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PinkMonkey Online Study Guide-Biology

The mycelium is made up of profusely branched, septate, multinucleated interwoven hyphae. The major part of the myceluim is underground as in mushrooms, while in parasitic fungi like rusts and smuts it is in the host. Some fungi like mushrooms produce an aerial fruiting body called a basidiocarp made up of stalk and cap bearing gills on the under-surface. Gills produce basidia giving rise to basidiospores, while some parasitic fungi like rusts and smuts produce more than one type of spores in addition to basidiospores outside the host. (Figure 14.46)

Reproduction : Asexual reproduction is uncommon. Sexual reproduction takes place by the formation of basidiospores which are produced by basidia exogenously.

Economic importance : Some mushrooms are used as food for their delicacy and high nutritive value. Some basidiomycetes are used as a source of medicinal compounds. Some are also used for "recreational" purposes. Some like rusts and smuts cause destruction of crop plants.

Figure 14.48 Aspergillus

Dikaryotization in Ascomycetes and Basidiomycetes


Sexual reproduction takes place by the hyphae of two opposite strains growing together in which their cytoplasms intermingles (plasmogamy). Within this fused structure the nuclei of two different strains come together in pairs, but they do not fuse. This is called dikaryotization. Dikaryotic condition continues for a considerable period of time. New hyphae develop from these fused structures and are called dikaryotic hyphae. These hyphae form a fruiting body called an ascocarp or basidiocarp, characteristic of the class.

Deuteromyucetes

They are also called imperfect fungi because of their imperfect life-cycle, the sexual stage being undescribed. These fungi reproduce asexually,( i.e. by means of conidia) and are closely related to Ascomycetes, while a few are related to Basidiomycetes. Like higher fungi the mycelium is made up of branched, multinucleated, septate, interwoven hyphae. Some of the hyphae penetrate the substratum to absorb nourishment,. while some aerial hyphae are called conidiophores. The latter produce conidia which further give rise to mycelia.

Examples of imperfect fungi are Aspergillas and Helminthosporium.

Economic importance : The fungus Penicillium is used for the production of antibiotic penicillin. A few species are used to give flavor and texture to cheese. Some are also commercially used for the preparation of organic acid like citric acid, fumaric acid, oxalic acid, etc. Some members cause ring worm and athlete's foot. Some cause diseases in plants.

Ascomycetes and basidiomycetes are economically important fungi. Some of them are used in various industries while other are distinctly destructive. Yeast is used widely by brewers and bakers to prepare alcohol and in raising bread. It is also the main source of vitamin B and hormones like cytokinins. Some mushrooms are used as food for their delicacy and high nutritive value. Fungi like rusts and smuts cause destruction of crop plants while many other cause spoilage of milk, eggs, meat, fish, vegetables, fruit, etc.


3. Decomposers and parasitic forms

Decomposers

These serve as an important component of the ecosystem. They release hydrolytic enzymes into the substratum and break down the complex organic compound into simpler ones, release minerals and make them available to plants for recycling.

Examples: Rhizopus, Mucor, Agaricus, Penicillium, If it was not for the actions of decomposers, nutrients would get locked up in the dead matter of organisms. Life on earth without these organisms eventually would become impossible.

Role of decomposers

(1) They decompose the dead matter of plants and animals and disperse their nutrients, thus acting as scavangers of nature.

(2) They help in the formation of humus (superficial layer of soil rich in organic compounds) which is important to increase the fertility of soil and healthy growth of plants.

(3) They play an important role in converting complex organic components into simple forms to continue biogeochemical cycles.

Parasitic forms

These are pathogenic fungi. Unlike saprophytes or decomposers, they do not secrete hydrolytic enzymes, They live on or inside the body of the other living organisms (called hosts) obtain ready-made food from the latter and produce a number of diseases in them. Common plant diseases are potato blight, wheat rust (Figure 14.45) corn smut, and powdery mildew.

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Table of Contents

14.0 Introduction
14.1 Kingdom : Monera
14.2 Kingdom : Protista
14.3 Kingdom : Plantae
14.4 Kingdom : Fungi

Chapter 15





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