The Living WorldMind Map

Living organisms are highly organised systems capable of interacting with their surroundings. NCERT discusses growth, reproduction, metabolism, cellular organisation and consciousness as major characteristics. Growth occurs in living organisms by internal cell division, but increase in mass can also occur in non-living objects such as mountains, so growth alone is not enough. Reproduction is common but not universal because some living organisms are sterile. Metabolism is the sum of all chemical reactions inside the body and is a defining feature of life. Cellular organisation is essential because all living organisms are made of cells. Consciousness, or response to stimuli, is the most obvious feature and includes responses to light, temperature, chemicals, touch, water and other organisms.

Biodiversity means the variety and variability of living organisms. It includes diversity at genetic, species and ecosystem levels. Earth contains an enormous number of organisms, many of which are still unknown, so biology needs a systematic method to identify, name and classify them. India is especially important because it has rich climatic, geographical and ecological variation, supporting forests, grasslands, deserts, wetlands, mountains, rivers and marine ecosystems. Biodiversity is important for ecological balance, food, medicine, agriculture, oxygen production, nutrient cycling and cultural value. For NEET, biodiversity in this chapter is mainly connected to the need for taxonomy: without scientific study, organisms cannot be correctly identified, compared, conserved or used.

Taxonomy is the science of identification, nomenclature and classification of organisms. Identification means finding the correct name and place of an organism by comparing its characters with known organisms. Nomenclature gives a standard scientific name, and classification groups organisms based on similarities and differences. Systematics is broader than taxonomy because it also considers evolutionary relationships. To study biodiversity, biologists use taxonomic aids such as herbaria, botanical gardens, museums, zoological parks and keys. Herbaria preserve dried plant specimens, botanical gardens maintain living plant collections, museums preserve plant and animal specimens, zoological parks keep live animals, and keys help identify organisms through contrasting characters. This topic is highly NCERT-based for NEET.

Taxonomic categories are the ranks used to classify organisms in a hierarchy. Each category represents a rank or level, and all categories together form the taxonomic hierarchy. Species is the basic and lowest category, containing individuals with maximum similarity and the ability to interbreed under natural conditions. Related species form a genus, related genera form a family, related families form an order, related orders form a class, related classes form a phylum in animals or division in plants, and related phyla or divisions form a kingdom. As we move from species to kingdom, similarity decreases and number of organisms increases. NEET frequently tests the correct order, definitions and examples such as human, housefly, mango, wheat and potato.

Binomial nomenclature is the two-word scientific naming system used globally for organisms. It was popularised by Carl Linnaeus and prevents confusion caused by local or common names. The first word is the genus name and begins with a capital letter. The second word is the specific epithet and begins with a small letter. Both words are Latin or Latinised and are printed in italics; when handwritten, they are separately underlined. The name may be followed by the author’s name in abbreviated form, such as Mangifera indica Linn. Scientific naming follows international codes such as ICBN for plants and ICZN for animals. NEET often tests formatting rules and examples.