Fungi - Overview, Characters, Classification, Examples, Importance

Overview.

Alexander Flemming stated the importance of Penicillium notatum while he was working on bacteria Staphylococcus.

According to  Alexopoulos

Fungi are nucleated with non chlorophyll bearing organisms, which  reproduce by both  asexually and sexually and their cell walls are made up of chitin.

The study of fungi is called Mycology.

They are saprophytic in nature because they grow on dead matter of  plants and animals and collect their food from these matter. They cannot make their own food due to lack of chlorophyll. They also act as Biofertilizer.

Fungi  reproduce by Vegetative reproduction,  Asexual reproduction and Sexual reproduction. They reproduce vegetatively by budding, fragmentation, fission and some fungi reproduce vegetatively by  special structure like rhizomorph and sclerotia.

Conidia, chlamydospore, endospores, basidiospore, uredospore, ascospores, pycniospores, teleutospore are spores in fungi that are formed in favourable condition. Fungi reproduce asexually by these spores. Sexual reproduction in fungi may be  isogamous, anisogamous and oogamous.

It occurs by fusion of egg and motile male gamete.

General characteristics of Fungi:

1.They are almost cosmopolitan in nature and found in soil, water, air and even in plants and animal bodies. They have a  thallus-like body structure. 

2. They are devoid of chlorophyll therefore they are not green in color.Due to lack of chlorophyll, they do not perform photosynthesis.

3. They exhibit a heterotrophic mode of nutrition, thus they are not capable of making their own food. They are completely dependent on other organisms for their  nutrition as Parasites and saprophytes.

4. They are saprotrophic  because they derive nutrition from the dead and decaying matter.

5. Their cell wall is mainly composed of chitin, a kind of polysaccharides. Along with the chitin, the cell wall of some fungi also have cellulose.

6. Some fungi prefer be  to live in darkness or in the absence of light hence they are  photophobic and some may live in the presence of light ,called photophilic

7.Body of fungi is composed of a network of thread-like structures called mycelium. The  mass of mycelium forms specific fungal tissue called pseudoparenchyma.

8. Fungi store reserve food material in the form of glycogen

9. Some fungi make symbiotic association with algae and root of higher plants known as lichen and mycorrhiza respectively.

Classification of fungi:

Fungi are classified into four major groups -

Zygomycetes: Members of this group are found in moist, damp places, dead and decaying matter. Their mycelium is coenocytic with many nuclei. Their network of  mycelium  is well developed.

They reproduce asexually  by motile and nonmotile spores called zoospores and aplanospores respectively.

They reproduce sexually by Zygospore that are formed by fusion of the protoplasts of two gametes.  During fusion of gamete, a conjugation tube is formed to make the fusion of protoplast between the two cells of fungi.Therefore they are also  called conjugation fungi.

When both  gametes are morphologically  similar that are involved in sexual reproduction, then reproduction is isogamous. In anisogamous or oogamous , both gametes are not morphologically similar. 

 Example: 1. Rhizopus or  Bread Mould 2 .Mucor. 3. Albugo, Parasite on Mustard.

Ascomycetes:

They are also called sac fungi and are regarded as higher fungi. It is the largest group of fungi including 1700 genus  and 15000 species. They are saprotrophs , decomposers and parasites.  They are also coprophilous because they may grow on cow dung. Their mycelium is branched and septate.

They reproduce asexually by the conidia. These conidia are produced on special mycelium called conidiophore. They reproduce sexually by the specialised sexual spores called ascospores. Ascospores are formed  usually eight in numbers and present within a  sac-like structure  called ascus.  Therefore they are called ascomycetes. They are mostly multicellular like penicillium  but some are unicellular like Saccharomyces.

For example- Aspergillus, Claviceps, Neurospora. Fusarium

👌👌Remember- Neurospora is widely used in biochemical and genetic experiments. 

Basidiomycetes:

The members  are commonly called mushroom or bracket fungi or puffball. They are found in soil or damp trees or moist places. They may also be present in the plant body as parasites in the form of smut and rust. Their mycelium is branched and separate. Asexual mode of reproduction is unknown but they reproduce in vegetable mode  by fragmentaion.

They do not have any sex organs but they reproduce sexually by fusion of protoplast between two different cells by plasmogamy  and form a club-shaped structure  called the basidium. Hence they are also referred to as club fungi.

Inside the basidium, by meiosis basidiospores are formed. These  basidiospores are arranged in  the fruiting bodies  called basidiocarps. 

Example: 1. Agaricus or Mushroom 2. Ustilago causes smut disease  3. Puccinia causes rust disease. 

Deuteromycetes:

They are also called imperfect fungi because the sexual stage is not known in members of this group. They reproduces by asexual means mainly through conidia like Ascomycetes. They were grouped initially in ascomycetes but due to absence of sexual stage,they have been placed in different group.They are pathogenic and cause harmful diseases in humans and animals.Their mycelium is branched and septate.They are saprotrophs or parasite .They are also involved in mineral cycling in nature. Example:  Alternaria, Colletotrichum, Trichoderma.

Commercial use of Fungi 

At  industrial scale, mushrooms are cultivated from fungi. Mushrooms have high nutritional value. Mushrooms are rich in vitamin B. It is  regarded as a source of protein. Yeasts are used in the bread making industry.  Yeast is also used in the production of wine, whisky, and beer , rum  industries because yeast produces  ethyl alcohol by fermentation.

Penicillium is enriched in protein,  vitamin A, vitamin B. It is added to increase the flavour to the cheese.  Aspergillus produces citric acid, Gallic acid which is used in the chemical industry.  Penicillin was the first antibiotic that was discovered from Penicillium notatum.

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