Audio Glossary

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  1. observations: With respect to the scientific method, facts learned by a scientist by observing that are used to formulate hypotheses.
  2. olfactory bulb: A part of the vertebrate brain that receives signals from the chemoreceptors lining the nasal passages and where some initial sorting of smells takes place prior to further processing elsewhere in the brain.
  3. omnivore: An organism that uses both plant and animal tissues as a source of nutrition.
  4. oncogene: A mutated gene that promotes excessive cell division, leading to cancer.
  5. oogenesis: The production of a mature ovum capable of being fertilized.
  6. open circulatory system: An internal transport system in which blood flows through the body cavity that surrounds the organs. Compare closed circulatory system.
  7. open ocean: An aquatic biome that covers the majority of Earth's surface and includes communities found in a shallow layer (100 to 200 meters deep) in which photosynthesis can occur, as well as in deeper waters where little light can penetrate.
  8. operator: In prokaryotes, a regulatory DNA sequence that controls the transcription of a gene or group of genes.
  9. opposable: In primates, of or referring to a thumb (or big toe) that moves freely and can be placed opposite other fingers (or toes).
  10. oral cavity: Another term for the mouth, where food first enters an animal's digestive system.
  11. order: The level in the Linnaean hierarchy that is above families and therefore comprises families, but that is below classes and so composes classes.
  12. organ: A self-contained collection of tissues, usually of a characteristic size and shape, that is organized for a particular function.
  13. organ of Corti: A structure in the cochlea of the inner ear that converts mechanical energy into a pattern of action potentials that vertebrates detect as sound.
  14. organ system: A group of organs that work together to carry out a particular function.
  15. organelle: A distinct, membrane-enclosed structure in a eukaryotic cell that has a specific function.
  16. organic compound: A carbon-containing compound of biological origin.
  17. organic farming: A method of farming that avoids the use of synthetic chemicals and genetically modified organisms.
  18. osmoregulation: The process of maintaining an internal water concentration that supports biological processes.
  19. osmosis: The passive movement of water across a selectively permeable membrane.
  20. osteocyte: A cell that either produces or reabsorbs the matrix of calcium and phosphorus compounds that makes up vertebrate bone.
  21. otolith: A dense crystal of calcium carbonate in the vestibular apparatus that indicates the direction of gravitational pull.
  22. outer ear: The outer portion of the mammalian ear, which consists of the pinna and the auditory canal and which funnels pressure changes from the environment to the eardrum.
  23. out-of-Africa hypothesis: A hypothesis stating that anatomically modern humans evolved in Africa within the past 200,000 years, then spread throughout the rest of the world. According to this idea, as they spread from Africa, modern humans completely replaced older forms of Homo sapiens, including advanced forms such as the Neandertals. Compare multiregional hypothesis.
  24. ovary: The reproductive structure in female animals that produces ova.
  25. oviduct: The release of an ovum from the ovary.
  26. ovulation: The release of an ovum from the ovary.
  27. ovum (pl. ova): The female gamete.
  28. oxidation: The loss of electrons by one atom or molecule to another. Compare reduction.
  29. oxidative phosphorylation: The shuttling of electrons down an electron transport chain in mitochondria that results in the production of ATP.
  30. oxygen-binding pigment: Any of various complex molecules used by animals to increase the oxygen capacity of their tissues.
  31. oxytocin: A hormone released by the pituitary gland that triggers, among other things, milk production in mammals.