Biology
Articles about living organisms, life processes and biological research.
Oomycete
Oomycete (water mold): biology, life cycle, and impact
Oophorectomy
Opisthokont
Opisthokonts: animals, fungi and their unicellular relatives
Opsin
Opsin — light-sensitive proteins that mediate photoreception
Optic nerve
Optic nerve (cranial nerve II)
Optic tectum
Optic tectum: structure, function, and evolutionary roles
Optic tract
Optic tract (visual pathway segment)
Order (biology)
Organ
Organ (biology, musical instrument, and institutional uses)
Organ (anatomy)
Organ donation
Organ system
Organelle
Organic
Organic: Concepts in Chemistry, Biology, and Agriculture
Organism
Organism: definition, features, organization, and borderline cases
Organotroph
Origin of birds
Origin of Birds: Evolutionary Transition from Theropod Dinosaurs
Origin of life
Ornithology
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Orthomyxoviridae
Orthomyxoviridae: family of segmented negative-strand RNA viruses
Orthomyxoviridae are enveloped, segmented negative-sense RNA viruses including influenza A, B and C, thogotoviruses and isaviruses. They infect birds, mammals, fish and some arthro
Orthonectida
Osmoregulation
Osmoregulation: how organisms control water and salt balance
Osmosis
Ossicles
Osteichthyes
Osteichthyes — the bony fishes
Osteoarthritis
Osteology
Osteoporosis
Ostreoida
Outbreak
Outcrossing
Ovary
Ovary — structure, function, and variation in animals
Ovipositor
Ovipositor: insect egg-laying organ and its forms
Ovum
Ovum (egg) — the female reproductive cell
Oxytocin
Oxytocin: the peptide hormone and neuropeptide
p53
p53 (TP53): the tumor suppressor and guardian of the genome
Palaeoptera
Palaeoptera — primitive winged insects that do not fold their wings
Palate
Palate (anatomy): structure, function, development and clinical notes
Palatine bone
Paleobiology
Paleobiology: study of ancient life and its biological context
Paleozoology
Paleozoology: study of ancient animal life and fossils
Palynology
Palynology: study of pollen, spores and microscopic particles
Pancreas
Pandoravirus
Pandoravirus: giant amoeba-infecting viruses with exceptionally large genomes
Paramecium
Paramecium: a common ciliate protist
Paramyxovirus
Paranasal sinuses
Paranasal sinuses: structure, function, development, and clinical relevance
Paraphyly
Paraphyly in biological classification