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Biology LibreTexts

25.21: Glossary: D

  • Page ID
  • data (singular, datum)

    observations collected in a scientific investigation in order to test a hypothesis

    dead zone

    area in the ocean or other body of water where low oxygen levels following excessive growth of algae have killed virtually all aquatic organisms

    death rate

    number of deaths per year per 1,000 people in a population

    deciduous teeth

    first set of 20 teeth that emerge in infancy and early childhood and are lost and replaced by permanent teeth during middle childhood; also called baby teeth


    organism that breaks down the remains of dead organisms or other organic wastes

    demographic transition

    major population shift in which the death rate falls and the population growth rate increases, followed later by the birth rate falling and the population growth rate decreasing


    scientific study of human populations


    extension of the cell body of a neuron that receives nerve impulses from other neurons

    dependent variable

    variable in a scientific experiment that is affected by another variable, known as the independent variable; also called outcome variable


    type of psychoactive drug that calms the brain, reduces anxious feelings, and induces sleepiness


    inner layer of skin that is made of tough connective tissue and contains blood vessels, nerve endings, hair follicles, and glands


    process in which salt is removed from ocean water to produce fresh water for human use

    descriptive statistics

    statistics such as the mean and standard deviation that describe and summarize data

    developmental adjustment

    nongenetic phenotypic change that occurs during development in infancy or childhood and that may persist into adulthood and become irreversible

    diabetes mellitus

    disease caused by problems with the pancreatic hormone insulin, which lead to high blood glucose levels and symptoms such as excessive thirst and urination; includes type 1 and type 2 diabetes

    diabetic nephropathy

    progressive kidney disease caused by damage to capillaries in the glomeruli of the kidneys due to poor blood sugar control in people with diabetes


    large, dome-shaped muscle below the lungs that allows breathing to occur when it alternately contracts and relaxes


    part of a heartbeat in which the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria


    process by which unspecialized cells become specialized into one of many different types of cells, such as neurons or epithelial cells


    type of passive transport that does not require the help of transport proteins


    process of breaking down food into nutrients that can be absorbed by blood or lymph

    digestive system

    organ system that breaks down food, absorbs nutrients, and eliminates any remaining wastes


    having two of each type of chromosome, or twice the number of chromosomes as a haploid gamete

    directional selection

    type of natural selection for a polygenic trait in which one of two extreme phenotypes is selected for, resulting in a shift in the phenotypic distribution toward that extreme


    sugar consisting of two monosaccharides


    condition associated with impairment of normal body functioning, generally causing signs or symptoms of illness

    disease burden

    impact of a disease on a population as measured by financial cost, mortality, morbidity, or other indicators

    disease outbreak

    event in which two or more people contract an infectious disease from a common source of infection

    disruptive selection

    type of natural selection for a polygenic trait in which phenotypes in the middle of the phenotypic distribution are selected against, resulting in two overlapping phenotypes, one at each end of the distribution


    disease in which one or more pouches (diverticula) in the large intestine become infected and inflamed


    condition in which pouches called diverticula form in the wall of the large intestine

    DNA (deoxyribonucleic acid)

    double-stranded DNA that makes up genes and chromosomes

    DNA replication

    natural process of copying DNA prior to cell division


    taxon in the revised Linnaean system that is larger and more inclusive than the kingdom


    referring to an allele that masks the presence of another allele for the same gene when the two alleles occur together in a heterozygote, or referring to a trait that is controlled by such an allele


    state in which a plant slows down cellular activity and may shed its leaves

    dorsal cavity

    major human body cavity that includes the head and the posterior (back) of the trunk and holds the brain and spinal cord

    double-blind experiment

    scientific experiment in which neither the subjects nor the researchers know in which group subjects have been placed to help avoid bias in the outcome

    double helix

    double spiral shape of the DNA molecule

    doubling time

    time it would take a population to double in size at its current rate of growth


    respiratory impairment from being in or under a liquid, whether or not death results

    drug abuse

    use of a drug without the advice of a medical professional and for reasons not originally intended

    drug addiction

    compulsive use of a substance such as a psychoactive drug despite negative consequences that such use may entail

    drug dependence

    condition in which stopping use of a substance such as a psychoactive drug produces physical and/or psychological symptoms


    first and shortest of three parts of the small intestine where most chemical digestion occurs