Download Introduction to fungi

L.1-G.Biology
Mycology
D.Ebtihal Muiz
Introduction to fungi
The fungi (singular fungus ) are a kingdom of eukaryotic organisms .
The are heterotrophic and digest their food externally , absorbing nutrient
molecules into their cells . Yeasts , molds and mushroom are examples of fungi .
The branch of biology involving the study of fungi is knownas mycology (Gr.
Mykes mushroom + logos = discourse).
Fungi and bacteria are the primary decomposer of organic matter in most
terrestrial ecosystem . Fungi are characterized by a life cycle that begins with
germination from a spore or resting structure , following by a period of growth
as substrate is exploited to produce biomass ..Finally there is a period of
sporulation , where propagules are formed that can be disseminated from the
parent mycelim.
Summary of Fungal Attributes
From our discussion on how fungi are able to carry out their various
activities, the following attributes can be used to characterize those organisms
that we classify as fungi:
A-They are heterotrophs. That is, they cannot manufacture their own
food from simple compounds as plants are able to do. So they are
dependent on other organisms to produce their foods, e.g., sugars,
starches, proteins, fats, etc. Fungi can be further divided into saprobes,
parasites, symbionts, facultative parasites and facultative saprobes.
B-The food gathering part of a fungus is made up of either
filamentous, hollow, branched tubes called mycelium or are single
cells called yeasts.
C-Structures called spores reproduce the fungus in the form of
mycelium or yeast cells.
D-They have cell walls. This is a characteristic generally attributed to
plants, but unlike plants, most fungal cell walls are composed of chitin,
a carbohydrate, and is the same material which makes up the
exoskeletons of insects. Plant cell walls are composed of cellulose.
E-Fungi are eukaryotes as are most other organisms with which you
are familiar. However, bacteria differ from fungi in that they are
prokaryotes.
F-Absorption: The process by which fungi "eat". This differs from the
way in which we eat in that a fungus will digest its food before eating
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it. Bacteria are the only other group of organisms that eat in this
fashion
Characteristics of "fungi" in the broad sense
1.
Achlorophyllous: Fungi cannot make their own food like plants. They
are heterotrophs and depend upon other organism for their carbon
source. Heterotrophs can further be divided into the following
categories:
a. Parasites: Organisms that derives their nutrition from
the protoplasm of another organism (=host).
b. Saprobes: Organisms that obtains their carbon source
(=food) from the by-products of organisms or dead
organisms. However, if the opportunity arises, some
saprobes may become parasitic. Such organisms are
said to be facultative parasites.
c. Symbiosis: In the strict sense, this term refers to the
habitual "living together" of different species. As such,
there are a number of different categories of
relationships that may fit under this term. However, we
will define it in its most common usage: "The intimate
association of two dissimilar organisms in a mutually
beneficial relationship, e.g. lichens and
mycorrhizae." This type of symbiosis is specifically
referred to as a mutualistic symbiosis.
2. Eukaryotic: Fungi have membrane bound organelles, i.e. nucleus,
mitochondrion, E.R., etc. Once upon a time filamentous bacteria called
Actinomycetes were classified with fungi, but this is no longer the case.
3.
The the body or assimilative part of the fungus (=thallus) usually takes
the following forms:
a.
Yeast: Unicellular fungi that reproduce, asexually,
by budding or fission (terms to be defined later).
b.
Mycelium: The collective, filamentous strands that
make up the fungal thallus. Strands of mycelium is
referred to as hyphae (sing.=hypha). Mycelium may
be of two types:
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1-Septate: Mycelium that is divided into discreet
cells by cell walls that are laid down at regular
intervals along the length of the mycelium.
These cell walls are called septa (sing.=
septum).
2- Coenocytic: Mycelium that is not divided
up by septa and forms a continuous tubular
network. Septa, however, are present
occasionally, especially where reproductive
structures occur and where the cell wall of the
mycelium has been compromised.
c. Some species may have have thalli that are mycelium
and yeast. Such fungi are said to be dimorphic (=two
forms).
4. The assimilative stage of the fungal body, i.e. mycelium or yeast, has a
cell wall. In the strict sense organisms classified as fungi have cell walls
composed primarily of chitin. However, we will be also be covering
"fungi" that do not have chitin in their cell walls.
5. Fungi have a common nutritional mode: Absorption: The transport
of food from their substrate into their cell walls. The following events
occur in this mode of nutrition:
a.
If the available food that the fungus is using is
soluble, i.e. a simple organic compound, such as
simple sugars and amino acids, the mycelium or yeast
cells can transport the food directly through their cell
wall.
b.
If the available food is insoluble, i.e. a large,
complex, organic compound, such as lignin, cellulose
and pectin, then production the food must first be
digested. Digestion is carried out by the production of
various enzymes that are substrate specific and will
break down insoluble food material to soluble
compounds that can be transported through the cell
wall. Although this appears to be very different from
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the way in which we (animals) digest food, it differs
only in the sequence of events that takes place. Where
we ingest food and then digest it, fungi first digest
their food before ingestion.
6.
Either sexual or asexual reproduction or both may occur by
spores. Spores and/or gametes can be motile or not.
However, in the strict sense as fungi are currently defined,
only those organisms that produce nonmotile spores and
gametes are classified as fungi. Nevertheless, we will be
going over organisms that have motile spores, called
zoospores, and motile gametes.
In summary then, the organisms that we call fungi represent a
heterogenous group, i.e., they are polyphyletic, that are not closely
related as you will soon see.
When I was an undergraduate, organisms that were defined as fungi
were heterotrophs, with cell walls, that have filamentous or yeast
thalli. Today, fungi that are classified in the Kingdom Mycetae
(=true fungi), have a more restrictive set of characteristics:
Eukaryotes with cell wall material composed primarily of chitin
and derive their nutrition by absorption.
Based on the phenotypic definition , fungi do not comprise a
single group of organisms , more than one evolutionary origin .
That is to say , not all " fungi " are members of the kingdom fungi .
Characters that separate the fungi ( = the kingdom fungi ) from "
fungi ".
Kingdom fungi
protistan fungi
mitochondria
cristae flattened
cristae tubular
motile cell
nomotile cells or
motile cells with
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posterior flagella
anterior or lateral
flagella
cell walls carbohydrate
lysine synthesis
phyla
chitin
cellulose
alpha-aminoadepic
diaminopimelic
acid (AAA)
(DAP)
Chytridiomycota
Oomycota
Zygomycota
Hyphochytriomycota
Basidiomycota
Ascomycota
Labyrinthulomycota
Slime molds
( Myxomycota ,
Acrasiomycota )
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Some advantages and disadvantages of fungi
Fungi are the agents responsible for much of disintegration of organic matter
, and a such they affect us directly by destroying food , fabrics , leather and
other consumers , good manufactured from raw materials subject to fungal
attack , they cause the majority of known plant diseases , and many diseases of
animals and of man , they are basis of number of industrial processes involving
fermentation , such as the making of bread , wines and the preparation of
cheeses , and are responsible for the manufacture of number of antibiotic drugs ,
notably penicillin . Fungi are both destructive and beneficial to agriculture, they
are responsible for damage to crops by causing plant disease, while on the other
they increase the fertility of the soil by inducing various changes which result in
the release of plant nutrients in a form available to green plants.
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