NCERT - DIVERSITY OF LIVING WORLD - 24 - 25

Defining Characteristics of Living Organisms

• All living organisms exhibit metabolism, but isolated metabolic reactions in vitro are not considered living.
• Cellular organization is a defining feature of life forms.
• The ability to sense and respond to environmental stimuli (physical, chemical, or biological) is a key characteristic.
• All organisms, from prokaryotes to eukaryotes, can sense and respond to their surroundings.
• Photoperiod influences reproduction in seasonal breeders, including plants and animals.
• All organisms regulate the chemicals entering their bodies.
• Human beings are the only organisms known to possess self-consciousness, making consciousness a defining property of living organisms.
• The definition of living state becomes more complex with human beings.
• Brain-dead patients, supported by machines, raise questions about the definition of living.
• Emergent properties arise at higher levels of organization due to interactions between constituent components.
• Living organisms can be characterized as self-replicating, evolving, and self-regulating interactive systems capable of responding to external stimuli.

Taxonomy - Classification Hierarchy

• Taxonomy is the science of classifying organisms based on shared characteristics.
• The hierarchical system of classification organizes organisms into categories ranging from species to kingdom.
• Species are the basic unit of classification, consisting of organisms capable of interbreeding and producing fertile offspring.
• Genus groups closely related species together.
• Family includes related genera with a lower level of similarity compared to genus and species.
• Order groups related families based on shared characteristics.
• Class includes related orders.
• Phylum/Division groups related classes based on a few common characters.
• Kingdom represents the highest and most inclusive category, grouping all organisms with similar fundamental characteristics.
• As one moves up the hierarchy from species to kingdom, the number of shared characteristics decreases.
• Lower taxonomic categories share more characteristics than higher ones, making classification more complex at higher levels.

Taxonomic Aids

• Herbarium is a collection of dried, pressed, and preserved plant specimens arranged according to a classification system.
• Botanical Gardens are living collections of plant species that are labelled with their scientific names and families.
• Museums house preserved plant and animal specimens for study and reference.
• Zoological Parks provide environments to study wild animals and their behavior in a protected setting.
• Keys are tools for identifying organisms based on contrasting characters presented in pairs (couplets).
• Flora provides information about the habitat and distribution of plants in a specific area.
• Manuals offer guidance on identifying plant species within a certain geographic region.
• Monographs focus on detailed information about a single taxon.
• Catalogues list and describe organisms in a specific collection.

Biology - Science of Life

• Biology is the study of living things and their processes.
• The living world exhibits a vast diversity of organisms.
• Early humans recognized the difference between inanimate objects and living organisms.
• Recognizing the shared similarities among living organisms led to the understanding that all living things on Earth are related.

Ernst Mayr

• Ernst Mayr was a renowned evolutionary biologist, often referred to as the "Darwin of the 20th century."
• His extensive research spanned ornithology, taxonomy, zoogeography, evolution, systematics, and the history and philosophy of biology.
• Mayr played a significant role in making the origin of species diversity the central focus of evolutionary biology.
• He defined the current understanding of a biological species.

What is 'Living'?

• Living organisms exhibit specific characteristics, such as growth, reproduction, response to stimuli, and metabolism.
• Growth involves an increase in mass and number of individuals.
• In multicellular organisms, growth occurs through cell division.
• Unicellular organisms grow by cell division.

Taxonomic Categories

• Classification involves a hierarchical system of categories, each representing a rank or taxonomic category.
• These categories are collectively known as the taxonomic hierarchy.
• Each category is a unit of classification, referred to as a taxon.
• Examples of taxa at different levels include: "Plants," "Wheat," "Animals," "Mammals," and "Dogs."

Systematics

• Systematics deals with the identification, nomenclature, and classification of organisms, considering their evolutionary relationships.
• The term "systematics" originates from the Latin word "systema," meaning systematic arrangement.
• Linnaeus used "Systema Naturae" as the title of his publication.

Taxonomic Aids

• Taxonomic studies assist in agriculture, forestry, industry, and understanding biodiversity.
• Herbarium: A collection of dried, pressed, and preserved plant specimens arranged according to a classification system.
• Botanical Gardens: Specialized gardens housing collections of living plants for reference.
• Museums: Storehouses of preserved specimens, including plants and animals.
• Zoological Parks: Contain living animals for observation and study.
• Manuals and Monographs: Provide information and descriptions for taxonomic studies.
• Taxonomic Keys: Tools used for identifying organisms based on their characteristics.

Defining Features of Life

• Metabolism: All living organisms undergo metabolic processes, but isolated in-vitro metabolic reactions are not themselves living.
• Cellular Organization: A defining feature of life is the cellular organization of the body.
• Sensing and Responding to Environment: All living organisms can sense and respond to environmental stimuli, such as light, water, temperature, chemicals, and other organisms.
• Self-Consciousness: Human beings are the only organisms known to have self-consciousness.
• Emergent Properties: Properties of living organisms arise from interactions between their components. These interactions result in emergent properties that are not present in the individual components.

The Importance of Naming and Classifying

• Taxonomy: Branch of biology dealing with identifying, naming, and classifying organisms.
• Binomial Nomenclature: The system of giving organisms a two-part scientific name, introduced by Carolus Linnaeus.
• Rules of Binomial Nomenclature:
  • Biological names are generally in Latin and written in italics.
  • The first word in the scientific name represents the genus, and the second word represents the specific epithet.
  • Both words are underlined when handwritten, indicating their Latin origin.
  • The genus name starts with a capital letter, while the specific epithet starts with a lowercase letter.
  • The author's name appears after the specific epithet, abbreviated, indicating the first person to describe the species.

Taxonomic Hierarchy

• Taxonomic Categories: Species, genus, family, order, class, phylum, and kingdom.
• Ascending Order: As you move up the hierarchy, the number of shared characteristics between organisms decreases.
• Kingdom Animalia: All animals are classified in this kingdom.
• Kingdom Plantae: All plants are classified in this kingdom.

Taxonomic Aids

• Botanical Gardens: Collections of living plant species, often labeled with their scientific names.
• Museums: Collections of preserved plant and animal specimens for study and reference.
• Zoological Parks: Places where wild animals are kept in protected environments, allowing for observation of their behaviors and food habits.
• Keys: Tools used for identification based on contrasting characteristics.
• Flora: Provide a systematic account of the plants found in a specific geographical region, including their habitats and distributions.
• Manuals: Offer information to help identify species found in a particular area.
• Monographs: Contain information on a single taxonomic group.

Characteristics of Living Organisms

• Growth is a characteristic of living organisms, but it is not a defining feature because non-living organisms can also grow in certain conditions.
• Reproduction is another characteristic of living organisms, but there are exceptions like mules, sterile worker bees, and infertile human couples.
• Metabolism is a defining characteristic of living organisms which involves a series of chemical reactions that occur constantly in all living organisms.

Diversity in the Living World

• There are millions of organisms in the world.
• Each organism belongs to a specific species.
• Biodiversity refers to the number and types of organisms present on earth.

Nomenclature: Naming Organisms

• All organisms should have a standardized name used worldwide.
• Scientific names are given based on agreed-upon principles and criteria.
• International Code for Botanical Nomenclature (ICBN) is used for plants.
• International Code of Zoological Nomenclature (ICZN) is used for animals.
• Scientific names have two components: Generic name (genus) and specific epithet (species). This system is called Binomial nomenclature.
• The genus starts with a capital letter, and the specific epithet starts with a lowercase letter. Both are written in italics or underlined when handwritten.
• Example: Mangifera indica (Mango):
  • Mangifera - genus
  • indica - specific epithet
• The author who first described the species is written after the specific epithet, e.g., Mangifera indica Linn (Linnaeus described Mango).

Classification: Grouping Organisms

• Classification involves grouping organisms based on shared characteristics.
• Different levels of classification are called taxa.
• Taxa can be arranged in a hierarchical system called taxonomic hierarchy.
• Taxonomic categories in ascending order are:
  • Species
  • Genus
  • Family
  • Order
  • Class
  • Phylum (animals)
  • Division (plants)
  • Kingdom
• The higher the category, the fewer common characteristics its members share.
• Kingdom Animalia includes all animals, and Kingdom Plantae includes all plants.
• Example: Housefly:
  • Species: Musca domestica
  • Genus: Musca
  • Family: Muscidae
  • Order: Diptera
  • Class: Insecta
  • Phylum: Arthropoda
  • Kingdom: Animalia

Systematics: Understanding Relationships

• Systematics is the branch of biology that studies the relationships among organisms, including their identification, nomenclature, classification, and evolution.
• It involves identifying and classifying organisms based on their characteristics and evolutionary history.
• Systematics helps us understand the development of the diversity of living organisms on Earth.

What is Living?

• Living organisms grow, reproduce, sense the environment, and respond to stimuli.
• Other characteristics include metabolism, self-replication, self-organization, interaction, and emergence.
• Growth can be observed in both multicellular and unicellular organisms.
• Unicellular organisms grow by cell division.
• Multicellular organisms grow by cell division, but in animals, this growth is limited to a certain age.
• Non-living objects can increase in mass, but this is not considered growth.
• Living organisms grow from the inside.

Taxonomy and Systematics

• Taxonomy is the science of classifying organisms into groups based on shared characteristics.
• The scientific term for these groups is taxa.
• Taxa can be at different levels, such as "plants," "wheat," "animals," "mammals," and "dogs."
• Modern taxonomic studies consider external and internal structure, cellular structure, developmental processes, and ecological information.
• The processes of characterization, identification, classification, and nomenclature are fundamental to taxonomy.
• Systematics is the study of the evolutionary relationships between organisms.
• Systematics encompasses identification, nomenclature, and classification.

Taxonomic Categories

• The classification of organisms involves a hierarchical system known as the taxonomic hierarchy.
• Each level of the hierarchy is a taxonomic category or rank, also known as a taxon.
• The major taxonomic categories are kingdom, phylum (or division for plants), class, order, family, genus, and species.
• The lowest category, species, is a group of organisms with fundamental similarities.
• Organisms are placed into these categories based on their characteristics, with more shared characteristics at lower levels and fewer shared characteristics at higher levels.

Species

• Species are defined as groups of organisms with fundamental similarities that distinguish them from other closely related species.
• Each species has a specific epithet, which is a descriptive term used to identify the species within its genus.
• For example, Mangifera indica (mango) has the specific epithet indica.
• Solanum tuberosum (potato) has the specific epithet tuberosum.
• Panthera leo (lion) has the specific epithet leo.

Genus

• A genus comprises a group of related species with more shared characteristics than species within other genera.
• For example, Solanum tuberosum (potato) and Solanum melongena (eggplant) are two different species but belong to the same genus, Solanum.
• Other examples include Panthera leo (lion), Panthera pardus (leopard), and Panthera tigris (tiger), all belonging to the genus Panthera.

Family

• Family is a higher category containing related genera with fewer similarities compared to genus and species.
• For example, the genera Solanum, Petunia, and Datura are all part of the family Solanaceae.
• In animals, the family Felidae includes the genera Panthera and Felis (cats).

Order

• Order is an even higher category that groups families with a few common characteristics.
• For example, the families Conolvulaceae and Solanaceae are included in the order Polymoniales, based on their floral characteristics.
• In animals, the order Carnivora includes families such as Felidae and Canidae (dogs).

Class

• Class includes related orders.
• For example, the order Primata (monkeys, gorillas, gibbons) and the order Carnivora are both assigned to the class Mammalia.

Phylum

• Phylum (or division for plants) is a category that groups related classes.
• For example, the classes containing fishes, amphibians, reptiles, birds, and mammals all belong to the phylum Chordata.

Kingdom

• Kingdom is the highest category in the taxonomic hierarchy.
• The animal kingdom, Animalia, includes all animals belonging to various phyla.
• The plant kingdom, Plantae, includes all plants from various divisions.

Characteristics of Living Organisms

• Growth is not a defining characteristic of living organisms. Living organisms grow under specific conditions, while non-living objects do not grow.
• Reproduction is another characteristic of living organisms. It encompasses both sexual and asexual reproduction.
• Metabolism is a defining feature of all living organisms. It involves chemical reactions that occur within the body, constantly transforming biomolecules.
• Cellular organization is the hallmark of living organisms.
• Responsiveness is a crucial aspect of life. This refers to the ability of organisms to perceive and react to their surroundings.
• Self-consciousness is unique to humans.
• Emergent properties appear at higher levels of organization. These properties arise from the interactions between components at lower levels.

Classification and Nomenclature

• Classification involves grouping organisms based on shared characteristics.
• Taxonomy is the science of classifying organisms.
• Nomenclature is the system of naming organisms.
• Binomial nomenclature uses two words – the genus and specific epithet – to name each organism.
• Taxonomic categories are hierarchical levels used for classification.
• Taxonomic hierarchy is a system of nested categories.

Taxonomical Aids

• Botanical gardens are collections of living plants, used for research, education, and conservation.
• Museums house preserved specimens of plants and animals for study.
• Zoological parks (zoos) provide a protected environment for wild animals, enabling observation of their behavior and food habits.
• Keys are tools used for identification based on contrasting characteristics.
• Flora is a detailed record of plants found in a specific area.
• Manuals provide information to help with species identification.
• Monographs focus on providing comprehensive information about a particular taxon.
• Catalogues list and describe organisms.

Biology & Living Organisms

• Biology is the study of life forms and living processes.
• Living organisms are diverse and can be distinguished from inanimate matter.
• Early humans recognized the awe or fear evoked by both inanimate and animate objects.
• Societies with anthropocentric views of biology had limited progress in biological knowledge.

Systematic Classification of Life Forms

• Early attempts at describing living organisms, including humans, were limited.
• Detailed identification, nomenclature, and classification systems were essential for the systematic description of life forms.
• The recognition of shared similarities among living organisms, both horizontally and vertically, was a significant outcome of these studies.
• The realization that all present-day organisms are related to each other, as well as to all organisms that have ever lived, led to a greater understanding of the interconnectedness of life and the importance of biodiversity conservation.

Ernst Mayr - "The Darwin of the 20th Century"

• Ernst Mayr, born in 1904, was a prominent evolutionary biologist at Harvard University.
• He contributed significantly to ornithology, taxonomy, zoogeography, evolution, systematics, and the history and philosophy of biology.
• Mayr's research helped establish the origin of species diversity as the central question of evolutionary biology.
• He also pioneered the now widely accepted definition of a biological species.
• Mayr received numerous prestigious awards, including the Balzan Prize, International Prize for Biology, and the Crafoord Prize.

Defining Characteristics of Living Organisms

• Growth: An increase in size and mass, often associated with an increase in cell number.
• Reproduction: The production of offspring with similar features to the parents, usually through sexual reproduction.
• Metabolism: The sum total of all chemical reactions occurring within a living organism, essential for energy production and maintenance.
• Cellular Organization: Consists of one or more cells, each with its own internal organization and functions.
• Sensing and Responding to Stimuli: The ability to detect and react to changes in the environment, whether physical, chemical, or biological.

Taxonomic Aids: Tools for Classification

• Taxonomic Studies: These studies are essential for understanding the diversity of life and are used in various fields such as agriculture, forestry, and industry.
• Herbarium: A collection of dried, pressed, and preserved plant specimens arranged according to a classification system.
• Botanical Gardens: Specialized gardens that contain living plant collections for reference.
• Museums: Collections of preserved animal specimens, including skeletons, taxidermied animals, and other artifacts.
• Zoological Parks: Living animal collections for education, conservation, and research.

Taxonomy: The Science of Classification

• Taxonomy involves the identification, naming, and classification of organisms.
• The binomial system of nomenclature is used to give each organism a unique two-word scientific name.
• The various categories within a taxonomic hierarchy are known as taxa.
• Taxonomists employ a range of tools and techniques to facilitate their studies, including manuals, monographs, and taxonomic keys.

What is ‘Living’?

• Living organisms display distinct characteristics:
  • Growth: increase in individual size and number through cell division. In plants, continuous growth. In animals, growth up to a certain age.
  • Reproduction: ability to generate new individuals, often mutually exclusive with growth in higher organisms.
  • Ability to sense & respond to environment.
  • Metabolism: chemical processes within living organisms.
  • Self-replicating: creating copies of themselves.
  • Self-organizing: maintaining internal order and structure.
  • Interacting: engaging with each other and the environment.
  • Emergent properties: characteristics arising from the complex interplay of components.

Diversity in the Living World

• Biodiversity refers to the variety of living organisms on Earth, estimated to be between 1.7-1.8 million known species.
• New species are continuously being discovered as scientific exploration continues.
• The need for standardized naming and classification arises due to the vast number of living organisms.

Nomenclature: Naming Living Organisms

• Nomenclature is the process of assigning scientific names to organisms.
• Scientific names are based on agreed principles and criteria, ensuring each organism has a unique, universally accepted name.
• The International Code for Botanical Nomenclature (ICBN) governs plant naming.
• The International Code of Zoological Nomenclature (ICZN) governs animal naming.
• Binomial nomenclature, introduced by Carolus Linnaeus, is the system of using two words to name an organism.

Classification: Grouping Living Organisms

• Classification categorizes living organisms based on shared characteristics, facilitating their study and understanding.
• The hierarchical classification system progresses from broader categories to narrower ones:
  • Kingdom: Broadest level, encompassing diverse life forms.
  • Phylum: Grouping organisms with fundamental similarities, e.g., Chordata (animals with a notochord).
  • Class: Includes related orders, e.g Mammalia.
  • Order: Assembles families with shared characteristics, e.g., Primates.
  • Family: Groups related genera, e.g., Felidae (cats).
  • Genus: Similar species with many shared traits, e.g., Mangifera (mango).
  • Species: Most specific level, defining a group of organisms that can interbreed and produce fertile offspring, e.g., Mangifera indica (mango).

Rules of Biological Nomenclature

• Scientific names are typically Latin and written in italics or underlined.
• The first word represents the genus and is capitalized.
• The second word is the specific epithet and is not capitalized.
• The author's name may be included after the specific epithet, often abbreviated, indicating who first formally described the species, e.g., Mangifera indica Linn.