Biology

Morphology: the study of form and structure across disciplines Morphology Morphology examines shape and structural organization in language, biology, geology, architecture and other fields, tracing concepts, methods, examples, and how disciplines differ…

Morphology (biology) Morphology in biology studies the form and structure of organisms—their external shapes and internal anatomy—its methods, history, and role in taxonomy, development, medicine, and…

Mosaicism (genetics) Mosaic (genetics) Mosaicism: the coexistence of two or more genetically distinct cell lines in one individual from a single fertilized egg — causes, types, history, detection, and clinical importanc…

Mosaic evolution: uneven change of traits across lineages Mosaic evolution Mosaic evolution describes how different traits of organisms evolve at different rates and times, producing species that combine ancestral and derived features; commonly documented…

Mother: biological parent, caregiver, and social role Mother Overview of the term mother, covering biological reproduction, parenting roles, adoption and legal status, cultural significance, and distinctions such as stepmothers and surrogacy…

Motile: Biological Movement and Motility in Living Organisms Motile Motile describes the ability of an organism or cell to move under its own power. Covers mechanisms, examples across life, ecological and medical importance, and distinctions from s…

Motor system (neurobiology) Motor system The motor system coordinates voluntary and involuntary movement through descending pathways, modulatory networks (basal ganglia, cerebellum) and peripheral motor units; vital for a…

Mouth (oral cavity): structure, function, and social role Mouth The mouth is the external opening of the digestive tract in humans and many animals; it enables ingestion, chewing, speech, taste and social interaction.

Mouthparts: structures, types, and roles in animal feeding Mouthparts A concise overview of animal mouthparts: types, components, evolution, and ecological significance across major animal groups.

Mucus: composition, functions, and roles across animals and human health Mucus Mucus is a gel-like secretion rich in mucins that lubricates and protects surfaces, traps microbes and particles, and supports respiration, digestion, reproduction and locomotion a…

Multicellular organism: structure, reproduction, and diversity Multicellular organism An introduction to multicellular organisms covering organization from cells to tissues, evolutionary origins, reproductive strategies, examples, and key distinctions from unicellul…

Multiple birth: twins, triplets and higher-order multiples Multiple birth Multiple birth is a single pregnancy producing more than one infant. It includes twins, triplets and higher-order multiples, with distinct biological types, causes, risks, prenatal…

Murinae (Old World rats and mice) Murinae Murinae, the Old World rats and mice, are a diverse subfamily of Muridae with roughly 560 species found across Africa, Eurasia, and Australasia; they include familiar commensal spe…

Muscle: structure, function, types, and biological importance Muscle Muscle is animal tissue specialized for contraction. This article explains types (skeletal, cardiac, smooth), basic structure, physiology, development, common conditions, and roles…

Mutant: biological meaning, types, history, and cultural use Mutant A mutant is an organism, gene, cell, or protein changed from its ancestral form by a mutation. Covers biological mechanisms, categories, history, practical importance, and cultural…

Mutation: Causes, Types, Effects, and Role in Biology Mutation An overview of genetic mutation: what it is, how mutations arise, major types, biological consequences, their role in evolution and medicine, and basic detection and repair concept…

Mutualism: biological interactions in which both partners benefit Mutualism Mutualism is a form of interspecific interaction in which two organisms gain fitness benefits. It includes diverse ecological roles, types (obligate vs facultative), examples, hist…

Mycelium: structure, ecology, and practical uses Mycelium Mycelium is the vegetative network of a fungus formed from hyphae. This article explains its structure, growth, ecological roles, cultivation, and applications in food, remediation…

Myco-heterotrophy: Plants That Obtain Carbon from Fungi Myco-heterotrophy Myco-heterotrophy describes plants that derive some or all of their carbon and nutrients from fungi rather than from photosynthesis. Covers biology, evolution, examples, research m…

Mycobacterium: overview, biology, diseases and clinical significance Mycobacterium Mycobacterium is a genus of slow-growing, lipid-rich bacteria that includes agents of tuberculosis and leprosy, environmental species, and nontuberculous mycobacteria with importan…

Mycobacterium leprae — the bacterium that causes leprosy Mycobacterium leprae Mycobacterium leprae is an acid-fast bacterium that causes leprosy (Hansen's disease). It grows very slowly, resists standard culture, has a lipid-rich cell wall, and is treated wi…

Mycology: Biology, Ecology, Uses and Importance of Fungi Mycology Comprehensive overview of mycology: fungal structure and life cycles, ecological roles, history and classification, human uses, hazards, research areas and notable facts about fung…

Mycoplasma: tiny wall‑less bacteria and their medical significance Mycoplasma Mycoplasma are a group of the smallest free‑living bacteria, lacking cell walls and often parasitic. This article covers their biology, history, diseases, detection, treatment, and…

Mycoplasma genitalium A very small, cell-wall–lacking bacterium that colonizes the urogenital and respiratory tracts; important as a sexually transmitted pathogen and a model for minimal-genome research…

Myelin: structure, function, development, and clinical significance Myelin Myelin is the fatty, insulating sheath that surrounds axons and speeds nerve impulses. This entry covers its composition, formation, role in conduction, development, and disorders…

Myocyte (muscle cell): types, structure, development and function Myocyte Myocytes are the cells that make up muscle tissue. This article describes their types (skeletal, cardiac, smooth), structure, development (myogenesis), functions, regeneration and…

Myoglobin: structure, function, physiology and clinical significance Myoglobin Myoglobin is a heme-containing, oxygen-binding protein in muscle that stores and facilitates oxygen diffusion; it has roles in physiology, meat color, diving adaptations and as a c…

Myosin: the actin-based motor proteins of eukaryotic cells Myosin Myosins are a large family of ATP-dependent motor proteins that bind actin to produce force and motion in eukaryotic cells, with conserved structure and many specialized classes.

Myxobacteria: social, gliding soil bacteria that form multicellular fruiting bodies Myxobacteria Overview of myxobacteria: their taxonomy, social gliding motility, multicellular life cycle, ecological roles, genomes, and significance in research and biotechnology.

Myxobolus cerebralis — parasite causing whirling disease in salmonids Myxobolus cerebralis Myxobolus cerebralis is a microscopic myxozoan parasite that infects salmonid fish, causing whirling disease. It requires an aquatic worm host and has spread across continents, aff…

Nail (anatomy): structure, function, growth and care Nail (anatomy) Comprehensive overview of fingernails and toenails: anatomy, composition, growth patterns, evolutionary context, common disorders, basic care and clinical significance.

Nasal bone Paired bones forming the bony bridge of the nose; anatomy, development, clinical significance, and comparative notes for the human nasal bones.

Natural killer cell (NK cell) Natural killer cell Innate lymphocyte that recognizes and kills infected or transformed cells without prior sensitization; performs early cytotoxic and cytokine responses important for antiviral and a…

Natural killer T cell (NKT cell) Natural killer T cell NKT cells are a distinct T‑lymphocyte subset that share features with natural killer cells, recognize lipid antigens presented by CD1d, release cytokines rapidly, and influence inf…

Natural selection: the mechanism of adaptive evolution Natural selection Natural selection is the process by which heritable traits that improve survival or reproduction become more common in populations, driving adaptation and shaping biological divers…

Nautiloid (Nautiloidea): chambered cephalopods and their fossil legacy Nautiloid Nautiloids are shelled cephalopods in the subclass Nautiloidea, originating in the Cambrian and diverse in the early Palaeozoic. A few modern species survive; thousands of fossil s…

Neanderthal Genome Project Large-scale effort begun in 2006 to sequence Neanderthal DNA, reconstruct archaic genomes, and study their relationship to modern humans. It advanced methods for ancient DNA recove…

Neck (anatomy): structure, function, and clinical significance Neck (body part) The neck links the head and trunk and contains the cervical spine, major vessels, airway and digestive passages, muscles, nerves, lymphatic tissue, and skin.

Need: essentials for living—biological and psychological requirements Need Overview of needs: essential biological necessities versus nonessential wants, types of human needs, historical and scientific perspectives, and why distinguishing needs from wants…

Nematomorpha (horsehair worms) Nematomorpha Nematomorpha, or horsehair worms, are long, thin parasitic worms whose larvae develop in arthropods; adults are free-living in water and notable for manipulating host behavior.

Neoptera: the wing-folding insects Neoptera Neoptera is the clade of insects that can fold their wings over the abdomen. It includes most living winged orders and is defined by specialized wing articulation, diverse life cyc…

Neornithes: modern birds, diversity, and evolutionary significance Neornithes Neornithes is the crown group that includes all living birds and their descendants, encompassing roughly 9,000–10,000 species with wide ecological roles, distinctive anatomy, and a…

Neoteny: retention of juvenile traits through altered developmental timing Neoteny Neoteny is a form of heterochrony in which somatic development is slowed relative to reproductive maturation, producing adults that retain juvenile traits. It is relevant across an…

Neotominae — New World rats and mice (subfamily of Cricetidae) Neotominae Neotominae is a subfamily of New World cricetid rodents including deer mice, packrats, and grasshopper mice, found mainly in North America and important in ecology, research, and p…

Nephron: Structure, Function, and Clinical Significance of the Kidney's Functional Unit Nephron A clear overview of the nephron: its anatomy, physiological roles (filtration, reabsorption, secretion, concentration), types, development, and importance in health and disease.

Nephrozoa (Eubilateria): the major bilaterian clade of protostomes and deuterostomes Nephrozoa Nephrozoa, or Eubilateria, is the large bilaterian clade that unites protostomes and deuterostomes. This article explains its defining traits, evolutionary context, diversity, and…

Nerve (anatomy, function, and clinical significance) Nerve A nerve is a bundle of axons that transmits signals between the body and the central nervous system; this article explains structure, types, roles, and clinical relevance.

Nerve cord A nerve cord is the principal longitudinal bundle of nerve fibers in many animals: ventral and segmented in most invertebrates, dorsal and hollow in chordates, and enclosed as the…