Biological Classification

• Aristotle used simple morphological characters to classify plants into trees, shrubs, and herbs
• Aristotle divided animals into two groups based on whether they had red blood or not
• Linnaeus developed a Two Kingdom system of classification with Plantae and Animalia kingdoms
• The Two Kingdom system did not distinguish between eukaryotes and prokaryotes, unicellular and multicellular organisms, and photosynthetic and non-photosynthetic organisms
• R.H. Whittaker proposed a Five Kingdom Classification: Monera, Protista, Fungi, Plantae, and Animalia
• The main criteria for classification in the Five Kingdom system include cell structure, body organisation, mode of nutrition, reproduction, and phylogenetic relationships
• The Three-domain system divides the Kingdom Monera into two domains and leaves the remaining eukaryotic kingdoms in the third domain, resulting in a Six Kingdom classification
• Bacteria are the sole members of the Kingdom Monera
• Bacteria are grouped based on their shape: Coccus (spherical), Bacillus (rod-shaped), Vibrium (comma-shaped), and Spirillum (spiral)
• Archaebacteria live in extreme habitats like salty areas, hot springs, and marshy areas
• Eubacteria are characterised by a rigid cell wall and may be photosynthetic autotrophs or heterotrophs
• Protista includes all single-celled eukaryotes and forms a link with plants, animals, and fungi
• Chrysophytes include diatoms and golden algae, found in fresh water and marine environments
• Dinoflagellates are mostly marine, photosynthetic, and have stiff cellulose plates on the outer surface
• Euglenoids are fresh water organisms with a protein-rich layer called pellicle instead of a cell wall
• Slime moulds are saprophytic protists that move along decaying organic material and form fruiting bodies bearing spores
• Protozoans are heterotrophs and live as predators or parasites, with four major groups: amoeboid, flagellated, ciliated, and sporozoans
• Fungi are heterotrophic organisms with a great diversity in morphology and habitat
• Fungi are used in various applications such as making bread, beer, antibiotics, and causing diseases in plants and animals
• Fungi are cosmopolitan and occur in air, water, soil, and on animals and plants
• Fungi prefer to grow in warm and humid places
• Food is kept in the refrigerator to prevent it from going bad due to bacterial or fungal infections
• Fungi are filamentous and their bodies consist of long, slender thread-like structures called hyphae
• The network of hyphae is known as mycelium
• Some hyphae are continuous tubes filled with multinucleated cytoplasm, known as coenocytic hyphae
• Fungi have cell walls composed of chitin and polysaccharides
• Most fungi are heterotrophic and absorb soluble organic matter from dead substrates, known as saprophytes
• Fungi that depend on living plants and animals are called parasites
• Fungi can also live in association with algae as lichens and with roots of higher plants as mycorrhiza
• Reproduction in fungi can occur by vegetative means such as fragmentation, fission, and budding
• Asexual reproduction in fungi is by spores called conidia, sporangiospores, or zoospores
• Sexual reproduction in fungi is by oospores, ascospores, and basidiospores
• Various spores in fungi are produced in distinct structures called fruiting bodies
• The sexual cycle in fungi involves fusion of protoplasms, fusion of nuclei, and meiosis resulting in haploid spores
• Some fungi have a dikaryotic stage before becoming diploid, known as a dikaryon and dikaryophase
• Fungi form fruiting bodies where reduction division occurs, leading to the formation of haploid spores
• The morphology of the mycelium, mode of spore formation, and fruiting bodies form the basis for the division of the kingdom into various classes
• Phycomycetes are found in aquatic habitats, on decaying wood, or as parasites on plants
• Ascomycetes are commonly known as sac-fungi and can be multicellular or unicellular
• Basidiomycetes include mushrooms, bracket fungi, and puffballs