Fungi: Definition,Characteristics,Classification and Economic Importance

In this essay we will discuss about Fungi. After reading this essay you will learn about: (1) Definition of Fungi (2) Characteristics of Fungi (3) Classification of Fungi (4) Economic Importance

(1) Definition of Fungi

Fungi show a great diversity in morphology and habitat. Fungi are heterotrophic organisms, they obtain their nutrients by absorption. The cell wall of fungi are mostly made up of carbohydrate chitin, while the cell wall in plants is made of cellulose. The carbohydrates stored in fungi is in the form of glycogen. The 'fruit' body of fungus is  only seen, while the living body of the fungus is a mycelium, it is made of tiny filaments called hyphae. The mycelium is hidden., Nutrition in fungi is by absorbing nutrients from the organic material in which they live. Fungi do not have stomachs, they digest their food before it pass through the cell wall into the hyphae. The hyphae secrets enzymes and acids that break down the organic material into simple compounds.

(2) Characteristics of Fungi

General characteristics of fungi are as follows:

• Fungi are eukaryotic organisms.
• They are non-vascular organisms. 
• They reproduce by means of spores. 
• Depending on the species and conditions both sexual and asexual spores may be produced. 
• They are typically non-motile.
• Fungi exhibit the phenomenon of alteration of generation.
• The vegetative body of the fungi may be unicellular or composed of microscopic threads called hyphae.
•  The structure of cell wall is similar to plants but chemically the fungi cell wall are composed of chitin.
• Fungi are heterotrophic organisms.
• They fungi digest the food first and then ingest the food, to accomplish this the fungi produce exoenzymes. 
• Fungi store their food as starch.
• Biosynthesis of chitin occurs in fungi.
• The nuclei of the fungi is very small.
• During mitosis the nuclear envelope is not dissolved.
• Nutrition in fungi - they are saprophytes, or parasites or symbionts.
• Reproduction in fungi is both by sexual and asexual means. Sexual state is referred to as teleomorph, asexual state is referred to as anamorph.

(3) Classification of Fungi

Based on the spore case in which the spores are produced fungi are classified into four divisions.

Division Ascomycota: Sac Fungi

The sac-fungi produce spores in small cup-shaped sacs called asci, hence the name ascomycota. The mature sac fungi spores are known as ascospores, they are released at the tip of the ascus breaks open. Yeast is the most common one-celled fungi. Yeast reproduces through asexual process called budding. The buds form at the side of the parent cell, they pinch-off and grow into new yeast cell which is identical to the parent cell. Examples of sac-fungi are morels, truffles, cup fungi and powdery mildews. Example: Aspergillus, Claviceps, Neurospora. 

Division Basidiomycota: Club Fungi

Basidiomycota includes the mushrooms, puff-balls, smuts, rusts and toadstools. The spores are borne on a club-shaped spore case called basidium. In mushrooms the basidia are lined at the gills under the cap. Huge numbers of spores are produced by the club fungi. In fact, an average sized mushroom produces over 16 billion spores. These spores rarely germinate or mature. Example: Agaricus(mushroom), Ustilago(smut), and Puccinia(rust fungus). 

Division Zygomycota: Zygote forming Fungi

These fungi are usually found on cheese, bread, and other decaying food. They are zygote forming fungi, hence the name zygomycota. The spores are produced in round-shaped case called sporangium. The grayish fuzz seen on bread and decaying food is actually mass of mature sporangia mold. Under the microscope they are seen as pinheads. When the sporangium breaks open hundreds of spores are released. Example: Mucor, Rhizopus (the bread mould) and Albugo. 

Division Deuteromycota: Imperfect Fungi

These organisms are known as imperfect fungi because they lack sexual reproduction. They reproduce by asexual spores known as conidia. Most of the fungi causes diseases to humans like ringworm, athlete's foot. Economically important imperfect fungi are Penicillium and Aspergillus. Other examples are Alternaria, Colletotrichum and Trichoderma. 

Kingdom Fungi Examples

Some of the examples of kingdom fungi are as follows:

• Sac-fungi : Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).
• Zygote-forming fungi : Mucor, Rhizopus (the bread mould) and Albugo. 
• Club fungi: Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus). 
• Imperfect fungi: Alternaria, Colletotrichum and Trichoderma.

(4) Economic Importance

Fungi have both positive ad negative roles in our daily life. So they are our friends as well as foes (enemy). They are described as below.

Beneficial Roles or Useful Activities.

i) Fungi are used as food. e.g. Mushrooms and Morels.
ii) Fungi are used in laboratory.
a) Baking Yeast (S. cerevisae)
b) Several alcoholic beverages such as wine, whiskey, beer, rum all are prepared by fermentation activity of sugar solution by wine yeast. (S. ellipsoidens)
c) Some fungi are used in production of enzymes like amylase, pectimase
iii) Some fungi are used in production of several antibiotics and antibiotics and other useful medicine like penicillin, streptomycin, ergotine and ephedrine respectively.
iv) Several fungi are used in commercial production of different organic products like citric acid, fumaric, lactic and oxalic acid.
v) Fungi in agriculture:
a) Being saprophytes they decompose the organic matter and enhance the fertility of the soil.
b) Some fungi develop symbiotic relation with roots of higher plant like Pinus and help them in absorption of nutrients. Such fungi are known as mycorrhiza.
vi) Some fungi are used to produce hormone like Gibberellin.



Harmful Activities:

i)    Food spoilage (destruction) caused by fungi like mucor and yeast.
ii)    Some yeasts causes huge loss in silk industry to attack silk worms and kill the same.
iii)    Several types of plant diseases caused by (different types of fungi) species of Nematospra they attack tomatoes, cotton and bean plants.

Similar disease like causal organisms

a.    Stem rust of wheat – Pucvinia graministice
b.    Early blight of potato – Alternaria solani
c.    Late blight of potato – Phytiphtoria infestans
d.    White rust of crucifer – Albugo candida
iv)    Some fungi (Cryptococcus neoformans) may cause human disease like meningitis and brain tumor.
v)    Some fungi are concerned with destruction of substances like attacks textile materials, paper, leather goods, rubber even optical instruments.
vi)    Some fungi are not edible mushroom like different species Amanita.