The Living World

NCERT lists key features of life. GROWTH: increase in mass and number of cells. In living organisms it is INTRINSIC (from inside), while in non-living (mountains, crystals) it is EXTRINSIC (by accumulation on surface). Growth and reproduction are NOT defining/foolproof properties (mules, sterile worker bees, infertile humans cannot reproduce; non-dividing cells do not grow). The ONLY DEFINING property is METABOLISM (sum of all chemical reactions). All living things have metabolism without exception. Memory aid: 'CRiMP' - Cellular organisation, Reproduction, Metabolism, self-consciousness (Property of). The most defining property at higher levels is SELF-CONSCIOUSNESS / self-replication, and cellular organisation is the defining feature of all living forms.

Metabolism = sum total of all chemical reactions in the body. It is the DEFINING characteristic of all living organisms without exception. No non-living object shows metabolism. Metabolic reactions can occur OUTSIDE the body in a cell-free system (in vitro) - such isolated reactions are NEITHER living NOR non-living; they are 'living reactions' but not 'living things'. Hence a cellular organisation of the body is the defining feature of life forms. Shortcut: Metabolism = universal & defining; Cellular organisation = defining; Growth & Reproduction = characteristic but NOT defining.

A mountain or boulder grows by accumulation of material on its OUTER surface (extrinsic growth). A living organism (e.g. a plant or animal) grows from WITHIN by cell division (intrinsic growth). In plants, growth continues throughout life (open form), whereas in most animals growth occurs only up to a certain age. Unicellular organisms (e.g. bacteria) show growth as increase in cell number, which overlaps with reproduction - here growth = reproduction (synonymous). Hence growth cannot be taken as a defining property of living organisms.

BIODIVERSITY = the number and types of organisms on Earth; about 1.7-1.8 million species described so far. To handle this diversity, Carolus Linnaeus gave BINOMIAL NOMENCLATURE - each scientific name has two components: GENUS (generic name) + SPECIES (specific epithet). Example: Mangifera indica (mango); Homo sapiens (human); Panthera tigris (tiger). Rules (ICBN/ICZN): (1) Names in Latin, italicised in print. (2) When handwritten, both words SEPARATELY UNDERLINED. (3) Genus starts with CAPITAL, species with small letter. (4) Author's name (abbreviated) written after species, e.g. Mangifera indica Linn. Memory aid: 'Genus Capital, species small; underline both, Latin for all'.

Biological names follow agreed principles. (1) LATIN origin, italicised in print. (2) First word = genus (Capital initial); second word = specific epithet (small initial). (3) When handwritten, each word is underlined SEPARATELY to indicate Latin origin and italics. (4) The name of the author appears after the specific epithet, in abbreviated form (e.g. Linn. for Linnaeus). ICBN = International Code for Botanical Nomenclature (plants); ICZN = International Code of Zoological Nomenclature (animals). Trick: 'CSS-AL' = Capitalise genus, Small species, Separately underline, Author last, Latin/italics.

Common NEET examples: Mango = Mangifera indica; Human = Homo sapiens; Tiger = Panthera tigris; Lion = Panthera leo; Wheat = Triticum aestivum; Pea = Pisum sativum; Frog = Rana tigrina; Housefly = Musca domestica; Pigeon = Columba livia. Note the genus is always capitalised and the species in lowercase. Mangifera indica Linn. - 'Linn.' indicates Linnaeus first described it. Spotting errors: 'mangifera Indica' is WRONG (genus must be capital, species small).

TAXONOMY = process of classification based on characteristics: characterisation, identification, classification and nomenclature. SYSTEMATICS = study of diversity and evolutionary relationships ('systema' = systematic arrangement of organisms); coined from the title of Linnaeus's 'Systema Naturae'. The TAXONOMIC HIERARCHY (descending): Kingdom > Phylum (animals)/Division (plants) > Class > Order > Family > Genus > Species. Memory aid: 'King Philip Came Over For Good Soup' (Kingdom, Phylum, Class, Order, Family, Genus, Species). SPECIES is the lowest/basic unit; KINGDOM is the highest. As we go up the hierarchy, number of common characters DECREASES and the category becomes more abstract.

SPECIES = group of individual organisms with fundamental similarities, capable of interbreeding to produce fertile offspring. In a binomial name, the species is the specific epithet. Example: in Panthera leo (lion) and Panthera tigris (tiger), 'leo' and 'tigris' are species while Panthera is the genus. Mangifera (genus) has one species indica. GENUS = group of related species having more characters in common than other genera. As you move from species → kingdom: number of organisms INCREASES, common characteristics DECREASE. Remember: lower category = more similar organisms; higher category = fewer common features.

HUMAN: Species sapiens → Genus Homo → Family Hominidae → Order Primata → Class Mammalia → Phylum Chordata → Kingdom Animalia. HOUSEFLY: Musca domestica → Family Muscidae → Order Diptera → Class Insecta → Phylum Arthropoda → Kingdom Animalia. WHEAT: Triticum aestivum → Family Poaceae (Graminae) → Order Poales → Class Monocotyledonae → Division Angiospermae → Kingdom Plantae. Note: animals use PHYLUM, plants use DIVISION. Mango and wheat share kingdom Plantae but differ at lower categories. The more categories two organisms share, the closer their relationship.

HERBARIUM: store house of collected, dried, pressed plant specimens on sheets, arranged according to a universally accepted classification system; sheets carry a LABEL (date, place of collection, name, family, collector). Acts as a quick referral system. BOTANICAL GARDENS: have living plant collections for reference, each plant labelled with botanical/scientific name and family. Famous: Royal Botanical Garden Kew (England), Indian Botanical Garden Howrah (Kolkata), National Botanical Research Institute Lucknow. MUSEUM: has collections of preserved plant/animal specimens; insects pinned/dried; larger animals preserved in PRESERVATIVES (formalin) or as STUFFED specimens/skeletons. Memory aid: Herbarium = DRIED plants on sheets; Botanical garden = LIVING plants; Museum = PRESERVED specimens.

ZOOLOGICAL PARKS (zoos): wild animals kept in protected/captive conditions resembling natural habitats; allow study of food habits and behaviour. KEY: a taxonomic aid for IDENTIFICATION based on similarities and dissimilarities; uses contrasting characters in pairs called COUPLETS; each statement is a LEAD. Keys are usually analytical and separate (different keys for family, genus, species). OTHER aids: FLORA (actual account of plants in an area - habitat & distribution), MANUALS (info for identification of names of species), MONOGRAPHS (info on any ONE taxon), CATALOGUES. Trick: 'Key = Couplet of two contrasting Leads'.

Quick comparison table (NEET favourite): HERBARIUM → dried, pressed plants on sheets + label. BOTANICAL GARDEN → living plants (Kew, Howrah, NBRI Lucknow). MUSEUM → preserved specimens (formalin), stuffed animals, skeletons, insect boxes. ZOOLOGICAL PARK → living wild animals in captivity. KEY → identification tool using couplets (paired contrasting statements/leads). FLORA → all plants of an area, habitat & distribution. MANUAL → identification of names. MONOGRAPH → details of one taxon. Largest herbarium / famous garden facts are commonly asked - Kew (England) is the most famous botanical garden.