Chapter 1: The Living World - Overview
Introduction
The living world is rich in variety. The wide range of living types—from cold mountains to hot springs—is amazing. The ecological conflict and cooperation among members of a population or community make us reflect on what life indeed is.
This question leads to two inquiries: the technical definition of living versus non-living, and the philosophical purpose of life. As scientists, we focus on the first question: What is living?
1.1 Diversity in the Living World
The number of species that are known and described range between 1.7-1.8 million. This refers to biodiversity or the number and types of organisms present on earth.
Nomenclature and Identification
To standardize the naming of living organisms such that a particular organism is known by the same name all over the world, we use a process called Nomenclature. This is only possible when the organism is described correctly, known as Identification.
- ICBN: International Code for Botanical Nomenclature (for plants).
- ICZN: International Code of Zoological Nomenclature (for animals).
Binomial Nomenclature
Biologists follow universally accepted principles to provide scientific names. Each name has two components: the Generic name and the specific epithet. This system, given by Carolus Linnaeus, is called Binomial Nomenclature.
Example: The scientific name of mango is written as Mangifera indica.
Universal Rules of Nomenclature
- Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.
- The first word represents the genus while the second component denotes the specific epithet.
- Both words, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.
- The first word denoting the genus starts with a Capital letter while the specific epithet starts with a small letter (e.g., Mangifera indica).
Note: The name of the author appears after the specific epithet in abbreviated form (e.g., Mangifera indica Linn.).
Taxonomy and Systematics
- Taxonomy: The process of classification based on characteristics. Characterisation, identification, classification, and nomenclature are the processes basic to taxonomy.
- Systematics: Derived from the Latin word 'systema' (systematic arrangement). It includes identification, nomenclature, classification, and takes into account evolutionary relationships. Linnaeus used Systema Naturae as the title of his publication.
1.2 Taxonomic Categories
Classification involves a hierarchy of steps where each step represents a rank or category, referred to as a Taxon (pl.: taxa). All categories together constitute the taxonomic hierarchy.
Species → Genus → Family → Order → Class → Phylum/Division → Kingdom
1.2.1 Species
A group of individual organisms with fundamental similarities. One should be able to distinguish one species from another closely related species based on distinct morphological differences.
- Mangifera indica (Mango)
- Solanum tuberosum (Potato)
- Panthera leo (Lion)
1.2.2 Genus
Comprises a group of related species which has more characters in common in comparison to species of other genera. Genera are aggregates of closely related species.
- Potato and Brinjal belong to the genus Solanum.
- Lion (Panthera leo) and Leopard (P. pardus) belong to the genus Panthera.
1.2.3 Family
A group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features.
- Plants: Genera Solanum, Petunia, and Datura are placed in family Solanaceae.
- Animals: Genus Panthera and genus Felis (cats) are in family Felidae (distinct from family Canidae/dogs).
1.2.4 Order
Identified based on the aggregates of characters. It is the assemblage of families which exhibit a few similar characters.
- Plants: Family Convolvulaceae and Solanaceae are included in order Polymoniales (based on floral characters).
- Animals: Families Felidae and Canidae are included in order Carnivora.
1.2.5 Class
Includes related orders.
- Order Primata (monkey, gorilla) and Order Carnivora (tiger, cat) are placed in Class Mammalia.
1.2.6 Phylum / Division
- Phylum (Animals): Classes comprising animals like fishes, amphibians, reptiles, birds, and mammals. Based on common features like presence of notochord and dorsal hollow neural system (e.g., Phylum Chordata).
- Division (Plants): Classes with a few similar characters are assigned to a Division.
1.2.7 Kingdom
- Kingdom Animalia: Heterotrophic multicellular organisms (animals).
- Kingdom Plantae: All plants from various divisions.
Organisms with their Taxonomic Categories (Table 1.1)
| Common Name | Biological Name | Genus | Family | Order | Class | Phylum/Div |
|---|---|---|---|---|---|---|
| Man | Homo sapiens | Homo | Hominidae | Primata | Mammalia | Chordata |
| Housefly | Musca domestica | Musca | Muscidae | Diptera | Insecta | Arthropoda |
| Mango | Mangifera indica | Mangifera | Anacardiaceae | Sapindales | Dicotyledonae | Angiospermae |
| Wheat | Triticum aestivum | Triticum | Poaceae | Poales | Monocotyledonae | Angiospermae |
Summary
The living world is rich in variety. Millions of plants and animals have been identified and described. The basics of taxonomy like identification, naming, and classification of organisms are universally evolved under international codes.
Based on resemblances and distinct differences, each organism is identified and assigned a correct scientific name using binomial nomenclature. An organism represents a place in the system of classification using taxonomic categories (taxa) which form a taxonomic hierarchy.