Biology Quickers

 *Classification of Fungi*

*Ascomycetes*

1.Commonly known as sac-fungi, the ascomycetes are unicellular, e.g., yeast (Sacharomyces) or multicellular, e.g., Penicillium.

2.They are saprophytic, decomposers, parasitic or coprophilous (growing on dung).

3.Mycelium is branched and septate.

4.The asexual spores are conidia produced exogenously on the special mycelium called conidiophores.

5.Sexual spores are called ascospores which are produced endogenously in sac like asci (singular ascus). These asci are arranged in different types of fruiting bodies called ascocarps.

6. Some examples are Aspergillus, Claviceps and Neurospora. Neurospora is used extensively in biochemical and genetic work. Many members like morels and buffles are edible and are-considered delicacies.

*Yeast*

1.Yeast was first described by Antony Von Leeuwenhoek in 1680.

2.Yeast are nonmycelial or unicellular, which is very small and either spherical or oval in shape.

3.However, under favourable conditions they grow rapidly and form false mycelium or pseudomycelium.

4.Individual cells are colourless but the colonies may appear white, red, brown, creamy or yellow:

5.The single cell is about 10mm in diameter. It is enclosed in a delicate membrane which is not made up of fungal cellulose but is a mixture of two polysaccharides known as mannan and glycogen.

Reproduction: Yeast reproduces by vegetative or asexual and sexual methods.

(1)  Vegetative reproduction: 'Yeast reproduce vegetatively either by budding or by fission.

(2)  Sexual reproduction: Sexual reproduction in yeasts takes place during unfavourable conditions, particularly when there is less amount of food.The sex organs are not formed in yeasts 'and the sexual fusion occurs between the two haploid vegetative cells or two ascospores which behave as gametes. The two fusing gametes are haploid and may be isogamous or anisogamous. Such kind of sexual reproduction is called gametic copulation. It is the best example of hologamy i.e., the entire vegetative thallus is transformed into reproductive body. The sexual fusion leads to the formation of diploid zygote. The zygote behaves as an ascus and forms 4 - 8 haploid ascospores. These liberate and function as vegetative cells.

*Basidiomycetes*

1.Commonly known forms of basidiomycetes are mushrooms, bracket fungi or puffballs.

2.They grow in soil, on logs and tree stumps and in living plant bodies as parasites, e.g., rusts and smuts.

3.The mycelium is branched and septate.

4.The asexual spores are generally not found, but vegetative reproduction by fragmentation is common.

5.The sex organs are absent, but plasmogamy is brought about by fusion of two vegetative or somatic cells of different strains or genotypes.

6.The resultant structure is dikaryotic which ultimately gives rise to basidium.

7.Karyogamy and meiosis take place in the basidium producing four basidiospores.

8.The basidiospores are exogenously produced on the basidium.

9.The basidia are arranged in fruiting bodies called basidiocarps.

10.Some common members are Agaricus (mushroom), 'Ustilago (smut) and Puccinia (rust fungus).

*Deuteromycetes*

1.Commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are known.

2.The deuteromycetes reproduce only by asexual spores known as conidia.

3.The mycelium is septate and branched.

4.Some members are saprophytes or parasites while a large number of them are decomposers of litter and help in mineral cycling. Examples: Alternaria, Colleiotrichum and Trichoderma.