Audio Glossary

You need Adobe Flash Player to listen to the pronunciations.

  1. B cell: A lymphocyte that produces antibodies.
  2. Bacteria: A domain of microscopic, single-celled prokaryotes that were the first organisms to arise.
  3. bacterial flagellum (pl. flagella): A rotary motor unique to bacteria that, in response to the flow of hydrogen ions across the bacterial plasma membrane, propels a bacterium. Compare eukaryotic flagellum
  4. bark: The protective outer covering of stems in woody plants that contains the cork cambium and the secondary phloem.
  5. base: (1) A chemical compound that can accept a hydrogen ion. Compare acid and buffer. (2) A nitrogen-containing molecule that is part of a nucleotide. See nitrogen base.
  6. base pairing: A process in which complementary nitrogen bases form hydrogen bonds with each other. In DNA, A pairs with T, and C pairs with G; in RNA, U replaces T.
  7. basilar membrane: A thin membrane lying in the inner ear that vibrates in response to vibrations passed to it from the middle ear.
  8. behavior: A coordinated response to a stimulus; particularly, a response that involves movement.
  9. behavioral mutualism: A mutualism in which each of two interacting species alters its behavior to benefit the other.
  10. benign: Of or referring to a relatively harmless cancerous growth that is confined to a single tumor and does not spread to other tissues in the body. Compare malignant.
  11. benthic zone: An aquatic biome, the communities of which are home to a wide variety of organisms that live on the bottom surfaces of rivers, lakes, wetlands, estuaries, and oceans.
  12. biennial: A plant that completes its life cycle in two years.
  13. bile: A substance produced by the liver that helps break up large fat globules in the small intestine.
  14. biodiversity: The variety of organisms on Earth or in a particular location, ranging from the genetic variation and behavioral diversity of individual organisms or species through the diversity of ecosystems.
  15. biological hierarchy: The hierarchy in which all living things are organized, from molecules at the lowest level to the entire biosphere at the highest level.
  16. biology: The study of life.
  17. biomass: The mass of organisms per unit of area.
  18. biome: A major terrestrial or aquatic life zone, defined either by its vegetation (terrestrial biomes) or by the physical characteristics of the environment (aquatic biomes). There are seven terrestrial biomes (tundra, boreal forest, temperate forest, chaparral, grassland, desert, and tropical forest) and eight aquatic biomes (lake, river, wetland, estuary, intertidal zone, coral reef, ocean, and benthic zone).
  19. biosphere: All living organisms on Earth, together with the environments in which they live.
  20. biosynthetic: Of or referring to chemical reactions that manufacture complex molecules in living cells. Compare catabolic.
  21. bipedal: Of or referring to an organism that walks upright on two legs.
  22. bivalent: A pair of homologous chromosomes. Bivalents form during prophase I of meiosis.
  23. blastocyst: The name for the blastula in mammalian development.
  24. blastula: The early stage of animal development in which the embryo forms a hollow ball of undifferentiated cells.
  25. blood: A fluid tissue consisting of liquid plasma and the blood cells that it carries. Blood plays a central role in carrying nutrients, oxygen, and wastes through the circulatory system.
  26. blood plasma: The fluid portion of animal blood.
  27. blood pressure: The pressure that pushes the blood from the heart to the respiring tissues. In humans, it is typically measured as the pressure in the arteries leading from the left ventricle.
  28. blood vessel: One of the interconnected tubes that make up the circulatory system.
  29. boreal forest: A terrestrial biome, the communities of which are dominated by coniferous trees that grow in northern or high-altitude regions with cold, dry winters and mild, humid summers.
  30. brain: A complex collection of neurons located at the head end of an animal that serves as the major clearinghouse for information in the nervous system.
  31. brain stem: A collective term for the midbrain and hindbrain, which together control many of the functions of the body that are not under conscious control.
  32. breathing: The process of drawing air into and out of the lungs to extract oxygen and expel carbon dioxide.
  33. bronchiole: One of the tiny tubes inside the lung that carry air from the bronchi to the alveoli.
  34. bronchus (pl. bronchi): One of two tubes that carry air from the trachea to the two lobes of the vertebrate lung.
  35. brush border: A series of microscopic, brushlike extensions of the cells lining the small intestine that help to provide a greatly increased surface area for nutrient absorption.
  36. bryophytes: Plants, such as mosses, that lack a true vascular system for transporting materials (nonvascular plants).
  37. Bt crop: A crop plant into which a gene from the bacteria Bacillus thuringiensis has been inserted, causing the plant to produce a toxin that provides protection from insect pests.
  38. buffer: A chemical compound that can both give up and accept hydrogen ions. Buffers can maintain the pH of water within specific limits. Compare acid and base.