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, Bacillus, Vibrio, and Spirillum
• Archaebacteria live in extreme habitats and have a different cell wall structure
• Eubacteria are characterised by a rigid cell wall and flagellum
• 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 form fruiting bodies bearing spores at their tips
• Protozoans are heterotrophs and live as predators or parasites
• Fungi are heterotrophic organisms with a great diversity in morphology and habitat
• Fungi are used to make bread, beer, antibiotics, and can cause 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
• The cell walls of fungi are 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 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
• In some fungi, a dikaryotic stage occurs before cells become diploid, known as dikaryon and dikaryophase
• 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 and on decaying wood, with aseptate and coenocytic mycelium
• Ascomycetes are mostly multicellular, saprophytic, decomposers, or parasites, with branched and septate mycelium
• Basidiomycetes include mushrooms, bracket fungi, and puffballs, with branched and septate mycelium
• Deuteromycetes are known as imperfect fungi and reproduce only by asexual spores, with septate and branched mycelium