Biological classification-II

Biological classification-II is the second part, read first part here

Biological classification , also known as taxonomy, is a fundamental system used by scientists to organize and categorize the vast diversity of life on Earth. This hierarchical system places all living organisms into distinct groups based on their shared characteristics, facilitating our understanding of their evolutionary relationships and helping us navigate the complexity of the natural world.

KINGDOM FUNGI

Diversity in Morphology and Habitat

• Fungi are a unique kingdom of achlorophyllous, heterotrophic, spore forming, eukaryotic organisms.
• They exhibit a wide diversity in both morphology and habitat.
• Common examples of fungi include those found on moist bread, rotten fruits, mushrooms, and toadstools.
• Fungi can also be parasitic, causing diseases in plants and animals, like wheat rust caused by Puccinia.
• Some fungi, like Penicillium, are a source of antibiotics.
• the study of fungi is called mycology

Distribution

• Fungi are cosmopolitan and can be found in various environments, including air, water, soil, and on animals and plants.
• They prefer to grow in warm and humid conditions.

Refrigeration and Fungal Infections

• Refrigeration is used to prevent food from spoiling due to bacterial or fungal infections.

Morphology of Fungi

• Except for yeasts, fungi are filamentous.
• Their bodies consist of long, slender thread-like structures called hyphae.
• The network of hyphae is known as mycelium.
• Some hyphae are coenocytic (continuous tubes filled with multinucleated cytoplasm), while others have septae (cross walls).
• Fungal cell walls are composed of chitin and polysaccharides.

Nutrition

• Most fungi are heterotrophic and obtain nutrients by absorbing soluble organic matter from dead substrates (saprophytes).
• Fungi can also be parasites, depending on living plants and animals, or symbionts, living in association with algae as lichens and with the roots of higher plants as mycorrhiza.

Reproduction

• Fungi can reproduce through vegetative means, such as fragmentation, fission, and budding.
• Asexual reproduction is through spores, including conidia, sporangiospores, and zoospores.
• Sexual reproduction involves the formation of oospores, ascospores, and basidiospores.
• These various spores are produced in distinct structures known as fruiting bodies.
• The sexual cycle includes plasmogamy (fusion of protoplasm), karyogamy (fusion of two nuclei), and meiosis in the zygote, resulting in haploid spores.

Dikaryotic Stage

• Some fungi, such as ascomycetes and basidiomycetes, have an intervening dikaryotic stage (n + n, dikaryon), called dikaryophase before the nuclei fuse to become diploid.

Classification Based on Morphology

• The morphology of the mycelium, mode of spore formation, and fruiting bodies form the basis for classifying fungi into various classes.
• Phycomycetes
  • Found In aquatic habitats, decaying wood, or as obligate parasites on plants.The mycelium is aseptate and coenocytic.Reproduction includes zoospores and aplanospores, and sexual reproduction involves the formation of zygospores.
  • Examples: Mucor, Rhizopus, Albugo.
• Ascomycetes
  • Ascomycetes are commonly known as sac-fungi.They can be multicellular (e.g., Penicillium) or rarely unicellular (e.g., yeast – Saccharomyces).
  
  
  • Ascomycetes can be saprophytic, decomposers, parasitic, or coprophilous (growing on dung).
  
  
  • Their mycelium is branched and septate.
  
  
  • Asexual spores called conidia are produced externally on specialized mycelium called conidiophores.
  
  
  • Conidia, when they germinate, give rise to new mycelium.
  
  
  • Sexual spores in ascomycetes are known as ascospores and are produced internally in sac-like structures called asci (singular ascus).
  
  
  • Asci is organized within various types of fruiting bodies called ascocarps.
  
  
  • Examples of ascomycetes include Aspergillus, Claviceps, and Neurospora.
  
  
  • Neurospora is commonly used in biochemical and genetic research.
  • Some ascomycetes like morels and truffles are edible and considered delicacies.
• Basidiomycetes
  • Basidiomycetes include mushrooms, bracket fungi, and puffballs.
  • They thrive in soil, on decaying logs, and as plant parasites (e.g., rusts and smuts).
  • Their mycelium is branched and septate.
  • Asexual spores are rare; fragmentation is a common means of reproduction.
  • They lack traditional sex organs but undergo plasmogamy by fusing different cell types, resulting in a dikaryotic structure.
  • Karyogamy and meiosis occur in the basidium, producing four basidiospores.
  • Basidiospores are produced externally on structures called basidia.
  • Fruiting bodies, called basidiocarps, house basidia.
  • Common examples include Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).
• Deuteromycetes
  • Known as imperfect fungi. (As sexual phase is unknow)
  
  
  • Saprophytes or parasites but mainly decomposer (helps in mineral recycling)
  
  
  • Reproduce only asexually through conidia.Mycelium is septate and branched.
  • Examples: Alternaria, Colletotrichum, Trichoderma.

Kingdom Plantae

Definition: Kingdom Plantae includes all eukaryotic chlorophyll-containing organisms commonly referred to as plants.

Heterotrophic Exceptions: Some members, like insectivorous plants and parasites, exhibit partial heterotrophy.

Examples: Bladderwort and Venus fly trap are insectivorous plants, while Cuscuta is a parasite.

Cell Structure: Plant cells possess eukaryotic structures with prominent chloroplasts and cell walls primarily composed of cellulose.

Taxonomic classification: Plantae encompasses a wide range of organisms, including algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.

Life Cycle: The life cycle of plants comprises two distinct phases: the diploid sporophyte and the haploid gametophytic phases, which alternate.

Variation in Phases: Different plant groups vary in the lengths of their haploid and diploid phases, and whether these phases are free-living or dependent on others. This phenomenon is termed alternation of generations.

Kingdom Animalia

• Heterotrophic eukaryotic organisms.
• Multicellular organisms.
• Lack cell walls in their cells.
• Directly or indirectly depend on plants for food.
• Digest their food in an internal cavity.
• Store food reserves as glycogen or fat.
• Holozoic mode of nutrition – ingestion of food.
• Higher forms exhibit elaborate sensory and neuromotor mechanisms.
• Most capable of locomotion.
• Sexual reproduction involves copulation of male and female.
• Followed by embryological development.

Viruses

• Viruses are not consider truly living.
• They are non-cellular organism.
• Viruses are obligate parasites.
• Out side the living cell, versus are inert crystalline structure.
• When infect living cell, they used host cell machinery to replicate and kill host cell.
• Dmitri Ivanowsky (1892): – discover mosaic disease of tobacco (tobacco mosaic virus)
• M.W. Beijerinek (1898): – coin term virus
• W.M. Stanley (1935) showed that viruses could be crystallised and crystals consist largely of proteins
• Viruses consist of protein and nucleic acid (RNA or DNA, but not both).
• Plant viruses are generally single stranded RNA.
• Animal viruses either single or double stranded RNA or double stranded DNA.
• Bacterial viruses (bacteriophages) are usually double stranded DNA viruses.
• The protein coat of virsus, called capsid made of small subunits called capsomeres, protects the nucleic acid.
• capsomeres are arranged in helical or polyhedralgeometric forms.
• Diseases: mumps, small pox, herpes, influenza and AIDS

Viroids

1. Discovery: In 1971, T.O. Diener in potato spindle tuber disease.
2. Unusual Characteristics: Viroids were notably smaller than viruses,
3. RNA-Based: no protein coat only RNA
4. Low Molecular Weight: viroids was their low molecular weight.

Prions

1. Introduction of Prions: Prions causes neurological diseases with a novel mode of transmission.
2. Abnormal Protein: composed of abnormally folded proteins.
3. Size Comparison:prion agents were roughly similar in size to viruses.
4. Notable Diseases: bovine spongiform encephalopathy (BSE), commonly referred to as “mad cow disease” in cattle, and its human analog, Creutzfeldt-Jakob disease (CJD).

Lichens

1. Symbiotic Associations: Lichens are intriguing examples of symbiotic associations ( mutually beneficial interactions between two distinct organisms.)
2. Components: In a lichen, there are two primary components. The algal component is referred to as the “phycobiont,” and the fungal component is known as the “mycobiont.” These two components have complementary roles.
3. Mutual Benefits: The algae within lichens are autotrophic and can photosynthesize, producing food for themselves. In contrast, the fungi are heterotrophic and cannot produce their own food. They rely on the algae for sustenance.
4. Symbiotic Harmony: This interdependence is so intimate that when observing a lichen in nature, it’s challenging to discern that it consists of two different organisms. They function harmoniously, with algae providing nourishment and fungi offering shelter, mineral nutrients, and water.
5. Environmental Indicators: Lichens have a fascinating ecological role as pollution indicators. They thrive in areas with minimal pollution but do not grow in heavily polluted environments, making them valuable tools for assessing environmental health.