Feb 1, 2013

The Fascinating World of Fungi: Characteristics and Taxonomy

A heavy lump of dough baked in the oven becomes a light, fluffy loaf of bread. A bland chunk of milk solids become cheese. In each case members of the fungi kingdom are at work. Fungi do not have root stem or leaves Fungi do not have chlorophyll. Fungi (sing: Fungus) can live in darkness and also in light. There are more than 100,000 species of fungi. The study of fungi is called mycology. The person who studies fungi is called mycologist.

 

Taxonomic Status of Fungi

According to five kingdom system of classification, ‘Fungi’ is now a separate kingdom. Fungi have resemblance with plants in (a) having cell wall (b) lack centrioles (c) are non-motile.

Fungi resemble animals in having (a) are heterotrophs (b) lack cellulose in their cell wall and contain chitin so it is thought that fungi and animals arise from common ancestors. Fungi are different from animals in having (a) cell wall (b) are absorptive heterotrophs (c) non-motile so fungi are neither plants nor animals. Fungi have (a) DNA different from all other organisms (b) They show “nuclear mitosis”. During nuclear mitosis nuclear envelope does not break, instead the mitotic spindle forms within the nucleus and the nuclear membrane constricts between the two clusters of daughter chromosomes. In some fungi nuclear envelope dismantles late.

 

General Characteristics of Fungi

Habitat: They occupy a wide range of habitats, aquatic, terrestrial and as parasites on plants and animals.

Mode of life: They can be parasites, saprotrophs or mutualists.

Size: They range in size from the unicellular yeasts to the large toad stool.

Nutrition: They lack chlorophyll, so they are non-photosynthetic. Thus mode of nutrition is heterotrophic. Digestion takes place outside the body and nutrients are absorbed directly.

Mycelium

Cell walls: Cell walls are rigid containing chitin as fibrillar material. It has a high tensile strength, gives shape to the hyphae and prevents osmotic bursting of the cells. Chitin is more resistant to decay than cellulose and lignin present in the plant cell wall.

Food storage: If carbohydrate is stored, it is usually as glycogen and not starch.

Thallus: The thallus or the body of most fungi is a multicellular structure known as mycelium. A mycelium (Greek: Mycelium, fungus filaments) is a network of filaments called hyphae (Greek: hyphae, web). Hyphae give the mycelium quite a large surface area per volume of cytoplasm, and this facilitates absorption of nutrients into body of the fungus.

Fungal Hyphae

Hyphae: The hyphae may be non-Septate (aseptate) or Septate. Non-Septate (L. septum, wall) hyphae have no cross walls, are multinucleated i.e. they have many nuclei in the cytoplasm such hyphae are called coenocytic hyphae e.g. Rhizopus. Septate fungi have cross wall e.g. Penicillium.

Motility: Fungi are non-motile, lack basal bodies and do not have flagella at any stage of their life cycle. They move towards a food source by growing towards it.

Reproduction: A fungus reproduces both asexually and sexually.




No comments:

Post a Comment