Introduction
Biology is the study of living organisms and their interactions with the environment. This chapter covers the characteristics of living things, biodiversity, and the basics of taxonomy.
Biodiversity
The term biodiversity refers to the variety (number and types) of living organisms present on Earth. New species continue to be discovered in both known and unexplored regions.
When observations are made over larger areas, the number and kinds of living organisms seen increase; for example, a dense forest has more species than a small garden.
Species
Each unique type of organism is called a species. The total number of known species in the world is approximately between 1.7 and 1.8 million.
Need for Standardized Naming (Nomenclature)
People often know organisms by local or common names, which can vary widely from place to place, even within the same country. This can be confusing when trying to communicate about specific organisms.
To avoid confusion, scientists use a standardized system of naming organisms called nomenclature. This means giving every organism a unique scientific name that is accepted globally.
Identification:
Before naming, the organism must be correctly identified — understanding exactly what it is. This ensures that the name attached corresponds to the correct organism.
Scientific Names
These names are universal and ensure that each organism has only one name worldwide. The description of the organism should be such that scientists anywhere can identify it and give it the same name.
- ICBN: For plants, scientific names are given according to the International Code for Botanical Nomenclature (ICBN).
- ICZN: For animals, names are assigned based on the International Code of Zoological Nomenclature (ICZN).
Binomial Nomenclature
Developed by Carolus Linnaeus, this system gives each organism a two-part name:
- Generic name (genus) — the first word, capitalized
- Specific epithet (species) — the second word, lowercase
Together, these two words form the scientific name of an organism.
Example: The scientific name of mango is Mangifera indica, where "Mangifera" is the genus and "indica" is the species.
Universal Rules of Nomenclature
- Biological names are written in Latin and italicized. These names are either Latin words or derived from other languages but Latinized.
- In a biological name, the first word represents the genus, while the second word indicates the specific epithet.
- When writing biological names by hand, both words must be underlined separately. When typed, they appear in italics to show their Latin origin.
- The genus name begins with a capital letter, while the specific epithet starts with a lowercase letter. For example: Mangifera indica
The author's abbreviated name follows the biological name (e.g., Mangifera indica Linn.). It indicates that this species was first described by Linnaeus.
Classification
Classification is the process of grouping organisms into convenient categories based on easily observable traits.
Example:
- When we say dogs, we associate specific features — not with cats.
- When we say mammals, we think of animals with external ears and body hair.
- Terms like wheat, rice, animals, plants are examples of such groupings.
Taxa
Taxa (singular: taxon) are the scientific categories used to classify organisms.
Examples of taxa:
- Dog, Mammal, and Animal are all taxa, but they represent different levels of classification.
- Taxa are hierarchical — e.g., Dog ⟶ Mammal ⟶ Animal.
Taxonomy
Taxonomy is the branch of science concerned with identification, nomenclature, and classification of organisms.
Taxonomy includes the processes of:
- Characterization – studying features
- Identification – finding what the organism is
- Classification – grouping based on characters
- Nomenclature – naming the organism
Basis of Modern Taxonomy:
- External and internal structures
- Cell structure
- Developmental processes
- Ecological information
Systematics
Derived from the Latin word ‘Systema’, meaning systematic arrangement, Systematics is the study of the diversity of organisms and their evolutionary relationships.
Originally used by Carolus Linnaeus as the title of his work “Systema Naturae”.
Scope of Systematics includes:
- Identification
- Nomenclature
- Classification
- Understanding evolutionary relationships
Taxonomy is not new — humans have always classified organisms, mainly based on their uses (food, shelter, clothing).
Early classification systems were utilitarian (based on usefulness).
Taxonomic Categories
- Hierarchy in Classification
Classification is not a single step but involves multiple levels.
Each level or step in this classification system is called a rank or category.
Since these are part of the taxonomic arrangement, they are called taxonomic categories.
All the taxonomic categories together form a taxonomic hierarchy.
- What is a Taxon?
A taxon (plural: taxa) is any rank or category used in classification.
It is a unit of classification, representing real, identifiable groups of organisms.
Example: Insects are a taxon — they share common features like three pairs of jointed legs.
How Are Organisms Classified into Categories?
Requires detailed study of the characteristics of the organism or group.
These characteristics help in:
- Identifying similarities and differences
- Grouping organisms based on shared features
- Distinguishing them from organisms of other kinds
Major Taxonomic Categories in Hierarchical Order:
From highest to lowest (broadest to most specific):
- Kingdom
- Phylum (used for animals) / Division (used for plants)
- Class
- Order
- Family
- Genus
- Species – the lowest and most specific category
Species
A species is a group of individual organisms that share fundamental similarities.
Species are distinct from other closely related species based on morphological differences.
Examples:
- Mangifera indica (mango)
- Solanum tuberosum (potato)
- Panthera leo (lion)
- Panthera tigris (tiger) shares the same genus as lion (Panthera leo).
- Solanum genus includes species like nigrum and melongena.
- Humans: Homo sapiens →
Genus: Homo
Species: sapiens
Key Point: A genus can include multiple species that are morphologically similar.
Genus
A genus includes a group of closely related species that share more common characteristics with each other than with species of other genera.
It is a higher taxonomic category than species.
Examples:
- Genus: Solanum
- Species: Solanum tuberosum (potato), Solanum melongena (brinjal)
- Genus: Panthera
- Species: Panthera leo (lion), Panthera tigris (tiger), Panthera pardus (leopard)
- Genus: Felis
- Includes domestic cats and differs from Panthera.
Key Point: Genera = Group of related species. Different genera (like Panthera vs Felis) have distinct differences, even though they may be in the same family.
Family
Family is a higher taxonomic category that includes a group of related genera.
- Fewer similarities are shared among members of a family compared to those within a genus or species.
- Classification into families is based on:
- Vegetative features (e.g., leaves, stems)
- Reproductive features (e.g., flowers, fruits)
Examples:
- Plants:
- Genera: Solanum, Petunia, Datura
- Family: Solanaceae
- Animals:
- Genera: Panthera (lion, tiger, leopard) and Felis (cats)
- Family: Felidae
- Cats and dogs show some similarities but also notable differences — they belong to different families.
Key Point: A family groups together several related genera based on structural similarities.
Similarity decreases as you go higher up in the taxonomic hierarchy.
Order
Order is a higher taxonomic category than family.
It includes a group of related families that share a few similar characteristics.
The number of shared features is less compared to those within a genus or a family.
Examples:
Plants:
Families: Convolvulaceae, Solanaceae
Order: Polymoniales (grouped mainly by floral characters)
Animals:
Families: Felidae (cats, tigers, lions) and Canidae (dogs, foxes)
Order: Carnivora
Key Point: Orders group related families based on common features, though fewer similarities exist compared to lower taxonomic ranks.
Class
A class includes a group of related orders.
It is a higher taxonomic category than order.
Example:
Class: Mammalia
Includes orders like:
1. Primata (monkey, gorilla, gibbon)
2. Carnivora (tiger, cat, dog)
Other mammalian orders are also part of this class.
Key Point: Classes are formed by grouping orders that share common characteristics.
Phylum (Animals) / Division (Plants)
Phylum is a higher category that groups related classes in animals.
In plants, the equivalent category is called Division.
Example (Animals): Phylum Chordata
Includes classes like:
- Fishes
- Amphibians
- Reptiles
- Birds
- Mammals
Based on common features like:
- Presence of notochord
- Dorsal hollow neural system
Key Point: Phylum (in animals) or Division (in plants) groups together classes with fundamental structural and functional similarities.
Kingdom
Kingdom is the highest taxonomic category in the classification system.
It includes all organisms that share a fundamental body plan and broad characteristics.
Examples:
Kingdom Animalia: Includes all animals grouped under various phyla.
Kingdom Plantae: Includes all plants grouped under different divisions.
As we move up the hierarchy:
- Number of shared characteristics decreases
- Complexity of classification increases
Lower categories (like species):
- More specific
- Members share more features
Higher categories (like kingdom):
- More general
- Members share fewer features
Key Point: Classification becomes broader but less detailed as we move from species to kingdom.