Biology
Articles about living organisms, life processes and biological research.
Reproductive isolation
Reproductive isolation: mechanisms and its role in speciation
Reptile
Reptile — overview, characteristics, evolution, and major groups
Reptiles are a diverse group of largely terrestrial, scaly, egg-laying vertebrates. This article explains their defining traits, evolutionary history, major living and extinct grou
Reptiliomorpha
Reptiliomorpha — early tetrapods on the amniote stem
Respiration
Cellular respiration: how organisms convert nutrients into usable energy
Respiratory arrest
Respiratory arrest: causes, signs, emergency care, and prognosis
Respiratory droplet
Respiratory failure
Respiratory failure — causes, types, diagnosis and management
Respiratory system
Respiratory tract
Resting potential
Restriction enzyme
Restriction enzyme (restriction endonuclease)
Rete testis
Rete testis: anatomy, function and clinical significance
Retina
Retina: structure, function, and clinical importance
Retrovirus
Reverse transcriptase
Rhinovirus
Rhinovirus: biology, symptoms, transmission and prevention
Rhipidistia
Rhipidistia — lobe-finned fishes ancestral to tetrapods
Rhizaria
Rhizaria: diverse amoeboid eukaryotes including foraminifera and radiolaria
Rhizobia
Rhizobia: nitrogen‑fixing bacteria that form symbiotic nodules on legumes
Rib
Rib (anatomy): structure, function, development and cultural notes
Rib cage
Rib cage (thoracic cage) — structure, function, and clinical notes
Riboflavin
Ribonuclease
Ribonuclease (RNase) — enzymes that degrade RNA
Ribose
Ribose: structure, biological roles, and uses of the five‑carbon sugar
Ribosome
Ribosome: the cellular machine that builds proteins
Ribozyme
Ricin
Rickettsia
RNA
RNA (ribonucleic acid): Structure, Types, and Biological Roles
RNA interference
RNA interference: cellular gene-silencing by small RNAs
RNA polymerase
RNA polymerase: function, types, mechanism, and biological importance
RNA splicing
RNA splicing: processing of pre-mRNA into mature messenger RNA
RNA vaccine
Messenger RNA (mRNA) vaccines: principles, development, and uses
RNA virus
Robert Brown
Robert Brown (1773–1858): Scottish botanist and pioneer of plant microscopy
Rod cell
Rod cell — the retina's low‑light photoreceptor
RuBisCO
Salinibacter ruber
Saliva
Saliva: composition, production, functions, and clinical importance
Salivary gland
Salivary glands
Salmonella
Salmonella enterica
Salmonella enterica: biology, disease, and public health
Saprophyte
Saprophyte (saprotroph): organisms that decompose dead organic matter
Sarcoidosis
Satellite DNA
Satellite DNA: structure, roles, and biological significance
Sauropsid
Sauropsida: the reptile-and-bird clade of amniote vertebrates