or

ask mattrab Visit www.askmattrab.com for more academic resources.

FUNGI : REPRODUCTION and NUTRITION

Vwhdezq

Fungi are reproduced by three methods: vegetative, asexual and sexual methods. The perfect fungi reproduce by all vegetative, asexual and sexual methods while the imperfect fungi reproduce only by vegetative and asexual methods. In both sexual and asexual reproduction, fungi produce smaller and lighter spores which scatter from the parent fungi. Spores germinate into new likelihood fungi on falling in suitable substrata under favourable conditions.

1 : VEGETATIVE REPRODUCTION : 

It is a type of reproduction in which somatic hyphal cells or mycelium involves for the development into new individuals of fungi without formation of seeds and spores.


Fungi produce different kinds of spores during asexual and sexual reproduction and thus named asexual spores and sexual spores. Usually, spores are uninucleate and non-motile while in some other fungi, they are multinucleate and motile. Thus, fungi are called pleomorphic or polymorphic as they produce more than one type of spores during reproduction. The spores produced inside the sporangia are known as endogenous spores (e.g. ascospores produced inside the ascus of yeast) and the spores developing exogenously on the terminal ends of sporophores (special structure i.e. basidium of mushroom in which basidiospores develops outside the basidium) are called exogenous spores.


Vegetative reproduction takes place by following methods:


a. Fragmentation

b. Budding

C. Fission

d. Oidia

e. Chlamydospores

f. Sclerotia and

g. Rhizomorphs 


2. ASEXUAL REPRODUCTION

For asexual reproduction, fungi produce single-celled, motile or non-motile, thin or thick-walled propagules called spores. Spores produced after meiosis are called meiospores or germ spores sexually produced spores eg ascospores, basidiospores. Other spores are called mitospores or asexually produced

spores eg. zoospores, sporangiospores, chlamydosopres, oidia, conidia, etc.

Different fungi reproduce asexually by the formation of different spores. Some of them are as follows:

a) Sporangiospores : The spores developed within a sac like-structure is called sporangium. The special aerial hypha bearing sporangium is called sporangiospore .The sporangium contains a large number of motile or non-motile spores called sporangiospores. The non-motile sporangiospores are called aplanospores. On maturity, sporangial wall gets burst at its tip and  Sporangiospones of cor spores disperse away by air. On falling suitable substratum, they germinate to new individual fungi. 


b) Zoospore :  Zoospores are thin-walled, uninucleate, motile biflagellate spores produced inside the sporangium of sporangiospores. These are called zoospores. The sporangium bearing many zoospores inside of it, is called zoosporangium. They are naked spores without the cell wall which, after the swarming period, i.e. encyst secrete a wall and germinate to germ tubes. The germ tubes grow to new mycellia. Examples are aquatic fungi like PYTHIUM 

c) Conidiophores :  Conidia are non-motile, thin walled mitospores formed externally as single cell (c.g. Pithi) or in chains (e.g. Aspergillus). They are developed on a conidiophore. The conidiophore may be simple or branched, septate or aseptate, singly and scattered in the mycelium. Sometimes,they arise in specialized structures called fruiting bodies. Based on their appearance, they are called pycnidia (flask-shaped), synnema, sporodochia, acervuli (saucer-shaped) or pustules. All the asexual spores are genetically identical. 


3. SEXUAL REPRODUCTION : 

 Most of the true fungi reproduce sexually except imperfect fungi. The sexual reproduction occurs bythe fusion of two compatible nuclei or male and female gametes from two parents in the life cycle of fungi. The process of sexual reproduction involves three principal events as mentioned below: 

 

a)Plasmogamy: Plasmogamy is the process which brings the fusion of cytoplasm of two different

gametes or cells. It brings two genetically different nuclei in the same cell. Such a cell with two nuclei is called dikaryotic and a pair of two such different nuclei in the cell is called dikaryon, 


b) Karyogamy : Karyogamy is the second phase of sexual reproduction. It involves the fusion of twohaploid nuclei to form a diploid zygote sooner or later after plasmogamy. In higher fungi (Ascomycetes and Basidiomycetes), however, karyogamy is somewhat delayed. The dikaryotic mycelium has a long vegetative phase in higher fungi.

 c ) Meiosis : This is the third phase of sexual reproduction. In it, the diploid nucleus undergoes meiosis to produce haploid nuclei. It also helps in the recombination of genetic material. The products of meiosis are called meiospores. Meiospores act as sexual spores which germinate to mycelium.



MODE OF NUTRITION IN FUNGI : 

Fungi lack chlorophyll and they depend upon other organisms for their food. So, they have heterotrophic mode of nutrition. They are either naprophytes or parasites or symbionts.

 (i) Saprophytic fungi : They absorb food from dead or decaying organic matters, eg. Macor, Rhizopus , Pencillium, Aspergillus. Some of them are only found in decaying substances not in the body of living organisms. They are called obligate saprophytes. Some are found both in the decaying substances and in the body of living organism. They are called facultative saprophyte or facultative parasites .

 (ii) Parasitic fungi : They obtain their nourishment from the protoplasm of the living plants or animals. The organisms, in which parasitic fungi are found are called their hosts. The parasites which only grow in living cells are called obligate parasites, eg. rusts, mildews, etc. They cause several diseases to their hosts.


(iii) Symbiotic fungi : Some fungi form partnerships with other group of plants by which both the plants and fungi are benefited. This type of association is called symbiosis and such fungi are called symbiotic fungi. For example, a group of fungi called mycorrhiza is associated with the roots of Pinus and other higher plants. The fungi get shelter and food from the plants. In return, they help the plants by absorbing minerals and water from the soil.