What Makes Fungi Unique in the Living World?
Fungus is any of the approximately 144,000 known fungi species, including yeasts, rusts, smuts, mildews, moulds, and mushrooms. Many fungus-like species, such as slime moulds and oomycetes, do not belong to the kingdom fungi yet are commonly referred to as fungi. The creatures in the kingdom fungi have a cell wall and are widely distributed. Among living beings, they are categorised as heterotrophs.
Fungi are heterotrophic, meaning they get their energy and carbon from complex organic substances rather than sunlight. Animals and fungi are more closely linked than plants. Fungi can reproduce asexually, sexually, or both ways. The majority of fungi create spores, which are haploid cells capable of mitosis and becoming multicellular, haploid people.
The article deals with the explanation of what is fungi, fungi examples. Although there are different types of fungi, the article describes the generalised characteristics of the kingdom fungi.
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Fungi Cell Structure
Fungi can be unicellular or multicellular. They are heterotrophic decomposers with strong cell walls that devour decomposing stuff and form thread entanglement. The hard cell walls of fungi include complex polysaccharides termed chitin and glucans, which provide mechanical rigidity. Ergosterol is a steroid component present in the cellular membrane that substitutes cholesterol in biological membranes. Fungi can be unicellular, multicellular, or dimorphic, which means that the fungi can be unicellular or multicellular based on the environment. The vegetative stage of fungi is characterised by a tangle of slender, thread-like hyphae, but the reproductive stage is generally more visible.
Fungi are eukaryotic organisms with complicated cellular structures. Fungal cells, like other eukaryotes, have a membrane-bound nucleus with DNA wrapped around the histone proteins. A few fungi contain structures that are similar to bacterial plasmids. Mitochondria and a complex system of internal membranes, including the endoplasmic reticulum and Golgi apparatus, are also found in fungal cells. Chloroplasts and chlorophyll are not found in fungus cells. Many fungi have vibrant hues, ranging from red to green to black, that are caused by different cellular pigments.
Chitin and glucans are complex polysaccharides found in the stiff regions of cell walls. The structural strength of fungal cell walls is provided by chitin, which is also present in the exoskeleton of insects. The cell's wall protects it from dehydration and predators. Fungi possess phospholipid bilayers comparable to those of other eukaryotes, except that ergosterol, a steroid compound that substitutes cholesterol in animal cell membranes, stabilises the structure. The majority of kingdom Fungi members do not move.
Growth in Kingdom Fungi
A fungal cell's vegetative body is known as the thallus, which can be unicellular or multicellular. Based on the environment, the dimorphic fungus can transition from single-celled to multicellular states. Yeasts are the common name for unicellular fungus. Unicellular fungi examples include Saccharomyces cerevisiae, also known as baker's yeast and Candida species, the agents of thrush, a common fungal illness. The vast majority of fungi are multicellular entities. There are two main morphological phases in which they might be found: vegetative and reproductive.
The vegetative stage is characterised by a tangle of slender thread-like structures known as hyphae. A mycelium is a mass of hyphae. It may grow on a surface, in soil or decomposing matter, liquids, and even live tissue. The mycelium of a fungus can be quite enormous, even if individual hyphae must be examined under a microscope. Endwalls termed septa partition most fungal hyphae into distinct cells. In most fungi phyla, microscopic openings in the septa allow nutrients and small molecules to pass quickly from cell to cell along the hypha. Perforated septa are how they're described. Fungi thrive in damp, somewhat acidic settings and may grow in the presence or absence of light.
Nutrition in Kingdom Fungi
Since we have learnt about fungi, the fungi cell structure and fungi examples let us look into the nutrition in kingdom fungi. Fungi, like mammals, are heterotrophs, meaning they get their carbon from complex organic substances instead of from the environment. Furthermore, the fungus does not absorb atmospheric nitrogen. In contrast to most mammals, which absorb food and then digest it inside specialised organs, the fungus does the opposite: digestion comes before ingestion. Exoenzymes will be first transferred out of the mycelium and into the atmosphere, where it digests food. The organic particles created by external digestion are then ingested by the mycelium's vast surface area. Instead of the starch found in plants, glycogen is the polysaccharide of preservation.
Fungi are usually saprophytes or microorganisms that get their nourishment from decomposing organic materials. They get their nourishment from rotting or dead organic waste, primarily plant materials. Exoenzymes from fungi can convert intractable polysaccharides like cellulose and lignin from decaying wood into easily absorbed glucose molecules. As a result, carbon, nitrogen, and other elements are released into the atmosphere. Fungi have a significant ecological function and are being studied as possible bioconversion techniques due to their diverse metabolic processes.
Reproduction in Fungi
Fungi may reproduce in both sexual and asexual ways. Imperfect fungi reproduce exclusively asexually, whereas perfect fungi reproduce both sexually and asexually (by mitosis). Fungi release spores that disseminate from the parent organism by drifting on the wind or catching a ride on an animal in both sexual and asexual reproduction. Plant seeds are larger and heavier than fungal spores. The massive puffball mushroom erupts, releasing trillions of spores. The large quantity of spores expelled improves the chances of their landing in a growth-friendly environment.
Types of Fungi
Let us look into the classification to understand the different types of fungi. Kingdom fungus may be divided into three groups based on its nutritional needs.
Saprophytic Fungus - The saprophytic fungus gets its sustenance from dead organic matter. Rhizopus, Penicillium, and Aspergillus are some of the fungi examples.
Parasitic Fungus - The parasitic fungus gets its sustenance by living on other living things and absorbing resources from them. Taphrina and Puccinia are two parasitic fungi examples.
Symbiotic - Symbiotic fungi are those that exist in an interdependent relationship with other species in which both parties benefit. Lichens and mycorrhizae are two examples. Lichens are the result of a symbiotic relationship between algae and fungus. Algae and fungus benefit from each other in this situation since fungi offer shelter for algae and algae give shelter for fungi.
There are different types of fungi based on their spores, which are mentioned below.
Zygomycetes - These are made up of two distinct cells that have fused together. Asexual spores are called sporangiospores, whereas sexual spores are called zygospores. The septa are missing from the hyphae.
Ascomycetes - Also known as sac fungi, are a kind of ascomycetes. Ascospores refer to sexual spores. Conidiospores are used for asexual reproduction. Saccharomyces cerevisiae is a good example of this type.
Basidiomycetes - The most prevalent basidiomycetes are mushrooms, which mainly survive as parasites. Basidiospores are responsible for sexual reproduction. Conidia, budding, and fragmentation are all examples of asexual reproduction. Agaricus is a good example.
In conclusion of the article, we have seen the fungi information on form and function of fungi, we have seen the fungi examples. The growth and reproduction of fungi are also being discussed.
FAQs on Fungi in Biology: Structure, Types, and Reproduction
1. What are the major characteristics of organisms in Kingdom Fungi?
Organisms in Kingdom Fungi are eukaryotic and primarily multicellular (with yeast being a notable exception). Their key characteristics include:
- Mode of Nutrition: They are heterotrophic, meaning they cannot produce their own food. They obtain nutrients by absorption, acting as saprophytes (on dead organic matter), parasites (on living hosts), or symbionts.
- Cell Wall: Their cell walls are composed of a tough, complex sugar called chitin, which is different from the cellulose found in plant cell walls.
- Body Structure: The body of a fungus consists of long, thread-like structures called hyphae. A network of these hyphae forms a mycelium.
- Reproduction: Fungi can reproduce both asexually (through spores like conidia or sporangiospores) and sexually (through oospores, ascospores, and basidiospores).
- Food Storage: They store food in the form of glycogen and oil droplets.
2. How are the four main classes of fungi distinguished from each other as per the CBSE syllabus?
The four main classes of fungi—Phycomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetes—are distinguished based on the morphology of the mycelium, the mode of spore formation, and fruiting bodies.
- Phycomycetes (Algal Fungi): Characterised by aseptate (coenocytic) mycelium. Asexual reproduction occurs via motile zoospores or non-motile aplanospores. Examples include Mucor and Rhizopus.
- Ascomycetes (Sac Fungi): They have a septate and branched mycelium. Sexual spores, called ascospores, are produced inside a sac-like structure called an ascus. Examples include Aspergillus, Penicillium, and Yeast.
- Basidiomycetes (Club Fungi): They also have a septate and branched mycelium. Sexual spores, known as basidiospores, are exogenously produced on a club-shaped structure called a basidium. Examples include mushrooms (Agaricus) and puffballs.
- Deuteromycetes (Fungi Imperfecti): This class includes fungi where the sexual stage is either absent or not yet discovered. They have a septate mycelium and reproduce asexually by conidia. Examples include Alternaria and Trichoderma.
3. What is the economic importance of fungi in industries and medicine?
Fungi are of immense economic importance. In medicine, they are the source of life-saving antibiotics, such as Penicillin from the fungus Penicillium notatum. In industry, yeasts (a type of fungus) are essential for fermentation processes used in baking to make bread rise and in brewing to produce alcoholic beverages. Certain fungi, like mushrooms and truffles, are consumed as food and are a source of protein and vitamins. Fungi also play a critical role as decomposers in ecosystems, recycling vital nutrients back into the soil.
4. Why are fungi classified in a separate kingdom and not under plants?
Fungi are placed in a separate kingdom because they possess fundamental differences from plants. The primary reasons are:
- Nutrition: Fungi are heterotrophic and obtain nutrients by absorbing them from their environment. In contrast, plants are autotrophic and produce their own food through photosynthesis.
- Cell Wall Composition: The cell walls of fungi are made of chitin. Plant cell walls are made of cellulose.
- Body Structure: Fungi lack true roots, stems, and leaves. Their body is a filamentous mycelium, which is structurally different from the differentiated tissues of plants.
- Food Storage: Fungi store excess food as glycogen, similar to animals, while plants store it as starch.
5. What is the difference between saprophytic and parasitic fungi?
The main difference between saprophytic and parasitic fungi lies in their source of nutrition. Saprophytic fungi, like mushrooms and bread mould (Rhizopus), are decomposers that obtain their nutrients from dead and decaying organic matter. They play a crucial role in nutrient cycling. In contrast, parasitic fungi, such as rusts and smuts, derive their nutrients from living plants and animals, often causing harm or disease to their host. For example, Puccinia causes wheat rust disease.
6. Explain the three main steps of the sexual cycle in fungi.
The sexual cycle in fungi, regardless of the specific class, involves three sequential steps:
- Plasmogamy: This is the first step, involving the fusion of protoplasm between two motile or non-motile gametes from compatible hyphae. This brings two haploid nuclei close together in a single cell, leading to a dikaryotic stage (n+n).
- Karyogamy: Following plasmogamy, the two haploid nuclei fuse together to form a single diploid nucleus (2n). The cell is now called a zygote.
- Meiosis: The diploid zygote undergoes meiotic division to produce haploid spores (e.g., ascospores, basidiospores). These spores can then germinate to form new haploid hyphae, completing the cycle.
7. How do fungi form important symbiotic relationships like lichens and mycorrhiza?
Fungi form two major types of mutually beneficial symbiotic relationships. Lichens are a composite organism arising from the symbiosis between a fungus (the mycobiont) and an alga or cyanobacterium (the phycobiont). The fungus provides shelter, water, and mineral absorption, while the alga performs photosynthesis to provide food for both partners. Mycorrhiza is a symbiotic association between a fungus and the roots of higher plants. The fungus helps the plant absorb essential minerals like phosphorus from the soil, and in return, the plant provides the fungus with energy-rich carbohydrates.
8. Why is the class Deuteromycetes often referred to as 'Fungi Imperfecti'?
Deuteromycetes are called 'Fungi Imperfecti' because this group historically included all fungi in which a sexual stage of reproduction has not been observed. The classification of fungi is largely based on the characteristics of sexual spores and fruiting bodies. Since only the asexual or vegetative phases of these fungi were known, they were considered 'imperfect.' When the sexual forms (perfect stages) of any member of this class are discovered, they are reclassified and moved to their correct class, typically Ascomycetes or Basidiomycetes.
