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life on earth can be divided in three different groups: prokaryotic, eukaryotic
and archea. Within these further sub distinctions can be made, resulting in a
branched and complex annotation of life.  Fungi are eukaryotic organisms, which constitutes
its own kingdom, along the plant and animal kingdoms. As other eukaryotic
cells, fungi cells accommodate organelles and a true nucleus, all contained
within a membrane, while they differ by having a cell wall consisting of chitin,
as well as lacking chlorophyll.

The general
scheme of a fungi is relatively simple. Composing of a main body, a mycelium, made
up by a branched network of tubes, hyphae. Through hyphae, nutrients are absorbed,
in which organic carbon, from either living or dead biological organisms,
function as the main energy source. Reproduction of fungi can occur in two separate,
yet connected, ways. Either reproduction takes place asexually, mainly through the
means of the release of small identical copies of parent fungi as spores, or
reproduction occurs sexually. Sexual reproduction varies between different
phylums and therefore a generic description does not make sense. Instead a
detailed description is integrated within the description of each phylum.

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The fungi
kingdom can be subdivided in 5 different phyla, these are named Chytridiomycota, Zygomycota, Ascomycota, Basidiomycota and Deuteromycota.

Phylum Chytridiomycota
all fungi, which at some point in their life cycles exists as flagellated
swimming cells and these fungi are therefore, primarily, found in aquatic
environments. These fungi reproduce asexually when a zoospore, who are
uniflagellate asexual spores, lands on a suitable substrate, after which a cell
wall forms around it, thus, creating a fungi body. Long threads, rhizoids,
attach to the substrate and through these nutrient is absorbed. After a period
of feeding, the fungi body is converted into a sporangium, a structure which
contains and subsequently releases zoospores. Sexual reproduction occurs by
fusing zoospores, thus creating a diploid zygote, which then hardens and
creates a meiosporangium. Later fusing of nuclei create meiospores, which can then
swim away to find a suitable substrate and form a new fungi body. Fungi of this
phyla are mostly harmless, saprotrophic fungi, although a few pathogens such as
dendrobatidis, which causes
chytridiomycosis in amphibious animals have been found.

Phylum Zygomycota clusters more than 1100 different species, mostly
saprotrophic soil fungi, who exploits nutrients by decomposing waste products,
such as rotten fruit. Their name, refers to their reproductive sexual
mechanism, as it forms a structure called zygosporangium, arising from the
conjugation between two compatible hyphae.  After conjugation, a cell wall is formed
behind the fusing hyphae, which at this point are called gametangia. Next to
this, the wall separating the two hyphae is broken down, leading to fusion of both
hyphae’s cell components into one organism, except their nuclei, which are
still separate entities. Following this, their nuclei fuse and the walls around
the zygosporangium grows even harder and thicker than before, this creates the
zygospore, responsible for the naming of the phylum. After a long resting
period, meiosis occurs, and the fused nuclei are divided into two separate
recombinant nuclei.  These are then later
integrated and released as meiospores. Asexual reproduction occurs by the
release of mitospores. Most Zygomycota are harmless to humans, although a few
are pathological causing a disease called mucormycose,
which arises when spores are inhaled from dusty environments. 

Fungi in the third
phyla, phylum Ascomycota, are the
most abundant phylum as more than 65.000 species belong here. Their trademark
is their structural component, the ascus, which is a sac-like unit, harboring
eight ascospores, in which sexual and asexual reproduction occurs. The formation
of this component arises when a spore lands on a suitable substrate, which
forms a haploid mycelium. From this, asexual structures can be produced, or
sexual structures, gametangia, can be formed. The female sexual structure is
called ascogonium, while the male sexual structure is an antheridium.  Fusing of these leads to plasmogamy (one
organism, with two nuclei) and forms an ascogonius hypha. Karyogamy (fusing of nuclei)
takes place at the tip of this hyphae, creating a diploid ascus, who undergoes
meiosis and thus produces 4 haploid nuclei. Followed by a round of mitosis
eight ascospores are formed, which can then be released and the cycle repeats. Due
to the sheer amount of species, phylum Ascomycota, exert both a positive and
negative effect on the human condition. Beneficial species such as Penicillium notatum and Saccharomyces cerevisiae contribute to
our health and or ability to produce beverages, while malign effects are seen
by species of the Aspergillus genus who can cause a respiratory disease, decay
food, synthetize carcinogenic toxins in nuts etc. The Aspergillus genus will be
investigated extensively later in this paper.

fourth phyla, Basidiomycata, are next
to Ascomycota the most abundant phyla with more than 30.000 separate species
and because of this abundance, their diversity is large and plentiful. This
phylum encompasses the largest and most complex fungi, in which most species share
a common structural component coined basidium. 
The basidium is a club shaped structure, in which meiosis takes place
and where basidiospores are synthesized, often located on fruiting bodies such
as mushrooms. Basidiomycota reproduce asexually by producing spores or by a
mechanism called budding, in which an extension of a cell is separated into its
own cell. Sexual reproduction happens when haploid hyphae meet and fuse, often
followed by the transfer of a nuclei from each parent hyphae to the other,
which reproduces mitotic, thus, creating a dikaryotic mycelium.  From dikaryotic mycelium a fruiting body
arises, by hyphae, who communicate and create different components. Some create
the stalk, other the gills of the fruiting body. The tips of the hyphae which
constitutes the gills is the basidium and when these swell, nuclei are fused
and a bit after 4 basidiospores are formed, which will then be ready to be
released. Basidiomycota play an important role in ecosystems, as they achieve
nutrient by breaking down decomposing organic material, unfortunately they also
break down wood, which have negative economical consequences.

The last phyla, phylum Glomerucyto, is a fairly new
addition to the additional four phylae. These fungi live in close association
with the roots of trees. Their relationship is symbiotic in which the roots
contribute with carbohydrates and carbon, while the fungi stacks essential
vitamins and minerals which the plant can utilize. Glomeromycota do not
reproduce sexually and cannot sustain life without support from plant roots.

The remaining fungi
that do not fit in any of these phyla, belong to a sixth informal phylum called
phylum Deuteromycata. These fungi all reproduce solely asexually are as
individuals closer to other phyla but not close enough to be considered a valid
part of these.

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