1.1 The Living World

What is Living?

Defining life is a fundamental question in biology. While there isn't a single, universally accepted definition, living organisms exhibit certain unique characteristics that distinguish them from non-living matter. These characteristics include:

Growth

Growth is defined as an increase in mass and an increase in the number of individuals.

• In living organisms: Growth occurs from within (intussusception) due to the accumulation of material inside the body. Plants grow continuously throughout their lifespan, while animals grow up to a certain age.
• In non-living objects: Growth can also be observed, but it occurs by the accumulation of material on the surface (accretion), such as the growth of mountains, boulders, or sand mounds.
• Key Point: Growth is not a defining characteristic of living organisms because non-living objects can also grow. However, intrinsic growth is unique to living organisms.

Reproduction

Reproduction is the process by which living organisms produce offspring similar to themselves. It ensures the continuity of species.

• Types of Reproduction:
  • Asexual Reproduction: Involves a single parent and produces genetically identical offspring (e.g., budding in yeast and Hydra, fragmentation in filamentous algae and fungi, spore formation).
  • Sexual Reproduction: Involves two parents and leads to offspring with genetic variation.
• Exceptions: Many organisms do not reproduce (e.g., mules, sterile worker bees, infertile human couples).
• Key Point: Reproduction is not a defining characteristic of living organisms because not all living organisms reproduce.

Metabolism

Metabolism refers to the sum total of all the chemical reactions occurring in a living organism. These reactions involve the conversion of energy and matter.

• Two main processes:
  • Anabolism (Constructive processes): Synthesis of complex substances from simpler ones (e.g., photosynthesis).
  • Catabolism (Destructive processes): Breakdown of complex substances into simpler ones (e.g., respiration).
• Key Point: Metabolism is a defining characteristic of all living organisms. Metabolic reactions can be demonstrated outside the body in cell-free systems (in vitro), but these isolated reactions are not considered living things themselves, though they are living reactions.

Cellular Organization

All living organisms are composed of one or more cells. The cell is the fundamental structural and functional unit of life.

• Unicellular organisms: Consist of a single cell (e.g., bacteria, amoeba).
• Multicellular organisms: Composed of many cells organized into tissues, organs, and organ systems.
• Key Point: Cellular organization is a defining characteristic of all living organisms.

Consciousness

Consciousness is the ability of an organism to sense its surroundings (environment) and respond to environmental stimuli. These stimuli can be physical, chemical, or biological.

• Response to stimuli: Organisms respond to light, water, temperature, other organisms, pollutants, etc.
• Self-consciousness: Humans are the only organisms that are aware of themselves (self-consciousness).
• Key Point: Consciousness is a defining characteristic of all living organisms.

Conclusion: The most defining characteristics of living organisms are metabolism, cellular organization, and consciousness.

Diversity in the Living World

The Earth is home to an astonishing variety of life forms, a phenomenon known as biodiversity.

Biodiversity

Biodiversity refers to the total number and types of organisms present on Earth.

• Estimated Species: Currently, 1.7 to 1.8 million species are known and described. This number includes both plants and animals.
• Need for Classification: The enormous diversity necessitates a system for naming and classifying organisms to study them effectively.

Nomenclature (Binomial Nomenclature)

Nomenclature is the process of giving scientific names to organisms. Scientific names are standardized and universally accepted, avoiding the confusion caused by common names which vary from region to region.

• Binomial Nomenclature: The most widely accepted system of naming, proposed by Carolus Linnaeus. Each scientific name has two components:
  1. Generic name (Genus): The first word, starting with a capital letter.
  2. Specific epithet (Species): The second word, starting with a small letter.
• Rules for Binomial Nomenclature:
  • Scientific names are typically in Latin and written in italics when typed, or underlined separately when handwritten.
  • The first word (genus) starts with a capital letter, and the second word (species) starts with a small letter.
  • The name of the author (who first described the species) is written in an abbreviated form after the specific epithet (e.g., Mangifera indica Linn.).
  • Both words in a biological name, when handwritten, are separately underlined or printed in italics to indicate their Latin origin.

Identification

Identification is the process of determining if a particular organism is already known or if it is a new species. It involves comparing the characteristics of the unknown organism with those of known organisms.

Classification

Classification is the process by which organisms are grouped into convenient categories based on some easily observable characteristics.

• Taxa (Categories): The scientific term for these categories is 'taxa' (singular: taxon). Examples of taxa include plants, animals, dogs, cats, insects, mammals, etc.
• Taxonomy: The branch of science dealing with the classification of organisms. It involves characterization, identification, nomenclature, and classification.
• Systematics: The study of the relationships among different kinds of organisms and their diversity. It includes taxonomy and also considers evolutionary relationships between organisms.

Taxonomic Categories

Classification is not a single step process but involves a hierarchy of steps, where each step represents a rank or category. These categories are part of an overall taxonomic arrangement, and they are collectively known as the taxonomic hierarchy.

Obligate Categories (from highest to lowest):

Kingdom

The highest taxonomic category. It includes all organisms that share a set of fundamental characteristics.

• Examples: Kingdom Plantae (all plants), Kingdom Animalia (all animals).

Phylum (for animals) / Division (for plants)

A group of related classes.

• Examples: Phylum Chordata (animals with a notochord), Division Angiospermae (flowering plants).

Class

A group of related orders.

• Examples: Class Mammalia (mammals), Class Dicotyledoneae (dicot plants).

Order

A group of related families.

• Examples: Order Primata (monkeys, gorillas, gibbons), Order Sapindales (mango, neem).

Family

A group of related genera. Families are characterized on the basis of both vegetative and reproductive features of plant species.

• Examples: Family Hominidae (humans), Family Solanaceae (potato, brinjal).

Genus

A group of related species that have more characteristics in common compared to species of other genera.

• Examples: Panthera (lion, tiger, leopard), Solanum (potato, brinjal, nightshade).

Species

The lowest and most fundamental taxonomic category. A group of individual organisms with fundamental similarities, capable of interbreeding to produce fertile offspring.

• Examples: Homo sapiens (humans), Mangifera indica (mango).

Mnemonic for remembering the hierarchy (from Kingdom to Species): King Philip Came Over For Good Soup.

Taxonomical Aids

Taxonomical aids are techniques, procedures, and stored information that are useful in identification and classification of organisms.

Herbarium

A storehouse of collected plant specimens that are dried, pressed, and preserved on sheets. These sheets are arranged according to a universally accepted system of classification.

• Purpose: Serves as a quick referral system in taxonomic studies. Each sheet carries a label providing information about the date and place of collection, English, local and botanical names, family, collector's name, etc.

Botanical Gardens

Specialized gardens that have collections of living plants for reference.

• Purpose: Provide identification of species, and plants are grown for research, conservation, and public education. Each plant is labeled with its botanical/scientific name and its family.
• Famous Botanical Gardens: Royal Botanical Garden, Kew (England); Indian Botanical Garden, Howrah (India); National Botanical Research Institute, Lucknow (India).

Museum

Biological museums are generally set up in educational institutes such as schools and colleges. They have collections of preserved plant and animal specimens for study and reference.

• Preservation: Specimens are preserved in preservative solutions in containers or jars. Plant and animal specimens may also be preserved as dry specimens. Insects are preserved in insect boxes after collecting, killing, and pinning. Larger animals like birds and mammals are usually stuffed and preserved. Skeletons of animals are also kept.

Zoological Parks (Zoos)

These are places where wild animals are kept in protected environments under human care and which enable us to learn about their food habits and behavior.

• Purpose: Provide a natural habitat for animals, facilitate conservation, and allow for public viewing and education.

Key

A taxonomical aid used for identification of plants and animals based on similarities and dissimilarities.

• Structure: The keys are based on the contrasting characters generally in a pair called a couplet. It represents the choice made between two opposite options. This results in acceptance of one and rejection of the other. Each statement in the key is called a lead.
• Nature: Keys are generally analytical in nature. Separate taxonomic keys are required for each taxonomic category such as family, genus, and species for identification purposes.

Monograph

Contains comprehensive information on any one taxon.

• Purpose: Provides detailed information about a single family, genus, or species.

Manual

Provide information for identification of names of species found in an area.

• Purpose: Useful for identifying species within a specific geographical region.

Flora

Contains the actual account of habitat and distribution of plants of a given area. These provide the index to the plant species found in a particular area.

• Purpose: Document the plant diversity of a specific region.

Catalogue

A list or register that enumerates all the species found in a particular area, along with their brief descriptions.

• Purpose: Provides a systematic listing of species.