What is Living?

• Biology is the science of life forms and living processes.
• The living world is rich in variety, with millions of plants and animals identified and described, but only a fraction have been studied.

What is Living?

• Living beings exhibit growth, reproduction, metabolism, ability to sense and respond to the environment, self-replicate, organize, interact, and emerge.
• Growth in living organisms involves an increase in mass and number of cells, which are twin characteristics of growth.
• Multicellular organisms grow by cell division, while unicellular organisms grow by cell division as well, but it's also considered reproduction.
• In plants, growth is continuous throughout their life, whereas in animals, growth is only up to a certain age.
• Non-living objects can also grow in size by accumulation of material on the surface, but this is not growth from within as seen in living organisms.
• Reproduction refers to the production of progeny possessing features similar to those of parents.
• Organisms reproduce asexually (e.g., fungi reproduce by spores) or sexually.
• Reproduction is not synonymous with life, as many organisms are sterile (e.g., mules, sterile worker bees).
• Metabolism is the sum total of all chemical reactions occurring in the body.
• Metabolism is a defining feature of life, present in all living organisms, including plants, animals, microbes, and fungi.
• Isolated metabolic reactions outside the body in a cell-free system are neither living nor non-living but are metabolic reactions.
• Cellular organization of the body is a defining feature of life forms.
• Consciousness, or the ability to sense and respond to environmental cues (light, water, temperature, pollutants, etc.), is present in all living organisms.
• The most technically complicated aspect of consciousness is human beings' self-consciousness.
• Living organisms respond to stimuli, both physical and chemical.
• Life is a defining characteristic of living organisms, implying self-replication, evolving, and self-regulation.
• Interactions of molecules in the cell lead to emergent properties at higher levels of organization.
• When considering humans, it is difficult to define 'living' when observing patients in comas supported by machines; it questions the definition of life itself.

Diversity in the Living World

• Biodiversity refers to the variety of organisms existing on earth, with estimates ranging from 1.7 to 1.8 million species identified.
• Nomenclature is the system of naming organisms to standardize their identification globally.
• Identification, nomenclature, and classification are essential in studying organisms.
• Binomial nomenclature, developed by Carolus Linnaeus, includes two names: a generic name (genus) and a specific epithet (species).
• Scientific names are generally in Latin and written in italics; when handwritten, they are underlined separately.
• The genus name starts with a capital letter, while the species name starts with a small letter.
• Biological classification is the process of grouping organisms into categories based on easily observable characters.
• Taxonomy is the study of principles and procedures of classification.
• Systematics considers evolutionary relationships between organisms, incorporating phylogeny (evolutionary history).
• Taxonomic categories form a hierarchy, including kingdom, phylum/division, class, order, family, genus, and species.
• Species is the basic unit of classification, defined as a group of closely related organisms capable of interbreeding and producing fertile offspring.
• Genus comprises a group of related species sharing common attributes.
• Family includes related genera with fewer similarities than genus and species.
• Order is an assemblage of families exhibiting a few similar characters
• Class is a collection of related orders.
• Phylum (for animals) or Division (for plants) consists of related classes.
• Kingdom is the highest taxonomic category.
• Taxonomical aids such as herbaria, botanical gardens, museums, zoological parks, and keys help in identification and classification of organisms.
• Herbarium is a storehouse of collected plant specimens that are dried, pressed, and preserved on sheets.
• Botanical gardens maintain living plants for reference.
• Museums have collections of preserved plant and animal specimens for study and reference.
• Zoological parks (zoos) are places where wild animals are kept in protected environments under human care, enabling study of their food habits and behavior.
• A key is an analytical tool used for identifying organisms based on similarities and dissimilarities.
• Keys are based on contrasting characters generally in a pair called a couplet.
• Flora, manuals, monographs, and catalogs are other tools to aid in identification.

Exploration of life's characteristics: growth, reproduction, metabolism, and environmental response. Growth involves increasing mass and cell number. Plants grow continuously, while animals grow to a certain age.