Q.9. Write in detail the classification of fungi given by Alexopoulos. (2006, 10)
Ans. Classification of Fungi According to Alexopoulos: -
AIexopoulos and Mins (1979) place the fungi including the slime molds in the kingdom Mycetae of the Superkingdom Eukaryota which, in addition, includes four other Kingdoms. They divide the Kingdom Mycetae into three divisions namely:
(i) Gymnomycota (ii) Mastigomycota, and (iii) Amastigomycota.
The division is subdivided into subdivisions, classes, subclasses and orders.
Division I: -
Gymnomycota: - It includes phagotrophic organisms devoid of cell walls. This division comprises two subdivisions. These are Acrasiogymnomycotina and Plasmodiogymnomycotina.
Subdivision 1. Acrasiogymnomycotina: - It includes a single class Acrasiomycetes.
Class 1. Acrasiomycetes: - Lacks flagellated cells except one species. This class comprises two subclasses Arcasiomycetidae and Dictyostelio mycetidae.
Subdivision 2. Plasmogymnomycotina: - It is divided into two classes:
Class 1. (i) Protosteliomycetes: -
Class 2. (ii) Myxomycetes: - It includes the true slime mold and comprises three subclasses namely ,
Subclass 1: - Ceratiomyxomycetidae: - It includes one order Ceratiomyxales.
Subclass 2: - Myxogasteomycetidae: - It comprises four orders namely, Licealer, Echinosteleales, trichlales and Physarales.
Subclass 3: - Stemonitomycetidae with one order Stemonitales.
Division II. Mastigomycota: - Includes fungi with absorptive nutrition unicellular or filamentous, mycelium coenocytic. It comprises two subdivisions:
Subdivision 1. Haplomastigomycotina: - It includes fungi with uni-orbi-flagellate zoospores. It comprises 3 classes:
Class 1. Chytridiomycetes: - Fungi producing zoospores furnished with a single whiplash flagellum inserted at the posterior end.
Class 2. Hyphochytridiomycetes: - Motile cells with a single tinsel flagellum inserted at the anterior end.
Class 3. Plasmodiophoromycetes: - Parasitic fungi producing biflagellate motile cells with both the flagella of whipless type inserted at the anterior end.
Subdivision 2: -
Diplomastigomycotina: - Sexual reproduction oogamous, Zoospores biflagellate, meiosis gametangial. This subdivision includes a single class:
Class 1.Oomycetes: - It comprises four orders namely Langenidiales, Saprolegniales, Leptomitales and Peronosporales.
Division III. Amastigomycota: - Fungi with absorptive nutrition, motile cells lacking, mycelium aseptate or septate. This division includes four subdivisions namely, Zygomycotina, Ascomycotina, Basidiomycotina and Deuteromycotina.
Subdivision 1. Zygomycotina: - It is divided into two classes -
Class1. Zygomycetes: - It include six orders.
Class 2. Trichomycetes: - It comprises five orders.
Subdivision 2. Ascomycotina: - Fungi usually with a septate mycelium producing haploid ascospores in sac-like cells called Asci. This subdivision is represented by a single class:
Class 1. Ascomycetes: - It is divided into five subclass:
Subclass 1: - Hemiascomycetidae comprising three orders.
Subclass 2: - Plectomycetidae with five orders.
Subclass 3: - Hymenoascomycetidae with ten orders.
Subclass 4: - Laboulbeniomycetidae including two orders.
Subclass 5: - Loculoascomycetidae with five orders.
Subdivision 3. Basidiomycotina: - Septate mycelium, produces, basidiospores (meiospores) exogenously on various types of basidia. The subdivision includes a single class.
Class 1. Basidiomycetes: - It is split into three subclasses:
Subclass 1: - Holobasidiomycetidae.
Subclass 2: - Phragmobasidiomycetidae.
Subclass 3: - Teliomycetidae.
Subdivision 4. Deuteromycotina: - It includes imperfect fungi in which sexual stage is unknown. It comrises a single form class.
Class 1: - Deuteromycetes with three form subclasses namely: - Blastomycetidae, coelomycetidae and Hyphomycetidae.
Q.10. Write short note on mechanism of nutrition in fungi (2012)
Ans. Nutrition: -
The fungi due to the lack of chlorophyll are unable to synthesize food. So they are heterotrophic in their mode of nutrition and they obtain the food from sources external to themselves.
Thus they live either as parasites or saprophytes. The fungi which obtain their food from dead organic materials are called as saprophytes. Where as the fungi obtaning their prepared food from living plants or animals are called the parasites. Some fungi grow in the association of other plants and are mutually beneficial. This association is called the symbiosis.