The Kingdom Fungi is in the domain Eukarya and
in the supergroup Unikonta. They are in the
group Opisthkonta with animals. Both groups
have different unicellular organisms that they are
their common ancestor. That fact indicates the
groups became multicellular organisms
independent of one another. Most closely related
protists group to the fungi are nucleariids.
Nucleariids are amoeboid organisms, with fine
pseudopodia unsupported by microtubules, with
or without hollow siliceous plates or spheres or
spines, the walls of which are a meshwork. Some
are uninucleate but others are multinucleate. No
flagellated stages known. Mostly described from
soils or freshwater
There are indications that the ancestor to the
fungi was a flagellated, unicellular eukaryote.
Most fungi no longer have any flagellated cells
except the chytrids. Fungi-are mostly multicellular
heterotrophs that obtain their nutrients by
absorption (saprophytes or parasites. Fungi must
secrete enzymes to break down the nutrients
before the nutrients are absorbed.
Most fungi exhibit a haploid lifecycle with sexual
reproduction; however there are some fungi that
only reproduce asexually or only sexually.
Fungal morphologyMulticellular fungi grow in cellular threads called hyphae.
A mass of hyphae is a mycelium. Some fungi when reproducing
sexually, will organize into fruiting bodies such a mushrooms.
except for ChytridsAll fungi produce spores (asexually or sexually)
in order to reproduce.
The cell walls of hyphae are made of chitin not cellulose. Chitin
contains nitrogen cross-links between glucose rings.
There are two general types of hyphae-1.
Hyphae that have cross walls forming
individual cells. Walls have pores so that
material can move between cells. Higher fungi have septate (walled)
hyphae. 2. Nonseptate fungi do not have cross walls and are multinucleate
(coencytic). Lower fungi are nonseptate fungi.
Specialized hyphae actually can form loops to kill prey. Haustoria are
specialized hyphae sending structures into cells to absorb nutrients.
Many fungi can reproduce asexually and also sexually. Most fungi are haploid. Since there are
no flagellated gametes, two different mating types of hyphae (+, -) join (plasmogamy). When that
occurs, quite often the nuclei remain distinct (dikaryon state n+n). Eventually the nuclei fuse
(karyogamy)
Meiosis occurs shortly after fertilization restoring the haploid state. Eventually fertilization or
fusion of the nuclei occurs or
karyogamy. General outline of fungi
reproduction
Phylum Chytridiomycota or
Chytrids-Most primitive fungi. Has
flagellated spores (zoospores).
Molecular evidence along with chitin
found in the cell walls indicate that
chytrids are fungi. Most species are
aquatic. Some species are unicellular, but most are aseptate. Most are saprophytes
Phylum Zygomycota (bread molds) is a lower fungi. Reproduction is asexual and sexual. The
hyphae are coencytic. During asexual reproduction an aerial hyphae emerges to form a
sporangium. Mitosis occurs to form spores. The sexual life cycle is the haploid life cycle. Two
different mating hyphae (+,-) are attracted and join. It forms a gametogania with several haploid
nuclei. They fuse to form a zygosporangia (fertilization), which is very resistant to drying out.
Inside the zygosporangia the diploid nuclei under go
meiosis to produce haploid spores that are released.
Phylum Glomeromycota is a lower fungi that forms
symbiotic relationships with the roots of many plants.
The fungi form arbuscular mycorrhizae that push into
plant root cells. The plant cells provide food for the
fungi and the fungi absorb nutrients (phosphate and
nitrates) and provide them to the plant. *Arbuscular
mycorrhizae penetrate root cells, ectomycorrhizae
form sheaths and do not penetrate the root cells.
Higher fungi are those fungi that form septate cells
and individual cells.
Phylum Ascomycota (sac fungi) are
fungi that produce sexual haploid spores
in structures called asci (ascus singular).
After meiosis, occurs mitosis takes place
so 8 spores are produced in the asci.
The asci are found on fruiting bodies
called ascocarps. Most ascomycetes can
also undergo asexual reproduction on
aerial hyphae. Yeast and morels are
also ascomycetes.
Phylum Basidiomycota
(club fungi) are fungi that
produce sexual haploid
spores on a structure called
basidium. Two different
mating types hyphae are
attracted and fuse forming
a dikaryon state. The
hyphae go in to form
fruiting bodies called
basidiocarps (mushrooms,
puffballs etc.) Within the
basidiocarp, club-like cells
form called basidium
(basidia pl.). The dikaryon
state fuses to become
diploid. Meiosis occurs to
produce four haploid
spores or basidio-spores.
Lichens are organisms with
a symbiotic relationship between fungi
(mostly ascomycota) and green algae
usually cyanobacteria. But the fungi
have been known to harvest the algae
which is a case of enslavement not
mutualism. Known to be the pioneer
species in primary succession
breaking down rock.
Fungi can also cause disease such as
smut on corn, rust on maple leaves
and ergots on wheat.