Biology

Coccyx (Tailbone): Structure, Function, and Clinical Significance Coccyx Small triangular bone at the base of the spine formed by fused vertebrae; provides pelvic floor and sitting support, site of muscle attachments, and a focus of coccydynia and child…

Cochineal (Dactylopius coccus): the insect source of carmine dye Cochineal Cochineal is a scale insect (Dactylopius coccus) whose carminic acid produces carmine, a longstanding natural red dye obtained from insects that live on prickly pear cacti.

Cochlea: anatomy, function, and clinical significance Cochlea The cochlea is the spiral, auditory portion of the inner ear that converts sound vibrations into nerve signals. This article covers its structure, fluids, sensory cells, evolution,…

Cocoon (insect pupal case) Cocoon A cocoon is a protective casing spun by many moth caterpillars and other larvae, often made of silk; used for pupation and, in some species, harvested for textile production.

Coelenterata: historical grouping of Cnidaria and Ctenophora Coelenterata Coelenterata was an older name for a simple aquatic animal group now split into Cnidaria (jellyfish, corals) and Ctenophora (comb jellies) after molecular and genetic studies clari…

Coevolution: reciprocal evolutionary change between interacting species Coevolution Coevolution is reciprocal evolutionary change driven by ecological interactions between species, including mutualisms, antagonistic arms races and diffuse networks that shape trait…

Collagen: structure, types, biological roles and common uses Collagen Collagen is the most abundant structural protein in animals, forming triple‑helical fibrils in skin, bone, cartilage, tendons and other connective tissues; used in medicine, food a…

Colon (anatomy) — structure, function, and clinical significance Colon The colon is the largest portion of the large intestine between the cecum and rectum. It absorbs water and electrolytes, hosts microbiota, forms feces, and is central to several co…

Colony (biology) A biological colony is a group of individuals of the same species that live together and interact closely, from loose aggregations to highly integrated modular organisms with share…

Colour vision: how organisms detect and interpret hue Colour vision Colour vision is the sensory ability to distinguish light by wavelength. This article explains mechanisms, variations across species, colour constancy, applications and notable dis…

Commensalism: biological interactions where one species benefits and the other is unaffected Commensalism Commensalism is an ecological relationship in which one organism benefits while the other experiences little or no effect. It contrasts with mutualism and parasitism and includes f…

Common descent (evolutionary concept) Common descent Common descent is the principle that organisms share ancestry, forming a branching tree of life supported by fossils, anatomy and molecular data; the concept underpins modern evolu…

Common name (vernacular name) Common name A common name is a non-scientific, language-dependent name used by the public for an organism or taxon. It varies by region, may be ambiguous, and differs from standardized scienti…

Comparative anatomy: structure, methods, history, and applications Comparative anatomy Comparative anatomy compares animal form and structure to infer function, development and relationships, using dissection, microscopy, collections and modern imaging and molecular…

Competition (biology) Interaction in which organisms or species reduce each other's fitness by using or defending limited resources; includes exploitative and interference forms and shapes ecological an…

Complement system Collection of blood proteins that augment antibodies and phagocytes to detect, mark, and destroy microbes; a central effector of innate immunity with roles in inflammation and dise…

Complementarity in molecular biology Complementarity (molecular biology) Complementarity describes how nucleic acid bases pair (A with T/U, C with G) to form double-stranded structures and enable replication, transcription, hybridization and many lab te…

Compound eye A compound eye is an arthropod visual organ made of many ommatidia. It provides a wide field of view, excellent temporal resolution, and in some species color and polarization sens…

Computational biology: algorithms, models and applications Computational biology Study of biological problems using algorithms, statistical models and computational tools; integrates biology with mathematics, engineering and computer science for research and pr…

Cone cell (photoreceptor): structure, function and role in color vision Cone cell Cone cells are retinal photoreceptors that mediate daytime vision, high spatial acuity and color discrimination. This article covers their anatomy, physiology, spectral types, dist…

Conjoined twins Conjoined twins are monozygotic twins physically joined at birth. This article explains causes, common types, diagnosis, medical and ethical issues, and notable historical examples…

Connective tissue: structure, types, functions and significance Connective tissue Overview of connective tissue: its composition (cells, fibers, extracellular matrix), major types (embryonic, proper, special), typical examples, functions, and notable facts about…

Conodonts: extinct tooth-bearing chordates important to paleontology Conodont Conodonts were small, eel-like marine chordates known from phosphatic tooth-like elements. Once enigmatic, they are now regarded as early vertebrate relatives and are key fossils f…

Conoidasida — apicomplexan protists with a conoid Conoidasida Conoidasida is a group of parasitic protists in the phylum Apicomplexa, distinguished by an apical conoid. Members include coccidia; they have complex life cycles and are important…

Conosa: subphylum of Amoebozoa including slime molds and archamoebae Conosa Conosa is a major subphylum of Amoebozoa that includes slime moulds and amitochondriate amoebae; it contains model organisms, parasites and diverse soil and aquatic species.

Conserved sequence: definition, detection, and biological significance Conserved sequence A conserved sequence is a stretch of DNA, RNA, protein, or other biomolecule that remains similar across species. This article explains what conserved sequences are, how they are i…

Contractile vacuole: osmoregulatory organelle in freshwater protists Contractile vacuole Contractile vacuole in freshwater protists expels excess water to maintain osmotic balance; this article explains its structure, ion-driven pumping mechanisms, and role in cellular…

Convergent evolution: independent emergence of similar traits Convergent evolution Convergent evolution describes unrelated organisms evolving similar traits in response to comparable environmental pressures, producing analogous structures and affecting how we in…

Coral bleaching: causes, process, impacts, and resilience Coral bleaching Coral bleaching is the loss of symbiotic algae from reef-building corals, driven primarily by heat stress and other environmental factors; it threatens reefs, biodiversity, and coa…

Clavarioid (coral) fungi: branching, club-shaped and forked mushroom forms Coral fungi Overview of clavarioid (coral) fungi: upright, branching, forked or club-shaped mushrooms with varied colors and rubbery textures; covers ecology, identification, and how similar f…

Coral reef — structure, ecology, and conservation Coral reef Coral reefs are underwater ecosystems built mainly by stony corals. This article describes their structure, formation, biodiversity, human uses, threats, and conservation, with not…

Cork cambium (phellogen): structure, function and role in plant secondary growth Cork cambium Cork cambium (phellogen) is a lateral meristem that generates protective cork in many vascular plants; this article explains its structure, origin, functions, occurrence and practi…

Coronaviridae: family of enveloped positive-sense RNA viruses Coronaviridae Coronaviridae are enveloped, positive-sense single-stranded RNA viruses with large genomes and distinctive surface spikes. They infect a wide range of vertebrates and include impor…

Coronavirus: biology, disease spectrum, and public health implications Coronavirus An overview of coronaviruses: their structure, genetics, host range, notable human diseases (SARS, MERS, COVID‑19), history, transmission, and relevance to public health and resear…

Corpora cavernosa: structure, function and clinical significance Corpora cavernosa The corpora cavernosa are paired erectile tissues present in male and female genitalia. This article explains their anatomy, physiology, development, and common clinical conditions…

Corpus callosum: structure, function, development and clinical significance Corpus callosum The corpus callosum is the largest cerebral commissure in placental mammals, linking left and right hemispheres to enable interhemispheric communication, coordination, and transfer…

Cortisol: the body’s primary glucocorticoid Cortisol Cortisol is a steroid glucocorticoid produced by the adrenal glands. It regulates metabolism, the stress response, inflammation and immune activity and is important in many medical…

Cosmopolitan distribution Cosmopolitan distribution describes species or taxa found across most of the world, often due to wide ecological tolerance, dispersal ability, or human influence.

COX-2 inhibitors: selective anti-inflammatory drugs — uses, risks, and history COX-2 inhibitors Selective inhibitors of cyclooxygenase‑2 (COX‑2) reduce inflammation and pain with less gastric irritation than nonselective NSAIDs but carry cardiovascular and renal risks; histor…

Cranial nerve: structure, function, and clinical significance Cranial nerve Cranial nerves are paired nerves emerging from the brain or brainstem that carry sensory, motor and autonomic signals for the head, neck and some thoracic or abdominal structures.

Cricetidae: hamsters, voles, lemmings and New World rats and mice Cricetidae Cricetidae is a diverse family of rodents—hamsters, voles, lemmings, and New World rats and mice—found across the Americas, Europe, and Asia, with nearly 600 species and important…

CRISPR: bacterial defense system and genome-editing technology CRISPR CRISPR is a family of DNA sequences and associated proteins used by bacteria as adaptive immunity and harnessed as a precise genome-editing tool in biology and medicine.

Crop (anatomy) A crop is an expanded, thin-walled part of the alimentary tract used for temporary food storage in various animals, notably many birds, some invertebrates, and certain extinct dino…

Crop milk: the avian nutritive secretion produced in the crop Crop milk Crop milk is a nutrient-rich, regurgitated secretion produced in the crop of certain birds (notably pigeons, flamingos and some penguins) to feed and protect very young chicks.

Crossing over (genetic recombination during meiosis) Crossing over Crossing over is the exchange of chromosome segments between homologous chromatids during meiosis, creating recombinant gametes, promoting genetic diversity, and aiding correct chr…

Crown group (cladistics and phylogenetics) Crown group A crown group is the clade formed by all living members of a lineage, their most recent common ancestor, and all descendants; used to distinguish extant-bearing clades from purely…

Crurotarsi: the ankled archosaurs and the crocodile-line assemblage Crurotarsi Crurotarsi is a historical name for the archosaur group defined by a distinctive crurotarsal ankle. The term covers crocodile-line relatives, many Triassic fossils, and reflects ch…

Crying: causes, types, physiology, social role, and clinical aspects Crying Overview of crying as tear shedding linked to emotions, its physiological mechanisms, evolutionary and social functions, distinctions from reflex tears, and clinical considerations…