LIVING WORLD in One Shot - Class 11 Tamil Nadu Board Zoology

The Living World

The living world encompasses the immense diversity of organisms on Earth, their classification, and the scientific principles used to study and name them. Understanding the living world involves recognizing the need for systematic classification, the principles of taxonomy and systematics, and the frameworks that organize biological diversity. This topic also covers the rules for scientific naming, the concept of species, and the tools used in taxonomy.

Diversity in the Living World

Biological diversity refers to the vast variety of living organisms, including plants, animals, microorganisms, and macroorganisms, that coexist in different habitats on Earth. Approximately…

The Living World

The living world encompasses the immense diversity of organisms on Earth, their classification, and the scientific principles used to study and name them. Understanding the living world involves recognizing the need for systematic classification, the principles of taxonomy and systematics, and the frameworks that organize biological diversity. This topic also covers the rules for scientific naming, the concept of species, and the tools used in taxonomy.

Diversity in the Living World

Biological diversity refers to the vast variety of living organisms, including plants, animals, microorganisms, and macroorganisms, that coexist in different habitats on Earth. Approximately 8.7 million species are estimated to exist, but more than 90% are yet to be discovered. Organisms are adapted to a wide range of habitats such as land, water, deserts, mountains, marine environments, fresh water, deep sea, and even extreme conditions like volcanic areas.

• Microorganisms: Include microbes that can live in diverse environments.
• Macroorganisms: Larger organisms like plants, animals, and humans.
• Habitats: Land, water, deserts, mountains, marine, fresh water, deep sea, volcanic regions.

Need for Classification

Classification is essential to organize the immense variety of living organisms for easier study and understanding. It helps in identifying, differentiating, and understanding evolutionary relationships among species. Classification also allows for the creation of phylogenetic trees and facilitates convenient study of organisms.

• Purposes of Classification:
  • To identify and differentiate closely related species.
  • To understand variations and evolutionary history.
  • To create phylogenetic relationships among organisms.
  • To enable systematic study of living organisms.

Taxonomy and Systematics

Taxonomy is the science of arranging living organisms, including their classification, description, identification, and naming. Systematics extends taxonomy by incorporating evolutionary history and phylogenetic relationships.

• Taxonomy:
  • Science of arrangement, classification, description, identification, and naming.
  • Term coined by A.P. de Candolle in 1813.
  • Aristotle is considered the father of classical taxonomy; Carolus Linnaeus is the father of modern taxonomy.
• Systematics:
  • Involves classification along with evolutionary history.
  • Focuses on phylogenetic relationships among organisms.

Historical Classification Systems

Classification systems have evolved from simple to complex frameworks. Early systems were based on observable characteristics, while modern systems use molecular and evolutionary data.

• Aristotle: Classified organisms based on locomotion (movable animals vs. immovable plants) and blood color (enaima and anaima).
• Theophrastus: Student of Aristotle, known as the father of botany.
• Carolus Linnaeus: Developed the two-kingdom classification (Plantae and Animalia).
• Three-Kingdom System: Introduced later to include fungi.
• Four and Five Kingdom Systems: Further divisions based on observable characters and composition (Monera, Protista, Fungi, Plantae, Animalia).
• Three Domain System: Based on differences in ribosomal RNA, cell wall composition, and RNA types.

Three Domains of Life

The three-domain system classifies all life into Archaea, Bacteria, and Eukarya based on molecular and cellular differences.

• Domain Archaea:
  • Survive in extreme conditions (hot, cold, acidic, salty).
  • Include extremophiles like methanobacterium, halophiles, and thermoacidophiles.
  • Chemoautotrophs: Prepare food using chemical substances, not sunlight.
• Domain Bacteria:
  • Prokaryotic, lack a definite nucleus, possess naked and circular DNA.
  • Have 70S ribosomes.
  • Can be heterotrophic, autotrophic, or decomposers.
  • Some are beneficial (e.g., curdling of milk, antibiotic production), others are harmful (cause diseases).
• Domain Eukarya:
  • Eukaryotic, have a definite nucleus and membrane-bound organelles.
  • Possess 80S ribosomes.
  • Include organisms with various nutritional modes: autotrophic, saprophytic, heterotrophic, holozoic.

Taxonomic Hierarchy

Taxonomic hierarchy is the system of arranging organisms into successive levels of classification, from the most specific to the most general.

• Major Ranks (from specific to general):
  • Species
  • Genus
  • Family
  • Order
  • Class
  • Phylum
  • Kingdom
  • Super Kingdom (includes Archaea, Bacteria, Eukarya)
• Intermediate Ranks:
  • Superphylum, subphylum, superclass, subclass, superorder, suborder, superfamily, subfamily, subgenus, subspecies.
• Species: Group of closely related organisms capable of mating and producing fertile offspring, sharing a common ancestor.
• Genus: Group of closely related species.
• Family: Group of related genera.
• Order: Group of related families.
• Class: Group of related orders.
• Phylum: Group of related classes.
• Kingdom: Group of related phyla.

Rules of Nomenclature

Scientific naming follows strict rules to ensure consistency and universality. The binomial system uses two names (genus and species), while the trinomial system adds a subspecies.

• Language: Names are derived from Greek and Latin, which are considered dead languages to avoid changes over time.
• Organizations: Indian Union of Botanical Nomenclature (IUBN) and Indian Union of Zoological Nomenclature (IUZN) regulate naming.
• Rules:
  • The first letter of the genus is capitalized.
  • The species name is in lowercase.
  • The subspecies name (if present) is also in lowercase.
  • All names are italicized or underlined if handwritten.
  • Author’s name can be added at the end (not italicized).
• Example: Mangifera indica Linn. (Mangifera = genus, indica = species, Linn. = author).

Concept of Species

Species is the basic unit of classification, defined as a group of organisms that are morphologically similar and capable of interbreeding to produce fertile offspring.

• Coined by: John Ray in his book "Historia Generalis Plantarum" (1693).
• Charles Darwin: Defined species as groups of morphologically similar organisms in one ecosystem.
• Species: Basic unit of classification and evolution.

Tools for Study of Taxonomy

Various tools and resources are used to study and classify organisms, aiding in identification, preservation, and research.

• Herbarium: Collection of preserved plant specimens.
• Botanical Garden: Living collections of plants for study and conservation.
• Zoological Park: Facilities for keeping and studying animals.
• Museum: Preserves body parts and specimens for educational purposes.
• Taxonomical Key: Tool based on similarities and dissimilarities for identification.
• National Parks and Wildlife Sanctuaries: Protect and study biodiversity in natural habitats.
• Marine Parks: Specialized for marine organisms.

Key Characteristics of Living Organisms

Living organisms share certain fundamental characteristics that distinguish them from non-living things.

• Metabolism: Includes both catabolic (breakdown) and anabolic (formation) reactions.
• Growth: Increase in size and number of cells.
• Nutrition: Intake and utilization of nutrients.
• Reproduction: Ability to produce offspring.
• Consciousness: Ability to respond to stimuli.
• Cellular Organization: Composed of one or more cells.
• Respiration: Process of energy production.
• Excretion: Removal of metabolic wastes.

Summary of Key Points

The study of the living world involves understanding diversity, the need for classification, taxonomy, systematics, hierarchical classification, rules of nomenclature, the concept of species, and the tools used in taxonomy. Mastery of these concepts is essential for answering both objective and subjective questions in examinations.