Fungi are saprophytic and parasitic spores producing eukaryotic typically filamentous organisms formerly classified as plants that lack chlorophyll and their cell wall is made up of chitin and polysaccharides. They grow in humid and warm places.

Structure: The kingdom of fungi consists of both unicellular (e.g. yeast, moulds) and multicellular (e.g. mushrooms) organisms. Fungi are filamentous, their bodies consist of slender and long, thread-like structures known as hyphae and their network is known as mycelium. Hyphae and others have cross walls or septae in their hyphae are called septae and multicellular.

Nutrition: 

• Fungi are heterotrophic and also known as saprophytes because they absorb organic matter which is soluble from the dead substances.
• They live as parasites.
• They also live in combination as the symbionts with algae known as lichens (algae + fungi) and with the higher plants’ roots as mycorrhiza.

Reproduction: 

The fungi reproduce by all three methods:-

1. Vegetative reproduction- fragmentation, fusion and budding.
2. Asexual reproduction- Fungi asexually reproduce by spore called sporangiospores, Zoospores or Conidia.
3. Sexual reproduction- it is occurred by oospores, basidiospores and ascospores

The spores are produced in different structures known as the fruiting bodies. The cycle of sexual reproduction involves the following steps-

Plasmogamy- protoplasm fusion between 2 gametes.

Karyogamy- two nuclei fusion.

Meiosis- to form haploid spores in zygote.

Classification of fungi?

The fungi kingdom had five major phyla which were defined according to their sexual reproduction mode or by their molecular data.

Those fungi which reproduce by the asexual cycle are pleased in a sixth group called Form Phylum.

By advancing molecular biology and RNA sequencing we find new relationships between different categories of fungi. The five phyla of fungi are mentioned below–

• Chytridiomycota (Chytrids)

• Zygomycota (conjugate Fungi)

• Ascomycota (Sac Fungi)

• Basidiomycota (Club Fungi)

• Glomeromycota

An informal group of nonrelated fungi is  Deuteromycota which reproduce by asexual cycle.

1. Chytridiomycota:-  Phylum Chytridiomycota is the class which is Chytridiomycetes. Chytrids are the most primitive and simplest fungi. More than 500 million years ago, during the late Precambrian period, the first Chytrids appeared.

Unlike other fungi, one Chytrids group contain chitin and cellulose both in the cell wall. Chytrids are mostly unicellular but some of them form multicellular microorganisms. Some species of Chytrids live in water while some are on the land. Some of them grow on plants and insects as parasites. Chytrid’s cycle of reproduction includes both sexual and asexual.

1. Zygomycota: They are called zygomycetes and are a relatively small group and belong to the Phylum Zygomycota. They are very familiar and generally found on the surface of bread, fruits and vegetables. Most species are found living off decaying organic material.

Zygomycetes reproduce asexually by producing sporangiospores. Generally, we find black tips on the bread surface. These black tips are the swollen sporangia which are packed with black spores. After finding a suitable substrate they produce a new mycelium. They can also reproduce sexually when the condition is not suitable for them.

1. Ascomycota: The most known fungi are from the Phylum Ascomycota group. It is identified by the formation of an ascus. The ascus is a sac-like structure that contains a haploid. Many Ascomycetes are used commercially for example; yeast used in baking, wine fermentation, plus truffles fermentation etc.

They can reproduce sexually and asexually. When reproducing asexually it produces conidiophores which release haploid conidiophores.

While reproducing sexually the strain produces an Antheridium and the female strain develops an Ascogonium. At the time of fertilisation, both strains combine in plasmogamy without nuclear fusion.

1. Basidiomycota: Fungi belonging to the Phylum Basidiomycota can be easily identified with the help of light microscopy because they had a club-shaved fruiting body called Basidia. Basidia are the swollen terminal cell of Hyphae and it is the reproductive organ for the fungi.

These are very familiar mushrooms and are commonly seen in the field after rain and in the market. They mainly reproduce through the sexual cycle.

1. Glomeromycota: It is a newly established Phylum and comprises about 230 species that live in the roots of trees. Glomeromycetes reproduce asexually and cannot survive without the presence of plant roots. After DNA analysis it found that all Glomeromycetes may be descended from a common ancestor, which makes them a monophyletic lineage. 

Conclusion

A fungus is a eukaryotic microorganism like moulds, yeast or mushrooms. These are heterotrophs and don’t follow the process of photosynthesis for their food uptake. Fungi is an ecological decomposer. The kingdom of fungi is extended from 2.2 million species to 3.8 million ones and out of which only 148,000 have been mentioned.