasidiomycetes,
Jelly Fungi, Various Yeasts, etc. (Other Hymenomycetes)
A Fungus (typically a sac fungus but sometimes a club fungus) Living
Together in One Body with An Alga (typically a unicellular green
alga but sometimes a blue-green alga)
that before modern genetic research, oomycetes
and slime molds were also classified as fungi;
and fungi were classed as plants (which also have cell walls and often reproduce by means of spores).
fungi live in salt- and freshwater, in and on the land (typically in moist
habitats), and in and on other living organisms.
together as the body of a lichen, the fungus provides a
"foothold" (as on a rock), moisture, and shade (from
over-intense sunlight); and the alga provides food (via photosynthesis) --
the alga can live alone, and often better alone; but the fungus cannot
survive without the alga.
mutually beneficial living arrangement ("symbiosis") of a fungus
growing in close association with the roots of a higher plant is called a
"mycorrhiza": The fungus helps control mineral uptake by
the roots, which in turn feed the fungus.
some fungi, notably yeasts, are unicellular, most fungi are mutlicellular,
forming often branched filaments, called "hyphae".
cell walls of fungi are reinforced with "chitin" -- a
nitrogen-enriched "polysaccharide" (a "polymer",
chain-like molecule, composed of sugars) -- as in the "exoskeleton" of
various arthropods. Only certain
chytrid fungi (presumably like the ancestors of all fungi) have cell walls
with "cellulose" (a different polysaccharide), as in various
algae and all higher plants. Fungi are truly
neither plants nor animals.
cross-walls within the hyphae of a fungal body are either porous or
absent: Each hypha typically has many nuclei (like likewise "coenocytic"
oomycetes or golden-green algae, from
which fungi probably evolved).
hyphae of the "vegetative body" of a fungus (as opposed to the
"fruiting bodies", as described below) typically grow together
as a weblike or leatherlike structure, known collectively as the
like animals but unlike plants, are "heterotrophic" (not able to
produce their own food molecules). Most fungi are
"saprophytic", consuming dead or other nonliving organic matter
and, thus, sometimes rotting valuable products but typically contributing
immensely to the absolutely vital recycling of waste materials in the
environment. Many fungi are parasitic, causing minor to
life-threatening diseases of plants and animals.
OF MATERIALS WITH THE ENVIRONMENT
the hyphae of a fungus secrete enzymes, which break large food molecules
in the environment down into molecules small enough to be absorbed.
fungi produce "haustoria", specialized hyphae that grow into and
absorb materials from the cells of other organisms.
are moved within each cell and throughout all the hyphae of the mycelium
(with porous or absent cross-walls) by the active process of cytoplasmic
growth and development of a fungus is under genetic control, and hormones
play a role in at least multicellular forms.
reproduce asexually by various means. Unicellular forms, such as
yeasts, reproduce by "budding" (simple fission). Some
multicellular forms reproduce asexually from pieces of hyphae, such as
hardened, unicellular "chlamydospores". Most fungi
reproduce asexually by means of spores, which may be mobile or nonmobile,
and either borne in "sporangia" or not encased.
for which no sexual means of reproduction has been observed were
traditionally classed as "imperfect fungi", a completely
artificial category; with genetic research etc., these species are being
reclassified into the other, naturally significant groups.
chytrids are undoubtedly the most primitive fungi: Their
"gametes" (sex cells) have propeller-like "flagella",
with which they swim through their aquatic environment. All other
fungi must grow together to affect sexual fertilization.
sexual reproduction of a fungus typically involves three distinct life
stages. The "diploid" stage (with both sets of
chromosomes) produces the "haploid" stage" (with just one
set of chromosomes), via "meiosis" (the form of cell division
that cuts the number of chromosomes in half). The haploid stage
which produces the "dikaryotic" stage (each cell or hypha with
twice as many (haploid) nuclei as normal). The dikaryotic stage
finally reproduces the diploid stage, via the fusion of the nuclei -- if
and only if the nuclei are compatible, which in some species means from
different hyphae (however, because they appear and grow similarly, such
hyphae are known as "plus" or "minus" strains, not
distinctly "male" or "female" sexes).
in Zygomycota (such as bread molds), if the tips of short hyphae
(branching off the main mycelia) of plus and minus strains happen to meet,
they will enlarge and be walled off from the rest of the hyphae, forming
"gametangia", each with many nuclei (haploid, like the rest of
the mycelium). The gametangia then fuse, producing a diploid
"zygote". The zygote develops a thick wall, becoming a
"zygospore", which eventually germinates into another haploid
in sac fungi, a haploid mycelium produces female and male gametangia, in
close contact with one another. "Gametes" (haploid male
and female cells) are produced within each gametangium. The
cytoplasm of a male gamete fuses with that of a female gamete, but their
nuclei do not fuse: The resulting, dikaryotic hyphae grows,
intermingled with the original, haploid mycelium, forming a ball-,
bottle-, or dish-like body (the "ascocarp"), which bears tiny
dikaryotic sacs ("asci") on its inner surface. Within each
ascus, the nuclei finally fuse; immediately, within this diploid cell,
haploid "ascospores" form, by meiosis (cell division halving the
number of chromosomes) followed by mitosis (the typical form of cell
division, not changing the number of chromosomes). After being
released, these ascospores germinate into other haploid hyphae.
in yeasts (unicellular, atypical sac fungi), the ascus is in effect the
diploid parent cell, in which are formed (via meiosis) the haploid
in club fungi, two haploid hyphae (or special cells from them) fuse,
producing a dikaryotic cell.
club fungi like mushrooms, the dikaryotic cell typically produces an
inconspicuous mycelium that grows into the visible mushroom, puffball, or
bracket-like body (the "basidiocarp"), on whose gills or in
whose pores are borne club-shaped dikaryotic cells (the "basidia"),
whose nuclei fuse. On their outer surface, the then diploid basidia
produce (via meiosis) haploid cells ("basidiospores"), which
after being released, germinate into new, haploid hyphae.
club fungi like rusts, the original dikaryotic cell is typically a
resistant "teliospore", which eventually germinates directly
into the basidium (there is no "mushroom" or other basidiocarp).
The nuceli of the basidium fuse, and this diploid basidium forms (via
meiosis, sometimes followed by mitosis) the haploid basidiospores.