THE LIVING WORLD

WHAT IS ‘LIVING’?

Introduction

• This chapter deals with the meaning of life, the defining characteristics of living organisms, the diversity seen in the living world, and the scientific methods used to identify, name, and classify organisms.
• It also introduces taxonomy and systematics as tools to study living organisms in an organised manner.

Defining Life and Living Organisms

• Life is a complex molecular organisation expressed through coordinated chemical reactions.
• These reactions lead to growth, development, responsiveness, adaptation, and reproduction.

• A living organism is a self-replicating, evolving, and self-regulating system capable of responding to external stimuli.

Defining ‘Living’

• Living organisms show certain distinctive characteristics that separate them from non-living things.
• Distinctive Characteristics
  • Growth
  • Reproduction
  • Metabolism
  • Cellular organisation
  • Sensing and responding to environment (consciousness)
  • Self-replication and self-organisation
  • Interaction with surroundings

Growth

• Growth refers to an increase in mass and/or number of individuals.

• In multicellular organisms, growth occurs by cell division.
• In plants, growth is continuous throughout life (indeterminate growth).
• In animals, growth occurs only up to a certain age (determinate growth), though cell division continues for repair and replacement.

• In unicellular organisms, growth occurs by cell division, so growth and reproduction are the same and can be observed by counting cells in cultures.

• Non-living objects like mountains or sand mounds also show growth, but this occurs by accumulation of material on the surface (accretion).

• In living organisms, growth occurs from inside.
• Dead organisms do not grow.

Hence, growth alone cannot be taken as a defining property of living organisms.

Reproduction

• Reproduction is the ability to produce new individuals similar to oneself.

• Multicellular organisms: reproduce sexually or asexually.

• Asexual reproduction examples:
  • Fungi – spores
  • Yeast and Hydra – budding
  • Planaria – regeneration
  • Algae and mosses – fragmentation

• In unicellular organisms, reproduction is synonymous with growth, as cell division increases number.

• Exceptions exist where living organisms do not reproduce, such as mules, sterile worker bees, and infertile humans.

Therefore, reproduction is not an all-inclusive defining feature of life, although no non-living object can reproduce on its own.

Metabolism

• Metabolism refers to the sum total of all chemical reactions occurring in a living organism.
• It includes:
  1. Anabolism – synthesis of complex molecules from simpler ones
  2. Catabolism – breakdown of complex molecules into simpler ones
• All living organisms, including plants, animals, fungi, and microbes, exhibit metabolism.
• Non-living objects do not show metabolism.
• In Vitro Reactions: Metabolic reactions can be demonstrated outside the body in cell-free systems.
  • Such reactions are not living, but they are living reactions.

Thus, cellular organisation is essential for life, making metabolism a defining feature of living organisms.

Cellular Organisation

• All living organisms are fundamentally made up of cells.
• The presence of organised cells carrying out metabolic reactions is a defining feature of life forms.

Sensing and Responding to Environment (Consciousness)

• All living organisms sense their environment and respond to stimuli.
• Stimuli may be physical, chemical, or biological.

Environmental Response Examples:

• Plants respond to light, water, temperature, and other organisms.
• Animals respond through specialised sense organs.
• Photoperiod affects reproduction in seasonal breeders.

• Self-awareness: All organisms are aware of their surroundings. Humans additionally show self-awareness or self-consciousness.

Therefore, consciousness is considered the defining property of living organisms.

Complexity and Aspects in Defining Life

• Coma Patients: Patients in coma may be supported by machines for breathing and circulation but lack consciousness, making the definition of “living” complex.
• Interactions:
  • Properties of tissues arise due to interactions among cells.
  • Properties of organelles arise due to interactions among molecules.
• These are called emergent properties and result from increasing organisational complexity at different levels.

Thus, living organisms are self-replicating, evolving, and self-regulating interactive systems capable of responding to external stimuli.

Conclusion

• Living organisms are self-replicating and evolving systems that maintain internal balance and respond to their environment.
• Biology is the study of life and the evolution of organisms on Earth.
• Genetic Links: All living organisms share genetic material to varying degrees, indicating common ancestry.

DIVERSITY IN THE LIVING WORLD

Biodiversity

• Variety Around Us: The living world shows immense diversity, including plants, animals, birds, insects, pets, and numerous unseen microorganisms.
• Biodiversity: Biodiversity refers to the number and types of organisms present on Earth.
• Species: Each distinct kind of organism represents a species.
  • Known Species: About 1.7–1.8 million species have been described so far.

Taxonomy and Systematics

• Taxonomy: involves the identification, classification, and naming of organisms (Nomenclature).
• Systematics: studies the evolutionary relationships among organisms.

Nomenclature (Naming of Organisms)

Need for Scientific Names

• Local names vary from place to place, causing confusion.
• Scientific names provide a universal and standard system of naming organisms.
• Naming is possible only after correct identification and description of the organism.

Scientific Naming Codes

• Plants – International Code for Botanical Nomenclature (ICBN)
• Animals – International Code of Zoological Nomenclature (ICZN)

Binomial Nomenclature

• Each organism is given a two-part scientific name:
  1. Generic name
  2. Specific epithet
• Example: Mango – Mangifera indica

Rules of Binomial Nomenclature

• Latin Origin: Names are generally in Latin or Latinised and written in italics.
• First Word (Genus): The first word (genus) starts with a capital letter.
• Second Word (Species): The second word (species) starts with a small letter.
• Underlining: When handwritten, both words are underlined separately.
• Author’s Name: The author’s name may be written in abbreviated form at the end, e.g., Mangifera indica Linn.

Tautonyms: If both generic and specific names are the same, they are called tautonyms, e.g., Catla catla.

Classification

• Classification is the grouping of organisms into convenient categories (taxa) based on observable characteristics.
  • These categories are called taxa.
• Taxa exist at different levels, such as:
  • Plants, animals
  • Mammals
  • Dogs

Importance of Classification

• Helps understand characteristics of groups by studying representative organisms.
• Aids in identification of new organisms.
• Reveals relationships among different groups of organisms.
• Essential for studying extinct and living organisms together.

Taxonomy

• Taxonomy includes the processes of characterisation, identification, classification, and nomenclature.
• Modern taxonomy uses external and internal structures, cell structure, developmental processes, and ecological information.

Systematics

Origin of Term: Systematics is derived from the Latin word “systema”, meaning systematic arrangement.

Systematics : Systematics includes identification, nomenclature, classification, and evolutionary relationships.

• Linnaeus’ Contribution: Systema Naturae, is a work (book) by Carl Linnaeus that laid the foundation for modern taxonomy by systematically classifying and naming organisms.
• Neosystematics, proposed by Julian Huxley, focuses on understanding evolutionary relationships using modern approaches.

TAXONOMIC CATEGORIES

Understanding Classification

• Classification is not a single-step process.
• It involves arranging living organisms through a series of hierarchical levels based on shared characteristics.

Taxonomic Hierarchy

• The taxonomic hierarchy is a system used to classify and organise living organisms into groups, ranging from very broad categories to very specific ones.

• Hierarchy
  • Each level in classification represents a rank or category.
• Taxonomic Category
  • Each unit of classification at a particular rank is called a taxonomic category.
• Taxon (plural: taxa)
  • A taxon represents a group of organisms at any rank of the hierarchy.

Common Taxonomic Categories

• The commonly used hierarchy levels are:
  1. Kingdom
  2. Phylum (called Division in plants)
  3. Class
  4. Order
  5. Family
  6. Genus
  7. Species

Species is the lowest and most specific category for both plants and animals.

Example: Human

Understanding Hierarchy Using an Analogy

To simplify the concept of classification, it can be compared with a postal address system.

Taxonomic Categories	Biological Taxon	Address Analogy	Address Example
Kingdom	Animalia	Country	India
Phylum	Chordata	State	Uttarakhand
Class	Mammalia	District	Dehradun
Order	Primates	City	Premnagar
Family	Hominidae	Neighborhood	Vasant Vihar
Genus	Homo	Street	02
Species	Homo sapiens	House Number	14

Summary of the Analogy

• Both biological classification and address systems move from broad to specific levels.
• With each lower level, the number of entities decreases and similarity increases.

• Kingdom is the broadest category with maximum diversity.
• Species is the most specific category with nearly identical members.

1. Species

• Definition:
  • Group of closely related organisms that share fundamental similarities and can interbreed to produce fertile offspring.
• Species is the basic unit of classification.
• Examples:
  • Mango: Mangifera indica.
  • Potato: Solanum tuberosum.
  • Lion: Panthera leo.
  • Human: Homo sapiens
• Specific (species) Epithet:
  • The second part of the scientific name (indica, tuberosum, leo) is called the specific epithet.
• Genus:
  • The first part of the name (Mangifera, Solanum, Panthera) represents the genus.

2. Genus

• Definition:
  • Group of closely related species that share more similarities with each other than with species of other genera.
• Thus, Genus = A group of related Species.
• Genus Examples:
  • Solanum: includes potato and brinjal.
  • Panthera: includes lion, leopard, and tiger.
• Comparison:
  • The genus Panthera is different from the genus Felis, which includes cats.

• Additional Points
  • A genus with a single species is called monotypic.
  • A genus with more than one species is called polytypic.

3. Family

• Definition:
  • Family is a group of related genera.
• Members of a family show fewer similarities than members of a genus or species.
• Characterization:
  • In plants, family classification is based on vegetative and reproductive features.
• Examples:
  • Plants: Solanum, Petunia, and Datura belong to the family Solanaceae.
  • Animals: Panthera (lion, tiger, leopard) and Felis (cats) belong to the family Felidae.
• Different Families:
  • Cats belong to Felidae, while dogs belong to Canidae, showing clear family-level differences.

4. Order

• Definition:
  • Order is a group of related families.
• It represents a higher category with fewer common characters than family.
• Examples:
  • Plants: Families Convolvulaceae and Solanaceae belong to the order Polymoniales.
  • Animals: Families Felidae and Canidae belong to the order Carnivora.

5. Class

• Definition:
  • Class is a group of related orders.
• Examples:
  • Order Primata: Monkey, gorilla, gibbon.
  • Order Carnivora: Tiger, cat, dog.
• But both orders belong to the class Mammalia.

6. Phylum/Division

• Definition:
  • Phylum is a group of related classes.
• Phylum Chordata
  • Animals Classes such as fishes, amphibians, reptiles, birds, and mammals are included in Phylum Chordata.
• Common Features of Chordates:
  • Presence of notochord
  • Dorsal hollow neural system

Terminology

• In Zoology (Animals): Phylum word is used.
• In Botany (Plants): Division word is used.

7. Kingdom

• Definition:
  • Kingdom is the highest taxonomic category.
• It includes all organisms that share a basic set of common characteristics.
• Examples:
  • Kingdom Animalia – all animals
  • Kingdom Plantae – all plants

Taxonomic Hierarchy

• Ascending order of hierarchy:
  • Species → Genus → Family → Order → Class → Phylum/Division → Kingdom

Characteristics of Hierarchy:

• Lower taxa (species, genus):
  • More common characteristics
  • Greater similarity among organisms
• Higher categories (phylum, kingdom):
  • Fewer common characteristics
  • Greater diversity and complexity

As we move higher in the hierarchy, determining relationships becomes more difficult.

Examples of Taxonomic Categories

Organism	Biological Name	Genus	Family	Order	Class	Phylum/Division
Man	Homo sapiens	Homo	Hominidae	Primates	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

Key Points

• Hierarchy Importance: Taxonomic hierarchy helps in systematic and organised classification of living organisms.
• Species: Species is the basic unit of classification.
• Taxonomic Studies: Taxonomic studies help identify similarities and differences among organisms.
• Classification Complexity: As we move higher in hierarchy, the number of shared characters decreases.
• Scientific Naming: Scientific naming and classification make identification and study of organisms accurate

Taxonomical Aids

• Taxonomic studies are essential for agriculture, forestry, industry, and for understanding biodiversity.
• Correct identification, naming, and classification of organisms require proper tools and techniques.
• The following are the major taxonomical aids used in biological studies.

1. Herbarium

• Definition:
  • A storehouse of collected plant specimens that are dried, pressed, and preserved on sheets.
• Arrangement:
  • Herbarium sheets are arranged according to a universally accepted system of classification.
• Information on Herbarium Sheet: Each sheet carries important details such as:
  • Date and place of collection
  • English name, local name, and botanical name
  • Family
  • Name of the collector
• Use:
  • Herbaria serve as permanent records and quick reference systems for future taxonomic studies.

Additional Points

• Standard size of a herbarium sheet is about 11.5 × 16.5 inches.
• A vasculum is a special box used to carry plant specimens from the field to the herbarium.

2. Botanical Gardens

• Purpose:
  • Botanical gardens maintain collections of living plants for identification, study, and reference.
• Labeling:
  • Each plant is labelled with its scientific (botanical) name and family.
• Use:
  • They help in the study of plant diversity, identification, and conservation.
• Famous Botanical Gardens:
  • Kew Gardens, England
  • Indian Botanical Garden, Howrah, India
  • National Botanical Research Institute, Lucknow, India

Special Term: A botanical garden that mainly grows trees and shrubs is called an Arboretum.

3. Museum

• Purpose:
  • Museums house collections of preserved plant and animal specimens for study and reference.
• Location:
  • They are commonly found in educational institutions such as schools, colleges, and universities.
• Methods of Preservation:
  • Specimens preserved in jars or containers with preservative solutions
  • Dry preserved plant and animal specimens
  • Insects preserved in insect boxes after pinning
  • Larger animals like birds and mammals preserved as stuffed specimens
• Additional Collections:
  • Museums often maintain skeletons of animals.
• Use:
  • Museums provide information about local as well as foreign flora and fauna.

4. Zoological Parks (Zoo)

• Definition:
  • Zoological parks are places where wild animals are kept in protected environments under human care.
• Purpose:
  • They help in studying animal behaviour, food habits, and adaptation.
• Environment:
  • Animals are provided conditions similar to their natural habitats.
• Common Name: Zoos.

5. Key

• Nature:
  • A key is an analytical taxonomical aid used for identification of plants and animals.
• Basis:
  • Identification is done based on similarities and differences among organisms.
• Structure:
  • Keys are made up of pairs of contrasting characters called couplets.
  • Each statement in a couplet is called a lead.
  • One lead is accepted while the other is rejected at each step.
• Types of Keys:
  1. Bracketed key
  2. Indented (yoked) key
• Categories:
  • Separate keys are prepared for different taxonomic categories such as family, genus, and species.

Other Taxonomical Tools

• Flora:
  • Provides an account of the habitat and distribution of plants of a particular area.
  • Acts as an index of plant species found in that region.
• Manuals:
  • Provide information useful for identifying names of species found in a specific area.
• Monographs:
  • Contain detailed and complete information about a single taxon.
• Catalogues:
  • Help in recording descriptions and ensuring correct identification of organisms.

Conclusion

• Taxonomical aids play a crucial role in the correct identification, classification, and systematic study of organisms.
• They form the foundation for understanding biodiversity and organising biological knowledge in a scientific manner.

Chapter Summary

• The living world shows enormous diversity.
• Millions of plants and animals have been identified and described, while many organisms are still unknown.
• Living organisms differ widely in size, colour, habitat, structure, and other features.

• To understand this diversity, it is necessary to identify the characteristics of living organisms.
• Biologists follow systematic rules for identifying, naming, and classifying organisms.
• This scientific study is called taxonomy.

• Taxonomy plays an important role in agriculture, forestry, industry, and the proper use and conservation of bio-resources.
• Identification, naming, and classification of organisms are carried out according to internationally accepted rules and codes.

• Each organism is given a scientific name consisting of two words, following the binomial system of nomenclature.
• Every organism occupies a definite position in a classification system.
• These positions are known as taxonomic categories or taxa.
• All taxonomic categories together form a taxonomic hierarchy, ranging from species to kingdom.

• For accurate identification and classification, taxonomists use various taxonomical aids.
• Specimens are collected from natural habitats using special techniques.
• These specimens are preserved and studied in herbaria, museums, botanical gardens, and zoological parks.
• Live specimens are maintained in botanical gardens and zoological parks for observation and study.

• In addition, taxonomists prepare manuals and monographs to record detailed information about organisms.
• Taxonomic keys are used as analytical tools to identify organisms based on their distinguishing characteristics.
• Together, these methods and tools help in the systematic study and organisation of the living world.