Dr. Paul's Virtually Biology Show.
www.jccc.net/~pdecell
T
Taxis.
A taxis is behavior consisting of a directed movement of the whole organism toward
or away from a stimulus.
Taxonomy.
In biology, the science dealing with the classification and identification of
organisms.
Telomere. A
region at the tip of a chromosome or chromatid that consists of repeating sequences
of nucleotide bases. Telomeres are important because as chromosomes replicate,
the telomere shrinks in size. In some cells and organisms the telomere is restored
to its original length by an enzyme called telomerase. If a particular cell does
not have telomerase, the cell can only undergo a set number of cell divisions
until dying out. Scientists believe this process is related to the aging process
of multicellular organisms including humans.
Temperature.
Temperature is really a way of measuring the average kinetic energy of all the
molecules or atoms of the substance being studied. Temperature differs from heat
in that heat is the total amount of kinetic energy in the substance being studied.
For instance, two rooms may both be at 27 degrees Celsius, but if the second room
has twice the volume, the room will contain twice the heat of the first room.
Tertiary Structure.
In proteins, the three dimensional folding of the protein due to hydrophobic and
hydrophilic interactions with water. The protein chain's primary and secondary
structure folds into a complex three dimensional shape. This shape is sensitive
to the charge environment of the solution. A change in pH can, for instance, alter
the shape of an enzyme activating it or rendering it inactive.
Territory.
An area containing a resource that is actively defended by an animal from other
animals be they of the same species or in some cases of different species. Note
that a territory is not the same thing as a home range in that a home range is
where the animal may tend to roam.
Test cross. A mating
designed to tell if an organism with the dominant phenotype is homozygous or heterozygous(carrying
a recessive allele). This is done by mating the individual with a homozygous recessive
individual. Of course, this isn't often practical and today for many genetic systems
there are biochemical tests which eliminate the need for test crosses.
Tetrad. A group
of four chromatids formed by the association of a pair of homologous chromosomes
during prophase I of meiosis.
Theory: A complex
set of well tested assumptions, well tested hypothesis which guides the research
within a particular area of science, leading to new hypothesis and predictions
within that area of science. Examples of theories include the theories of relativity,
quantum mechanics in physics, and the theory of evolution in biology.
Thermophile.
An organism that thrives at temperatures above those where life normally can be
found. Usually 50 degrees Celsius or above. Some thermophiles in hot springs and
in deep sea thermal vents live at near the boiling point of water.
Thigmotropism.
An orientation toward or away from a touch stimulus. Found in the tendrils of
many vines.
Threshold.
The electrical potential across a neuron cell membrane that is just sufficient
to trigger an action potential.
Thylakoid.
A flattened membranous sac that comprises part of the granum in a chloroplast.
The pigment systems and electron transport systems for the light dependent reactions
of photosynthesis are part of the thylakoid membrane.
Tissue. A group
of similar cells bound together by intercellular material that carry out a common
set of functions.
T Lymphocyte.
Cells that form the basis of the cell mediated part of the immune system. These
cells do not respond to free antigens in the blood stream and do not produce anti-bodies.
Trachea. In
vertebrates, the tube leading from the pharynx into the thorax where it branches
to form the primary bronchi into the lungs. In insects and many other arthropods
one of the air tubes that forms part of the insect respiratory system.
Transformation.
The incorporation of naked DNA into the cells of bacteria causing an alteration
in the bacteria cell's phenotype.
Translation.
The process of taking the sequence of nucleotide triplets(codons) in a strand
of messenger RNA and using that sequence to make a polypeptide.
Translocation.
The movement of organic compounds , especially sucrose, through a plant by means
of the phloem tissue.
Transpiration.
Water loss by evaporation from a plant, especially through the stomates on the
leaves.
Transport Proteins.
Proteins found in the membranes of cells and organelles that are responsible for
the movement of many substances into the cell or to the outside of the cell. Sometimes
these proteins are passive gateways for substances to diffuse into or out of the
cell. Other transport proteins use energy to actively pump molecules into the
cell or to the outside.
Transposon.
A segment of DNA capable of shifting from one position in the eukaryote genome
to another. Often transposons code for enzymes that facilitate the transposon's
movement. Sometimes called "jumping genes".
Transcription.
The process of making an RNA molecule based on a sequence of DNA nucleotide bases.
Transducer.
A structure, mechanical or biological that translates one form of energy into
electrical energy. For instance the rods and cones in the eye are transducers
that translate light into electrical energy.
Transfer RNA(tRNA).
A type of RNA that carries an amino acid at its back end and has the so called
anticodon at its front end to complement the messenger RNA codons in translation.
Triglyceride.
A lipid synthesized from one glycerol and three fatty acid molecules. Includes
what we call animal fats and vegetable oils.
Tropism. A tropism
is behavior consisting of an orientation toward or away from a stimulus. In contrast
to a taxis, tropisms do not involve movement of the whole organism relative to
the stimulus.
Turgid. Swollen
and firm from fluids. Used in reference to plants kept in a hypotonic solution
allowing water to enter and swell the plant cells.