Audio Glossary

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  1. eardrum: A delicate membrane at the end of the auditory canal that converts pressure changes in the environment into physical movements.
  2. ecological experiment: A procedure in which an investigator alters one or more features of the environment and observes the effect of that change.
  3. ecological footprint: The area of productive ecosystems needed throughout a year to support a population and cope with its waste materials.
  4. ecology: The scientific study of interactions between organisms and their environment.
  5. ecosystem: A community of organisms, together with the physical environment in which the organisms live. Global patterns of air and water circulation link all the world's organisms into one giant ecosystem, the biosphere.
  6. ecosystem service: An action or function of an ecosystem that provides a benefit to humans, such as pollination by insects or water filtration by wetlands.
  7. ectoderm: The cell layer in animal development that forms the exterior of the gastrula and gives rise to the epidermis and nervous system. Compare endoderm, mesoderm.
  8. ectotherm: An organism that relies on environmental heat for most of its heat input. Compare endotherm.
  9. edema: Swelling of the tissues.
  10. effector cell: A lymphocyte that is actively involved in attacking pathogens.
  11. egg: The large, immobile, haploid gamete that is produced by sexually reproducing female eukaryotes. Compare sperm.
  12. electrocardiogram (EKG): A recording of the signals from the sinoatrial and atrioventricular nodes of the heart.
  13. electron: A negatively charged particle found in atoms. Each atom contains a characteristic number of electrons. Compare proton.
  14. electron transport chain (ETC): A group of membrane-associated proteins that can both accept and donate electrons. The transfer of electrons from one ETC protein to another releases energy that is used to manufacture ATP in both chloroplasts and mitochondria.
  15. element: A substance made up of only one type of atom. The physical world is made up of 92 natural elements.
  16. embryo: The early stage of animal development extending from the zygote to the early development of organs and organ systems. Compare fetus.
  17. embryo sac: The small, multicellular haploid stage of the flowering plant life cycle in which eggs are produced. Compare pollen grain.
  18. encapsulation: The formation of a protective capsule around especially large pathogens by macrophages.
  19. endangered: In danger of extinction.
  20. endocrine gland: A structure that produces hormones and releases them directly into the circulatory system.
  21. endocrine system: The collection of glands and other tissues in animals that produce signaling molecules called hormones and release them directly into the circulatory system without using ducts.
  22. endocytosis: A process by which a section of a cell's plasma membrane bulges inward as it envelops a substance outside of the cell, eventually breaking free to become a closed vesicle within the cell.
  23. endoderm: The cell layer in animal development that forms the interior of the gastrula and gives rise to the gut and associated organs. Compare ectoderm, mesoderm.
  24. endometrium: The layer of cells lining the wall of the mammalian uterus.
  25. endoplasmic reticulum: An organelle composed of many interconnected membrane sacs and tubes; the major site of protein and lipid synthesis in eukaryotic cells.
  26. endoskeleton: A skeleton that is surrounded by the soft tissues it supports. Compare exoskeleton.
  27. endosperm: The nutritive tissue produced within a plant seed.
  28. endotherm: An organism that relies on metabolic heat for most of its heat input. Compare ectotherm.
  29. energy carrier: A molecule that can store energy and donate it to another molecule or a chemical reaction. ATP is the most commonly used energy carrier in living organisms.
  30. enzyme: A protein that acts as a catalyst, speeding the progress of chemical reactions. All chemical reactions in living organisms are catalyzed by enzymes.
  31. epinephrine: A hormone produced by the adrenal glands that regulates the availability of glucose in conjunction with norepinephrine.
  32. epistasis: A gene interaction in which the phenotypic effect of the alleles of one gene depends on which alleles are present for another, independently inherited gene.
  33. epithelial tissue: A type of animal tissue that is specialized to regulate how the animal's internal environment exchanges water, solutes, and heat directly with the external environment.
  34. ER: See endoplasmic reticulum.
  35. esophagus: The portion of the digestive system that uses waves of muscular contraction to push food from the mouth to the stomach.
  36. essential amino acid: An amino acid that a consumer cannot synthesize and must therefore obtain from its food.
  37. estrogen: One of a class of steroid hormones that stimulate cells to develop the characteristics of femaleness. Compare androgen.
  38. estuary: An aquatic biome found in tidal regions where rivers flow into the ocean.
  39. ETC: See electron transport chain.
  40. eugenics movement: An effort to breed better humans by encouraging the reproduction of people with certain genetic characteristics and discouraging the reproduction of people with other genetic characteristics.
  41. Eukarya: The domain that encompasses the eukaryotes.
  42. eukaryote: A single-celled or multicellular organism in which each cell has a distinct nucleus and cytoplasm. All organisms other than the Bacteria and the Archaea are eukaryotes. Compare prokaryote.
  43. eukaryotic flagellum: A hairlike structure found in eukaryotes that propels the organism by means of waves passing from its base to its tip. Compare bacterial flagellum and cilium.
  44. eustachian tube: A thin tube that connects the middle ear to the throat, allowing mammals to equalize the pressure in these two structures.
  45. eutrophication: A process in which enrichment of water by nutrients (often from sewage or runoff from fertilized agricultural fields) causes bacterial populations to increase and oxygen concentrations to decrease.
  46. evaporation: The conversion of a substance from a liquid to a gas.
  47. evolution: Change over time in a lineage of organisms. See also macroevolution and micro evolution.
  48. evolutionary innovation: key adaptation of a group that originated in that group.
  49. evolutionary tree: A diagrammatic representation showing the order in which different lineages arose, with the lowest branches having arisen first.
  50. term: A diagrammatic representation showing the order in which different lineages arose, with the lowest branches having arisen first.
  51. exchange pool: A source such as the soil, water, or air where nutrients are available to producers.
  52. exocytosis: A process by which a vesicle approaches and fuses with the plasma membrane of a cell, releasing the substance it contains into the cell's surroundings.
  53. exon: A DNA sequence within a gene that encodes part of a protein.
  54. exoskeleton: A skeleton that surrounds the soft tissues of the animal it supports. Compare endoskeleton.
  55. experiment: controlled manipulation of nature designed to test a hypothesis.
  56. exploitation: An interaction between two species in which one species benefits (the consumer) and the other species is harmed (the food organism). Exploitation includes the killing of prey by predators, the eating of plants by herbivores, and the harming or killing of a host by a parasite or pathogen.
  57. exploitative competition: A type of competition in which species compete indirectly for shared resources, with each reducing the amount of a resource available to the other. Compare interference competition.
  58. exponential growth: A type of rapid population growth in which a population increases by a constant proportion from one generation to the next.
  59. extracellular matrix (pl. matrices): A coating of nonliving material, released by the cells of multicellular animals, that often holds those cells together.
  60. extremophile: An organism, such as many Archaea, that lives in extreme environments, such as boiling hot geysers or on salted meat.