The Living World — Class 11 Biology

This opening chapter asks what distinguishes the living from the non-living and how biologists make sense of the enormous diversity of life, with between 1.7 and 1.8 million species described so far. Because local names vary from place to place, a universal system of naming is needed; this is nomenclature, and it works only after an organism is correctly identified. Each scientific name has two parts under binomial nomenclature, given by Carolus Linnaeus: a generic name and a specific epithet, written in Latin and in italics, as in Mangifera indica for mango. Plant names follow the ICBN and animal names the ICZN. Classification groups organisms into convenient categories called taxa, and the study of classification with its underlying rules of identification, naming and arrangement is taxonomy, while systematics additionally considers evolutionary relationships. The chapter then builds the taxonomic hierarchy from species upward through genus, family, order, class, phylum or division, and finally kingdom. As one moves up this ladder the number of shared characters decreases, so higher categories are harder to relate. Worked examples for man, housefly, mango and wheat show how each organism occupies a definite place at every rank.