Biological Classification

Kingdom Fungi

You must have seen fungus on your stale food. Haven’t you? It feels so disgusting and yucky! Isn’t it? But, do you know that fungi have a kingdom of their own? We are going to learn about them in this chapter. We will look at the characteristics and classifications of fungi.

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Characteristics of Fungi

Now, we will look at the various characteristics of the fungi kingdom.

Thallus Organisation

The plant body of true fungi is a thallus. It may be non-mycelial or mycelial. The non-mycelial forms are unicellular. However, they may form a pseudomycelium by budding. In mycelial forms, the plant body is made up of thread-like structures called hyphae(sing. hypha).

Cell Organisation

The cell wall of fungi is mainly made up of chitin and cellulose. Chitin is a polymer of N-acetyl glucosamine. On the other hand, cellulose is nothing but a polymer of d-glucose. Besides, the cell wall may be made up of cellulose-glycogen, cellulose-chitin or polygalactosamine-galactan.

Nutrition

The fungi are achlorophyllous organisms. Hence, they cannot prepare their food. They live as heterotrophs i.e., as parasites and saprophytes. Some forms live symbiotically with other green forms.

  • Parasites: They usually obtain their food from a living host. A parasite could be facultative or obligate. The obligate parasites survive and settle on a living host throughout their life. The facultative parasites are saprophytes that have turned parasitic.
  • Saprophytes: These organisms procure their nutrition from dead and decaying organic matter. The saprophytes are either obligate or facultative. An obligate saprophyte remains saprophytic during its entire lifetime. While a facultative saprophyte is nothing but a parasite that has secondarily become saprophytic.
  • Symbionts: Some fungi develop in symbiotic association with the green or blue-green algae. These constitute the lichen. Here the algal component is photosynthetic. While the fungal component plays the reproductive part.

Reproduction

The fungi either reproduces vegetatively, asexually or sexually:

  • Vegetative Reproduction
    • Fragmentation: Some forms belonging to Ascomycotina and Basidiomycotina multiply by breakage of the mycelium.
    • Budding: Some unicelled forms multiply by budding. A bud arises as a papilla on the parent cell and then after its enlargement separates into a completely independent entity.
    • Fission: A few unicelled forms like yeasts and slime moulds multiply by this process.
  • Asexual Reproduction
    • Sporangiospores: These are thin-walled, non-motile spores formed in a sporangium. They may be uni-or multinucleate. On account of their structure, they are also called as aplanospores.
    • Zoospores: They are thin-walled, motile spores formed in a zoosporangium.
    • Conidia: In some fungi, the spores are not formed inside a sporangium. They are born freely on the tips of special branches called conidiophores. Thus, these spores are conidia.
  • Sexual reproduction: With the exception of Deuteromycotina (Fungi imperfecti), we find sexual reproduction in all groups of fungi. During sexual reproduction, the compatible nuclei show a specific behaviour which is responsible for the onset of three distinct mycelial phases. The three phases of nuclear behaviour are as under:
    • Plasmogamy: Fusion of two protoplasts.
    • Karyogamy: Fusion of two nuclei.
    • Meiosis: The reduction division.

Classification of Fungi

Fungi

What is  Kingdom Animalia ?.

Phycomycetes

We can find these in aquatic habitats and on decaying wood in moist and damp places. The mycelium is aseptate and coenocytic. Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile).

Rhizopus/Mucor

They are the cosmopolitan and saprophytic fungus, living on the dead organic matter. Rhizopus stolonifera occurs very frequently on moist bread. Hence, they are black bread mould.

Albugo

Albugo is a member of Phycomycetes. It is an obligate parasite and grows in the intercellular spaces of host tissues. It is parasitic mainly on the members of families Cruciferae, Compositae, Amaranthaceae and Convolvulaceae. The disease caused by this fungus is white rust or white blisters. The most common and well-known species is Albugo candida. It attacks the embers of the mustard family (Cruciferae).

Ascomycetes

They are saprophytic, decomposers, parasitic or coprophilous (growing on dung). Some examples are Aspergillus, Claviceps and Neurospora. Neurospora is used extensively in biochemical and genetic work.

Yeast

Antony Von Leeuwenhoek in 1680 first described yeast. Yeast is nonmycelial or unicellular, which is very small and either spherical or oval in shape. Individual cells are colourless but the colonies may appear white, red, brown, creamy or yellow. Yeast reproduces by vegetative or asexual and sexual methods.

Basidiomycetes

The most common forms of basidiomycetes are puffballs, mushrooms and bracket fungi. They grow in soil, on logs and tree stumps and in living plant bodies as parasites, e.g., rusts and smuts. They have branched and septate mycelium. These organisms do not have sex organs. But, plasmogamy takes place by fusion of two vegetative or somatic cells of different strains or genotypes.

Solved Examples for You

Question: Write a note on Deuteromycetes.

Answer: They are imperfect fungi because we only know about the asexual or vegetative phases of these fungi. The Deuteromycetes reproduce only by asexual spores. These spores are conidia. Some members are saprophytes or parasites. However, a large number of them are decomposers of litter. They are very helpful in mineral cycling. Examples: Alternaria, Colletotrichum and Trichoderma.

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