Kingdom Mycota or Fungi

The kingdom Mycota includes exclusively the fungi. The fungi are a group of organisms which has a plant body called thallus that may be unicellular or multicellular. They are achlorophyllous and non-vascular. Fungi represent another major group of decomposers along with some of the heterotrophic monerans and protistans. Many of them occur as parasites causing diseases and damage to the host. Some of them are beneficial to man and are widely used in food and chemical industries. The study of fungi has emerged into a separate branch of biology called mycology.

Fungi occur in almost every habitat where organic matter is available. They can grow in regions with total darkness since they are non-photosynthetic organisms. The most common habitat of fungi is, wet soil rich in humus. Some members like Saprolegnia are aquatic. Most others are seen growing on any kind of moist object such as shoes, leather goods, clothes, wooden logs and even food items (like bread, jam, pickles, fruits and vegetables). Many members of fungi are parasitic on plants and animals including humans. Some fungi grow on dung (coprophilous) while a few others are found in symbiotic association with other organisms.

The body of a fungus can be described as a thallus since it is not differentiated into root system and leaves. The thallus may be unicellular as in Syncharium and Saccharomyces (yeast) or multicellular as in most other examples. In most of the multicellular forms, the thallus consists of long, tubular, branched filament called hyphae (singular-hypha). A collection of hyphae is called mycelium. The entire mycelium develops from a single spore. In the unicellular fungus yeast, several cells may become attached to form a chain called pseudomycelium.

fig. 8.18 - Different Forms of Fungal Thalli

The individual fungal cells are bound by definite cell wall made up of chitin or cellulose or both. Chitin also called as fungal cellulose, is normally found in association with other compounds like proteins and lipids. The cell wall encloses protoplasts which are differentiated into plasma membrane, cytoplasm, nucleus and vacuoles. Except plastids, all other cell organelles are present. The reserve food is glycogen or oil droplets.

The filamentous hyphae may be either septate (processing crosswalls) or aseptate (without cross walls).

The aseptate mycelium is usually multinucleate, appearing as a single, continuous sheet of cytoplasm with several nuclei. This condition is described as coenocytic.

Each cell in a multicellular mycelium may be uninucleate or binucleate or multinucleate. In the binucleate mycelium (dikaryotic) both the nuclei may belong to the same strain (homokaryotic) or two opposite strains (heterokaryotic).