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Biology LibreTexts

25.12: Glossary: T

  • Page ID
  • T3 (triiodothyronine)

    endocrine hormone secreted by the thyroid gland that increases the rate of metabolism in cells throughout the body

    T4 (thyroxine)

    endocrine hormone secreted by the thyroid gland that increases the rate of metabolism in cells throughout the body

    target cell

    type of cell on which a particular hormone has an effect because it has receptor molecules for the hormone

    taste bud

    small structure on the tongue containing chemoreceptor cells that sense chemicals in food

    TATA box

    regulatory element that is part of the promotor of most eukaryotic genes

    taxon (plural, taxa)

    level of organization in a biological classification system such as the Linnaean system; for example, species or genus


    science of classifying organisms

    T cell

    type of lymphocyte that kills infected or cancerous cells (killer T cell) or helps regulate the immune response (helper T cell)


    emergence of deciduous (baby) teeth during infancy and early childhood


    region of repetitive nucleotide sequences at the end of a chromosome that becomes shorter each time a cell divides


    last stage of mitosis during which chromosomes uncoil to form chromatin, the spindle breaks down, and new nuclear membranes form

    temporal lobe

    part of each hemisphere of the cerebrum that controls hearing, memories, and sensations


    inflammation of a tendon when it is over-extended or worked too hard without rest


    tough connective tissue that attaches skeletal muscle to bones

    terrestrial biome

    any land-based biome

    testicular cancer

    cancer of the testes, which is relatively common in young men

    testis (plural, testes)

    one of two male reproductive organs that produce sperm and secrete testosterone; male gonad


    male sex hormone secreted mainly by the testes


    part of the inner brain that is a major hub for nerve impulses traveling back and forth between the cerebrum and spinal cord


    type of inherited anemia caused by abnormal hemoglobin that is a genetic adaptation to malaria in the Mediterranean region, parts of Africa, and South and Southeast Asia

    thermal pollution

    pollution by heat energy, typically occurring when heated water is discharged into a river or lake


    type of sensory receptor that senses temperature

    thoracic cavity

    body cavity in the chest that holds the lungs and heart

    thrifty gene hypothesis

    idea that “thrifty genes” evolved in some human populations because they allowed people to burn fewer Calories and store the rest as body fat, which would help them survive famines


    organ of the lymphatic system where lymphocytes called T cells mature

    thyroid gland

    large endocrine gland in the neck whose hormones control the rate of cellular metabolism and help maintain calcium homeostasis


    group of cells, generally of the same kind, that perform a particular function in an organism


    first part of early childhood that covers the ages 1 to 3 years


    one of four paired secondary lymphatic organs that encircle the inner throat and filter pathogens out of lymph


    ability to sense pressure, vibration, temperature, pain, and other tactile stimuli


    common parasitic disease that may be a selective agent maintaining both Rhesus-positive (Rh+) and Rhesus-negative (Rh-) blood type alleles in human populations


    tubular organ of the respiratory system that carries air between the larynx and bronchi; also called windpipe


    process in which genetic instructions in DNA are copied to form a complementary strand of mRNA

    trans fat

    type of harmful, artificial fat that is added to some foods to help preserve freshness and improve taste

    transfer RNA (tRNA)

    type of RNA that brings amino acids to ribosomes where they are joined together to form proteins

    transgenic crop

    crop that has been genetically modified with new genes that code for traits useful to humans


    process in which genetic instructions in mRNA are “read” to synthesize a protein


    process in which plants give off water vapor through tiny pores, called stomata, in their leaves

    transport protein

    protein in a cell membrane that helps other substances cross the membrane to enter or leave the cell


    taxon between the subfamily and genus in the Linnaean system of classification


    common, sexually transmitted infection that is caused by the protozoan parasite Trichomonas vaginalis


    type of lipid that contains glycerol and makes up body fat in animals


    one of three, approximately three-month periods into which a pregnancy is divided

    trophic level

    feeding position in a food chain or food web, such as producer, primary consumer, or secondary consumer


    outer cell layer of a blastocyst that implants in the uterus and eventually develops into the fetal portion of the placenta

    tubal ligation

    surgical sterilization procedure in females in which the Fallopian tubes are blocked so sperm cannot reach and fertilize an egg


    abnormal mass of cells that may be cancerous

    tumor-suppressor gene

    gene that normally inhibits division of abnormal cells and may cause cancer if it mutates

    type 1 diabetes

    autoimmune disorder in which the immune system destroys insulin-secreting beta cells in the pancreas, leading to loss of glucose control and high levels of blood glucose

    type 2 diabetes

    multifactorial disorder in which a combination of insulin resistance and impaired insulin production lead to loss of glucose control and high levels of blood glucose


    system of discrete categories, such as races, that are sometimes used for classifying variation