T

T cell A type of lymphocyte derived from bone marrow stem cells that matures into an immunologically competent cell under the influence of the thymus. T cells are involved in a variety of cell-mediated immune reactions; also known as a T lymphocyte.

tachyzoite Small, merozoitelike stages of Toxoplasma. They develop in the host cells' parasitophorous vacuole by endodyogeny.

tactile (touch) receptor A sensory receptor in the skin that detects light pressure; formerly called Meissner's corpuscle.

tactile Pertaining to touch.

tadpole larva The larva of tunicates.

tagma, A compound body section of an arthropod resulting from embryonic fusion of two or more segments; for example, head, thorax, abdomen.

tagmatization The specialization of body regions of a metameric animal for specific functions. The head of an arthropod is specialized for feeding and sensory functions, the thorax is specialized for locomotion, and the abdomen is specialized for visceral functions.

taiga Areas of coniferous forests north of 50degree latitude having extended cold and snow cover winter conditions.

tailings Mining waste left after mechanical or chemical separation of minerals from crushed ore.

taking Unconstitutional confiscation of private property.

tall grass prairie A grassland biome characterized by many tall grasses up to 5 meters tall.

tangential cut A longitudinal section cut at right angles

tannin A secondary product found in many plants that have been widely utilized as stains, dyes, inks, or tanning agents for leather; believed to function in plants by discouraging herbivores.

tantulus Larva of a tantulocaridan (subphylum Crustacea).

tapetum The nutritive somatic tissue surrounding the microsporocyte.

tapeworms Parasitic flatworms, typically consisting of a chain of repeated units.

taproot system A system of roots characterized by the presence of one dominant axis (the primary root) and several lateral, subordinate roots.

Tardigrada A phylum of animals whose members live in marine and freshwater sediments and in water films on terrestrial lichens and mosses. Possess four pairs of unsegmented legs and a proteinaceous cuticle. Water bears.

target cell The cell influenced by a specific hormone.

Tarsal tarsus = the ankle.

tarsus Most distal podomere of the insect or acarine limb; articulates proximally with the tibia and usually is subdivided into two to five subsegments in insects.

taste buds Structures in the mouth and other locations of fishes that are sensitive to chemical stimuli.

taxis Directed reactions to a stimulus involving an orientation of the long axis of the body in line with the stimulus source.

taxon A group of organisms that are genetically (evolutionarily) related.

taxonomy The description of species and the classification of organisms into groups that reflect evolutionary relationships. See phylogenetic systematics, evolutionary systematics, and numerical taxonomy. Also systematics.

technological optimists Those who believe that technology and human enterprise will find cures for all our problems. Also called Promethean environmentalism.

technopolis Also called a vertical city; this model of city development proposes that cities grow vertically instead of horizontally.

tectonic estuary An estuary that results from the sinking of land due to movements of the crust.

tectonic plates Huge blocks of the earth's crust that slide around slowly, pulling apart to open new ocean basins or crashing ponderously into each other to create new, larger landmasses.

tectum A rooflike structure, for example, dorsal part of capitulum in ticks and mites.

tegmen External epithelium of crinoids (phylum Echinodermata).

tegument Surficial covering of a multicellular organism, an integument.

telencephalon The most anterior vesicle of the brain; the anterior-most subdivision of the prosencephalon that becomes the cerebrum and associated structures.

teleology The philosophical view that natural events are goal directed and are preordained, as opposed to the scientific view of mechanical determinism.

teleomorphic The sexual phase, or perfect stage, in a fungal life cycle.

teliospore A thick-walled spore found in the rust and smut fungi; karyogamy occurs within the teliospore and it gives rise to the basidium.

telmophage Blood-feeding arthropod that cuts through skin and blood vessels to cause a small hemorrhage of blood from which it feeds.

telocentric Chromosome with centromere at the end.

telolecithal Having the yolk concentrated at one end of an egg.

telome theory A theory that regards the primitive vascular plant as consisiting of upright, dichotomously branched axes, some of which bear terminal sporangia and from which, through a series of geometric, architectural modifications, the reproductive and vegetative organs of other vascular land plants evolved.

telophase Stage in mitosis during which daughter cells become separate structures; the two sets of separated chromosomes decondense, and become enclosed by nuclear envelopes.

telson Posterior projection of the last body segment in many crustaceans.

temnospondyls A large lineage of amphibians that extended from the Carboniferous to the Triassic.

temperate deciduous forest An ecosystem that occurs in regions with moderate climate and well-defined seasons; deciduous trees predominate; animals include insects, white-tailed deer, and wolves.

temperate rain forest A biome dominated by coniferous trees, high rainfall, and high humidity; moist coniferous forest.

temperate Characterized by a mild or moderate temperature.

temperature A measure of the speed of motion of a typical atom or molecule in a substance.

temperature-compensated rhythm The relative insensitivity of biological rhythms to the effects of temperature; this contrasts with the fact that many chemical reactions double in rate for every 10C increase in temperature.

template A pattern or mold guiding the formation of a duplicate; often used with reference to gene duplication.

temporary parasite Parasite that contacts its host only to feed and then leaves. Also called an intermittent parasite or micropredator.

tendon Fibrous band connecting muscle to bone or other movable structure.

tendril A modified leaf or stem in which only a slender strand of tissue constitutes the entire structure.

teneral Newly emerged adult arthropod that is soft and weak.

tension wood The reaction wood produced along the upper side of leaning woody trees, straightening the trunk by contracting and "pulling" the tree upright.

tentacle A flexible, elongate appendage.

Tentaculata The class of ctenophorans with tentacles that may or may not be associated with sheaths into which tentacles can be retracted. Pleurobranchia.

tentaculocyst One of the sense organs along the margin of medusae; a rhopalium.

Tentorium An extension of the parietal bone between the cerebral and cerebellar hemispheres; actually an ossification of the meninges.

tepal Members of the perianth that are not differentiated into sepals and petals.

teratogens Chemicals or other factors that specifically cause abnormalities during embryonic growth and development.

terebra Functional unit of a hymenopteran ovipositor, formed from first and second valvulae.

tergite Main dorsal sclerite of a somite of an arthropod.

tergum Dorsal part of an arthropod body segment.

terminal bud scale scars The scars left by the reduced leaves that enclose the apical meristem of a twig. The distance between successive terminal bud scale scars represents one year's growth.

terminal bud The meristematic tissue located at the tip of a stem.

terpene An unsaturated hydrocarbon formed from an isoprene building block; found in many plants in the form of essential oils.

terpenes A group of secondary compounds composed of two to many isoprene units in a chain or ring; sometimes categorized as hydrocarbons only, sometimes to include terpenoids.

terpenoids A term referring to all compounds composed of isoprene units.

terracing Shaping the land to create level shelves of earth to hold water and soil; requires extensive hand labor or expensive machinery, but it enables farmers to farm very steep hillsides.

terrarium A closed biological system in which plants and animals coexist without external inputs or discharges; H2O, CO2, O2, and nutrients cycle in the closed system.

terrestrial Pertaining to the land.

territoriality An intense form of intraspecific competition in which organisms define an area surrounding their home site or nesting site and defend it, primarily against other members of their own species.

territory A restricted area preempted by an animal or pair of animals, usually for breeding purposes, and guarded from other individuals of the same species.

tertian malaria Malaria in which fevers recur every 48 hours. Caused by Plasmodium vivax, P. ovale, and P. falciparum.

tertiary treatment The removal of inorganic minerals and plant nutrients after primary and secondary treatment of sewage.

test A shell or hardened outer covering.

testa Seed coat.

testcross Crossing an organism having a dominant expression for a trait with an organism having a homozygous recessive genotype for that trait to determine the genotype of the organism expressing the dominant phenotype.

testing Application of theories to examine repeatability and accuracy, should have comparisons to known information.

testis Primary reproductive organ of a male; a sperm-cell producing organ.

testosterone Male sex hormone secreted by the interstitial cells of the testes.

Tethys Sea A shallow sea that once separated the Eurasian and African sections of the supercontinent Pangaea. It eventually gave rise to the modern Mediterranean Sea.

tetracotyle Strigeoid metacercaria in the family Strigeidae.

tetrad A pair of homologous chromosomes during synapsis (prophase I of meiosis). A tetrad consists of four chromatids.

tetrapods A nontaxonomic designation used to refer to amphibians, reptiles, birds, and mammals.

tetrathyridium Only metacestode form known in the tapeworm cyclophyllidean genus Mesocestoides. A large, solid-bodied cysticercoid.

thalamus An oval mass of gray matter within the diencephalon that serves as a sensory relay area.

Thaliacea A class of urochordates whose members are planktonic. Adults are tailless and barrel shaped. Oral and atrial openings are at opposite ends of the tunicate. Water currents are produced by muscular contractions of the body wall and result in a weak form of jet propulsion.

thallus The complete body of a seaweed.

thecodonts A large assemblage of Triassic archosaurian diapsids of the order Thecodontia and characterized by having teeth set in sockets.

theileriosis Disease of cattle and other ruminants, caused by Theileria parva. Also called East Coast fever.

thelyotoky, thelytoky Type of parthenogenesis in which all individuals are uniparental and essentially no males are produced.

theory of evolution by natural selection A theory conceived by Charles Darwin and Alfred Russell Wallace on how some evolutionary changes occur.

theory of inheritance of acquired characteristics The mistaken idea that organisms develop new organs, or modify existing organs as environmental problems present themselves, and that these traits are passed on to offspring.

theory An idea that is well supported by data (information) but not known to be universally true.

therapsids Extinct Mesozoic mammal-like reptiles from which true mammals evolved.

thermal plume A plume of hot water discharged into a stream or lake by a heat source, such as a power plant.

thermal pollution Pollution by heated water.

thermal stratification The layering of different temperatures of water or air caused by different densities, less dense floating on more dense layers.

thermocline Layer of water separating upper warmer and lighter water from lower colder and heavier water in a lake or sea; a stratum of abrupt change in water temperature.

thermoconformer To conform to the temperature of one's external environment.

thermodynamics The branch of science that deals with heat, energy, and the interconversion of these; the study of energy transformations.

thermogenesis The generation of heat by muscle contraction.

thermoplastics Soft plastics composed of single-chain, unlinked polymers, such as polyethylene, polypropylene, polyvinylchloride, polystyrene, and polyester, that can be remelted and reformed to make useful products.

thermoreceptor A sensory receptor that is sensitive to changes in temperature; a heat receptor.

thermoregulation Heat regulation.

thermoset polymers Hard plastics composed of cross-linked molecular networks, such as acrylic, phenolic, or epoxy resins, that cannot be remelted or recycled.

thermosphere The highest atmospheric zone; a region of hot, dilute gases above the mesosphere extending out to about 1600 km (1000 mi) from the earth's surface.

Third World Less-developed countries that are not capitalistic and industrialized (First World) or centrally-planned socialist economies (Second World); not intended to be derogatory.

thoracic Pertaining to the thorax or chest.

thorn forest The dry end of a savanna community; hotter and drier than a typical savanna, these areas are characterized by dense, thorny small trees.

thorn A modified stem terminating in a sharp point.

threatened species While still abundant in parts of its territorial range, this species has declined significantly in total numbers and may be on the verge of extinction in certain regions or localities.

threshold The minimum stimulus necessary to initiate an all-or-none response.

thrombin. Enzyme catalyzing fibrinogen transformation into fibrin. Percursor is prothrombin.

thrombocyte See platelet.

thrombus Blood clot in a blood vessel or in one of the cavities of the heart.

thylakoid membrane A saclike photosynthetic membrane in chloroplasts; stacks of thylakoids form the grana.

thylakoid The lamellar structure of the grana of chloroplasts.

thymine A pyrimidine base occurring in DNA but not in RNA.

thymus gland A ductless mass of flattened lymphoid tissue situated behind the top of the sternum; it forms antibodies in the newborn and is involved in the development of the immune system.

thyroid gland An endocrine gland located in the neck and involved with the metabolic functions of the body.

thyroid An endocrine gland near the shield-shaped cartilage of the larynx.

Ti plasmid The tumor-inducing plasmid from the bacterium, Agrobacterium tumefaciens; commonly used as a vector for recombinant DNA studies in plants.

tibia Podomere of an insect or acarine leg that articulates proximally with the femur in insects and patella in acarines and distally with the tarsus in insects or with the metatarsus or tarsus in acarines.

tidal bore A steep wave generated as high tides move up some estuaries and rivers.

tidal current A current that is generated by tides.

tidal energy Energy that can be harnessed as a result of the movement of tides.

tidal marsh See salt marsh.

tidal range The difference in water level between successive high and low tides.

tidal station A dam built across a narrow bay or estuary traps tide water flowing both in and out of the bay. Water flowing through the dam spins turbines attached to electric generators.

tide pool A depression that holds seawater at low tide.

tide table A table that gives the predicted time and height of tides for particular points along a coast.

tide The periodic, rhythmic rise and fall of the sea surface.

tied ridges Series of ridges running at right angles to each other so that runoff is blocked in all directions and water is allowed to soak into the soil.

Tiedemann's bodies Four or five pairs of pouchlike bodies attached to the ring canal of sea stars, apparently functioning in production of coelomocytes.

tight junction. Region of actual fusion of cell membranes between two adjacent cells.

tillering The production of lateral buds and shoots near the ground to result in a plant with several shoots instead of one; particularly important in grasses and grain crops.

timberline In mountains, the highest-altitude edge of forest that marks the beginning of the treeless alpine tundra.

tintinnids Ciliates that secrete vase-like cases, or loricas.

tissue A group of similar cells that performs a specialized function.

titer Concentration of a substance in a solution as determined by titration.

tolerance limits See limiting factors.

tolerance range The range of variation in an environmental parameter that is compatible with the life of an organism.

tonicity The state of tissue tone or tension; in body fluid physiology, the effective osmotic pressure equivalent.

tonoplast The membrane surrounding the vacuole.

tool-making revolution The invention of tools--probably first of stone, wood, or bone_ sometime in the early Paleolithic period. Knowledge of tool-making and tool-using technologies may have predated modern humans, as evidenced by tool utilization by other primates.

top carnivore The consumer at the end of a food chain or web; a carnivore that ordinarily has no predator under those ecological conditions.

topography The surface condition of an area of land; relief features.

topsoil The first true layer of soil; layer in which organic material is mixed with mineral particles; thickness ranges from a meter or more under virgin prairie to zero in some deserts.

tornado A violent storm characterized by strong swirling winds and updrafts; tornadoes form when a strong cold front pushes under a warm, moist air mass over the land.

tornaria A free-swimming larva of enteropneusts that rotates as it swims; resembles somewhat the bipinnaria larva of echinoderms.

torpor A time of decreased metabolism and lowered body temperature that occurs in daily activity cycles.

torsion A developmental twisting of the visceral mass of a gastropod mollusc that results in an anterior opening of the mantle cavity and a twisting of nerve cords and the digestive tract.

tortoiseshell The polished shell of hawksbill turtles.

total fertility rate The number of children born to an average woman in a population during her entire reproductive life.

total growth rate The net rate of population growth resulting from births, deaths, immigration, and emigration.

toxic colonialism Shipping toxic wastes to a weaker or poorer nation.

toxicyst Structures possessed by predatory ciliate protozoa, which on stimulation expel a poison to subdue the prey.

toxin present in certain dinoflagellates that cause red tides.

toxins Poisonous chemicals that react with specific cellular components to kill cells or to alter growth or development in undesirable ways; often harmful, even in dilute concentrations.

trabecula In general anatomical usage, a septum extending from an envelope through an enclosed substance, which, together with other trabeculae, forms part of the framework of various organs; here referring specifically to the cell processes connecting the perikarya of cestode and trematode tegumental cells with the distal cytoplasm. Also called internuncial process.

trabecular net Network of living tissue formed by pseudopodia of amebocytes in Hexactinellida (phylum Porifera).

trace element an element needed for normal metabolism but available only in minute amounts from the environment

trace elements Microelements of plant nutrition, needed in small quantities such as boron, zinc, and copper.

trace mineral Dietary minerals that are required in minute quantities.

trachea The windpipe. Also, any of the air tubes of insects.

tracheae The small tubes that carry air from spiracles through the body cavity of an arthropod; arthropod tracheae are modifications of the exoskeleton.

tracheal system System of cuticle-lined tubes in many insects and acarines that functions in respiration; opens to outside through spiracles.

tracheid An elongated, tapering xylem cell that is specialized for conducting water and support with lignified pitted walls.

tracheophytes Plants with a well-defined vascular system.

tract A bundle of nerve fibers within the central nervous system.

tradable permits Pollution quotas or variances that can be bought or sold. If you have a permit to emit a certain amount of some pollutant, I might buy a portion of that amount from you rather than put pollution controls on my equipment. You, in turn, would have to reduce your emissions accordingly.

trade winds Steady winds that blow from east to west toward the Equator, replacing the hot air that rises at the Equator.

tradition A behavior pattern that is passed from one generation to the next by learning.

tragedy of the commons An inexorable process of degradation of communal resources due to selfish self-interest of "free riders" who use or destroy more than their fair share of common property. See open access systems.

transcription The formation of a messenger RNA molecule that carries the genetic code from the nucleus to the cytoplasm of a cell.

transducer A receptor that converts one form of energy into another.

transduction. Condition in which bacterial DNA (and the genetic characteristics it bears) is transferred from one bacterium to another by the agent of viral infection.

transection The severing of a nerve to determine its specific function(s).

transfer RNA (tRNA). A form of RNA of about 70 or 80 nucleotides, which are adapter molecules in the synthesis of proteins. A specific amino acid molecule is carried by transfer RNA to a ribosome-messenger RNA complex for incorporation into a polypeptide.

transform fault A large horizontal displacement in the mid-ocean ridge.

transformation. Condition in which DNA in the environment of bacteria somehow penetrates them and is incorporated into their genetic complement, so that their progeny inherit the genetic characters so acquired.

transforming factor A substance that can be passed from one cell to another and cause a permanent change in heredity.

transgenic Cells or organisms that contain genes that were inserted into them from other organisms using the techniques of genetic engineering.

transitional mutants A type of mutation in which a single purine-pyrimidine base pair is replaced by another.

transitional zone A zone in which populations from two or more adjacent communities meet and overlap.

translation The second stage of protein synthesis in which the codon of mRNA pairs with the anticodon of tRNA at the surface of the ribosome.

translocation Moving animals from one location to another, for instance to determine whether and how soon they shift their activity cycle to match the photoperiod and/or other features in their new location.

transmission electron microscope The type of microscope that produces highly magnified images of ultrathin tissue sections or other specimens.

transpiration The evaporation of water from plant surfaces, especially through stomates.

Transpiration-Cohesion Theory The theory that explains water movement in the xylem; the driving force is the pull of transpiration and the cohesion of water molecules.

transpirational pull Water molecules being "pulled" up the xylem are triggered by transpirational water loss at the leaf surface.

transplantation The movement of neural or hormonal tissue from one area of an animal to another or from one animal to another. Also, the movement of individuals or colonies from one location to another.

transport host Paratenic host.

transporter. See permease.

transverse cut A section cut at right angles to the long axis. Also termed a cross section.

transverse plane A plane or section that lies or passes across a body or structure.

transversional mutant A type of mutation in which a purine-pyrimidine base pair is replaced by a pyrimidine-purine base pair.

Trapezium trapez = a table.

trauma Injury caused by accident or violence.

Trematoda The class of platyhelminthes that has members that are all parasitic; several holdfast devices present; have complicated life cycles involving both sexual and asexual reproduction.

trematodes See flukes.

trench A narrow, deep depression in the sea floor.

trench deep area in the ocean floor, generally deeper than 6,000 m

triactinomyxon Stage in the life cycle of a myxozoan, formerly assigned to a separate class.

tribocytic organ Glandular, padlike organ behind the acetabulum of a strigeoid trematode.

trichinosis A disease resulting from infection by Trichinella spiralis (Nematoda) larvae by eating undercooked meat; characterized by muscular pain, fever, edema, and other symptoms.

trichocysts An anchoring structure present in the ectoplasm of some ciliates. A bottle-shaped extrusible organelle of the ciliate pellicle.

trichogon Spiny male larva of a rhizocephalan cirripede that comes to lie within a special receptacle in the female.

trichome An epidermal appendage, such as a hair or scale.

Trigeminal tri = three; geminus = twin.

triglyceride A type of lipid formed from three fatty acids bonded to a molecule of glycerol; a fat or oil.

Trilobitamorpha The subphylum of arthropods whose members had bodies divided into three longitudinal lobes. Head, thorax, and abdomen present. One pair of antennae and biramous appendages. Entirely extinct.

Trimerophytophyta An extinct division of early vascular plants characterized by a monopodial axis, dichotomously branched lateral axes bearing terminal sporangia. Believed to have been the ancestor of the ferns and progymnosperms.

trimerous Body in three main divisions, as in lophophorates and some deuterostomes.

tripartite See trimerous.

triplet A group of three nucleotides on a nucleic acid that codes for a particular amino acid.

triploblastic Animals whose body parts are organized into layers that are derived embryologically from three tissue layers: ectoderm, mesoderm, and endoderm. Platyhelminthes and all coelomate animals are triploblastic.

triploid A cell or nucleus that contains three sets of chromosomes; common in endosperm.

Triquetrum A carpal bone.

trisomy 21 See Down syndrome.

tritonymph Third nymphal stage in most acarines.

tritosternum Ventral, bristlelike sensory organ just behind the gnathosoma of a mesostigmatid mite.

triungulin First instar larva of some parasitic, hypermetamorphic Neuroptera and Coleoptera and of the Strepsiptera, which is an active, campodeiform oligopod.

trochanter Podomere of an insect or acarine leg that articulates basally with the coxa and distally with the femur; usually fixed to the femur in insects.

Trochanter trochanter = runner. Two processes on the proximal femur.

Trochlea trochlea = a pulley.

trochophore larva A larval stage characteristic of many molluscs, annelids, and some other protostomate animals.

trochophore A free-swimming ciliated marine larva characteristic of most molluscs and certain ectoprocts, brachiopods, and marine worms; an ovoid or pyriform body with preoral circlet of cilia and sometimes a secondary circlet behind the mouth.

trochophore early free-swimming, ciliated larval stage of many marine mollusks, annelid worms, ectoprocts, and brachiopods

trombe wall An interior, heat-absorbing wall; may be water-filled glass tubes that absorb heat rays and let light into interior rooms.

trophallaxis Exchange of food between young and adults, especially certain social insects.

trophi Jaw-like structures in the mastax of rotifers.

trophic Pertaining to feeding and nutrition.

trophic hormones Hormonal or neurosecretory products from endocrine glands or neurosecretory cells that influence the production and release of other hormone products from endocrine glands.

trophic levels The feeding level of an organism in an ecosystem; green plants and other autotrophs function at producer trophic levels; animals function at the consumer trophic levels.

trophoblast Outer ectodermal nutritive layer of blastodermic vesicle; in mammals it is part of the chorion and attaches to the uterine wall.

trophont Stage in the life cycle of gregarines.

trophosome Organ in poganophorans bearing mutualistic bacteria, derived from midgut.

trophozoite Active, feeding stage of a protozoan, in contrast to a cyst. Also called the vegetative stage.

tropic Related to the tropics (tropical); in endocrinology, a hormone that influences the action of another hormone or endocrine gland.

tropical rain forest An ecosystem characterized by very high rainfall and temperatures between 20 and 25C; very diverse life-forms; broad-leaved, nondeciduous trees; highly stratified forest.

tropical seasonal forest Semievergreen or partly deciduous forests tending toward open woodlands and grassy savannas dotted with scattered, drought-resistant tree species; distinct wet and dry seasons, hot year-round.

tropics Equatorial regions with year-round warm weather.

tropomyosin Low-molecular weight protein surrounding the actin filaments of striated muscle.

troponin Complex of globular proteins positioned at intervals along the actin filament of skeletal muscle; thought to serve as a calcium-dependent switch in muscle contraction.

tropopause The boundary between the troposphere and the stratosphere.

troposphere The layer of air nearest to the earth's surface; both temperature and pressure usually decrease with increasing altitude.

true language Communication that includes the use of symbols to represent abstract objects or ideas, and syntax, where those symbols convey different messages depending on their sequence.

true navigation The ability to maintain or establish reference to a goal without the use of landmarks.

trypomastigote Form of Trypanosomatidae with an undulating membrane and the kinetoplast located posterior to the nucleus. An example is Trypanosoma.

tsetse fly Bloodsucking fly of the genus Glossina.

tsunami Giant seismic sea swells that move rapidly from the center of an earthquake; they can be 10 to 20 meters high when they reach shorelines hundreds or even thousands of kilometers from their source.

tube feet (podia) .Numerous small, muscular, fluid-filled tubes projecting from body of echinoderms; part of water-vascular system; used in locomotion, clinging, food handling, and respiration.

tube nucleus One division of the microscope nucleus in a pollen grain that is responsible for the formation of a pollen tube from the stigma through the style to the ovule.

tuber An enlarged, fleshy, underground stem tip, such as the potato.

tubercle Small protuberance, knob, or swelling.

Tuberculum Process on some bones.

Tuberosity A normal raised area on a bone, such as the deltoid tuberosity, which is the site of insertion of the deltoid muscle.

tuberous roots Modified fibrous roots that have become fleshy and enlarged with food reserves.

tubular eyes Specialized eyes of many midwater animals that allow upward or downward vision.

tubular nerve cord A hollow nerve cord that runs middorsally along the back of chordates; one of four unique chordate characteristics; also called the neural tube and, in vertebrates, the spinal cord.

tubulin Globular protein forming the hollow cylinder of microtubules.

tumor necrosis factor. A cytokine, the most important source of which is macrophages, that is a major mediator of inflammation.

tumor A spherical mass of cells in which cell divisions occur at random and often in an uncontrolled fashion.

tundra Terrestrial habitat zone, located between taiga and polar regions; characterized by absence of trees, short growing season, and mostly frozen soil during much of the year.

tunic In tunicates, a cuticular, cellulose-containing covering of the body secreted by the underlying body wall.

tunicates Chordates that show the three basic chordate characteristics only in the larva.

Turbellaria The class of Platyhelminthes that has members that are mostly free living and aquatic; external surface usually ciliated; predaceous; possess rhabdites; protrusable proboscis; mostly hermaphroditic. Examples: Convoluta, Notoplana, Dugesia.

turbellarians Mostly free-living flatworms.

Turbinate Folded parts of the ethmoid bone.

turbulence random, nonlaminar flow of a fluid

turf The intertwined fibrous roots of grasses forming a mass with the soil just below ground level.

turgid A swollen, distended cell that is firm due to water uptake.

turgor pressure The real pressure developed in living cells by pressing against a membrane.

turning over The mixing of thermal zones in a standing body of freshwater due to cold, more dense water "sinking" from the top through the other layers.

turnover rate the rate at which members of a population or community replace themselves

turpentine A solvent that includes two terpenes--camphor and pinene.

tusk shells Molluscs that have an elongate, tapered shell that is open at both ends.

tympanal (tympanic) organs Auditory receptors present on the abdomen or legs of some insects.

tympanic bulla bony case in the middle ear that encloses the sound-processing structures of mammals

tympanic Relating to the tympanum that separates the outer and middle ear (eardrum).

type specimen. A specimen deposited in a museum that formally defines the name of the species that it represents.

typhlosole A longitudinal fold projecting into the intestine in certain invertebrates such as the earthworm.

typology A classification of organisms in which members of a taxon are perceived to share intrinsic, essential properties, and variation among organisms is regarded as uninteresting and unimportant.