BN01 — The Living World & Classification

Taxonomic hierarchy (broad to narrow): Kingdom → Phylum → Class → Order → Family → Genus → Species. Mnemonic: 'King Phillip Came Over For Good Soup.' Domain sits above Kingdom in the three-domain system (Bacteria, Archaea, Eukarya).

Rules of binomial nomenclature: (1) Genus — first letter capitalised, (2) Species epithet — all lowercase, (3) Both parts italicised in print, or underlined in handwriting, (4) Author name may follow in non-italics. Example: Homo sapiens Linnaeus.

Panthera leo (lion) and Panthera tigris (tiger) share the genus name Panthera, indicating they are closely related big cats. Different first words (Felis vs Canis; Homo vs Pan) indicate different genera. Rana and Bufo are different genera of frogs and toads respectively.

Kingdom Monera contains all prokaryotes — organisms with no membrane-bound nucleus or membrane-bound organelles. Includes bacteria (Eubacteria) and Archaebacteria. Blue-green algae (cyanobacteria) are also in Monera despite performing photosynthesis.

Penicillium (the mould from which penicillin was discovered) belongs to Kingdom Fungi — eukaryotic, heterotrophic, chitinous cell walls. Mushroom = Fungi (not Plantae); Amoeba = Protista (not Monera, as it is eukaryotic); Nostoc = Monera (prokaryote, not Protista).

Viruses are acellular — they have genetic material (DNA or RNA) enclosed in a protein coat (capsid), but no cytoplasm, no ribosomes, no cell membrane, and no metabolic machinery. They replicate only inside living host cells, using the host's cellular machinery.

Canis lupus familiaris (domestic dog) is classified as a subspecies of Canis lupus (grey wolf). Dogs were domesticated from wolves ~15,000-40,000 years ago. The third name (familiaris) indicates it is a subspecies — trinomial nomenclature.

Archaebacteria (Archaea) are ancient prokaryotes that thrive in extreme environments: thermophiles (hot springs), halophiles (salt lakes), methanogens (anaerobic, produce CH₄). Unique feature: membrane lipids with ether linkages (vs ester linkages in eubacteria).

The Biological Species Concept (Ernst Mayr, 1942): a species is a group of organisms that can interbreed in nature and produce fertile offspring, but are reproductively isolated from other species. A mule (horse × donkey cross) is infertile — horses and donkeys are different species.

The three-domain system (Carl Woese, 1990): Bacteria, Archaea, Eukarya. Humans (and all eukaryotes — plants, animals, fungi, protists) belong to Domain Eukarya. This system is based on ribosomal RNA sequences and is more fundamental than the five-kingdom system.

Fungi are heterotrophic (cannot photosynthesise) — they secrete digestive enzymes outside the body and absorb the digested nutrients (absorptive heterotrophs). They are eukaryotic, have chitinous cell walls, and reproduce by spores. They are decomposers in ecosystems.

Cladistics classifies organisms based on shared derived characters (synapomorphies) and evolutionary (phylogenetic) relationships — resulting in a cladogram (phylogenetic tree). More scientifically rigorous than classical taxonomy based solely on morphology.

NCBI (National Center for Biotechnology Information, USA) maintains GenBank — the world's largest collection of publicly available DNA sequences — and PubMed (biomedical literature). Essential resource for bioinformatics, genomics, and molecular biology research.

Haeckel's three-kingdom system had Protista, Plantae, Animalia. Whittaker (1969) added Kingdom Monera (prokaryotes) and Kingdom Fungi (to separate fungi from plants — they have chitin walls and are heterotrophic). This gave the five-kingdom system used in most textbooks.

DNA barcoding uses a short, standardised genomic region (the CO1 — cytochrome c oxidase I gene — for animals; rbcL and matK for plants) to identify species — like a biological barcode. Developed by Paul Hebert (2003). Used in customs to identify trafficked wildlife, food fraud detection.

Convergent evolution occurs when distantly related organisms independently evolve similar features due to similar selective pressures. Examples: wings of birds and insects; eyes of vertebrates and cephalopods; fins of fish and dolphins. Produces analogous organs, not homologous.

Under the International Code of Nomenclature for algae, fungi, and plants (ICN), a validly published species name should include the author citation — the abbreviated name of the botanist who first formally published the name. Example: Mangifera indica L. (L. = Linnaeus).

Protista is called the 'dustbin' kingdom because it contains all eukaryotes that don't fit neatly into Fungi, Plantae, or Animalia. It includes: protozoa (Amoeba, Paramecium), algae (Chlorella, diatoms), slime moulds, and Plasmodium. It is highly diverse and polyphyletic (not a natural group).

Order Primates includes: prosimians (lemurs, lorises), monkeys (Old World and New World), apes (gibbons, orangutans, gorillas, chimpanzees), and humans (Family Hominidae, Genus Homo). Primates share forward-facing eyes, grasping hands, and large brains.

A taxon (plural: taxa) is any formal taxonomic group at any level in the classification hierarchy — it can refer to a species, genus, family, order, class, phylum, or kingdom. Taxonomy is the science of naming, describing, and classifying organisms into taxa.