What is Living?
Defining vs. Non-Defining Properties
- Growth: Increase in mass and increase in number of individuals are twin characteristics. Plants grow continuously (indefinite); animals grow up to a certain age (definite). Non-living objects grow extrinsically (accumulation of material on the surface). Living organisms grow intrinsically (increase in mass from inside only) AIPMT 2011 Mains.
- Crucial detail: Growth is not a defining property because non-living objects also grow in mass.
- Reproduction: Production of progeny. Fungi reproduce via asexual spores; Yeast and Hydra via budding; Planaria (flatworms) via true regeneration; Fungi, filamentous algae, and moss protonema via fragmentation.
- Crucial detail: In unicellular organisms, reproduction is synonymous with growth AIPMT 2016-II. Mules, sterile worker bees, and infertile human couples do not reproduce. Thus, reproduction is not a defining property.
- Metabolism: The sum total of all chemical (anabolic + catabolic) reactions in the body. Defining property.
- Crucial detail: Isolated metabolic reactions in vitro are not living things, but they are surely living reactions AIPMT 2011 Mains.
- Cellular Organization: All living organisms are made of cells. Biological organization begins at the submicroscopic molecular level AIPMT 2007. Defining property.
- Consciousness: The most technically complicated feature. The ability to sense the environment and respond to stimuli AIPMT 2011 Mains, AIPMT 2007. Defining property.
- Crucial detail: Photoperiod affects reproduction in seasonal breeders (both plants and animals) AIPMT 2016-II. Human beings are the only organisms aware of themselves (self-consciousness).
Diversity & Taxonomy
Nomenclature & Systematics
- Biodiversity: Represents the diversity in the organisms living in a given geographical region AIPMT 2011 Mains. Approximately 1.7-1.8 million species are described.
- Taxonomy: The branch dealing with identification, nomenclature, and classification. The practical purpose of classification is to facilitate the identification of unknown species AIPMT 1999.
- ICBN: International Code for Botanical Nomenclature AIPMT 2007. ICZN stands for Zoological Nomenclature.
- Binomial Nomenclature: Proposed by Carolus Linnaeus NEET 2023, AIPMT 1993, AIPMT 1990. Consists of two components: the Generic name and the Specific epithet NEET 2023, AIPMT 1990.
- Rules: Names are Latinized (written in italics or separately underlined), the Genus starts with a capital letter, and the specific epithet starts with a small letter.
- Crucial Example: The correctly written scientific name of Mango, first described by Linnaeus, is Mangifera indica Linn. NEET 2019. Plasmodium falciparum is correctly described as a protozoan pathogen causing serious malaria AIPMT 2012 Mains.
- Systematics: Derived from Systema (systematic arrangement). Linnaeus wrote Systema Naturae. It includes taxonomy plus the study of evolutionary relationships (phylogeny).
- Crucial details: The term "New Systematics" was introduced by Julian Huxley AIPMT 1988. Biosystematics classifies organisms based on evolutionary history and establishes phylogeny on the totality of various parameters AIPMT 2003.
Taxonomic Categories
Hierarchy & Taxon Concepts
- Taxonomic Hierarchy: The ascending sequence of categories: Species → Genus → Family → Order → Class → Phylum/Division → Kingdom NEET 2022, AIPMT 1999.
- As we go higher from species to kingdom, the number of common characteristics strictly decreases.
- Taxon: A unit of classification representing a group of organisms of any rank AIPMT 1996, AIPMT 1992, AIPMT 1991. The term "Phylum" was coined by Ernst Haeckel AIPMT 1992.
Detailed Categories
- Species: The real basic unit / smallest taxon of classification AIPMT 2003, AIPMT 1990. The static concept of species was put forward by Linnaeus AIPMT 1988. The modern biological species concept (based on reproductive isolation) was given by Ernst Mayr AIPMT 2016-II.
- Genus: Aggregates of closely related species. A species is less general in characters compared to a genus AIPMT 2001.
- Family: Characterized on the basis of both vegetative and reproductive features. Example: Solanaceae includes genera Solanum, Petunia, and Datura. Felidae includes Panthera (lion, tiger) and Felis (cats).
- Order: Assemblage of families exhibiting a few similar characters. Example: Convolvulaceae and Solanaceae are included in order Polymoniales. Gorilla, chimpanzee, monkeys, and humans all belong to the same order, Primata AIPMT 1993.
High-Yield Taxonomic Classification (NCERT Mapping)
| Common Name | Biological Name | Genus | Family | Order | Class | Phylum/Division |
|---|---|---|---|---|---|---|
| Man | Homo sapiens | Homo | Hominidae | Primata | Mammalia | Chordata |
| Housefly | Musca domestica | Musca | Muscidae NEET 2023, NEET 2021 | Diptera | Insecta | Arthropoda AIPMT 2016-II, AIPMT 2011 Pre |
| Mango | Mangifera indica | Mangifera | Anacardiaceae | Sapindales | Dicotyledonae | Angiospermae |
| Wheat | Triticum aestivum | Triticum | Poaceae | Poales | Monocotyledonae | Angiospermae |
Taxonomical Aids
Preservation & Reference Tools
- Herbarium: Storehouse of collected plant specimens that are dried, pressed, and preserved on sheets. The label provides information about the date and place of collection, English/local/botanical names, family, and the collector's name.
- Botanical Gardens: Specialized gardens containing collections of living plants for reference and identification (e.g., Kew, Howrah, Lucknow).
- Museum: Collections of preserved dead plant and animal specimens for study. Insects are kept in boxes (collecting, killing, pinning); larger animals are stuffed.
- Zoological Parks (Zoos): Places where wild animals are kept in protected environments under human care (used for ex situ conservation).
Literature Aids
- Key: Used for the identification of plants and animals based on similarities and dissimilarities. Based on contrasting characters in a pair called a couplet. Each statement is a lead. Keys are analytical in nature.
- Flora: Contains the actual account of habitat and distribution of plants of a given area (provides the index).
- Manuals: Provide information for identifying the names of species found in an area.
- Monographs: Contain comprehensive descriptive information on any one taxon.