The Living World

The One Thing

The living world is defined by the combined characteristics of cellular organisation, metabolism, responsiveness and other life processes, rather than by any single feature alone. Biology studies this diversity at multiple levels, while taxonomy provides a systematic and universal method for identifying, naming and classifying organisms.

Reactions, Processes and Experiments

Key Terms

• Biology: The scientific study of life and living organisms, including their structure, functions, origin, evolution and interactions.
• Biodiversity: The variety of living organisms found on Earth, including diversity among genes, species and ecosystems.
• Growth: A permanent and irreversible increase in size, mass or cell number. In organisms, growth may occur internally through cell division.
• Reproduction: The biological process by which organisms produce new individuals of their own kind. It may be sexual or asexual.
• Metabolism: The total of all chemical reactions occurring inside a living organism, including constructive and degradative reactions.
• Consciousness: The ability to sense surroundings and respond to stimuli.
• Cellular organisation: The arrangement of living organisms into cells, which are the basic structural and functional units of life.
• Taxonomy: The science of identification, nomenclature and classification of organisms.
• Systematics: The study of organismal diversity and evolutionary relationships, including classification and historical relationships.
• Identification: The process of recognising an organism and determining its correct identity.
• Nomenclature: The system of assigning standard scientific names to organisms.
• Classification: The arrangement of organisms into groups based on similarities, differences and evolutionary relationships.
• Binomial nomenclature: The two-word scientific naming system in which the first word is the genus and the second word is the specific epithet.
• Genus: A taxonomic category containing closely related species; it is written with a capital initial letter in a scientific name.
• Species: The basic unit of classification, generally consisting of organisms with similar characteristics that can reproduce among themselves under natural conditions.
• Taxonomic hierarchy: The ordered arrangement of classification categories from lower to higher levels: species, genus, family, order, class, phylum or division, kingdom and domain.
• Taxon: A group of organisms assigned to any particular rank in the taxonomic hierarchy.
• Herbarium: A collection of preserved plant specimens that are mounted, labelled and arranged for study and reference.
• Botanical garden: A place where living plants are grown, labelled and maintained for research, education and conservation.
• Museum: A collection of preserved plant or animal specimens used for scientific study and teaching.
• Zoological park: A facility where living wild animals are maintained in protected conditions for observation, education and conservation.
• Key: A taxonomic aid used to identify organisms by selecting between contrasting statements based on observable characteristics.
• Couplet: A pair of contrasting statements in a taxonomic key.
• Flora: The plant life of a particular region or period.
• Fauna: The animal life of a particular region or period.
• Monograph: A detailed account or description of a single taxon or a particular group of organisms.
• Taxonomic category: A rank in the classification system, such as species, genus, family or kingdom.
• Morphology: The study of the external form and structure of organisms.
• Anatomy: The study of the internal structure of organisms.
• Physiology: The study of the functions of organisms and their parts.
• Cell biology: The study of cells, their structure and their functions.
• Genetics: The study of heredity and variation.
• Ecology: The study of interactions between organisms and their environment.
• Evolution: The study of changes in organisms and their relationships over time.
• Biotechnology: The application of biological systems or organisms for practical purposes.
• Microbiology: The study of microorganisms.
• Environmental biology: The study of organisms in relation to environmental conditions and protection.

Easily Confused

• Growth and reproduction: Growth is an increase in size, mass or cell number, whereas reproduction produces new individuals.
• Growth in living organisms and crystal growth: Organisms may grow internally through cell division, whereas crystals increase in size through external accumulation; therefore, growth alone does not define life.
• Reproduction and a defining characteristic of life: Reproduction is common among living organisms but is not universal because mules, sterile worker bees and infertile human individuals cannot reproduce.
• Taxonomy and systematics: Taxonomy concerns identification, nomenclature and classification, whereas systematics also examines organismal diversity and evolutionary relationships.
• Identification and classification: Identification determines what an organism is, whereas classification places it into groups based on similarities, differences and evolutionary relationships.
• Genus and specific epithet: The genus is the first word of a scientific name and begins with a capital letter; the specific epithet is the second word and begins with a lowercase letter.
• Species and genus: Species is the lowest and most basic category, whereas a genus contains closely related species.
• Phylum and division: Phylum is generally used in animal classification, whereas division is commonly used in plant classification.
• Flora and fauna: Flora refers to the plant life of a region or period, whereas fauna refers to its animal life.
• Herbarium and botanical garden: A herbarium contains preserved plant specimens, whereas a botanical garden maintains living labelled plants.
• Museum and zoological park: A museum contains preserved plant or animal specimens, whereas a zoological park maintains living wild animals.
• Taxonomic category and taxon: A taxonomic category is a rank, such as species or kingdom, whereas a taxon is a group assigned to a particular rank.

What Gets Asked

• Defining characteristics of life: Questions may ask why no single feature defines all living organisms. Marks are lost by treating growth or reproduction as universally defining without considering crystals, mules, sterile worker bees and infertile human individuals.
• Metabolism and responsiveness: Questions may require identification of strong indicators of life. The key points are coordinated chemical reactions in living cells and the ability to sense and respond to environmental stimuli.
• Binomial nomenclature: Questions may ask for the parts and correct formatting of Homo sapiens. Marks are lost by reversing the genus and specific epithet, using incorrect capitalisation, or omitting italics or separate underlining.
• Taxonomic hierarchy: Questions may require the sequence from species to domain. Marks are lost by omitting categories or confusing the use of division in plants with phylum in animals.
• Taxonomic aids: Questions may ask about herbariums, botanical gardens, museums, zoological parks or keys. Marks depend on distinguishing preserved specimens, living plants, living animals and identification through contrasting characters.
• Scope and applications of biology: Questions may connect morphology, anatomy, physiology, cell biology, genetics, ecology, evolution, biotechnology, microbiology and environmental biology with agriculture, medicine, public health, environmental protection, food production and conservation.