Kingdom Fungi
It is a unique kingdom of heterotrophic organisms, showing extracellular digestion. The organisms are unicellular (yeast) or multicellular and filamentous (Penicillium). Unicellular organisms have a protoplast with many nuclei e.g. Rhizopus or with a single nucleus e.g. yeast. Filamentous organisms consists of a body called mycelium in which a number of thread-like structures called hyphae are present. The hyphae may be with septa (septate) or without septa (aseptate). They may be unior multi-nucleated. The non-septate multinucleated hyphae are called coenocytic hyphae.
The cell wall in fungi is composed of chitin or fungal cellulose. Fungi contain well-organized membrane-bound cell organelles except the chloroplasts.
The fungi exhibit heterotrophic mode of nutrition. Most of the members are saprophytes and absord food which is decomposed (digested) outside. Thus absorption is the mode of nutrition. Some are parasites or predators and some are symbiotic. Reproduction is vegetative, asexual or sexual.
The fungi are further classified as follows -
Phycomycetes : These are commonly called algal fungi and consist of coenocytic hyphae. They commonly grow in moist and damp habitats on decaying organic matter. They reproduce by endogenous spores produced inside sporangia Examples-Mucor, Rhizopus, etc. Albugo is an examples of parasitic phycomycetes.
Ascomycetes : They are mostly multicellular and are commonly called sac fungi. When multicellular, their thallus or somatic body is composed of branched septate hyphae. They produce endogenous sexual spores called ascospores in sac like structures called asci. Some produce fruiting bodies (ascocarps) which enclose asci. The sexual and exogenously produced spores are called conidia which are at the tips of special hyphae called conidiophores. Examples- Aspergillus, penicillium, Neurospora etc. Yeast is an examples of unicellular ascomycetes.
Basidiomycetes : These fungi commonly celled club fungi, include mushrooms, bracket fungi, rusts, smuts, etc. They have branched septate hyphae. Asexual reproduction is absent, but vegetative reproduction takes place by fragmentation. Sex organs are lacking. The fusion of two vegetative cells or somatic cells (somatogamy) produces a dikaryotic mycelium which gives rise to basidia or a fruiting body called basidiocarp. Basidiocarp contains many basidia which produce sexual spores called basidiospores contains many basidia which produce sexual spores called basidiospores exogenously.
Examples - Agaricus, Ustilago; Puccinia, etc.
Deuteromycetes : It is a temporary group of fungi which are known to reproduce only asexually. They are commonly called imperfect fungi. Whenever their sexual reproduction is discovered they are transferred to the respective groups. They are mostly decomposers while a few are parasitic.
Examples : Alternaria, Colletotrichum, Trichophyton etc.