Biology

Female: Biological role, characteristics, and social distinctions Female Overview of 'female' as a biological category and social term, describing reproductive roles, anatomical traits, plant and animal variations, health care, and distinctions from gen…

Femoral artery: anatomy, function, and clinical importance Femoral artery Major artery supplying the lower limb; origin, course, branches, surface landmarks, clinical uses and common problems including access for procedures and trauma management.

Femur (thigh bone): structure, function, and clinical significance Femur The femur is the long bone of the thigh connecting hip and knee. This article covers its anatomy, development, biomechanics, clinical importance, and variation across tetrapods.

Fermentation: biological process, history, and practical applications Fermentation Fermentation is a metabolic process cells use to extract energy from sugars without oxygen and a set of techniques for producing food, beverages and chemicals using microbes.

Fertility: Biological, Demographic and Agricultural Perspectives Fertility Fertility denotes the ability to produce living offspring or support growth. This entry describes biological fertility in humans and animals, soil fertility, measures, influences,…

Fertilization (biological process) Fertilization Fertilization is the fusion of two gametes to form a zygote, initiating development. It occurs across eukaryotes and includes diverse mechanisms such as internal/external fertiliza…

Fetus (developmental stage) Fetus The fetus is the prenatal stage of a developing animal after the embryonic period, characterized by rapid growth and organ maturation; in humans it extends from after embryogenesis…

Fibrinogen — blood-clotting protein and acute-phase reactant Fibrinogen Fibrinogen is a liver-made blood protein that converts to fibrin to form clots, links platelets, and acts as an acute-phase reactant; measured in diagnostics and important in bleed…

Fibroin: the structural protein of silk Fibroin Fibroin is the insoluble structural protein that forms the fibrous core of silk produced by silkworms and spiders. It has distinctive beta-sheet structure, notable mechanical prope…

Fibrous protein (scleroprotein): structure, types and biological roles Fibrous protein Fibrous proteins (scleroproteins) are elongated, mostly insoluble structural proteins—including keratin, collagen, elastin and fibroin—providing mechanical support, elasticity and…

Fibula: the slender bone of the lower leg Fibula The fibula is the thinner, lateral bone of the lower leg in humans and many tetrapods. It provides muscle attachments, lateral stability to the ankle and knee, and has clinical imp…

Fight-or-Flight Response: The Acute Stress Reaction in Animals and Humans Fight or flight response Overview of the fight-or-flight (acute stress) response: triggers, physiological changes, history, evolutionary purpose, clinical relevance, and distinctions from related responses…

Filamentation (bacterial cell elongation without division) Filamentation Filamentation is a bacterial response in which cells keep elongating but do not form division septa, often triggered by DNA damage, stress, antibiotics or nutritional changes; it a…

Filozoa: the clade linking animals and their closest unicellular relatives Filozoa Filozoa is the evolutionary group within Opisthokonta that contains animals and their nearest single-celled relatives (choanoflagellates and filastereans). It is central to studies…

Fimbria (fimbriae of the fallopian tube) Fimbria Fimbriae are fingerlike fringes at the ovarian end of the fallopian tube that help capture the ovulated ovum; this article explains their structure, function, development and clini…

Fin (hydrodynamic and aerodynamic surface) Fin A fin is a surface that produces lift, thrust or steering forces in a fluid. Found on fish, marine mammals and engineered vehicles, fins serve propulsion, control and stability rol…

Firmicutes Firmicutes are a major phylum of mostly Gram‑positive bacteria that include spore‑formers, lactic acid bacteria, common gut microbes and important pathogens and industrial species.

Fish farm (aquaculture): methods, species, history and environmental issues Fish farm Fish farms (aquaculture) are controlled rearing systems for fish and other aquatic organisms. This article explains methods, common species, history, uses, environmental concerns a…

Fish hatchery: purpose, operation, species, and environmental considerations Fish hatchery Comprehensive overview of fish hatcheries: how they operate, common species, uses (stocking, aquaculture, conservation), management practices, and environmental and policy issues.

Fitness (biology): reproductive success and evolutionary significance Fitness (biology) Biological fitness describes an organism's relative ability to survive and reproduce, contributing genes to future generations. Covers definitions, measures, causes, examples, and…

Flagellate A flagellate is a cell bearing one or more whip-like flagella. This article explains their structure, diversity across life, functions, evolutionary role, and differences from bact…

Flagellum — cellular locomotor and sensory appendage Flagellum A flagellum is a long, whip-like appendage used by many cells and microorganisms for propulsion and sensing. Prokaryotic and eukaryotic flagella are structurally distinct and serve…

Flaviviridae: an overview of the virus family Flaviviridae Flaviviridae is a family of enveloped, positive‑sense RNA viruses that includes mosquito- and tick-transmitted flaviviruses and non‑vector genera like Hepacivirus and Pestivirus, c…

Flavivirus: overview of the genus, biology, transmission and public health importance Flavivirus Flavivirus is a genus of enveloped, single-stranded RNA viruses that includes dengue, Zika, yellow fever and West Nile viruses. They are typically transmitted by mosquitoes or tick…

Fledge (avian development) Fledge Fledge describes the stage and process by which a young bird develops the feathers, muscles and behaviors necessary for flight; meanings and timing vary by species and context.

Flesh: anatomy, function, culinary use and cultural meanings Flesh Flesh refers to the soft tissues between skin and bone—muscle, fat and connective tissue—important in anatomy, medicine, food systems and many cultural expressions and idioms.

Flipper: aquatic limb and swim fin — form, function, and types Flipper A flipper is a flattened, paddle-like appendage used by animals and people for propulsion and steering in water. Covers anatomy, evolution, human swim fins, and differences from fi…

Folate (Vitamin B9): roles, sources, cooking effects and health importance Folate Folate (vitamin B9) is a water‑soluble vitamin essential for DNA/RNA synthesis, cell division and fetal development. Covers functions, dietary sources, cooking tips, deficiency sig…

Follicle-stimulating hormone (FSH) Follicle-stimulating hormone FSH is an anterior pituitary glycoprotein hormone that regulates gamete development and gonadal function in both sexes. It is central to fertility, sexual maturation, and is measur…

Food chain: how energy and nutrients move through ecosystems Food chain A food chain traces who eats whom in an ecosystem, showing producers, consumers, decomposers, and the flow of energy and matter. It highlights trophic levels, ecological roles, and…

Food web: ecological networks of feeding relationships and energy flow Food web A food web maps the complex feeding relationships among producers, consumers and decomposers, showing energy transfer, trophic structure, ecological roles, and how human actions al…

Foraminifera: single-celled protists with shells and a rich fossil record Foraminifera Foraminifera are mostly marine single-celled rhizarians with tests (shells). They play major roles in marine ecosystems, paleoceanography and biostratigraphy and show diverse morph…

Foreskin (prepuce): anatomy, function, development, and cultural aspects Foreskin The foreskin (prepuce) is a fold of skin protecting the glans penis in uncircumcised males. This article explains its structure, development, functions, common conditions, and cult…

Form taxon: classification by appearance rather than ancestry Form taxon A form taxon groups organisms by shared morphological features rather than by evolutionary relationships. Used in everyday language, paleontology and historical taxonomy, it highli…

Fragmentation (asexual reproduction) Fragmentation (reproduction) Fragmentation is an asexual reproductive process where an organism splits into parts that regenerate into complete individuals; it occurs in some algae, fungi, plants and many anim…

Francisella — bacterial genus containing the agent of tularemia Francisella Francisella is a genus of small, Gram-negative bacteria in the family Francisellaceae. It includes species such as F. tularensis that cause tularemia and relatives found in environ…

Francisella tularensis Francisella tularensis is a highly infectious, gram-negative bacterium that causes tularemia. It infects many animals and humans, can spread by ticks or aerosols, and is a recogniz…

Frenulum (frenum): anatomical fold in humans and animals Frenulum A frenulum (or frenum) is a small fold of mucous membrane or tissue that restricts movement of a mobile part. Common types include the lingual and labial frenula, penile frenulum,…

Freshwater Biology: Life and Processes in Inland Waters Freshwater biology Study of organisms, communities and processes in non‑marine waters — rivers, lakes, ponds, wetlands and engineered systems — with emphasis on ecology, monitoring, management and co…

FrogWatch — citizen science programs for monitoring frogs and toads FrogWatch FrogWatch refers to several citizen science initiatives in which volunteers record amphibian calls and environmental data to help monitor populations, biodiversity, and environment…

Frontal bone — anatomy, development, function and clinical significance Frontal bone The frontal bone forms the forehead and the roof of the eye sockets. This article covers its parts, development, evolutionary variation (including Neanderthal browridges), and clin…

Frontal lobe: anatomy, functions, and significance Frontal lobe Overview of the frontal lobe in mammals, its main regions and roles (motor control, decision-making, social behavior), development, clinical relevance, and notable distinctions.

Function (biology) An overview of biological function: definitions, philosophical accounts, examples in organisms, evolutionary origins, medical relevance, and how function differs from purpose.

Fungi lacking known sexual stages: history, classification, and examples Fungi imperfecti Fungi lacking documented sexual stages — history of the Deuteromycota label, modern molecular reclassification, and notable examples with roles in medicine, food production, agricu…

Fungus: biology, forms, ecology, and human uses Fungus An overview of fungi: their structure, life cycles, ecological roles, history, and the ways people study and use them.

GABA: the brain’s primary inhibitory neurotransmitter GABA Overview of gamma‑aminobutyric acid (GABA): chemistry, synthesis, receptors, physiological roles, clinical importance and pharmacology in the nervous system.

Gallbladder — structure, function, and clinical significance Gall bladder Compact overview of the human gallbladder: anatomy, role in digestion, common disorders, and clinical considerations.

Gamete (sex cell) Gamete A gamete is a haploid reproductive cell that fuses with another gamete during sexual reproduction. Gametes arise by meiosis, vary in form across species, and are central to heredit…