Biology

Melanin: pigment, production, functions, and clinical significance Melanin Melanin is a natural pigment produced by melanocytes that colors skin, hair and eyes and provides partial protection from ultraviolet radiation. Covers types, synthesis from tyrosi…

Melanocyte: pigment-producing skin cells and their roles Melanocyte Melanocytes are specialized cells that synthesize melanin, contributing to skin, hair and eye color and protecting against UV damage. This article covers structure, development, re…

Melatonin: role in circadian rhythms, biological action, uses, and safety Melatonin Melatonin is a naturally occurring hormone produced across life forms that signals night, helps regulate sleep and circadian timing, has antioxidant activity, and is commonly avail…

Membrane: biological barriers and synthetic films Membrane A membrane is a thin layer that separates spaces or phases. This article explains biological membranes (cellular and tissue), synthetic membranes, structure, functions, history, an…

Membrane protein Proteins that attach to or span biological membranes; they mediate transport, signaling, catalysis and structural roles, constitute a large fraction of genomes and are major drug t…

Mendelian inheritance: principles, history, and applications Mendelian inheritance Overview of Mendelian inheritance: the classical laws of segregation, independent assortment and dominance, Mendel's pea experiments, common examples, and known limitations in mode…

Meninges: Layers and Role in Protecting the Central Nervous System Meninges The meninges are three protective membranes that surround the brain and spinal cord, containing cerebrospinal fluid and playing key structural, immunological and clinical roles.

Menopause: causes, symptoms, stages, and management Menopause Menopause is the permanent end of menstruation caused by ovarian decline in reproductive hormones. This article explains stages, common symptoms, health effects, and management opt…

Menstrual cycle Recurring physiological cycle in reproductive-age people that prepares the uterus for pregnancy; includes bleeding, ovulation, hormonal regulation, and clinical variations.

Meselson–Stahl experiment: demonstration of semiconservative DNA replication Meselson–Stahl experiment Classic 1958 experiment by Meselson and Stahl using isotopic nitrogen and density-gradient centrifugation to show that DNA replication is semiconservative; outlines method, results…

Metabolic rate: definition, measurement, and biological importance Metabolic rate Metabolic rate is the speed at which organisms convert nutrients into usable energy. This article explains types, measurement methods, major influences, ecological roles and clinic…

Metabolism — the cellular chemical networks that sustain life Metabolism Comprehensive introduction to metabolism: the enzyme-driven chemical reactions and pathways that convert nutrients to energy and building blocks, their organization, evolutionary c…

Metacarpal bones: structure, function, and clinical importance Metacarpal bones Metacarpal bones are the five long bones forming the intermediate skeleton of the hand, linking fingers to the wrist. Article covers anatomy, development, function, common injuries…

Metalloprotein: proteins containing metal ion cofactors Metalloprotein Metalloproteins are proteins that incorporate metal ion cofactors. They perform catalysis, redox chemistry, transport, storage and regulation and make up a large and diverse fracti…

Metamorphosis: Biological transformation from juvenile to adult Metamorphosis Metamorphosis is the developmental process in which an animal changes its body form, often through distinct stages such as larva, pupa or nymph, to reach its adult morphology and l…

Metatarsal bones Five long bones in the foot that connect the tarsal bones to the toe phalanges; important for weightbearing, gait, and common sites of fracture and injury.

Metroid (species) Metroids are fictional parasitic organisms from Nintendo's Metroid series, known for draining bioenergy. They appear in several life stages and variants and serve as a recurring pl…

Microanatomy: the microscopic structure of tissues and cells Microanatomy Microanatomy examines the structures of cells, tissues and organ components using microscopes and preparation techniques; it underpins pathology, developmental biology and clinical…

Microbial cyst: dormant survival stage in microbes Microbial cyst A microbial cyst is a resting, thick-walled stage formed by many protozoa and some bacteria to survive adverse conditions; it permits transmission, environmental persistence, and l…

Microbial mats: layered communities of microorganisms Microbial mat Thick, multi‑layered assemblages of bacteria and archaea that form cohesive sheets on wet surfaces; ancient, chemically diverse ecosystems with roles in Earth's history and modern…

Microbiology — the study of microorganisms and their roles Microbiology Microbiology is the branch of biology that examines microorganisms — bacteria, archaea, viruses, fungi, protozoa and algae — including their structure, genetics, ecology and practi…

Microorganism Microscopic life forms—bacteria, archaea, protists, fungi and viruses—that inhabit nearly every environment, drive biogeochemical cycles, and play roles in health, industry and eco…

Microtubule Microtubules are hollow, filamentous polymers of tubulin that form part of the cytoskeleton; they give cells shape, enable intracellular transport, and drive motility and chromosom…

Microvillus and Microvilli: structure, function, distribution, and clinical notes Microvillus Microvilli are microscopic, actin-supported membrane projections that expand cell surface area for absorption, secretion and sensation. This article covers their structure, roles,…

Midge (small flies in several families) Midge Midges are a diverse informal group of small flies in the Nematocera. This article covers their appearance, life cycle, ecology, roles as pests and pollinators, and notable example…

Mimicry (biological imitation and deception) Mimicry Mimicry is the resemblance evolved between organisms or traits that gives an advantage by deception or signaling, common in insects, plants and animals and arising through natural…

Mimivirus Mimivirus is an unusually large virus first isolated from amoebae. It challenged definitions of viruses with its size, complex genome, and cellular-like features and influenced stu…

Mitochondria: structure, function, and roles in cellular metabolism Mitochondria Mitochondria are double-membraned organelles in eukaryotic cells that generate ATP, participate in metabolism and signalling, contain their own genome, and influence development, d…

Mitochondrial DNA (mtDNA) Mitochondrial DNA Mitochondrial DNA (mtDNA) is the small genome inside mitochondria that encodes components of cellular energy production. It is usually maternally inherited and important in medicin…

Mitosis: process, stages, and biological significance Mitosis A concise, neutral overview of mitosis: the organized division of a cell’s nucleus that produces two genetically identical daughter nuclei, its stages, components, roles, and diffe…

Mixotroph — organisms using multiple energy and carbon strategies Mixotroph A mixotroph is an organism able to obtain energy and carbon by more than one metabolic mode, switching or combining autotrophy and heterotrophy; common in microbes and some plants…

Mobile genetic elements Mobile genetic elements are DNA sequences that move within or between genomes, shaping evolution, spreading traits like antibiotic resistance, and serving as tools in genetics and…

Model organism (biological research) Model organism A model organism is a non-human species intensively studied to reveal biological processes applicable across life, used in genetics, development, medicine, and ecology with known l…

Modern evolutionary synthesis The modern evolutionary synthesis is the 20th-century integration of Mendelian genetics with Darwinian natural selection, forming a unified framework for understanding evolution, p…

Molar (tooth) — structure, function, development, and variation Molar Molars are large, complex teeth at the back of mammalian mouths used for crushing and grinding. This article covers their anatomy, development, variations across species, and commo…

Molecular biology: study of life’s processes at the molecular scale Molecular biology Molecular biology examines cellular molecules—DNA, RNA and proteins—their interactions, mechanisms of gene expression and regulation, historical development, techniques, and applic…

Molecular clock A method that estimates the timing of evolutionary divergences by comparing genetic or protein changes over time; used with calibration to infer lineage ages and rates of molecular…

Molecular cloning: methods, components, history and applications Molecular cloning An overview of molecular cloning: what it is, the main components and laboratory steps, historical development, modern techniques, common uses and safety considerations.

Molecular evolution: how DNA, RNA and proteins change through time Molecular evolution Examination of the processes that alter DNA, RNA and proteins across generations, combining molecular biology, population genetics, genomics and bioinformatics to explain divergenc…

Mollicutes: the wall-less bacteria (Mycoplasma, Spiroplasma, Phytoplasma) Mollicutes Mollicutes are a group of very small bacteria without a cell wall. They include Mycoplasma, Ureaplasma, Spiroplasma and Phytoplasma and are important parasites of humans, animals a…

Monocyte: circulating precursor immune cells that become macrophages and dendritic cells Monocyte Monocytes are circulating white blood cells that replenish tissue macrophages and dendritic cells, participate in phagocytosis, antigen presentation and inflammation, and are impor…

Monogenea: ectoparasitic flatworms of fish and other aquatic hosts Monogenea Monogenea are a class of small, primarily ectoparasitic flatworms (Platyhelminthes) that live on the skin, gills or fins of aquatic animals. They have direct life cycles and distin…

Monophyly in Evolutionary Biology: Defining Clades, Paraphyly, and Polyphyly Monophyly Overview of monophyly in evolutionary biology: what defines a clade and how paraphyly and polyphyly differ, with examples, classification implications, and molecular evidence.

Monoplacophora — limpet-like molluscs: fossil record, anatomy and rediscovery Monoplacophora Monoplacophora are cap-shelled, deep-sea molluscs known from Paleozoic fossils and a 20th-century rediscovery; notable for serially repeated organs and importance to molluscan evol…

Moraxella — a genus of Gram-negative bacteria Moraxella Moraxella is a genus of Gram-negative bacteria commonly found on mucous membranes; includes species such as M. catarrhalis associated with respiratory and ocular infections and not…

Moraxellaceae: a family of gram-negative bacteria Moraxellaceae Moraxellaceae is a family of gram-negative bacteria that includes environmental species and clinically important genera such as Moraxella and Acinetobacter, with roles in ecology,…

Morganucodon: an early mammaliaform and its role in mammal evolution Morganucodon Morganucodon is a small, early mammaliaform from the latest Triassic–earliest Jurassic. Known from abundant fossils, it shows a mix of primitive and mammalian traits important for…

Morphogenesis: the biological generation of form and pattern Morphogenesis Morphogenesis is the set of biological processes that produce an organism's shape and spatial cell organization during development, regeneration, and disease.