Biology

Gorgonops — late Permian saber-toothed therapsid predator Gorgonops Gorgonops, a genus of gorgonopsian therapsids from the Late Permian, was a dominant carnivore with long canine teeth and mammal-like features. Fossils are known mainly from souther…

Gram staining (Gram's method) Gram staining A microbiological staining technique that classifies bacteria as gram-positive or gram-negative based on cell wall properties; widely used for identification and guiding clinical d…

Gram-negative bacteria Gram-negative Bacteria that do not retain crystal violet in the Gram stain due to an outer membrane and thin peptidoglycan layer; important for classification, clinical treatment, and innate imm…

Gram-positive bacteria: characteristics, classification and significance Gram-positive Overview of Gram-positive bacteria: how Gram staining works, cell envelope features, examples, clinical and industrial importance, and limits of the Gram classification.

Granule (cell biology) Small, often dense cellular structures visible by light microscopy. Includes secretory granules, storage granules and membrane-less ribonucleoprotein granules involved in secretion…

Granulocyte A type of white blood cell with cytoplasmic granules and a multilobed nucleus, involved in innate immunity. Includes neutrophils, eosinophils and basophils with distinct roles in i…

Granzyme: cytotoxic proteases in immune defense Granzyme Granzymes are serine proteases stored in cytotoxic lymphocyte granules that trigger death or dysfunction of infected or transformed cells; different granzymes have distinct targets…

Green algae Photosynthetic eukaryotes in several algal lineages, green algae are diverse aquatic and terrestrial organisms that share chlorophylls a and b and gave rise to land plants.

Green fluorescent protein Green fluorescent protein (GFP) is a naturally fluorescent protein used as a genetically encoded marker in biological research. This entry summarizes its structure, history, varian…

Green sulfur bacteria A group of obligately anaerobic, anoxygenic photoautotrophic bacteria that use hydrogen sulfide as an electron donor, possess unique chlorosomes, and play key roles in anoxic aquat…

Grey matter (central nervous system tissue) Grey matter Grey matter is tissue in the brain and spinal cord made of neuronal cell bodies and glia; it mediates processing, integration and reflexes and contrasts with white matter rich in m…

Gribble (Limnoriidae): marine wood‑boring isopods and their ecology Gribble Small pale marine isopods (family Limnoriidae) that bore into wood, seaweed and seagrass. Notable for producing endogenous cellulase enzymes, they can damage coastal timbers and ar…

Griffith's experiment (1928): transformation in bacteria Griffith's experiment A concise encyclopedia entry on Frederick Griffith's 1928 experiment showing bacterial 'transformation', its methods, interpretation, later confirmation, and significance for genet…

Growth factor (biological signaling proteins) Growth factor Proteins or peptides that regulate cell proliferation, differentiation, survival and migration by binding receptors and activating intracellular signaling pathways; important in de…

Growth hormone (somatotropin): roles, regulation, medical uses and risks Growth hormone Overview of growth hormone (GH), its production and mechanisms, physiological effects, clinical applications, diagnostic testing, and safety considerations.

Growth ring: structure, interpretation, and uses in biology and chronology Growth ring Growth rings are concentric layers produced during periodic growth in trees, corals, shells and some other organisms; they record age and environmental history and support dating a…

Grypania: an early tube-like fossil and its scientific significance Grypania Grypania is a Proterozoic tubular fossil, possibly the oldest known eukaryotic alga; its age, morphology and interpretation remain debated and important for understanding early mul…

Gut flora (gut microbiota): composition, functions, and health Gut flora An accessible overview of gut flora — the community of microorganisms in the digestive tract — covering composition, roles in health and disease, development, and notable distincti…

Habit (biology): Form and Behaviour of Organisms Habit (biology) Habit in biology denotes the typical form, growth pattern or behavioural tendencies of an organism. It covers plant growth forms, animal postures and recurring actions with ecologi…

Habitat: Definition, Types, Components, and Ecological Importance Habitat Habitat — the natural place where an organism lives — its physical and biological components, major types, differences from niche, and why habitats matter for biodiversity and cons…

Habituation (non-associative learning) Habituation Habituation is a basic form of learning in which an organism's response to a repeated, irrelevant stimulus decreases, allowing attention and behavior to focus on novel or important…

Haemocyanin — the copper-based oxygen carrier of many invertebrates Haemocyanin Haemocyanin is a large, copper-containing oxygen-transport protein found chiefly in molluscs and many arthropods. It circulates dissolved in haemolymph and turns blue when oxygenat…

Haemolymph: the circulatory fluid of arthropods and many molluscs Haemolymph Haemolymph is the blood-like fluid that bathes organs in most arthropods and many molluscs. It functions in transport, immunity and hydraulics within an open circulatory system.

Hair: structure, types, functions, and cultural uses Hair Overview of hair in mammals: composition, types (fur, wool, vellus, terminal), growth cycle, functions, evolution, human cultural roles and common uses of hair and fibers.

Hair follicle: structure, function, growth cycle and clinical relevance Hair follicle A hair follicle is a skin organ that produces hair. This article explains its anatomy, growth cycle, functions, clinical issues, and notable facts about development and regeneratio…

Hallux (Big Toe): Anatomy, Function, Evolution and Clinical Notes Hallux The hallux, or big toe, is the innermost and typically largest toe. This article covers its anatomy, role in gait, evolutionary variations, common conditions, and basic prevention…

Halophile — organisms adapted to salty environments Halophile Halophiles are organisms that require elevated salt concentrations to grow. This article covers their biology, habitats, adaptations, examples, and uses in biotechnology and ecolog…

Haplodiploidy: biology, occurrence, and evolutionary consequences Haplodiploidy Haplodiploidy is a genetic system where unfertilized eggs produce haploid males and fertilized eggs produce diploid females; it shapes kin relationships and social evolution in sev…

Haplogroup (genetics): maternal and paternal lineage groups Haplogroup Haplogroups are branches of the human genetic tree defined by shared inherited mutations on non-recombining DNA (Y-chromosome or mitochondrial DNA), used to track deep ancestry and…

Haploid: definition, biology, examples and significance Haploid Haploid describes a cell or organism with a single set of chromosomes. This article explains the concept, how it arises, examples in animals and plants, its role in life cycles, an…

Haplorhini (Dry-nosed Primates): Overview, Classification, and Significance Haplorhini Haplorhini are the 'dry-nosed' primates including tarsiers and all simians (New World monkeys, Old World monkeys and apes, including humans). This article covers traits, classifica…

Healing: biological processes, types, and clinical importance Healing An overview of healing processes in living organisms, explaining regeneration and repair, stages of tissue healing, factors that affect recovery, and medical implications.

Heart valve: structure, function, disorders and treatments Heart valve A heart valve regulates one-way blood flow through the heart. This article covers the main valves, their anatomy and mechanics, common diseases, diagnosis, and treatment approaches…

Helcionelloida — extinct early shelled molluscs Helcionelloida Extinct class of small, cap-shaped molluscs known from Cambrian 'small shelly' fossils. Important for the study of early biomineralization and mollusc origins; taxonomy revised by…

Helicobacter pylori: biology, disease, diagnosis and treatment Helicobacter pylori Helicobacter pylori is a spiral, urease-producing bacterium that colonizes the stomach lining and is a major cause of gastritis and peptic ulcers. This article covers its biology,…

Hematophagy: the biology and impact of blood-feeding animals Hematophagy Hematophagy is the practice of feeding on the blood of other animals. This article describes adaptations, examples, evolution, ecological and medical significance, and distinctions…

Hematopoiesis: formation and function of blood cells Hematopoiesis Hematopoiesis is the process by which blood cells are produced from hematopoietic stem cells, primarily in bone marrow; it underpins oxygen transport, immunity, and clotting and is…

Hemichordata: wormlike deuterostomes and their place in animal evolution Hemichordata Hemichordata are marine deuterostome animals including acorn worms and pterobranchs; they have simple body regions, fossil graptolites, and are important for understanding chordate…

Hemoglobin: Structure, Function, and Clinical Significance Hemoglobin Hemoglobin is the iron‑containing protein in red blood cells that reversibly binds oxygen and participates in gas transport. This article covers its structure, role, variants, and…

Heredity (Inheritance of Traits) Heredity Heredity is the biological transfer of traits from parents to offspring. This article summarizes mechanisms, classical and modern study methods, patterns of inheritance, epigenetic…

Hermaphrodite: biological meaning, types, and human context Hermaphrodite Overview of hermaphroditism in biology and mythology, its forms in animals and plants, historical origins, examples, and distinctions from intersex in humans.

Herpetology: the scientific study of reptiles and amphibians Herpetology Herpetology is the zoological discipline that studies reptiles and amphibians—their biology, diversity, evolution, behavior, and conservation across habitats worldwide.

Hershey–Chase experiment: demonstration that DNA is the genetic material Hershey–Chase experiment A 1952 pair of experiments by Alfred Hershey and Martha Chase using bacteriophages showed that DNA, not protein, is the material of heredity—an important milestone in molecular bio…

Heterobranchia — a diverse clade of snails and slugs Heterobranchia Heterobranchia is a major group of gastropod molluscs that includes marine, freshwater and terrestrial snails and slugs. It is morphologically varied and its internal relationships…

Heterochrony: changes in developmental timing and their evolutionary effects Heterochrony Heterochrony is the alteration in the timing or rate of developmental events. It explains many morphological differences between related species and is central to evolutionary deve…

Heterokonts (Stramenopiles): diversity, structure and ecological roles Heterokont Heterokonts, also called stramenopiles, are a major group of eukaryotes—mostly algae— including diatoms, brown seaweeds and oomycetes. They feature unequal flagella and shape globa…

Heterotroph A heterotroph is an organism that relies on organic compounds produced by other organisms for carbon and often energy, encompassing animals, fungi, many microbes, and diverse ecolo…

Heterozygote advantage Heterozygote advantage occurs when individuals with two different alleles at a gene locus have higher fitness than either homozygote, helping maintain genetic diversity through bal…