Biodiversity and Classification

Definition: The term 'Biodiversity' is derived from 'bios' (life) and 'diversity' (variety). It refers to the variety of organisms present in different ecosystems on Earth. It encompasses the diversity of species, genetic variability within species, and the variety of ecosystems they inhabit.

Magnitude: Biologists have identified and described approximately 1.7 to 1.8 million species. This includes about 270,000 species of vascular plants and over 1 million species of animals (mostly insects).

Importance: Biodiversity provides humans with food, drugs, and industrial materials (fibers, dyes, resins, gums, adhesives, rubber, and oil). It plays a crucial role in maintaining ecosystems through recycling nutrients and providing fertile soils.

Taxonomy: It is the branch of biology that deals with classification. It involves the characterization, identification, nomenclature (naming), and classification of organisms into groups and sub-groups (taxa) based on similarities and differences.

Systematics: It is a broader field that includes taxonomy but also focuses on the evolutionary history (phylogeny) of organisms. Systematics attempts to determine the evolutionary relationships among organisms alongside their classification.

• Aristotle (384-322 BC): He classified known organisms into two groups: Plantae (plants) and Animalia (animals). He further divided animals into those with red blood and those without.
• Abu Usman Umer Al-Jahiz: Described the characteristics of 350 animal species in his book.
• Carolus Linnaeus (1753): Formalized the Two Kingdom System (Plantae and Animalia) and introduced Binomial Nomenclature.
• Ernst Haeckel (1866): Proposed the Three Kingdom System by adding Kingdom Protista to accommodate unicellular organisms (like Euglena and bacteria) that did not fit neatly into Plantae or Animalia.
• E. Chatton (1937): Introduced the terms Prokaryotique (prokaryotes) and Eukaryotique (eukaryotes) to distinguish bacteria from other cells.
• Herbert Copeland (1938): Proposed the Four Kingdom System by separating bacteria into a new Kingdom Monera.
• Robert Whittaker (1969): Proposed the Five Kingdom System based on cellular levels of organization (prokaryotic, unicellular eukaryotic, multicellular eukaryotic) and modes of nutrition (photosynthesis, absorption, ingestion).

Modification: Lynn Margulis and Karlene Schwartz (1988) modified Whittaker's system by integrating cellular organization, mode of nutrition, and genetic analysis (cytology and genetics).

• Kingdom Monera (Prokaryotae): Includes prokaryotic organisms (bacteria and cyanobacteria). They lack a true nucleus.
• Kingdom Protista (Protoctista): Includes eukaryotic organisms that are unicellular (e.g., Amoeba) or simple multicellular (e.g., Algae). It is a collection of organisms that do not fit into the other eukaryotic kingdoms.
• Kingdom Fungi: Eukaryotic, multicellular decomposers/reducers. They have cell walls made of chitin and obtain food by absorption (heterotrophs). Examples: Mushrooms, Yeast.
• Kingdom Plantae: Eukaryotic, multicellular autotrophs. They have cell walls made of cellulose and produce food via photosynthesis. Examples: Mosses, Ferns, Flowering plants.
• Kingdom Animalia: Eukaryotic, multicellular consumers (heterotrophs). They lack cell walls and ingest food. Examples: Insects, Birds, Mammals.

Viruses are at the borderline of living and non-living. They are acellular (not made of cells) and crystalline in nature outside a host. They contain hereditary material (DNA or RNA) enclosed in protein but lack metabolic machinery. Since classification systems categorize cellular organisms, viruses are excluded from the Five Kingdom System.

Definition: The system of giving each species a unique, scientific name consisting of two parts: the Generic name (Genus) and the Specific epithet (Species).

Rules:

1. Scientific names are usually in Latin/Greek.
2. The first name is the Genus (capitalized, e.g., Homo).
3. The second name is the species (lowercase, e.g., sapiens).
4. When printed, they are italicized (e.g., Homo sapiens). When handwritten, they are underlined separately.

Examples:
Onion: Allium cepa
Human: Homo sapiens
Potato: Solanum tuberosum

Taxa: The groups into which organisms are classified. They are arranged in a ladder-like hierarchy.

• Kingdom: The largest taxon (e.g., Animalia).
• Phylum (Division in plants): A group of related classes (e.g., Chordata).
• Class: A group of related orders (e.g., Mammalia).
• Order: A group of related families (e.g., Primates).
• Family: A group of related genera (e.g., Hominidae).
• Genus: A group of related species (e.g., Homo).
• Species: The basic unit. A group of organisms capable of interbreeding to produce fertile offspring (e.g., Homo sapiens).