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Biology LibreTexts

25.12: Glossary: L

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  • labia (singular, labium)

    “lips” of the vulva, consisting of folds of tissue that protect the urethral and vaginal openings


    general term for the process of childbirth, which includes three stages: dilation of the cervical canal, birth of the child, and delivery of the placenta (afterbirth)


    enzyme needed to digest the milk sugar lactose

    lactase persistence

    ability to produce lactase and digest milk after early childhood


    production of breastmilk to feed an infant

    lactic acid fermentation

    type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to lactic acid and the formation of NAD+


    disaccharide sugar that makes up 2-8 percent of milk by weight

    lactose intolerance

    inability to digest the lactose in milk, generally because of lack of the enzyme lactase


    communication of thoughts and feelings through a system of arbitrary symbols called words that are represented by vocal sounds and in many cases also by written marks


    fine, colorless hair that covers a fetus’s face and body until it is shed close to the time of birth

    large intestine

    organ of the digestive system that removes water and salts from food waste and forms solid feces for elimination


    organ of the respiratory system between the pharynx and trachea that is also called the voice box because it contains the vocal cords that allow the production of vocal sounds

    last universal common ancestor (LUCA)

    hypothetical early cell (or group of cells) that gave rise to all subsequent life on Earth


    concentration of particular functions in one hemisphere of the cerebrum of the brain

    law of conservation of mass

    law stating that mass is neither created nor destroyed in chemical reactions

    law of independent assortment

    Mendel’s second law stating that factors controlling different characteristics are inherited independently of each other

    law of segregation

    Mendel’s first law stating that the two factors controlling a characteristic separate and go to different gametes


    hormone produced mainly by fat cells that normally inhibits appetite by inducing a feeling of satiety


    group of cancers of the blood-forming tissues in bone marrow


    white blood cell produced by bone marrow to fight infections

    Leydig cell

    type of cell found between seminiferous tubules in the testes that produces and secretes testosterone

    life cycle

    series of stages a sexually reproducing organism goes through from one generation to the next

    life expectancy

    average time an individual is expected to live, or the average age at death


    band of fibrous connective tissue that holds bones together

    limiting factor

    any factor that constrains the population size of a species in an ecosystem

    linked genes

    genes that are located on the same chromosome

    Linnaean classification system

    system of classifying organisms based on observable physical traits; consists of a hierarchy of taxa, from the kingdom to the species


    class of biochemical compounds that includes fats and oils


    organ of digestion and excretion that secretes bile for lipid digestion and breaks down excess amino acids and toxins in the blood


    position of a gene on a chromosome

    logistic growth

    pattern of population growth in which growth slows and population size levels off as the population approaches the carrying capacity

    lower gastrointestinal (GI) tract

    part of the GI tract that includes the small and large intestines


    one of two paired organs of the respiratory system in which gas exchange takes place between the blood and the atmosphere

    lung cancer

    malignant tumor characterized by uncontrolled cell growth in tissues of the lung

    luteinizing hormone (LH)

    pituitary gland hormone that stimulates the testes to secrete testosterone and the ovaries to secrete estrogen


    fluid that leaks out of capillaries into spaces between cells and circulates in the vessels of the lymphatic system

    lymphatic system

    system of the body that produces lymphocytes and filters pathogens from lymph and blood

    lymph node

    one of many small structures located along lymphatic vessels where pathogens are filtered from lymph and destroyed by lymphocytes


    type of leukocyte produced by the lymphatic system that is a key cell in the adaptive immune response to a specific pathogen or tumor cell