Notes on various aspects of fungi

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Fungi cause a variety of diseases. They are eukaryotic protests which differ from bacteria in several ways.

MORPHOLOGY OF FUNGI

1. Yeast is the simplest fungus. It is unicellular and it grows by budding.

2.. Hypha is an elongated cell which is a tubular thread like structure.

3. Mycelium is a tangled mass of hyphae. Fungi which form mycelia are called molds (or filamentous fungi).

4. Hyphae are called spectate when they show branching Non- spectate hyphae do not show branching.

Vegetative mycelium

The mycelium which grows below inside the medium is called vegetative mycelium. The mycelium which projects on the surface is called aerial mycelium.

Morphological classification of fungi

Depending on the cell morphology, fungi can be divided into four classes: yeasts, yeast-like fungi, molds and dimorphic fungi.

Yeasts

They are unicellular fungi. They occur as spherical or ellipsoi­dal cells. They reproduce by simple budding. The only yeast which can produce diseases Cryptococcus neoformans.

Yeast-like fungi

They grow partly as yeast and partly as elongated cells resem­bling hyphae (psudomycelium). Candida albinos is a pathogenic yeast-like fungus.

Mounds

They are filamentous fungi. They form true mycelia. Also they reproduce forming different types of spores. Dermatophytes are pathogenic molds. (

Dimorphic fungi

Grow as filaments or as yeasts depending on the conditions of growth. In cultures at 37° C or in tissues they may grow as yeasts. In cultures at 22° C or in the soil they may grow as molds.

Systematic classification of fungi

It is based on sexual spore formation. According to this, fungi are classified as:

1. Lower fungi Phycomycetes

2. Higher fungi Ascomycetes Basidiomycetes Fungus imperfect.

Lower fungi

They are phycomycetes. They have non-septet hypha. They may form asexual or sexual spores.

Asexual spores are called sporangiospores which are con­tained within sporangia. Sexual spores are of two types: oospores in some fungi and zygospores in some others.

Higher fung'

They have septate hyphae. They are divided into three types: Ascomycota's, Basidiomycetes and Fungi imperfect. All of them produce asexual and sexual spores. The asexual spores of all of them are called conidia. But the sexual spores are different in all the three:

1. Ascomycota form sexual spores called ascosporic which are present in a sac called accuse.

2. Basidiomycetes form basidiospores which are present on a basidium or a base.

3. Fungi imperfect consists of fungi whose sexual phases are not clearly known.


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