Biology

Deuterostomes Deuterostome Deuterostomes are a major clade of bilaterian animals in which the blastopore usually becomes the anus; includes chordates, echinoderms and hemichordates and encompasses all verteb…

Developmental Biology: Growth, Patterning, and Differentiation in Living Organisms Developmental biology Study of the processes that transform a fertilized egg into a mature organism, including cell division, differentiation, morphogenesis, pattern formation and their genetic control.

Diapause: adaptive developmental arrest in animals Diapause Diapause is a programmed, reversible pause in development that helps many animals, especially insects and some fish embryos, survive predictable adverse environmental conditions.

Diaphragm (mammalian respiratory muscle) Diaphragm The diaphragm is a dome-shaped skeletal muscle that separates thoracic and abdominal cavities in mammals and plays the central role in breathing, posture, and several physiological…

Diastole: the heart's relaxation and filling phase — physiology and clinical importance Diastole Diastole is the phase of the cardiac cycle when the heart relaxes and fills with blood. This article explains its phases, relation to blood pressure, clinical significance and how…

Diatom — silica-walled algae central to aquatic ecosystems Diatom Diatoms are single-celled, photosynthetic algae with silica cell walls. They are major components of phytoplankton, key players in global carbon and silicon cycles, and useful as e…

Dickinsonia — an Ediacaran organism and its place in early multicellular life Dickinsonia Dickinsonia is a flat, segmented Ediacaran organism known from impressions in ancient sediments; its anatomy, ecology and classification have been widely studied and remain importa…

Dictyostelids (cellular slime molds) Dictyostelid Dictyostelids are 'social' amoebae that alternate between solitary feeding cells and a multicellular fruiting body. They illustrate cell communication, differentiation, and coopera…

Differences between butterflies and moths A clear, neutral guide to how butterflies and moths differ in appearance, life cycle, taxonomy, behavior, ecology and how to tell them apart in the field.

Digestion: How the Body Breaks Down, Absorbs and Uses Food Digestion Comprehensive overview of human digestion: stages, organs, enzymes, absorption, microbial roles, regulation, variation across species and common clinical issues affecting nutrient…

Digestive system: structure, function, and clinical relevance Digestive system Overview of the digestive (gastrointestinal) system: organs, processes of digestion and absorption, accessory glands, comparative biology, and common clinical considerations.

Dinoflagellates: biology, ecology, and significance Dinoflagellate Dinoflagellates are a diverse group of mostly marine, flagellated protists—photosynthetic, heterotrophic, or symbiotic—important in plankton, bioluminescence, coral symbioses and h…

Dinosauromorpha — the dinosaur lineage and its close relatives Dinosauromorpha Dinosauromorpha is the bird-line archosaur group that contains dinosaurs and their nearest relatives. It frames the evolutionary steps leading to dinosaurs and, ultimately, to bird…

Diplura: two‑pronged bristletails — biology, diversity and ecology Diplura Diplura are a small order of primitive, wingless hexapods known as two‑pronged bristletails. This article summarizes their anatomy, lifestyle, diversity, and role in soil ecosystem…

Directed evolution: iterative engineering of proteins and nucleic acids Directed evolution Directed evolution uses iterative cycles of mutation and selection to produce proteins, enzymes and functional RNAs with improved or novel properties for research, medicine and ind…

Display (zoology): animal signalling for courtship, rivalry and territory Display (zoology) Behaviours animals use to communicate fitness, intent or ownership—courtship displays, threat rituals, territorial signals and species recognition across taxa.

Dissection: anatomical examination by careful cutting Dissection Dissection is the methodical opening and separation of tissues to study internal structure, used in biology, medicine and research; it includes techniques, history, educational use…

Ditrysia: the major clade of moths and butterflies Ditrysia Ditrysia is the dominant clade of Lepidoptera whose females have two separate genital openings; it includes most moths and all butterflies and accounts for the vast majority of des…

DNA (deoxyribonucleic acid): structure, function and biological roles DNA DNA is the hereditary molecule that stores genetic information in living organisms. This article explains its structure, cellular organization, gene expression, replication, variat…

DNA construct: engineered nucleic acid segments for research and therapy DNA construct A DNA construct is an engineered nucleic acid sequence assembled to carry genes and regulatory elements for expression, silencing, or genetic modification in cells and organisms.

DNA damage theory of ageing Theory proposing that accumulation of unrepaired DNA damage drives physiological ageing; discusses mechanisms, evidence, mitochondrial vs nuclear roles, repair pathways and implica…

DNA methylation: epigenetic control of gene expression DNA methylation Addition of methyl groups to DNA bases—mainly cytosine—that influences gene activity without changing sequence; essential in development, cellular identity, imprinting and disease.

DNA polymerase: function, mechanism, diversity, and laboratory uses DNA polymerase DNA polymerases are enzymes that synthesize DNA strands, ensure genomic fidelity, participate in repair and recombination, and underpin techniques such as PCR and sequencing.

DNA repair: mechanisms, significance, and cellular pathways DNA repair Comprehensive overview of cellular processes that detect and correct DNA damage, major repair pathways, cellular responses, disease links and therapeutic relevance.

DNA replication: mechanism, components, and biological importance DNA replication DNA replication copies the genetic material before cell division. This article outlines the semi-conservative mechanism, key enzymes, organismal differences, historical context, an…

DNA virus A DNA virus carries deoxyribonucleic acid as its genetic material. This article explains their genome types, replication strategies, major families and medical relevance, and contr…

Docodonta: Mesozoic mammaliaforms with specialized molars Docodonta Docodonta are an extinct group of Mesozoic mammaliaforms known for complex molars, dentary jaws, and diverse ecologies including terrestrial and semi‑aquatic forms such as Castoroc…

Domain (biology): the highest rank in the classification of life Domain (biology) Domain is the highest taxonomic rank, grouping life into major clades (commonly Bacteria, Archaea, Eukarya). It reflects deep evolutionary divisions revealed by molecular data and…

Domestication: Origins, Processes, and Human Uses Domestication Domestication is the long-term genetic and behavioral change of wild species through human management, producing crops, livestock, pets, and ornamental plants adapted to people.

Dopamine reuptake inhibitor (DRI): mechanism, uses, and risks Dopamine reuptake inhibitor Dopamine reuptake inhibitors block the dopamine transporter to increase synaptic dopamine. This entry covers how they work, clinical uses and examples, safety concerns, and how the…

Dormancy in Living Organisms: Types, Mechanisms, and Ecological Roles Dormancy Dormancy is a reversible state of reduced metabolic activity adopted by many organisms to survive unfavorable conditions; this article explains forms, triggers, examples across lif…

Dorsal (anatomical term) Dorsal Dorsal describes the back or upper surface of an animal or body part. Used across zoology and human anatomy to indicate location relative to the back or upper side, contrasted with…

Dromaeosaurus Dromaeosaurus, a Late Cretaceous North American dromaeosaurid, is known for a robust skull, recurved serrated teeth and a stockier build than some relatives; fossils come from west…

Drosophila (fruit flies): biology, diversity, and scientific importance Drosophila Drosophila is a genus of small flies often called fruit or vinegar flies. Widely diverse, many species feed and breed on fermenting fruit; several are key model organisms in geneti…

Drosophila melanogaster — the common fruit fly Drosophila melanogaster A concise encyclopedia entry on Drosophila melanogaster: appearance, life cycle, history as a genetic model, research uses, husbandry, limitations, and distinctions from related sp…

Drosophilidae: the fruit fly family and its scientific importance Drosophilidae Drosophilidae is a cosmopolitan family of small flies with over 4,000 species. Best known for Drosophila melanogaster, they are foundational in genetics, development and ageing res…

Duct (anatomy): form, function, and clinical importance Duct A duct is a tubular structure that conveys secretions or fluids from glands or organs. This article explains structural features, types, functions, common examples and clinical iss…

Dunaliella salina — a salt‑tolerant microalga producing beta‑carotene and glycerol Dunaliella salina Halophilic green microalga that thrives in hypersaline ponds, accumulates beta‑carotene and glycerol, and is cultivated for pigments, supplements and studies of extreme‑environment…

Duodenum — the first segment of the small intestine Duodenum The duodenum is the initial short section of the small intestine where most chemical digestion begins; it receives bile and pancreatic secretions, neutralizes gastric acid, and beg…

Earliest known life forms on Earth Earliest known life forms Survey of the oldest evidence for life on Earth: fossil, chemical and geological signs, proposed timelines, habitats where early organisms lived, and implications for origins and a…

Ebola virus: overview, symptoms, transmission, history and prevention Ebola virus Ebola virus (Ebolavirus) causes Ebola virus disease, a severe hemorrhagic fever. This article explains its biology, symptoms, transmission, history, public-health response, treatme…

Ecdysozoa: the molting animals (arthropods, nematodes and allies) Ecdysozoa Ecdysozoa is a major clade of protostome animals united by ecdysis (molting). It includes arthropods, nematodes and several smaller phyla and is supported by molecular and morpholo…

Ecological genetics: genetics and evolution in natural populations Ecological genetics Study of genetic variation and evolutionary processes in wild populations, linking field observation with laboratory analysis to understand traits that affect survival and reproduc…

Ecological niche: role, types, and significance in ecosystems Ecological niche An ecological niche describes how a species fits into and uses its environment — its role, required resources, behaviors and interactions. Covers key concepts, history, types, exam…

Ectopic pregnancy: causes, diagnosis, treatment and risks Ectopic pregnancy Ectopic pregnancy occurs when a fertilized egg implants outside the uterine cavity. This article explains locations, symptoms, diagnosis, treatment options, risks and important dis…

Ediacaran biota: the earliest large multicellular organisms Ediacaran biota Enigmatic assemblage of late Precambrian soft-bodied organisms (Ediacaran Period). Fossils show unusual body plans and provide clues to early animal evolution and pre-Cambrian ecos…

Egg An egg is the reproductive body produced by many animals and a common human food—typically consisting of shell, membranes, albumen and yolk, serving roles in development, nutrition…

Egg (biology) A biological egg is the reproductive cell or structure that surrounds and nourishes an animal embryo. Eggs vary widely across animal groups in structure, protection, and developmen…