We all like rain, either playing in rain water or watching it through the window. Sometimes we go on a walk in the rain by putting on those rain boots. Have you observed mushrooms after rain in your surroundings? Mushrooms grow rapidly after rain and appear overnight as large as 3 - 4 inches long. They sprout out of the ground normally in damp conditions from the mycelium which is living in the ground.
GIF: Sprouting mushrooms
Most of the people will pluck the edible mushrooms and make a variety of dishes. Now tell me what are mushrooms? Yes, they are eukaryotic saprophytic organisms belonging to the Kingdom Fungi. This Kingdom contains a variety of organisms which are useful to human beings in many ways. In this article we are going to discuss Kingdom Fungi in depth.
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It includes achlorophyllous, heterotrophic, spore bearing eukaryotic organisms. They often possess glycogen as the reserve food. The branch of biology dealing with the study of Fungi is known as Mycology. Examples include mushrooms, yeasts, and moulds.
Most fungi are terrestrial while few inhabit aquatic ecosystems. They generally grow in warm and humid places. Terrestrial fungi are further classified into the following:
They are generally multicellular exceptions including yeast, which is unicellular. They possess a cell wall, made up of chitin (a polysaccharide), exceptions include members of class Oomycetes which have a cell wall that possess cellulose. They are achlorophyllous (Lack chlorophyll) and hence heterotrophic in nature. They store food in the form of glycogen and oil bodies. They produce characteristic sexual and asexual spores. Examples include Rhizopus.
Fig: Rhizopus (Bread mould)
The bodies of multicellular fungi are composed of long, tubular, filamentous structures called hyphae which form a mass known as mycelium. Hyphae is of different types based on the location and the presence of septa.
The hyphae is of two types such as aerial hyphae and vegetative hyphae based on the location in the substratum.
This hyphae is present inside the substratum. It helps in the distribution of water, nutrients, and signalling molecules across the fungal colony. More of these types of hyphae are seen in the vegetative phase of the fungi.
Fig: Vegetative hyphae
These hyphae appear above the medium and help in the formation of spores. More of these hyphae are seen in the reproductive phase of the fungi.
Fig: Aerial hyphae
Hyphae is of two types based on septa as follows:
Cross wall or septum is present in between hyphae.
Fig: Septate hyphae
Cross walls are absent in between hyphae which makes them appear as continuous tubes with multinucleated cytoplasm.
Fig: Aseptate hyphae
Fungi lack chlorophyll and they depend on other organisms for food. Hence they are said to be heterotrophic. Heterotrophic nutrition in Fungi can be of three different types as follows:
These fungi obtain their own food by absorbing soluble organic matter from dead and decaying matter such as bread, rotting fruits and vegetables. Examples include Rhizopus (Bread mould).
These fungi obtain their nutrition from living plants and animals. Examples include Puccinia, Ustilago etc. These fungi cause harm to the host and sometimes even kill them. Parasitic fungi are mostly pathogenic in nature.
Some fungi are found symbiotically associated with plants to obtain nourishment. For example, symbiotic association of fungi with algae forms lichens. Some fungi are symbiotically associated with the roots of higher plants like Pinus and form mycorrhiza.
Fig: Mode of nutrition in Fungi
Fungi reproduces vegetatively, asexually and sexually.
Fig: Reproduction in Fungi
It occurs by fragmentation, budding or fission.
Fig: Vegeatative reproduction in Fungi
In this method the mycellia breaks into fragments and each of which grows into separate mycellia. This occurs due to mechanical injury, deacy etc.
A small outgrowth or bud develops from the parent body and develops into a new organism, as is seen in yeast.
Unicellular fungi like yeasts reproduce vegetatively by fission. The parent cell undergoes cell division to form two daughter cells here.
It occurs by the formation of different types of spores. These spores are formed by mitotic division and are called mitospores. Asxual spores are usually haploid in nature and germinate into new haploid organisms.
Fig: Types of asexual spores
They are formed in sporangia formed at the tip of special hyphae called sporangiophores. Numerous sporangiospores are present in the sporangia and are released by rupture of the sporangia. The formation of sporangiospores takes place endogenously. Sporangiospores are of two types as follows:
These are flagellated and motile spores
These are non-flagellated and non-motile spores which are dispersed by wind
The sporangia bearing the zoospores are called as zoosporangia
The sporangia bearing the aplanospores are called aplano sporangia.
The spores are usually naked without a cell wall
Spores have a thin wall
The formation of conidia takes place exogenously. These conidia are thin-walled, non-motile spores that are borne at the tip of the special hyphae called conidiophores.
The formation of oidia occurs by fragmentation of hyphae. They are produced under conditions of excess water, sugar and certain salts. Examples include Rhizopus.
Fungi reproduces sexually by the formation of sexual spores. Sexual reproduction in fungi complestes in the following three steps:
This is the first stage of sexual reproduction in which the protoplasts of two cells belonging to two different mycellia fuse with each other but their nuclei do not fuse. This results in the formation of a single cell with two nuclei. This binucleate or dikaryotic stage is called dikaryon (n+n).
In this stage, the nuclei present in the cell fuse with each other to form a diploid nucleus which is known as synkaryon.
In this stage, the diploid zygote cell undergoes meiotic division to form haploid sexual spores or meiospores which upon germination form new fungal filaments.
Fig: Sexual reproduction in fungi
Fungi reproduces sexually by the formation of sexual spores such as oospores, zygospores, ascospores, basidiospores.
Fig: Sexual spores
Fusion between gametes during sexual reproduction in Fungi can be of three types as follows:
It is the fusion between gametes of the same size.
It is the fusion between gametes of dissimilar size.
It is the fusion between a smaller motile male gamete and a larger non-motile female gamete.
Fungi are classified on the basis of type of mycelium, type of sexual and asexual spores they produce.
Fig: Classification of Fungi
They are mainly found in aquatic environments and moist decaying wood. They are obligate parasites. Hyphae is aseptate (without septa) and coenocytic (multinucleated protoplasm). They reproduce asexually by sporangiospres and sexually by zygospores or oospores. The male sex organ is antheridia and female sex organ is oogonia. The fusion between gametes can be isogamous or anisogamous. Phycomycetes are classified into two categories as follows:
Fig: Classification of Phycomycetes
They are commonly known as ‘sac fungi’. Hyphae is branched and septate. Some rare varieties of Ascomycetes, such as yeast, are unicellular. Members of ascomycetes are saprophytic decomposers or parasitic. Many saprophytic varieties are coprophilous, that means they grow on dung. They reproduce vegetatively by budding and asexually by conidia (exogenously). Sexual reproduction occurs by ascospores produced endogenously within sac like structures called ascus which are borne on ascocarps. 4 to 8 ascospores are present in one ascus. Examples include Neurospora and Penicillium.
They are commonly known as ‘club fungi’. Hyphae is branched and septate. They are mainly found in soil, on logs, tree stumps and as parasites in living plant bodies. Some varieties are plant pathogens and cause diseases such as rusts and smuts. Asexual spores are generally not found but these fungi generally propagate vegetatively by fragmentation. The sexual spores are the exogenously produced basidiospores and are formed in basidia. Basidia are borne on basidiocarp. Examples include mushrooms.
They are called ‘fungi imperfecti’; because sexual reproduction is unknown in this group of Fungi. When the sexual forms of this fungi are discovered they will be moved either to Ascomycetes or Basidiomycetes based on the type of spores they produce. Their hyphae are septate and branched. They reproduce asexually by conidia. They show a saprophytic or parasitic mode of nutrition. Some varieties help in mineral cycling and decomposition. Examples include Trichoderma, Alternaria, Colletotrichum etc.
Solution: Organisms that obtain nutrients from dead and decaying organic matter are called saprophytes. These organisms break down the organic molecules from the decomposing organic matter and absorb the nutrients. Examples include Mucor, mushroom etc. Hence the correct option is ‘c’.
(a) Cell membrane
(c) Cell wall
Solution: A bacteriophage is made up of a polyhedral head, a collar and a helical tail. The tail contains the base plate and the long tail fibres. The genetic material is present inside the polyhedral head. The inner genetic material of a bacteriophage is double-stranded DNA. Fungal cells also contain DNA as the genetic material. This proves that the presence of DNA is the common factor between bacteriophages and fungi. Bacteriophage is a virus that infects bacterial cells and hence they are acellular. Cell wall, cell membrane and organelles are absent in the bacteriophages. But in the case of fungal cells, there are cell organelles in each cell and the cells are surrounded by cell walls and cell membranes. Hence the correct option is ‘b’.
Solution: Mostly Fungi are moulds that consist of filamentous hyphae. The collection of vegetative hyphae is termed mycelium (Mucor and Albugo). Fungi may be unicellular (yeast) or multicellular (mushrooms). Yeast is the exception of the filamentous structure of fungi as it has a unicellular structure. Yeast is oval-shaped and microscopic. Yeast usually reproduces asexually through the process of budding. Hence the correct option is ‘a’.
GIF: Yeast (Saccharomyces)
(a) are saprobes
(b) bear ascocarps
(c) are pathogens
(d) bear basidiocarps
Solution: Rust (Puccinia), smut (Ustilago esculenta) and mushrooms are Fungi belonging to Basidiomycetes. In these fungi, fusion of hyphae of different strains, during sexual reproduction, gives rise to a club-like basidium which contains four basidiospores. The basidia are borne on basidiocarps. Mushrooms are saprobes which feed on dead decaying organic matter. Rusts and smuts are plant parasites and not saprobes. Rusts are pathogens which cause plant diseases. Smut is also pathogenic and affects crops of the family Poaceae and Cyperaceae. However, mushrooms are non pathogenic. Ascocarps are fruiting bodies present in fungi belonging to the group Ascomycetes. Hence they lack ascocarps. So the correct option is ‘d’.
Answer: The following are the major economic importances of Kingdom Fungi:
Answer: All the parts of the fruiting bodies of mushrooms are edible. It includes gills, cap, ring and stem. But, it also depends on the species. There are poisonous mushrooms too.
Answer: Three common poisonous mushroom species of India include Mycena pura, Omphalotus olivascens, and Chlorophyllum molybdites. It is seen at Kolli Hills, Eastern Ghats, in South India.
Fig: Poisonous mushrooms
Answer: The common symptoms of mushroom poisoning include abdominal pain and vomiting.
Fig: Common symptoms of mushroom poisoning