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Biology LibreTexts

25.9: Glossary: I

  • Page ID
  • ileum

    final of three parts of the small intestine where vitamin B12 and bile salts are absorbed


    movement of individuals into a population

    immune surveillance

    function of the immune system in which it identifies and eliminates tumor cells

    immune system

    organ system that defends the body form pathogens and cancer


    ability to resist a pathogen due to the formation of memory lymphocytes (B or T cells) to that specific pathogen


    deliberate exposure of a person to a pathogen in order to provoke an immune response and the formation of memory cells specific to that pathogen


    inability of the immune system to fight off pathogens that a normal, healthy immune system would be able to resist because the immune system is damaged


    treatment for an allergy in which a patient is gradually desensitized to an allergen through periodic injections with increasing amounts of the allergen; or treatment for cancer that attempts to stimulate the immune system to destroy cancer cells


    process in which a blastocyst embeds in the endometrium lining the uterus


    one of eight (four upper and four lower) blade-like teeth at the front of the mouth that are used to slice off pieces of food

    incomplete dominance

    relationship between the alleles for a gene in which one allele is only partly dominant to the other allele, producing an intermediate phenotype

    incubation period

    length of time between infection with a pathogen or other agent of disease and the first appearance of symptoms

    independent variable

    variable in a scientific experiment that is manipulated by the researcher to investigate its effect on another variable, known as the dependent variable; also called the manipulated variable


    first year of life after birth in humans


    human being between birth and the first birthday

    infant mortality rate

    annual number of infant deaths per 1,000 live births in a population, often used as a reliable indicator of the overall level of health of the population


    invasion of an organism’s tissues by pathogens

    infectious disease

    any disease caused by pathogens; also called communicable or contagious disease

    infectious dose

    amount of a pathogen that must infect an organism to cause disease

    inferential statistics

    statistics such as the t-test that help researchers interpret data to test hypotheses


    failure to achieve a successful pregnancy after at least one year of regular, unprotected sexual intercourse


    response of the innate immune system that establishes a physical barrier against the spread of infection and repairs tissue damage while causing redness, swelling, and warmth

    inflammatory bowel disease

    type of disease in which the immune system attacks the intestines, causing diarrhea and abdominal pain; for example, Crohn’s disease or ulcerative colitis

    inheritance of acquired characteristics

    mistaken idea of Jean Baptiste Lamarck that evolution occurs through the inheritance of traits that an organism develops in its own life time

    innate immune system

    subset of the immune system that makes generic attacks such as inflammation against invading pathogens

    insoluble fiber

    nondigestible carbohydrates in food that do not dissolve in water but provide bulk and stimulate peristalsis in the digestive tract


    endocrine hormone secreted by beta cells of the pancreas that normally helps cells take up glucose from the blood, thereby decreasing the blood glucose level

    integumentary system

    human body system that includes the skin, nails, and hair


    type of neuron that carries nerve impulses back and forth between sensory and motor neurons


    stage of the eukaryotic cell cycle when the cell grows, synthesizes DNA, and prepares to divide

    interspecific competition

    relationship between two species that depend on the same limiting resources in their ecosystem

    intrauterine device (IUD)

    T-shaped contraceptive structure containing copper or a hormone that is inserted into the uterus by a physician and may be left in place for months or years

    intrauterine growth restriction (IUGR)

    abnormally slow growth of a fetus, which may be due to maternal, fetal, or placental factors


    process in which a male’s penis deposits sperm in a female’s vagina


    region of DNA or RNA that does not code for a protein

    invasive species

    species that is introduced (usually by human actions) into a new habitat where it may out-compete native species


    atom that has gained or lost electrons so it has more or fewer electrons than protons and a negative or positive charge


    referring to a muscle contraction in which muscle tension increases but muscle length remains the same


    referring to a muscle contraction in which muscle length decreases but muscle tension remains the same


    alternate form of an atom, with the same number of protons but a different number of neutrons