KINGDOM FUNGI
General Characteristics
- Fungi
are achlorophyllous, spore bearing and non-vascular organisms.
- Fungal
cell wall is made up of chitin-the fungal cellulose.
- They
are usually filamentous with branched somatic bodies.
- They
are heterotrophic and reproduce generally by spores.
- They
can be parasitic, saprophytic or symbiotic.
- They
occur in long lasting beneficial association with the roots of
gymnosperms. This association is called mycorrhiza.
- They
range from unicellular forms to thread like structures known as mycelium.
- The
interconnected filaments of mycelia are called hyphae.
- Each
hypha is bounded by a chitinous cell wall.
- Multinucleate
forms are known as coenocytic.
Cell Structure
- Fungal
cell is eukaryotic with a chitinous cell wall.
- Hyphal
or fungal cell wall encloses the protoplast which is differentiated into
plasma membrane, cytoplasm and nucleus/ei.
- Reserve
food is in the form of glycogen and lipid globules.
- Membranous
vesicles called lomasomes are found attached to the cell membrane.
- Cytoplasm
is colourless and vacuolated.
- Fungal
hyphae may be septate or aseptate with one, two or more nuclei.
- In
case of aseptate hyphae the the cross wals are not formed after nuclear
divisions and hence such forms are multinucleated or coenocytic.
- In
case of septate hyphae the cross walls are laid down after nuclear
divisions and such forms are called acoenocytic forms.
- Septa
are generally perforated with pores, which can be simple or dolipores.
- Dolipores
are barrel shaped with swollen edges.
Stages in the development of a branched hypha
Phases in the life cycle of Fungi
Reproduction in Fungi
- Vegetative
Reproduction
(a)
Fragmentation-
Vegetative hyphae get broken into fragments accidentally and the fragments
develop into new mycelia eg. Rhizopus,
Mucor.
(b)
Fission-
In this case, the parent cell splits into two daughter cells by constriction eg.
Yeasts.
(c)
Budding-
A small outgrowth appears in the vegetative cell and enlarges in size eg.
Yeasts.
(d)
Sclerotia-
These are more or less rounded,cushion-like cylindrical or irregular
structures. They grow under favourable conditions to produce mycelia eg. Claviceps.
(e)
Rhizomorphs-
They are rope like twisted subterranean masses of several interwoven hyphae
with well-defined apical growing point.
- Asexual
Reproduction
- Sexual
Reproduction
Classification of Fungi
S.No.
|
Group
|
General Features
|
Examples
|
Diagrams
|
-
|
Phycomycetes
(Algal
fungi)
|
- Mycelium
is coenocytic.
- Wall
of hyphae contains cellulose.
- Asexual
reproduction involves formation of sporangia, which produce zoospores,
aplanospores.
- Sexual
reproduction is by gametangial contact.
- Gametes
are usually nonflagellete.
- Ptroduct
of sexual reproduction is oospore. Hence, they are also called as
oomycetes.
- They
may be parasites or saprophytes.
|
Phytophthora,
Albugo,Pythium
|
|
-
|
Zygomycetes
(Conjugation
Fungi)
|
- Mostly
saprophytes, some may be parasites on plants and animals.
- Cell
wall is mainly composed of fungal chitin.
- Mycelium
is well developed, profusely branched, filamentous and coenocytic.
- Asexual
reproduction takes place by sporangiospores, aplanospores or by conidia.
- Sexual
reproduction takes place by conjugation and hence are called conjugation
fungi.
- Sexual
reproduction produces a resting diploid zygospore.
- Zygospore
produces germ sporangiophore which bears terminal germ sporangium, which
in turn produces meiospores called germ spores.
|
Rhizopus,
Mucor
|
|
-
|
Ascomycetes
(Sac
Fungi)
|
- Saprophytes
or parasites.
- Are
haploid fungi and their mycelium is composed of septate hyphae.
- Cell
wall is made up of fungal cellulose.
- Motile
structures are absent throughout their life cycle.
- Most
distinctive feature of this group is the formation of sac like
structure, the ascus, in which eight ascospores are produced.
- Asexual
reproduction occurs by oidia, conidia nad chlamydospores.
- Sexual
reproduction occurs by gametangial copulation, gametangial contact,
spermatisation and somatogamy.
- Fertilisation
involves plasmogamy and karyogamy.
|
Saccharomyces,
Penicillium, Neurospora
|
|
-
|
Basidiomycetes
(Club
Fungi)
|
- The
mycelium is perennial, septate and multicellular composed of branched
hyphae.
- Mycelia
are of two type- primary and secondary.
- Primary
mycelia develop by the germination of basidiospores and its cells are
monokaryotic.
- Primary
mycelium is short and multiplies by oidia or conidia.
- Motile
structures are all together absent.
- Sexual
reproduction occurs between + and – strains in three steps- plasmogamy,
karyogamy and meiosis.
- Secondary
mycelium is long lived and consists of profusely branched, filamentous
hyphae which are septate and binucleate.
- Septa
consist of dolipores.
- Secondary
mycelia multiply by chlamydospores, ascidiospores etc.
- They
penetrate into the soil or wood by sclerotia or rhizomorphs.
- Karyogamy
and meiosis takes place in the basidia.
|
Agaricus
campestris, Puccinia, Amanita
|
|
-
|
Deuteromycetes
(Fungi
Imperfectii)
|
- They
are saprophytes or parasites.
- Mycelia
consist of septate and branched hyphae.
- Septa
are perforated and multinucleate.
- Reproduction
is by conidia, oidia or chlamydospores.
- Sexual
reproduction is absent
|
Alternaria
solani, Fusarium
|
|