THE LIVING WORLD

WHAT IS ‘LIVING’?

Introduction

In this chapter, we will explore the definition of life, the diversity and characteristics of living organisms, their classification through taxonomy and systematics, and the various tools used in taxonomic studies. Let’s get started.

• First of all lets define Life and Living organism which forms the living world ultimately.
• Life is a complex molecular organization expressed through chemical reactions, leading 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’

• Distinctive Characteristics: Growth, reproduction, sensing environment, metabolism, self-replication, self-organization, interaction.
• Growth:
  • Increase in mass and number of individuals.
  • Multicellular Organisms: Growth by cell division; continuous in plants, limited in animals.
  • Unicellular Organisms: Growth by cell division; observable by counting cells in in vitro cultures under a microscope..
  • Non-living Objects: Growth by external accumulation (e.g., mountains).
  • Living Organisms: Growth from inside; not in dead organisms.
• Reproduction:
  • Production of similar progeny.
  • Multicellular Organisms: Perform sexual and asexual reproduction.
  • Asexual Examples: Fungi (spores), yeast and hydra (budding), Planaria (regeneration), algae and mosses (fragmentation).
  • Unicellular Organisms: Reproduction synonymous with growth i.e., increase in number of cells..
  • Exceptions: Mules, sterile bees, infertile humans do not reproduce.
• Metabolism:
  • Chemical reactions in organisms.
  • Living Organisms: Metabolism occurs in all, including plants, animals, fungi, microbes.
  • Non-living Objects: Do not exhibit metabolism.
  • In Vitro Reactions: Metabolic reactions outside the body are not living but show living reactions.
• Cellular Organization: means organisms are fundamentally made up of cells. This is also a defining feature of life forms.
• Sensing and Responding (Consciousness)
  • Environmental Response: All living organisms sense changes/signals (Stimuli) and respond to surroundings (Stimuli).
    • Stimuli: may be physical, chemical, or biological.
    • Examples: Sense organs in humans, plants respond to light, water, temperature.
    • Self-awareness: Humans are self-conscious.
    • Consciousness: Hence a defining property of living organisms.

Complexity and Aspects in Defining Life

• Coma Patients: Brain-dead (lacking consciousness) but supported by machines; challenging to define living status.
• Interactions: Properties of tissues and organelles arise from interactions among cells and molecules.
• Emergent Properties: Result from organizational complexity at all levels.

Conclusion

• Self-replicating, Evolving Systems: Living organisms respond to stimuli, self-regulate.
• Biology: Study of life, evolution of organisms on earth.
• Genetic Links: All living organisms share common genetic material to varying degrees.

DIVERSITY IN THE LIVING WORLD

Observing Diversity

• Living Variety Around Us: Plants, insects, birds, pets, unseen organisms.
• Biodiversity: refers to the number and types of organisms on Earth.
• Species: Each kind of organism represents a species.
  • Known Species: 1.7-1.8 million described species (biodiversity).
• Taxonomy : involves the identification, classification, and scientific naming of organisms (Nomenclature).
• Systematics : studies the evolutionary relationships among organisms.

Nomenclature (Naming Organisms)

• Why need arise for Standard (Scientific) names ? : Because local names vary with region, causing confusion.
• Scientific Names: Universal naming system, doesn’t vary with region.
• Identification: Correct description attached to the name.
• Scientific Naming Codes/Rules:
  • Plants: International Code for Botanical Nomenclature (ICBN).
  • Animals: International Code of Zoological Nomenclature (ICZN).

Binomial Nomenclature

• Two-Part Names: Generic name and specific epithet.
  • Example: Mango – Mangifera indica.
• Rules:
  • Latin Origin: Names in Latin, written in italics.
  • First Word (Genus): Capitalized.
  • Second Word (Species): Lowercase.
  • Underlining: When handwritten, both words underlined.
  • Author’s Name: Can be written in abbreviated form at the end (e.g., Mangifera indica Linn.). Here Linn. indicates Linnaeus, who described this species for first time.

Classification

Classification is the grouping of organisms into categories (taxa) based on their characteristics.

• Grouping Organisms: Based on observable characteristics.
• Categories (Taxa): Convenient groups like plants, animals, dogs, cats.
• Examples:
  • Plants: Wheat, rice.
  • Animals: Mammals, dogs.
• Levels of Taxa: Different categories at different levels like animals, mammals, dogs.

Importance of Classification:

• Allows understanding of group features by studying representative organisms instead of each one individually.
• Aids in identifying new organisms.
• Reveals relationships among different organism groups.
• Essential for studying historical (extinct) organisms.

Taxonomy

• Processes: Characterization, identification, classification, nomenclature.
• Modern Basis: External and internal structures, cell structure, development, ecological information are taken into care while classification.

Systematics

Systematics : is the study of the evolutionary relationships among organisms.

• Origin of Term: From Latin “systema” (systematic arrangement).
• Linnaeus’ Contribution: Systema Naturae, is a work (book) by Carl Linnaeus that laid the foundation for modern taxonomy by systematically classifying and naming organisms.
• Scope: Includes identification, nomenclature, classification, evolutionary relationships.

TAXONOMIC CATEGORIES

Understanding Classification

• Not Single Step Process: Involves multiple levels.
• Taxonomic Hierarchy: is a system for classifying and organizing living organisms into groups based on shared characteristics, ranging from broad to specific categories (ranks).
  • Hierarchy: Each level is a rank or category in Hierarchy.
• Taxonomic Category: Each unit of classification.
• Taxon (plural: taxa): Represents each rank.

Example: Human

Common Taxonomic Categories

• Hierarchy Levels: Kingdom, phylum (division for plants), class, order, family, genus, species.
• Species: Lowest category for both plants and animals.

Okay, I think you may be a bit confused. Let’s clarify this classification concept by using a daily life example alongside a biological one.

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

In this table:

• Rank: is different levels within Hierarchical taxonomy (e.g., Kingdom is higher than Phylum)

Summary of the Analogy

Both biological taxonomy and address hierarchy move from broad to specific categories, with each level down reducing the number and increasing the similarity of entities.

• Kingdom vs. Country: Broadest category, diverse members.
• Phylum vs. State: Narrower, more specific features.
• Class vs. District: Further refinement.
• Order vs. City: Fewer members, more common traits.
• Family vs. Neighborhood: Even more specific commonalities.
• Genus vs. Street: Very small, closely related group.
• Species vs. House Number: Most specific, nearly identical members.

1. Species

• Definition: Group of closely related organisms with fundamental similarities that can interbreed and produce fertile offspring.
• Examples:
  • Mango: Mangifera indica.
  • Potato: Solanum tuberosum.
  • Lion: Panthera leo.
• Specific (species) Epithet: Second part of the name (indica, tuberosum, leo).
• Genus: First part of the name (Mangifera, Solanum, Panthera).
• Human: Homo sapiens.

2. Genus

• Definition: Group of closely related species with more similarities.
• Thus Genus = A group of related Species.
• Genus Examples:
  • Solanum: Potato (Solanum tuberosum) and brinjal.
  • Panthera: Lion (Panthera leo), leopard (P. pardus), tiger (P. tigris).
• Comparison: Panthera genus differs from Felis genus (includes cats).

3. Family

• Family = A group of related Genera (Plural of Genus).
• Show fewer similarities than genus and species.
• Characterization: Based on vegetative and reproductive features in plants.
• Examples:
  • Plants: Genus Solanum, Petunia, and Datura falls in the family Solanaceae.
  • Animals: Genus Panthera (lion, tiger, leopard) and Felis (cats) in the family Felidae.
  • But Different Families: Cats (Felidae) and dogs (Canidae) are two different Families.

4. Order

• Order = A group of related families with a few similar characters.
• A Higher Category
• Examples:
  • Plants: Convolvulaceae and Solanaceae families in the order Polymoniales.
  • Animals: Families Felidae and Canidae in the order Carnivora.

5. Class

• Class = A group of interconnected (related) orders.
• Examples:
  • Primata Order: Monkey, gorilla, gibbon.
  • Carnivora Order: Tiger, cat, dog.
  • Class: But both Primata and Carnivora in class Mammalia.

6. Phylum/Division

• Phylum = A group of interconnected Classes
• Animals Classes like fishes, amphibians, reptiles, birds, and mammals falls under Phylum Chordata.
  • Common Features of Chordates: Presence of notochord, dorsal hollow neural system.
• In Zoology (Animals): Phylum word is used.
• In Botany (Plants): Division word is used.

7. Kingdom

• Kingdom = A grouping of interconnected phyla (Phylum plural).
• Highest Category: e.g. All animals in Kingdom Animalia.
  • Animal Kingdom: Kingdom Animalia.
  • Plant Kingdom: Kingdom Plantae.
• Broad Categories: From species to kingdom.

Taxonomic Hierarchy

• Ascending Order: From species to kingdom.
• Characteristics:
  • Lower Taxa (species and genus): More shared characteristics.
  • Higher Categories (phylum and kingdom): Fewer common characteristics, more complexity.
  • e.g. Dogs (species) share many traits with other Dogs, but share fewer traits with mammals (class) and even fewer with animals (kingdom).

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: Helps in systematic classification.
• Species: Basic units in taxonomic hierarchy.
• Taxonomic Studies: Identify similarities and differences.
• Classification Complexity: Increases at higher levels as amount of similar characters decreases among organisms.
• Scientific Naming: Helps in identifying and categorizing organisms accurately.

Taxonomical Aids

Taxonomic studies help in agriculture, forestry, industry, and understanding biodiversity. These studies need proper classification and identification of organisms. Below are some key tools and techniques used in taxonomic studies:

1. Herbarium

• Definition: A storehouse of dried, pressed, and preserved plant specimens.
• Arrangement: Specimens are arranged on sheets according to a classification system.
• Information: Herbarium sheets include details like date and place of collection, names (English, local, botanical), family, and collector’s name.
• Use: Serve as references for future taxonomic studies.

2. Botanical Gardens

• Purpose: Collections of living plants for identification and study.
• Labeling: Each plant is labeled with its scientific name and family.
• Famous Gardens:
  • Kew Gardens (England)
  • Indian Botanical Garden, Howrah (India)
  • National Botanical Research Institute, Lucknow (India)

3. Museum

• Purpose: Collections of preserved plant and animal specimens for study and reference.
• Location: Usually in educational institutions like schools and colleges.
• Preservation Methods:
  • Containers or jars with preservative solutions.
  • Dry specimens.
  • Insect boxes for insects.
  • Stuffed specimens for larger animals.
• Additional Collections: Often include skeletons of animals.

4. Zoological Parks (Zoo)

• Definition: Places where wild animals are kept in protected environments under human care.
• Purpose: To learn about animals’ food habits and behavior.
• Environment: Animals are provided with conditions similar to their natural habitats.
• Common Name: Zoos.

5. Key

• Nature: Analytical method.
• Purpose: Used for the identification of plants and animals based on similarities and differences.
• Structure: Consists of pairs of contrasting characters called couplets.
  • Each choice leads to the acceptance of one option and rejection of the other.
  • Each statement in the key is called a lead.
• Categories: Separate keys for each taxonomic category (family, genus, species).

Other Taxonomical Tools

• Flora: Provides an account of the habitat and distribution of plants in a specific area.
• Manuals: Useful for identifying the names of species found in an area.
• Monographs: Contain detailed information on one specific taxon.
• Catalogues: Help in recording descriptions and correct identification.

These aids are essential for correct identification, classification, and study of various organisms.

Chapter Summary:

• The living world has a rich variety.
• Millions of plants and animals are identified and described.
• Many organisms are still unknown.
• Organisms vary in size, color, habitat, and features.
• We need to identify the characteristics of living organisms.
• Biologists use rules for identification, naming, and classifying organisms.
• This study is called taxonomy.
• Taxonomy helps in agriculture, forestry, industry, and understanding bio-resources.
• Identification, naming, and classification follow international codes.
• Each organism has a scientific name with two words (binomial system).
• Organisms have positions in a classification system.
• These positions are called taxonomic categories or taxa.
• All categories form a taxonomic hierarchy.
• Taxonomists use aids for identification, naming, and classification.
• Specimens are collected from the field.
• Specimens are preserved in herbaria, museums, botanical gardens, and zoological parks.
• Special techniques are needed for specimen collection and preservation.
• Live specimens are found in botanical gardens and zoological parks.
• Taxonomists create manuals and monographs for studies.
• Taxonomic keys help identify organisms based on characteristics.