KINGDOM
FUNGI
The fungi
constitute unique kingdom of heterotrophic organisms. Members of this kingdom
are called fungi. They show great diversity in their morphology and habitat.
They can be seen on moist bread, butter, leather, wood, pickle, rotten fruits
and vegetables or as parasites on plants and animals. It grow in warm and humid
places so, we keep food in refrigerator, which prevents food from going to bad
due to bacterial or fungal infections and cosmopolitan in nature occurs in air,
water, soil and on animals & plants. It does not have chlorophyll and
chloroplasts. Most of fungi are heterotrophs. On the basis of source of food,
fungi are of two types
(A) Saprophytic :- These fungi obtain
their own food from dead and decaying organic matter such as bread, rotting
fruits, vegetables and dung.
(B) Parasitic :-
These obtain their own food from living organisms such as plants,
animals and human beings.
Some fungi are found symbiotically associated with algae and
form lichens. Some fungi are found symbiotically in the roots of higher plants
and form mycorrhiza. With the exception of yeasts which are unicellular, fungi
are filamentous. Their body consists of long, slender thread- like structures
called hyphae. The network of hyphae are called mycelium. Some hyphae are
continuous filled with multinucleated cytoplasm (coenocytic hyphae), other have
septa or cross walls in their hyphae. Cell wall composed of chitin (fungal
cellulose) and polysaccharides, but cell wall of the members of class-
oomycetes is mainly made up of cellulose. In fungi, the stored food is present
in the form of glycogen and oil.
MODE
OF REPRODUCTION
Reproduction in fungi can take place by vegetative means –
fragmentation, budding or fission. Asexual reproduction is by spores called
conidia or sporangiospore (zoospores, aplanospores) and sexual reproduction by
oospore, zygospore, ascospores and basidiospores.
(i)
Vegetative
reproduction
(a) Fragmentation – Sometimes the fungal
filament breaks into small pieces due to any reason. Now each piece forms a new
fungal filament and start working like normal filament.
(b) Budding – Vegetative type of
reproduction in which tuber or bud forms in parent cell and after sometimes
this bud separates and form new bud.
E.g. – yeast (saccharomyces)
(c) Binary fission – Method of
reproduction in which single parent cell divided into two daughter cell. E.g.- yeast (schizosaccharomyces)
(ii)
Asexual
reproduction – Asexual reproduction takes place by the formation of different
types of spores (conidia/sporangiospores). These spores are formed by mitotic
division.
(iii)
Sexual
reproduction- Fusion of gametes (syngamy)
Sexual reproduction in
fungi completes in three steps :-
(a) Plasmogamy – Fusion of protoplasm of
two motile or nonmotile gametes. In this stage two sex cells or two haploid
hyphae of compatible mating types come together and fuse. In phycomycetes the
fusion of two haploid cells immediately result in diploid cells (2n). However, in other fungi( ascomycetes and
basidiomycetes), an intervening dikaryotic stage (n+n) occurs. Such a condition
is called dikaryon and phase is called dikaryophase of fungus.
(b) Karyogamy – In this stage the
parental nuclei fuse with each other to form diploid nucleus which is known as
synkaryon.
(c) Meiosis (Reduction division) – In
this stage meiosis takes place. Meiosis in zygote/synkaryon/diploid nucleus
resulting in haploid nuclei or haploid spores.
Process of sexual reproduction
(1) Gametangial contact -
(a) In this process, first of all male
and female sex organs are formed on two different hypha of same mycelium. Male
sex organ is called antheridium and female sex organ is called oogonium.
(b) In mature antheridium & oogonium
both have one – one nucleus. Antheridium and oogonium come close to each other
and perform plasmogamy and karyogamy, then oospore(2n) is formed. Now meiotic
division takes place in oospore(2n), as a result of which haploid spores are
formed. Now each spore germinates and gives rise to a new mycelium.
(2) Gametangial Copulation :-
(a) In this process, two identical
gametangia directly fuse to perform plasmogamy and karyogamy resulting in
formation of diploid zygospore.
(b) Now meiotic division takes place in
zygospore(2n), as a result of which haploid spores are formed. Now each spore
germinates and gives rise to a new mycelium.
(3) Somatogamy – In it sex organs are not
formed. Only two hyphae come close to each other and their cells fused.
CLASSIFICATION OF FUNGI
(A) PHYCOMYCETES
· Phycomycetes are also called as lower
fungi and algae fungi.
· Members of phycomycetes are found in
aquatic habitat and on decaying wood in
moist and damp places or as obligate parasites on plants.
· Mycelium : The fungal filament of all
the fungi included in this class are coenocytic, aseptate and branched.
· Asexual reproduction takes place by
zoospore, aplanospores and conidia.
· Sexual reproduction may be isogamous,
anisogamous and oogamous.
On the basis of type of sexual reproduction
i)
Oomycetes
:
Asexual reproduction – By
sporangiospores (zoospores) & conidia.
Sexual reproduction -By
gametangial contact, Oogamous.
Examples :-
(a) Phytophthora infestans – Causes “Late blight
of potato.”
(b) Albugo candida or cystopus candida –
White spot / rust diseases of mustard
(c) Phythium species
ii)
Zygomycetes
:
Asexual reproduction – By
sporangiospores (aplanospores)
Sexual reproduction – By Gametangial
copulation, Isogamous
Examples – Rhizopus &
mucor – Bread mould
(B) ASCOMYCETES
· It is also known as “sac fungi”.
· They are saprophytic, decomposers,
parasitic or coprophilous (growing on dung).
· Members of ascomycetes are
multicellular but rarely unicellular, like yeasts.
· Mycelium : Uninucleate branched and
septate
Asexual reproduction – By
conidia
Sexual reproduction- By “Somatogamy”
· Sexual spores are called ascospores
which are produced endogenously in sac- like asci so they are named as
ascomycetes.
· There are three stage in sexual reproduction
(i) Plasmogamy (ii) Karyogamy (iii) Meiosis
Examples :-
(i)
Penicillium
notatum – First antibiotic penicillin
(ii)
Aspergillus
niger – Known as weed of laboratory and produce citric acid
(iii)
Neurospora
– Drosophila of plant kingdom
(iv)
Claviceps
purpurea – Ergot diseases of bajra
(v)
Morchella
- Also called morels ( it is edible)
(vi)
Truffle
– Edible
(vii)
Yeast
- Saccharomyces cerevisiae is also
called “Baker’s yeast” or Brewing yeast and yeast is a unicellular fungi.
(C) BASIDIOMYCETES
· It is also called club fungi.
· They grow in soil, and on thick
wooden pieces tree stumps or parasites on living plant
· Mycelium : Branched , septate and
uninucleated
Clamp connection:- It
is a tubular relationship between two neighbouring cells. With the help of this
connection the nucleus of one cell can migrate to the neighbouring cell, due to
which the other cell become dikaryotic (binucleated).
Asexual reproduction :- The asexual spores are generally not
found, but the vegetative reproduction by fragmentation is common.
Sexual reproduction :- sexual reproduction performed by somatogamy.
Examples: -
(i)
Rust
fungi- wheat rust diseases caused by puccinia
(ii)
Smut
fungi – Loose smut diseases caused ustilago
(iii)
Mushroom
– Delicious or edible mushroom
· Toadstool – Poisonous mushroom
· Delicious of edible – Agaricus
bisporous
(iv)
Puffball
(v)
Bracket
fungi
(D) DEUTEROMYCETES
· Deuteromycetes is a imperfect fungi.
· Some members are saprophytic or
parasitic, while a large number of members of this class are decomposers of
litter and help in mineral cycling. e.g. Trichoderma
· Mycelium : Septate and branched.
· Asexual reproduction takes place with
the help of conidia.
Examples – Alternaria solani ( Early blight of potato) ,
Colletotrichum falcatum (Red root diseases of sugarcane) and Trichoderma
0 Comments