Q.11. Describe the reproduction in fungi.
Ans. Reproduction: -
The fungi reproduces vegetativelly, asexually and sexually-
1. Vegetative reproduction-It take place by-
(a) Fragmentation: - The hyphae break up into two or more pieces due to some external force and each of them develops into new one.
(d) Fission: - Normally some unicellular fungi like yeast bacteria reproduces by this method. In this the vegetative cell elongates and divides into daughter cells by simple construction or transverse wall.
(c) Budding: - In this case the parent cells buds off new cell which separates from the parent cell and develop into new individual e.g. yeast cell.
(d) Sclerotia: - This is a modification of mycelium. It is hard, resting storage object. It also serves as a means of perennation and vegetative propagation. With the return of favourable condition it germinates.
2. Asexual reproduction: - It takes place by means of several types of spores some of which are as follows.
(a) Motile zoospore: - The motile zoospores may be uni or biflagellate pear shaped structures produced by the lower fungi in spherical pear sporangium e.g., Synchytrium, Albugo, etc.
(b) Conidia: - These are non-motile spore produced exogenously by constriction at the ends of special hyphal branches called conidiophores. They may be produced single (e.g., pythium, phytophthora) or in chains (e.g., Aspergillus Penicillium).
(c) Oidia: - Some fungi like Mucor, the hyphae forming mycelium often become divided by transverse walls into a large number of short segments, each of which is capable of germinating and developing into a new plant. These segments which may remain united in chains or become free other are known as oidia.
(d) Chlamydospores: - The chlamydospores also produced like that of oidia, but they differ from the latter in being thick walled and colored black or brown. They may terminal or produced at irregular intervals along the hyphae.
(e) Spores: -These are simple reproductive units usually unicelluar and with certain food reserve. Their size, shape and colour very in different species. In higher fungi like Ascomycetes and Basidiomycetes, the spores ascospors and basidiospores are produced.
3. Sexual Reproduction: - The sexual reproduction is a subsidary process in the fungi. In case of fungi like other organisms the sexual reproduction takes place by the union of two compatible nuclei and consists of three phase.
1. Plasmogamy: - It involves the fusion of two protoplasts bringing two haloid nuclei close together in the same cell.
2. Karyogamy: - It involves the fusion of two haploid nuclei brought together during plasmogamy. This results in the formation of a diploid structure the zygote.
3. Meiosis: -It follows nuclear fusion which eventually takes place in all sexually reproducing fungi. It again reduces the number of chromosomes from diploid zygote nucleus to orginal haploid number in the daughter nuclei.
The sexual reproduction in fungi is varied. It may be of following types:
(a) Planogametic copulation: - Planogametes are motile gametes. This involves the fusion of two naked gametes. The fusing gametes may be isogametes, anisogametes or heterogametes.
(b) Gametangial contact: - In this case the gametes are transferred directly from on gametangium to the other. These gametes are undifferentiated protoplasts and represesented by nucleus. Actually they never fuse.
(c) Gametangial copulation: - It involves the fusion of the entrie contents of the gametangia.
(d) Spermatization: - In certain case e.g. Ascomycetes and Basidiomycetes there is the formation of certain non-motile, male cells the spermatia. This spermatia are brought in contact with female gametangia receptive hyphae or somatic hyphae to which they are attached. The partition wall dissolve and contents of spermatia pass into female organ.
(e) Somatogamy: - In most of the members of Ascomycetes and Basidiomycetes there are no sexual organs produced and the sexual act is accomplished by the fusion of two nuclei from somatic cells. This fusion result the formation of zygote, or zygospore. They produce spores which in there turn develop in mycelium.
Q.12. Describe economic importance of fungi. (2006, 13)
Related Question-
Q. Jastify the statement that ‘Fungi’ are not only our foes but friends also. (2012)
Q. Write a short note on edible fungi. (2004)
Ans. Economic Importance of Fungi: -
The fungi are closely related to man, animals and plants. Infact they are intimately linked with us and play an important role in our life. Some fungi are harmful while a few are useful to us.
Some Useful Activities of Fungi: - The fungi are useful to us in many ways:
1. Destruction of Organic Waste: - The saprophytic fungi decompose plant and animal remains. CO2 is released in this process, which is used by green plants.
2. In Industry - 1. Many organic acids and vitamins are prepared by different fungi as Aspergillus niger, A.glances, Aclavatus, Citromyces citricus many acids like gluconic acid, lactic acid etc. are prepared from them. Aspergillus, Fusarium (different species) are the source of riboflovin, and vitamin B.
2. Several fungi have been found to be the basis of entire alcohlic industry in the production of ethyl alcohol by the fermentation of sugar solution by yeast.
C6H1206
2C2H5OH + 2CO2
2C2H5OH + 2CO2
3. Saccharomyces is an important basis of basis of baking industries.
4. Use of Penicillium in preparation of certain cheeses. From yeasts vitamins like thiamine riboflavin, nicotinic acid are obtained.
5. In Medicines: -Many fungi produce certain antibiotic drugs which inhibit the growth of pathogenic microagent is. Some important medicines produced by. fungi are as follows.
(a) Penicillin obtained from Penicillium notatum used kill to bacteria causing pneumonia.
(b) Steptomycin from Streptomyces griesius.
(c) Ergot from Claviceps purpurea.
(d) Chloromycetin from Streptomyces venezuela.
6. In Plastic Manufacturing: - Certain fungi like Odium loctis is widely used in the plastic industry.
7. Nutrition of Plant: - Several members of the Phycomycetes, Ascomycetes Basidiomycetes and fungi imperfects are involved in the formation of mycorrhizae which are believed to be of fundamental importance in .the nutrition of trees like Cycus Zamia, Pinus etc.
Harmful Activities of Fungi: -
The fungi are reponsible for a number of human, animal and plant diseases: -
1. Many fungi cause immense loss to our timber trees by causing rot, e.g., Armillarva mella and species Polypores.
2. Some of mould fungi like Rhizopus Mucor, Aspergillus spoil our foods like jams, pickels, jelly -bread and fruits.
3. Several parasitic fungi are the causative agents of diseases of our crops, fruits and other economic plants. Among them are rust and smuts.
The rust produces yellow, orangs, black pustules on cereal plants and some smuts attack reproductive orange and produces black powderly mass of smut spore. They causesmany diseases and a great loss to crops.
Some fungal diseases are as follows : -
(a) White rust of crucifers by Cystopus candidus.
(b) Powdery mildew by Erysiphae species.
(c) Downy mildew of crucifers by Pernospora species.
(d) Late blight of potato by Phytophthora infentense.
(e) Stem galls of coriandrum by Protomyces macrosporus.
4. Some parasitic fungi also cause diseases to animals. Saprolegnia occurs saprophyte on dead fishe. It causes serious disease to crops and gold fishe, thus causing harm.
5. Some fungi cause diseases in human beings. Several species of Aspergillus as A.niger, A. flavus, A. fumigatus are common human pathogens. They cause disease known as aspergilloses similar to aspergillose of Iungs ears etc. Many parasitic fungi live in the mucous membranes of throat branchia and lungs. Few fungi cause skin discolouration. A well known skin disease ring worm is also a fungal disease.