Fungi: Characteristics

GENERAL CHARACTERISTICS OF FUNGI

1)They are cosmopolitan in distribution and can occur in any habitat where life is possible. Some fungi occur in fresh or marine water, others are terrestrial and still others are air borne. Many species are parasitic, infecting plants, animals and human-beings.

2)The plant body of fungi typically consists of branched and filamentous hyphae,which form a net-like structure, known as mycelium.

3)The hyphae are aseptate and coenocytic (as in Phycomycetes) or septate and uni-. bi-or multinucleate (as in Ascomycetes, Basidiomycetes and Deuteromycetes).

4) The septa usually have simple pores but in Basidiomycetes septa with dolipore occur. On both the sides of the dolipore, a double membranous structure -septal pore cap or parenthosome occurs. These septal pores form a valve like structure.

5) With the exception of slime molds, the protoplast remains surrounded by a distinct cell well. The main component of the cell wall is the fungal cellulose, also known as chitin. In some lower fungi (e.g., members of Oomycetes), the cell wall is composed of cellulose and glucan.

6) The hyphae contain colourless and vacuolated cytoplasm. Besides endoplasmic reticulum,mitochondria and Golgi odies, many non-living substances, like reserve food also occur in the cytoplasm.

(7) Fungi are entirely devoid of chlorophyll, but carotenoids are normally present.

8) The hyphae are homo-or heterokaryotic,haploid, dikaryotic or diploid (diploid phase is usually ephemeral). 

9) The higher fungi (Ascomycetes, Basidiomycetes and Deuteromycetes) are immotile, i.e., motile cells donot occur in their life-cycle at any stage. But in lower fungi (Phycomycetes) the reproductive cells (gametes and asexual zoospores) are uni- or biflagellate.

10) The flagella are of two types:(i) whiplash (acronematic) flagella are smooth with 9+2 organisation, and (ii) tinsel (pantonematic) flagella with numerous minute hair-like mastigonemes on their surface; the mastigonemes originate from the axial filament of flagella.

11) In majority of fungi the hyphae form a felt-like structure, but in some advanced fungi they may undergo certain modifications in response to functional needs. The hyphal structure is variously modified into: rhizomorph, prosenchyma, sclerotium, haustoria, hyphal strap etc.

12) They are heterotrophic in nutrition. The obtain their nutrition through saprophytic Or parasitic or symbiotic mode. 

13) In most of the fungi only a part of the vegetative mycelium forms reproductive unit and the rest remains vegetative. Such fungi are known as eucarpic. However, in unicellular fungi whole vegetative cell is transformed into a reproductive unit, and as such they are known as holocarpic.

14)They reproduce by vegetative, asexual and sexual means.

15) The vegetative reproduction may take place by fragmentation (e.g., Rhizopus, Mucor, Aspergillus, Alternaria), fission (e.g., yeast) and budding (e.g., yeast, Ustilago).

16) About 20% fungi propagate only by asexual means. Asexual reproduction takes place during favourable conditions by the formation of a variety of conidia or spores. The spores may be unicellular (e.g., Aspergillus, Penicillium) ormulticellular (e.g., Alternaria, Cercospora). They may be endogenous, when developed in specialized structure like pycnidia Or sporangia.