Audio Glossary

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  1. immune system: A system of defensive proteins and white blood cells in vertebrate animals that destroys invading pathogens.
  2. imprinting: A type of learning in which an offspring forms an association or bond with its parent early in its development.
  3. incomplete dominance: The situation in which heterozygotes (Aa individuals) are intermediate in phenotype between the two homozygotes (AA and aa individuals) for a particular gene.
  4. independent assortment of chromosomes: The random distribution of maternal and paternal chromosomes into gametes during meiosis.
  5. indeterminate growth: A feature of some organisms that grow throughout their entire lives, adding new body parts as needed.
  6. index of sustainable economic welfare: A measure of economic output that includes a wider range of the benefits and costs of economic activities than does the traditional gross domestic product (GDP). Compare gross domestic product
  7. individual: A single organism, usually physically separate and genetically distinct from other individuals.
  8. induced defense: A plant defensive response that is directly stimulated by attacking herbivores.
  9. infectious disease: A disease that is transmitted from one host to another by the transfer of a pathogen.
  10. inflammatory response: The characteristic swelling and reddening of an area of tissue damage; part of the nonspecific response to invading pathogens.
  11. ingestion: The act of taking food into the mouth, or eating.
  12. inner cell mass: The cluster of cells inside the trophoblast that eventually develops into the embryo.
  13. inner ear: The portion of the ear where physical movements in the middle ear are converted into the action potentials that vertebrates detect as sound.
  14. insect: Any of a group of six-legged arthropods that includes grasshoppers, beetles, ants, and butterflies; the most species-rich group of animals on Earth.
  15. insertion: A mutation in which one or more nitrogen bases are inserted into the DNA sequence of a gene. Compare deletion and substitution.
  16. insulin: A hormone produced by the pancreas that regulates blood sugar levels in conjunction with its antagonist, glucagon. Compare glucagon.
  17. interference competition: A type of competition in which one organism directly excludes another from the use of resources. Compare exploitation competition.
  18. interferon: A chemical released by virus-infected cells that attaches to the plasma membranes of nearby cells, interfering with the ability of the virus to enter and infect those cells.
  19. intermediate filament: One of a diverse class of ropelike protein filaments that serve as structural reinforcements in the cytoskeleton.
  20. intermembrane space: The space between the inner and outer membranes of a chloroplast or a mitochondrion.
  21. interneuron: A neuron in the central nervous system that processes signals from sensory neurons, then passes those signals on to other neurons. Compare sensory neuron, motor neuron.
  22. interphase: The period of time between two successive mitotic divisions, during which most of the preparations for cell division occur.
  23. interstitial fluid: The body fluid that surrounds and bathes the cells.
  24. intertidal zone: An aquatic biome found in coastal areas where the tides rise and fall on a daily basis, periodically submerging a portion of the shore.
  25. introduced species: A species that does not naturally live in an area but has been brought there either accidentally or on purpose by humans.
  26. intron: A sequence of nitrogen bases within a gene that does not specify part of the gene's final protein or RNA product. Enzymes in the nucleus must remove introns from mRNA, tRNA, and rRNA molecules for these molecules to function properly.
  27. invasive species: An introduced species that proliferates rapidly and becomes a major pest in its new environment.
  28. inversion: A mutation in which a fragment of a chromosome breaks off and returns to the correct place on the original chromosome, but with the genetic loci in reverse order.
  29. ion: An atom or group of atoms that has either gained or lost electrons and therefore has a negative or positive charge.
  30. ionic bond: A chemical linkage between two atoms based on the electrical attraction between positive and negative charges. Compare covalent bond and hydrogen bond.
  31. irregular fluctuations: A pattern of population growth in which the number of individuals in the population changes over time in an irregular manner.
  32. islet cells: Specialized endocrine cells within the pancreas that produce and release the hormones insulin and glucagon.
  33. isotonic solution: A solution that has the same solute concentration as the cytosol of a cell, resulting in an equal amount of water flowing into the cell and out of it.
  34. isotope: A variant form of a chemical element that differs in its number of neutrons, and thus in its atomic mass number, from the most common form of that element.