Biology

Australian green tree frog (Litoria caerulea) Australian green tree frog Litoria caerulea, the Australian green tree frog or White's tree frog, is a large, docile arboreal frog native to Australia and New Guinea, common near people and studied for skin…

Autonomic nervous system — control of internal organs and homeostasis Autonomic nervous system The autonomic nervous system (ANS) is the involuntary branch of the peripheral nervous system that regulates heart rate, digestion, respiration, glands and other internal functions…

Autophagy: cellular self-digestion, mechanisms, and biological roles Autophagy Autophagy is a conserved cellular process that degrades and recycles internal components. This article explains its mechanisms, types, physiological roles, medical relevance, and k…

Autopoiesis: self-producing systems and biological self‑maintenance Autopoiesis Autopoiesis is the property of a system that produces and maintains its own organization. Coined for living cells, the concept has been applied to cognition, systems theory and soc…

Autotroph An autotroph is an organism that produces organic matter from inorganic substances, using light or chemical energy; primary producers that sustain food webs and biogeochemical cycl…

Auxin: Plant Growth Regulators and Their Roles in Development Auxin Auxins are plant hormones that coordinate growth, cell elongation, tropisms and organ formation. This article covers chemistry, biosynthesis, transport, signaling, physiological ro…

Avery–MacLeod–McCarty experiment: identifying DNA as the transforming principle Avery–MacLeod–McCarty experiment A 1944 study that provided strong evidence that DNA, not protein, carries hereditary information in bacteria, establishing a foundation for molecular genetics and later work on gen…

Avialae: birds and their closest extinct relatives Avialae Avialae is the clade that comprises modern birds and the extinct theropod lineages closest to them, encompassing the evolutionary transition from non‑avian dinosaurs to flying bird…

Axillary nerve (circumflex nerve) Axillary nerve Peripheral nerve arising from C5–C6 roots of the brachial plexus; supplies deltoid and teres minor and skin over the lateral shoulder. Travels through the quadrangular space and is…

Axon: structure, function, and biological significance Axon Axons are the long, slender projections of neurons that transmit electrical impulses to other cells. This article explains axon anatomy, conduction, development, history, and medic…

B cell (B lymphocyte) B cell B cells are white blood cells of the adaptive immune system that recognize antigens, produce antibodies, present antigen to T cells, form memory, and differentiate into plasma cell…

B vitamins (B-complex): roles, types, sources and deficiency B vitamins Group of eight water‑soluble vitamins essential as coenzymes for metabolism, nervous system and blood; found in varied foods. Covers types, functions, deficiency signs, history and…

Baby: definition, development, care, and cultural perspectives Baby Comprehensive overview of babies: terminology, physical and neurological development, common health and safety guidance, feeding and sleep, prematurity and stillbirth, cultural pra…

Bacillales: an order of Gram-positive bacteria Bacillales Bacillales is a diverse order of Gram-positive bacteria that includes spore-formers and non-spore-formers; members range from soil-dwelling decomposers and industrial strains to hu…

Bacillus — rod-shaped, endospore-forming bacteria Bacillus Bacillus is a widespread genus of Gram-positive, rod-shaped bacteria notable for endospore formation; species range from harmless soil microbes used in industry to pathogens such a…

Bacillus (shape) — rod-shaped bacteria Bacillus (shape) Bacillus describes rod-shaped bacteria in general or, when capitalized and italicized, the specific genus Bacillus. Covers form, arrangements, staining differences, ecology, uses,…

Bacillus anthracis — the bacterium that causes anthrax Bacillus anthracis Bacillus anthracis is a gram-positive, rod-shaped bacterium that forms hardy spores and causes anthrax in animals and humans. Noted for its toxins, capsule, medical history, and bi…

Bacillus subtilis Bacillus subtilis is a gram-positive, rod-shaped, endospore-forming soil bacterium used as a model organism in genetics and biotechnology; source of bacitracin, industrial enzymes,…

Bacteria: structure, diversity, and roles in the environment and human life Bacteria Single-celled prokaryotes lacking a nucleus. Bacteria are metabolically diverse organisms that shape ecosystems, human health, industry, and scientific research.

Bacterial conjugation: direct transfer of genetic material between cells Bacterial conjugation Bacterial conjugation is horizontal gene transfer by direct cell contact, often mediated by conjugative plasmids or transposons; it spreads traits such as antibiotic resistance and…

Bacterial microcompartment Protein-based, membrane-less compartments inside bacteria that enclose enzymes to optimize metabolism and sequester intermediates; examples include carboxysomes and metabolosomes.

Bacteriology: study, methods, history and practical applications Bacteriology Bacteriology is the branch of microbiology concerned with bacteria: their structure, classification, roles in health and environment, laboratory methods, history, and practical use…

Bacteriophage (phage): viruses that infect bacteria Bacteriophage Bacteriophages, or phages, are viruses that infect bacteria. This article explains their structure, life cycles, ecological roles, history, applications such as phage therapy, and…

Bacteroides: Characteristics, Ecology, Clinical Importance, and Taxonomy Bacteroides Bacteroides is a genus of gram-negative, obligate anaerobic bacteria common in the human gut. This article covers their biology, ecological roles, clinical significance, laboratory…

Bacteroidetes — a diverse phylum of environmental and gut bacteria Bacteroidetes Bacteroidetes are a widespread phylum of Gram-negative bacteria that break down complex organic matter in soils, oceans and animal microbiomes. Some species support digestion; othe…

Balancing selection: maintenance of genetic diversity in populations Balancing selection Balancing selection comprises evolutionary processes that preserve multiple alleles at a locus within populations, including heterozygote advantage and frequency-dependent selectio…

Baldness (Alopecia): Causes, Types, History, and Management Baldness An encyclopedic overview of baldness (alopecia): its types, biological causes, history, cultural aspects, diagnosis and common approaches to management and treatment.

Bartholin's gland (greater vestibular gland) Bartholin's gland Small paired vulvar glands located beside the vaginal opening that produce lubrication; often discussed in relation to cysts, abscesses, and treatments in reproductive-age people.

Bartonella — genus of intracellular bacterial pathogens Bartonella Bartonella is a genus of Gram-negative, intracellular bacteria that infect mammals and are transmitted by arthropod vectors, causing a range of human and animal diseases from mild…

Basal (phylogenetics): definition, use and common misunderstandings Basal In phylogenetics, 'basal' denotes a lineage or clade near the root of a rooted tree. It is a relative, neutral term—used to indicate earlier branching, not intrinsic primitiveness.

Basal ganglia: structure, function, and clinical significance Basal ganglia An overview of the basal ganglia (basal nuclei): their components, circuits, roles in movement, learning and motivation, and relevance to neurological and psychiatric conditions.

Base pair: definition, structure, and biological significance Base pair A base pair is two complementary nucleotides bonded across the DNA (or RNA) double helix. This article explains pairing rules, chemistry, role in genomes, variants, and practical i…

Basidiomycota — the club fungi (mushrooms, rusts, smuts and relatives) Basidiomycota Basidiomycota are a major phylum of fungi defined by basidia-bearing spores. They include mushrooms, bracket fungi, puffballs, rusts and smuts and play key roles as decomposers, sy…

Basidium: the spore-producing cell of Basidiomycota Basidium A basidium is the characteristic microscopic cell in many fungi that produces sexual spores (basidiospores). This article explains its form, function, diversity, and ecological imp…

Basophil — rare granulocyte involved in allergy and parasite responses Basophil Basophils are circulating white blood cells that store histamine and other mediators. This article explains their appearance, origin, roles in immunity and allergy, differences fro…

Bedbug (Cimicidae): biology, behavior, detection and control Bedbug A compact, neutral overview of bedbugs (family Cimicidae): their biology, life cycle, behavior, health effects, detection, prevention and common control measures.

Beehive: natural nests and man-made hives Beehive A beehive is the shelter where honey bees live, raise young and store food. Articles cover structure, types of human-made hives, history, uses such as pollination and honey product…

Beekeeping (Apiculture): Overview, Practices, History, and Importance Beekeeping Beekeeping, or apiculture, is the management of honey bees for products, pollination, and conservation. This article explains hives, methods, history, uses, and notable distinction…

Beeswax: properties, history and common uses Beeswax Natural wax secreted by honeybees and used for hive construction, candles, cosmetics, food glazing and polishes. Overview of composition, production, historical use and modern appl…

Being: meanings, grammar, and categories of entities Being A concise overview of the word and concept “being”: its grammatical roles, senses as organism or entity, philosophical use in ontology, cultural and religious examples, and common…

Benthos (benthic organisms) Benthos Organisms—plants and animals—that live on, in, or near the bottom of seas, lakes and other water bodies; ecology, classification, zones, roles, and human impacts.

Bergmann's rule: body size variation with climate Bergmann's rule Bergmann's rule describes the tendency for larger-bodied members of a taxonomic group to occur in colder climates and smaller ones in warmer climates, with notable exceptions and d…

Biceps (biceps brachii): anatomy, function and clinical notes Biceps Overview of the biceps brachii muscle: structure (long and short heads), actions (elbow flexion, forearm supination), comparative anatomy, common injuries and clinical relevance.

Bikont — eukaryotes ancestrally bearing two flagella Bikont Bikont: a proposed major eukaryotic grouping whose members ancestrally have two flagella. Covers defining traits, representative lineages, evolutionary evidence, and classification…

Bile (gall): composition, function, and clinical notes Bile Bile, also called gall, is a liver secretion that aids fat digestion, carries pigments and cholesterol, and travels via the gallbladder and bile ducts; clinically important in gall…

Binary fission — asexual cellular division in prokaryotes and protists Binary fission Binary fission is a simple asexual division that produces two daughter cells from one parent; it is the principal means of reproduction for many bacteria and some single-celled euk…

Binocular vision: how two eyes create depth and a unified view Binocular vision Binocular vision is the visual process that integrates input from both eyes to produce depth perception, a single fused image, and a wide field of view. It underpins stereopsis, st…

Binomial nomenclature: two-part scientific naming system for species Binomial nomenclature Overview of binomial nomenclature, the two-part scientific naming system that gives each species a unique genus and specific epithet, with rules for formatting, authorship, history…