[Biology] Kingdom-fungi

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INTRODUCTION

  • The word fungus is originated from the Latin word for mushrooms.
  • A typical fungal cell is eukaryotic and comprises of a true nucleus and membrane-bound organelles.
  • The kingdom Fungi comprise of an enormous variety of living organisms which are generally referred to as Ascomycota, or true Fungi.
  • Scientists have successfully identified about 100,000 species of fungi; however, this is only a fraction of the 1.5 million species of fungus probably present on earth.
  • Organisms such as Edible mushrooms, yeasts, black molds, and Penicillium notatum, are all members of the kingdom Fungi, which have its place in the domain Eukarya.
  • Fungi are more closely associated to animals than plants

SALIENT FEATURES OF FUNGI

  • Fungi are eukaryotic organisms, thereby having a true nucleus which is enclosed in nuclear membrane and membrane bound organelles.
  • They are non-vascular organisms and devoid of transport tissues such as xylem and phloem.
  • Fungal cells are surrounded by cell walls. However, in contrast to plant cell wall, their cell wall is made up of chitin.
  • Fungi can reproduce both sexually and asexually. Both processes involve spore formation.
  • Sexual spores are referred to as Oospores, Zygospores, Ascospores, Basidiospores, etc.
  • Asexual spores include Sporangiospores, Aplanospores, Zoospores, Conidia, etc.
  • In terms of movement, fungi are typically non-motile.
  • Fungi undergo the phenomenon of alteration of generation. They comprise of both haploid and diploid stages in their life cycle.
  • Hypae (singular hypa) are the branching filamentous structures of a fungus that bear the spores.
  • Hyphae can grow and result into a network called a mycelium.
  • Yeasts are unicellular fungi that are unable to produce hyphae.
  • Fungi are unable to carry out photosynthesis.
  • They are heterotrophic in nutrition because they use complex organic compounds as sources of energy and carbon

CLASSIFICATION OF FUNGI

REPRODUCTION IN FUNGI

  • Fungi reproduce by both sexual an asexual means.
  • However, method of reproduction varies in different members of kingdom fungi.
  • Perfect fungi reproduce both sexually and asexually.
  • While imperfect fungi reproduce only asexually (by mitosis)

ASEXUAL REPRODUCTION

Fungi reproduce asexually by following methods

  1. Fragmentation
  2. Budding
  3. Spores

FRAGMENTATION

  • An asexual process in multicellular organisms in which the organism give rise to offspring by splitting into fragments.
  • During Fragmentation, a fungal mycelium splits into pieces and component grows into a separate mycelium.
  • Fragments of hyphae can grow new colonies.

BUDDING

  • During budding, an outgrowth forms on the side of the cell. The cytoplasm of the parent cell is continuous with the cytoplasm of the outgrowth.
  • the nucleus of the parent cell divides mitotically. One of the daughter nuclei migrate to the bud while the other remains in the parent cell.
  • The bud then detaches itself from the parent cell resulting in a fully functional daughter cell.
  • This type of asexual reproduction is observed in yeast and some filamentous fungi.

PRODUCTION OF SPORES

  • Asexual spores are released by one parent only and are genetically identical to that parent.
  • Spores help fungi to expand their distribution and colonize new environments.
  • They may be released from the parent into a special reproductive sac called a sporangium.

SEXUAL REPRODUCTION

  • Sexual reproduction is the cause of genetic variation in a population of fungi.
  • In fungi, sexual reproduction often occurs in reference to adverse environmental conditions.
  • There are two mating types;
    • homothallic
    • heterothallic.
  • When both mating types occur in the same mycelium, it is called homothallic, or self-fertile.
  • Heterothallic mycelia involve two different, but compatible, mycelia to reproduce sexually.
  • The sexual reproduction of fungi occurs in following three stages:
  • Plasmogamy
  • Karyogamy
  • Meiosis
  • During Plasmogamy, two haploid cells fuse and form a dikaryotic stage where two haploid nuclei coexist in a single cell.
  • During karyogamy (“nuclear marriage”), the haploid nuclei fuse to produce a diploid zygote nucleus.
  • At last, meiosis occurs in the gametangia organs, where gametes of different mating types are produced.
  • During this stage, spores are dispersed into the environment.

SOME IMPORTANT FUNGI

Following are some of the most salient members of kingdom fungi.

Mushrooms

  • All mushrooms are fungi, but not all fungi are categorized as mushrooms.

  • The above-ground (visible) portion of mushroom is the fruiting body and is analogous to a flower or a fruit in plants.
  • Mushroom forms microscopic spores that are similar to pollen or seeds
  • Many mushroom-producing species act as decomposers, particularly of wood.
  • These species are often relatively easy to cultivate.
  • Most of the mushroom-producing fungi are members of the phylum Basidiomycota or Ascomycota.

VARIOUS TYPES OF MUSHROOMS

POISONOUS MUSHROOMS

  • The common mushroom; death cap (Amanita phalloides) or its relatives can be fatal if eaten. .
  • Many more species, including the commonly illustrated Amanita muscaria, can cause stomach pains, vomiting, or diarrhea.
  • There are several other varieties that can be deadly if eaten, but all known species can be handled safely.
  • Even the popular “morel” is fatal if eaten raw.

MEDICINAL MUSHROOMS

  • Some varieties of mushrooms have been used as medicine for thousands of years, mainly in China and Japan.
  • Some mushrooms, such as Ganodema lucidum and Trametes versicolor have anti-cancer effects and also boost immune system.
  • Regular consumption of oyster mushrooms has been found to reduce cholesterol .

LICHENS

  • A lichen is a combination of a green alga or cyanobacterium and an ascomycete fungus, having a symbiotic relationship.

  • Lichens can be found on almost any surface (especially rocks) or in the form of epiphytes when they grow on other plants.
  • The fungus can acquire photosynthates (sugars resulting from photosynthesis) from the algae or cyanobacterium and the algae or cyanobacterium can live in a drier environment than it could otherwise not tolerate.
  • In simple words, the lichen symbiotic relationship extends the ecologic range of both partners.
  • Lichens are slow growers and can live for centuries.
  • The structure of lichens is generally composed of layers of fungi and algae.
  • The body of lichen is called as thallus
  • The thallus consists of an outer, tightly packed fungal layer called a cortex, and an inner, loosely packed fungal layer called a medulla
  • Lichens have hyphal bundles called rhizomes for attachment to the substrate

DIVERSITY IN LICHENS

The lichen body may have four different shapes:

  1. Foliose: flat leaf-like lichens.
  2. Crustose: crust-like lichens which may be buried in a tree bark, or even between the crystals of rocks
  3. Fruticose: miniature shrub-like lichens. —a famous example of this is “reindeer moss” of Lapland.
  4. Squamulose: scaly lichens composed of numerous, small rounded scales called Squamules; whose size is intermediate between foliose and crustose lichens.

REPRODUCTION, DISPERSAL AND DISTRIBUTION

  • Lichens are capable of reproducing asexually by various methods. The most common method is fragmentation.
  • In fragmentation method, a fragment breaks off from the lichen thallus which grows into a new thallus.
  • The new thallus formed is genetically identical to the parent thallus
  • Many lichens become brittle in dry environment and thus are easily fragmented, for instance by some animal stepping on dry thallus.
  • Reproduction by fragmentation is typical of foliose and crustose species.
  • Fragmentation in lichens is also termed as accidental vegetative reproduction
  • Only the fungal partner reproduces sexually, and the spores produced as a result are released in a long-lived saucer-like structure called an apothecium.

USES OF LICHENS

  • Lichens are more commonly used for the treatment of wounds, skin disorders, respiratory and digestive problems.
  • Foliose lichens are utilized to represent trees in model train layouts.
  • Lichens also make about 400 “secondary products”.
  • These chemicals are released by lichens as defense against various disease and parasites, and, in some cases, they make the taste of lichen unpleasant to animals.
  • Some of these secondary compounds are now used as anti-viral and anti-bacterial medications.
  • Some lichens are very sensitive to pollution and have been used as environmental indicators
  • Lichens are also used to scent Wool and make perfumes.

MYCORRHIZAE

  • Mycorrhiza are fungi that live inside the plant’s roots, or on the surfaces of the roots
  • Mycorrhiza is a mutually beneficial relationship between the root of a plant and a fungus that colonizes the plant root.
  • In this mutualistic relationship, the fungus facilitates water and nutrient uptake in the plant, whereas in return the plant provides food and nutrients created by photosynthesis to the fungus.
  • This exchange is an important factor in nutrient cycles of the plants.
  • It is not necessary that all plants should have mycorrhizal associations. In nutrient rich and hydrated soil environments plants do not require the assistance of mycorrhizal fungi.

TYPES OF MYCORRHIZAE

There are two predominant types of mycorrhizae:

  1. Ectomycorrhizae
  2. Endomycorrhizae.

ECTOMYCORRHIZAE

  • Ectomycorrhizae is the type of mycorrhizae in which there is a symbiotic association of fungi with the feeder roots of higher plants.
  • In this relation, both the partners are mutually benefited.
  • Ectomycorrhizae inhabit on the outside of the root.
  • Overall, only about 5-10% of terrestrial plant species have ectomycorrhizae.

ENDOMYCORRHIZAE

  • Endomycorrhizal relationship involves the penetration of the cortical cells of the plant by the fungi.
  • 80% of the plant species exhibit Endomycorrhizae association-including crops and greenhouse plants such as most vegetables, grasses, flowers, and fruit trees.
  • It is a more invasive relationship as compared to that of the Ectomycorrhizae.
  • Examples of Endomycorrhizae include; Arbuscular Mycorrhizae, Ericaceous Mycorrhizae and Arbutoid Mycorrhizae.

IMPORTANCE AND USES OF FUNGI

  • Fungi are important decomposers in most ecosystems.
  • Fungi are responsible for most of the recycling in environment which returns dead material to the soil in a form in which it can be reused.
  • Fungi, as food, are agents of fermentation in the production of bread, cheeses, alcoholic beverages, and numerous other food preparations.
  • Secondary metabolites of fungi such as antibiotics and anti-coagulants are utilized as medicines.
  • Fungi such as the Chinese caterpillar fungus act as biological control, which parasitize insects and can control insect pests of crops
  • Fungi are used as model organisms for the study of eukaryotic genetics and metabolism.

REFERENCES

  • Arihant’s handbook of biology. Biological classification. Page no: 7-23.
  • NCERT biology; textbook for class 11. Biological classification. Page no: 16-28.
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