Biology

Crypsis (biological concealment and detection avoidance) Crypsis Crypsis describes the strategies and traits organisms use to avoid detection or recognition by other organisms, including visual, chemical and auditory methods such as camouflage,…

Cryptomonads (Cryptophyta): small flagellate algae with complex plastids Cryptomonad Cryptomonads are mostly unicellular, flagellated algae found in fresh, brackish, and marine waters. Many contain complex chloroplasts with a nucleomorph and can be photosynthetic,…

Cryptosporidium: overview, transmission, diagnosis, treatment, and prevention Cryptosporidium Cryptosporidium is a microscopic protozoan that causes diarrheal illness. This article covers its biology, transmission routes, clinical effects, laboratory diagnosis, treatment op…

Cryptozoology: study of hidden, unverified, and rediscovered animals Cryptozoology Cryptozoology examines reports and legends of animals whose existence is unproven or disputed, exploring methods, history, notable examples, and the scientific and cultural controv…

Ctenophore (comb jellies) Ctenophore Ctenophores, or comb jellies, are gelatinous marine animals with eight rows of cilia and sticky colloblasts. They occur worldwide, from surface plankton to deep seas, and occupy im…

Cunnilingus: anatomy, practice, history and safety Cunnilingus Cunnilingus is oral stimulation of the female genitals. This article explains anatomy, common approaches, health and safety considerations, cultural history, and communication and…

Cuticle: outer protective layer in plants, animals, and other organisms Cuticle Cuticle is a protective outer layer found across many organisms — from plant leaf waxes to arthropod exoskeletons and the human nail fold — serving roles in water retention, defens…

Cuttlebone: structure, function and human uses Cuttlebone Cuttlebone is the lightweight, porous internal support of cuttlefish made mainly of calcium carbonate. It aids buoyancy and is used by humans for pet calcium supplements, polishing…

Cyanobacteria: photosynthetic bacteria that transformed Earth's atmosphere Cyanobacteria Cyanobacteria are a diverse group of photosynthetic bacteria (once called blue‑green algae) important for oxygen production, nitrogen fixation, ancient stromatolites and modern eco…

Cycliophora: tiny commensal animals and their unique phylum Cycliophora Cycliophora are a microscopic phylum of animals (genus Symbion) living on cold‑water lobsters. They have a distinctive body plan and complex life cycle and were discovered and desc…

Cycloneuralia Cycloneuralia is a proposed assemblage of ecdysozoan animals characterized by a circumpharyngeal nerve ring. It includes scalidophoran and nematoid groups and is important for stud…

Cyclostomes: the jawless fishes (lampreys and hagfish) Cyclostome Cyclostomes are the living jawless fishes — lampreys and hagfish. This article explains their anatomy, evolution, ecology, and significance as the only extant Agnatha.

Cyst: definition, structure, common types, causes, diagnosis and treatment Cyst A cyst is a closed sac with a distinct membrane that can occur in many tissues. This article covers its structure, causes, common examples, diagnostic steps, treatment options and…

Cytochrome: hemoproteins that mediate biological electron transfer Cytochrome Cytochromes are heme-containing proteins that shuttle electrons in respiration and photosynthesis, participate in redox chemistry, and include diverse families such as respiratory…

Cytogenetics: study of chromosomes, karyotypes, and cell division Cytogenetics Cytogenetics is the field that analyzes chromosome structure and behavior in cells, combining microscopy and molecular methods to diagnose genetic disorders, study cancer, and expl…

Cytokine Small proteins and glycoproteins that mediate intercellular signaling in immunity, inflammation, and development; act locally or systemically and are detected or manipulated in dia…

Cytokinesis: separation of the cell cytoplasm after nuclear division Cytokinesis Cytokinesis is the process that partitions a cell's cytoplasm to form two daughter cells after mitosis or meiosis. Mechanisms differ between animal, plant and microbial cells and a…

Cytokinins: plant hormones that regulate growth and development Cytokinin Cytokinins are plant hormones that promote cell division, influence organ formation and delay senescence; they occur naturally and synthetically and are widely used in research and…

Cytology: the study of cells, their structure, function and clinical importance Cytology Cytology is the scientific study of cells—their form, internal structures, behavior, and role in organisms and medicine, including microscopy techniques and diagnostic applications…

Cytoplasm: structure, composition and cellular roles Cytoplasm The cytoplasm is the gel-like interior of a cell that surrounds the nucleus, contains organelles and the cytoskeleton, and provides the medium for metabolism, transport and structu…

Cytoplasmic streaming (protoplasmic streaming) Cytoplasmic streaming Cytoplasmic streaming is the directed flow of cytoplasm within cells — a motor-driven process that redistributes organelles, nutrients and signals, especially in large plant and an…

Cytosine Cytosine is a pyrimidine nucleobase found in DNA and RNA, pairing with guanine. It is chemically reactive (deaminates to uracil) and is a central substrate in epigenetic methylatio…

Cytoskeleton: cellular framework of structure, movement and transport Cytoskeleton The cytoskeleton is a dynamic protein network in cells that provides shape, mechanical support, intracellular transport, motility and a scaffold for division and signaling.

Cytosol (intracellular fluid): composition, functions, and significance Cytosol The cytosol is the aqueous part of the cell interior where many metabolic reactions, signaling events, and dynamic assemblies occur; this article explains its composition, properti…

Cytotoxic T cell (CD8+ T lymphocyte) Cytotoxic T cell A cytotoxic T cell is a type of T lymphocyte that recognizes peptide antigens on MHC I and kills infected, malignant, or damaged cells via targeted cytotoxic mechanisms.

Darwinism: theory, history, and modern meanings Darwinism Darwinism denotes ideas originating with Charles Darwin about evolution by natural selection and later scientific developments; the term's use has shifted and is sometimes extended…

Database of Molecular Motions A curated resource that catalogs and illustrates conformational changes in proteins and some RNAs, classifying motion types and providing animations, examples, and links to structu…

Death: biological end of life, medical definitions, and cultural responses Death An overview of death as the cessation of biological life, medical criteria and investigation, common causes, and the cultural and religious beliefs and practices that surround huma…

Decomposer (ecology) Decomposer Organisms, primarily bacteria and fungi, that break down dead organic matter into simpler molecules and recycle nutrients, supporting soil health and ecosystem processes.

Decomposition: Biological and Chemical Breakdown of Organic Matter Decomposition Process by which organic material is broken down by biological, chemical, and physical means; covers microbial and fungal action, animal consumers, environmental controls, ecologic…

Defecation: physiology, health, and sanitation Defecation Defecation is the final stage of digestion when the body expels feces. This article covers physiology, stool characteristics, disorders, diagnostic uses, and public-health and cult…

Defence against predators: strategies, evolution, and examples Defence against predators Comprehensive review of how animals and plants avoid being eaten: physical, chemical, behavioural and group defences, evolutionary causes, ecological roles, trade-offs and notable…

Defensin — small antimicrobial peptides in animals and plants Defensin Defensins are short cationic host-defense peptides found in animals and plants. They disrupt microbial membranes, act against bacteria, fungi and viruses, and play roles in innate…

Deinococcus radiodurans — exceptionally radiation‑resistant bacterium Deinococcus radiodurans Deinococcus radiodurans is a nonmotile, red-pigmented bacterium notable for extreme tolerance to ionizing radiation, desiccation and DNA damage; studied for its repair systems and…

Deinococcus–Thermus: radiation‑resistant and thermophilic bacteria Deinococcus–Thermus A concise overview of the Deinococcus–Thermus bacterial phylum: key traits, ecology, notable genera, uses in biotechnology, and taxonomic background.

Demosponge (Class Demospongiae) Demosponge Demosponges are the largest and most diverse class of sponges, characterized by skeletons made from spongin, silica spicules, or both; they play key ecological and biotechnological…

Dendrite: structure, function, development, and biological significance Dendrite Dendrites are branched neuronal projections that receive and integrate synaptic input, enabling electrical signaling, plasticity, and complex computation across nervous systems.

Dendritic cell: antigen-presenting sentinels of the immune system Dendritic cell Dendritic cells are professional antigen-presenting leukocytes that link innate and adaptive immunity. They detect, process and display antigens, directing responses in infection,…

Dendrology: the study of trees and other woody plants Dendrology Dendrology is the branch of botany that focuses on trees, shrubs and lianas — their identification, classification, structure, and role in ecosystems and human use.

Dental formula: notation and meaning of mammal teeth counts Dental formula A dental formula is a concise way to record the number and types of teeth in one side of a mammal's mouth. This article explains the notation, examples, calculation of totals, and…

Dental pulp: structure, function, development, and clinical importance Dental pulp Dental pulp is the soft, living tissue at a tooth's core. This article covers its anatomy, cells, roles in sensation and dentin formation, common diseases, treatments, development,…

Denticles (tooth serrations): form, function, and significance Denticle (teeth) Small serrations or bumps along a tooth's cutting edge used for slicing food and for identifying fossil teeth in paleontology.

Dentin: structure, formation, and clinical significance Dentin Dentin is the calcified tissue forming the bulk of a tooth beneath enamel and surrounding the pulp. This article explains its composition, development, types, function, and dental…

Dentition: types, development, and biological significance Dentition Overview of dentition: tooth types, dental formulas and development, tooth anatomy and variation across vertebrates, evolutionary adaptations, clinical relevance, and uses in paleo…

Deomyinae: the African spiny‑ and brush‑furred mouse clade Deomyinae Deomyinae is a small subfamily of muroid rodents (four genera, ~36 species) united by genetic evidence. Includes spiny mice (Acomys), the link rat (Deomys) and brush‑furred genera;…

Deoxyribose: the sugar of DNA Deoxyribose Deoxyribose is a five‑carbon sugar that forms the central sugar component of DNA. It differs from ribose by lacking a 2′ hydroxyl group, which influences structure, stability, and…

Detritivore: organisms that consume and break down dead organic matter Detritivore Detritivores are organisms that consume dead organic matter, fragment it and accelerate decomposition; they support nutrient cycling, soil formation, carbon flow and many ecosystem…

Detritus: non-living organic particulate matter in ecosystems Detritus Detritus is dead organic matter — fragments, feces and decaying tissue — that fuels decomposition, nutrient cycling and food webs in terrestrial and aquatic environments.