Characteristics of Fungi
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What is Fungi?
Fungi are eukaryotic organisms means that include microorganisms such as yeasts, moulds and mushrooms. They have true nucleus which are enclosed in membranes.
The organisms Yeast, Moulds and Mushrooms are classified under kingdom fungi.
What kind of cell wall obtain in fungi?
- The organisms found in Kingdom fungi contain a cell wall and are omnipresent.
- They are classified as heterotrophs among the living organisms.
- They are non-vascular organisms. They do not have vascular system. Xylem and Phloem are absent.
- Fungi have cell walls (plants also have cell walls, but animals have no cell walls).
- There is no embryonic stage for fungi.
Reproductive System of Fungi:
They reproduce by means of spores. There are sexual and asexual spores. Sexual spores are Oospores; Zygospores; Ascospores; Basidiospores, etc. and Asexual spores are Sporangiospores, Aplanospores, Zoospores, Conidia, etc.
Depending on the species and conditions both sexual and asexual spores may be produced.They are typically non-motile.
General Characteristics of Fungi:
- Fungi are eukaryotic, non-vascular, non-motile and heterotrophic organisms.
- They may be unicellular or filamentous .
- They reproduce by means of spores.
- Fungi exhibit the phenomenon of alternation of generation.
- Fungi lack chlorophyll and hence cannot perform photosynthesis.
- Fungi store their food in the form of starch.
- Biosynthesis of chitin occurs in fungi.
- The nuclei of the fungi are very small.
- The fungi have no embryonic stage. They develop from the spores.
- The mode of reproduction is sexual or asexual.
- Some fungi are parasitic and can infect the host.
- Fungi produce a chemical called pheromone which leads to sexual reproduction in fungi.
- Examples include mushrooms, moulds and yeast.
∆ Fungi are achlorophyllous, which means they lack the chlorophyll pigments present in the chloroplasts in plant cells and which are necessary for photosynthesis.
∆ The vegetative body of the fungi may be unicellular or composed of microscopic threads called hyphae.
∆ Hyphae can grow and form a network called a mycelium.
∆ Yeasts are unicellular fungi that do not produce hyphae.
∆ The structure of cell wall is similar to plants but chemically the fungi cell wall are composed of chitin (C8H13O5N)n.
∆ The cell membrane of a fungus has a unique sterol and ergosterol.
∆ Fungi are heterotrophic organisms. They obtains its food and energy from organic substances, plant and animal matters.
∆ Fungi grow best in acidic environment (tolerate acidic pH).
∆ Fungi digest the food first and then ingest the food, to accomplish this the fungi produce exoenzymes like Hydrolases, Lyases, Oxidoreductase, Transferase, etc.
∆ Fungi store their food as starch.
∆ Biosynthesis of chitin occurs in fungi.
∆ Many of the fungi have a small nuclei with repetitive DNA.
∆ During mitosis the nuclear envelope is not dissolved.
∆ Nutrition in fungi – they are saprophytes (gets energy from dead and decaying matters), or parasites (lives in a host, attack and kill) or symbionts (mutually beneficial).
∆ Optimum temperature of growth for most saprophytic fungi is 20-30°C while (30-37)°C for parasitic fungi.
∆ Growth rate of fungi is slower than that of bacteria.
∆ Reproduction in fungi is both by sexual and asexual means.
∆ Sexual state is referred to as teleomorph (fruiting body), asexual state is referred to as anamorph (mold like).
∆ Reproduction occurs by both asexual (Axamorph) and sexual (Teliomorph) mode:Asexual methods: fragmentation, fsomatic budding, fission, asexual spore formation
∆ Sexual methods: gametic copulation, gamate-gametangium opulation, gametangium copulation, somatic copulation and Spermatization.
∆ Pheromone is a chemical substance produced by fungi, which leads to the sexual reproduction between male and female fungi cells.
∆ Some fungi are macroscopic and can be seen by naked eyes. Mold or mushrooms are examples of macroscopic form of fungi.
∆ In 1991, a landmark paper estimated that there are 1.5 million fungi on the Earth.
∆ Only about 300 species of fungi are infectious to human.
Classification:
Based on Mode of nutrition:
On the basis of nutrition, kingdom fungi can be classified into 3 groups.
A) Saprophytic – The fungi obtain their nutrition by feeding on dead organic substances. Examples: Rhizopus, Penicillium and Aspergillus.
B) Parasitic – The fungi obtain their nutrition by living on other living organisms (plants or animals) and absorb nutrients from their host. Examples: Taphrina and Puccinia.
C) Symbiotic – These fungi live by having an interdependent relationship with other species in which both are mutually benefited.
Examples: Lichens and mycorrhiza.
Lichens are the symbiotic association between algae and fungi. Here both algae and fungi are mutually benefited as fungi provide shelter for algae and in reverse algae synthesis carbohydrates for fungi. Mycorrhiza is the symbiotic association present between fungi and plants. Fungi improve nutrient uptake by plants, whereas, plants provides organic molecules like sugar to the fungus.
Based on Spore Formation
Kingdom Fungi are classified into the following based on the formation of spores:
A) Zygomycetes – These are formed by the fusion of two different cells. The sexual spores are known as zygospores, while the asexual spores are known as sporangiospores. The hyphae are without the septa.
Example – Mucor.
B) Ascomycetes – They are also called sac fungi. They can be coprophilous, decomposers, parasitic or saprophytic. The sexual spores are called ascospores. Asexual reproduction occurs by conidiospores.
Example – Saccharomyces.
C) Basidiomycetes – Mushrooms are the most commonly found basidiomycetes and mostly live as parasites. Sexual reproduction occurs by basidiospores. Asexual reproduction occurs by conidia, budding or fragmentation.
Example- Agaricus.
D) Deuteromycetes – They are otherwise called imperfect fungi as they do not follow the regular reproduction cycle as the other fungi. They do not reproduce sexually. Asexual reproduction occurs by conidia.
Example – Trichoderma.