Biology

Transduction (physiology) Conversion of physical or chemical stimuli into electrical or chemical signals in biological systems, including sensory receptors and synaptic events; mechanisms, examples, and sig…

Transfection: introduction of nucleic acids into cells Transfection Transfection is the deliberate introduction of DNA or RNA into cells by chemical, physical, or viral methods. Used in research, biotechnology and gene therapy, it enables expressio…

Transformation (genetics) Transformation is the process by which a cell takes up and expresses external DNA. It occurs naturally in some bacteria and is widely used in laboratories for cloning, genetic engi…

Transitional fossil Fossils showing anatomical features intermediate between distinct groups; key evidence for evolutionary change. Explains rarity, examples (Archaeopteryx, Tiktaalik), and common mis…

Translation (genetics): ribosomes synthesise proteins from mRNA Translation (genetics) Translation is the cellular process that decodes messenger RNA to build polypeptides. This article explains its mechanism, components, cellular contexts, and biological significanc…

Transposable element (transposon) Transposable element A transposable element is a DNA sequence that can change position within a genome, affecting mutation, regulation, and genome size. Two major classes and their roles are summarized…

Trapezius muscle — anatomy, function, and clinical relevance Trapezius muscle Large superficial back muscle that shapes the upper back and neck. Covers anatomy, divisions, actions on the scapula and arm, innervation, clinical issues, rehabilitation and histo…

Tree of life (biology): evolutionary relationships and phylogenetic concepts Tree of life (biology) A summary of the biological 'tree of life' concept: its meaning, history, data and methods, limits such as horizontal gene transfer, and its uses in classification and research.

Trematode (fluke): parasitic flatworms and their life cycles Trematode Trematodes (flukes) are parasitic flatworms in the phylum Platyhelminthes. Most have complex life cycles with snail intermediate hosts and vertebrate definitive hosts and include m…

Tremor: involuntary rhythmic muscle movement and its causes Tremor Tremor is an involuntary, rhythmic muscle movement found in many conditions and in normal physiology. This article explains types, causes, diagnosis, treatment, and important disti…

Treponema: overview of the spirochete genus and related human infections Treponema Treponema is a genus of spiral-shaped bacteria that includes species causing syphilis, yaws, bejel and pinta. This article covers features, species, diseases, diagnosis, treatment…

Triatominae (kissing bugs): biology, distribution, and public health importance Triatominae Triatominae are blood-feeding true bugs (subfamily of Reduviidae) known as kissing or conenose bugs. Many species transmit Trypanosoma cruzi, the agent of Chagas disease; control f…

Tribe (biology): a taxonomic rank between subfamily and genus Tribe (biology) A tribe is an intermediate taxonomic rank used in zoology and botany to group related genera within a family, often reflecting evolutionary relationships and aiding classification.

Triceps brachii muscle The triceps brachii is the three-headed muscle on the back of the upper arm responsible primarily for elbow extension; its structure, innervation, actions, and clinical relevance a…

Trichomonas gallinae: avian protozoan parasite and disease overview Trichomonas gallinae Trichomonas gallinae is a single-celled parasite of birds that causes oropharyngeal disease (canker/frounce). This article summarizes its biology, hosts, signs, transmission, diagn…

Trinomen (zoological trinomial name) Trinomen A trinomen is the three-part scientific name used in zoology to identify a subspecies: genus, species, and subspecies epithets. It follows specific formatting and nomenclature rule…

Trinomial nomenclature (three-part scientific names) Trinomial nomenclature A naming system in biology that gives organisms three-part scientific names for taxa below species level, indicating genus, species, and an infraspecific or subspecific epithet und…

Trochophore — marine larval form of many lophotrochozoans Trochophore A trochophore is a free-swimming larval stage found in several lophotrochozoan phyla. It is defined by bands of cilia used for locomotion and feeding and is important in dispersal…

Trophallaxis: social transfer of food and information Trophallaxis Trophallaxis is the direct transfer of food or fluids between individuals, especially in social insects. It distributes nutrients, symbionts and chemical signals and helps coordina…

True bug (Hemiptera): overview, traits, diversity and importance True bug True bugs are insects of the order Hemiptera, characterized by piercing–sucking mouthparts. This article explains their features, diversity, life cycle, ecological roles and impact…

Trunk: meanings and uses of 'trunk' in nature, anatomy, transport and technology Trunk Concise guide to the principal senses of 'trunk'—tree and animal structures, the human torso, luggage and vehicle storage, and technical uses in communications and software—plus hi…

Trypanosoma: parasitic kinetoplastid protozoa and their medical importance Trypanosoma Trypanosoma is a genus of single-celled, flagellated parasites in the kinetoplastid group. Species cause human and animal disease, use invertebrate vectors, and have a distinctive…

Trypanosomatida: parasitic kinetoplastid protists Trypanosomatida Trypanosomatida are single-flagellated, single-mitochondrion protozoa (kinetoplastids) that include insect-restricted species and important human and animal parasites such as Leish…

Tryptophan Tryptophan is an essential aromatic amino acid used in protein synthesis and as a biochemical precursor to serotonin, melatonin and niacin; it is obtained from dietary protein.

Tube feet (podia) — locomotion, feeding and respiration in echinoderms Tube feet Tube feet (podia) are small, tubular appendages of echinoderms used for locomotion, adhesion, feeding and gas exchange. They operate by a water vascular system and vary among sea s…

Tube worm Sessile marine invertebrates that build protective tubes. Includes bristle worms, fan-head worms, beard worms and horseshoe worms; notable forms include Riftia and Lamellibrachia.

Tubule: small tubular structures in biology and anatomy Tubule A tubule is a very small tubular structure found in organs and glands. This article covers its structure, common types (renal, glandular, reproductive), functions, histology, and c…

Turgor (cellular turgidity) Turgor Turgor is the pressure exerted by fluid inside living cells or tissues that makes them firm. It is central to plant rigidity, growth, stomatal function and responses to water avail…

Twin (Biological and Human Context) Twin An overview of twins: biological mechanisms, main types (identical and fraternal), development and medical issues, roles in research, and cultural and historical notes.

Type species: definition, rules and role in biological nomenclature Type species Overview of the type species concept: definitions, how species are fixed as types under different Codes, practical importance for nomenclatural stability, and key distinctions betw…

Type specimen (biology) Type specimen A type specimen is a preserved example of an organism (or part of one) that serves as the fixed reference for the application of a scientific name in biological nomenclature.

Ulna: anatomy, function, and clinical importance Ulna The ulna is the medial bone of the forearm. This article explains its parts, articulation with the radius and humerus, role in movement, variation, and common injuries.

Umbilical cord: structure, function, and clinical significance Umbilical cord Overview of the umbilical cord: anatomy, development, variations, clinical problems, cord care and cord blood use. Explains physiology, prenatal monitoring and perinatal considerat…

Unicellular organism (single-celled life) Unicellular organism A unicellular organism is a single cell that carries out all life functions. This article explains types (prokaryotes and unicellular eukaryotes), cell features, evolution, roles i…

Unikont (Unikonta): historical eukaryote supergroup Unikont Unikont (Unikonta) was a proposed eukaryote supergroup including Opisthokonta and Amoebozoa; the name is now largely replaced by Amorphea in modern classifications.

Uracil: the pyrimidine base of RNA Uracil Uracil is one of the four main nucleobases in RNA. A pyrimidine, it pairs with adenine, replaces thymine in RNA, and occurs in diverse biological and medical contexts.

Urinary system (renal system) Urinary system The urinary system produces, stores, and excretes urine. It removes metabolic waste, helps regulate fluids, electrolytes and blood pressure. Main parts: kidneys, ureters, bladder,…

Urination (micturition) Urination Urination, or micturition, is the physiological process by which animals and humans eliminate urine produced by the kidneys; it has anatomical, clinical, and social dimensions.

Urine: physiology, composition, and uses Urine Urine is the watery waste fluid produced by the kidneys, stored in the bladder and expelled through the urethra. This article covers composition, formation, clinical uses, common v…

Urinogenital: the urinary and reproductive systems and their openings Urinogenital Urinogenital (urogenital) describes the combined urinary and reproductive systems or their shared openings. It covers anatomy, embryology, species differences (including cloaca), a…

Uterus (womb): structure, function, and clinical significance Uterus Overview of the uterus: anatomy, role in menstrual cycle and pregnancy, common conditions, and clinical considerations in women’s reproductive health.

Vacuole (cell organelle): structure, functions and biological roles Vacuole A vacuole is a membrane-bound compartment in eukaryotic cells that stores substances, maintains turgor, aids digestion and recycling, and performs specialized roles in plants, fung…

Vagina (female reproductive canal) Vagina The vagina is a muscular, flexible canal in the female reproductive system that carries menstrual fluid, receives the penis during intercourse, and serves as the birth passage. It…

Vaginal flora: composition, function, disturbances and clinical significance Vaginal flora Vaginal flora (microbiota) are communities of bacteria and fungi that maintain vaginal health. This article explains their makeup, roles, common disturbances, diagnosis, treatments…

Vaginal lubrication: physiology, causes of dryness, and management Vaginal lubrication Natural wetness produced by vaginal tissues and glands during arousal. Explains how lubrication forms, what it contains, causes of reduced lubrication, clinical importance, and com…

Vagrancy (biology): causes, occurrences, and ecological significance Vagrancy (biology) Vagrancy describes animals found far outside their normal geographic range. This article explains causes, which groups show vagrancy, its ecological importance, how it is studied,…

Biological variation: causes, types and role in evolution Variation Overview of biological variation: genetic and non‑genetic sources, how scientists measure it, and its importance for evolution, biodiversity, conservation and applied biology.

Vas deferens (ductus deferens) Vas deferens The vas deferens is the paired muscular tube that carries sperm from each epididymis to the ejaculatory ducts and urethra. It is central to male reproduction and is commonly involv…