Glossary ❮ 335stomataStructure through which CO 2 enters a
plant, and water vapor and O 2 leave.
stop codons (UGA, UAA, UAG) Codons that stop
the production of a protein.
storage diseasesDiseases such as Tay-Sachs that
are caused by the absence of a particular lysosomal
hydrolytic enzyme.
strain Groups into which bacterial species are placed.
stroma The inner fluid portion of the chloroplast
that plays host to the light-independent reactions
of photosynthesis.
stylePathway in flower that leads to the ovary.
substratesSubstances that enzymes act upon.
succession Shift in the local composition of species
in response to changes that occur over time.
sulfhydryl group A functional group that helps sta-
bilize the structure of many proteins.
survivorship curvesA tool used to study the popula-
tion dynamics of species.
symbiosis A relationship between two different
species that can be classified as one of three main
types: commensalism, mutualism, and parasitism.
sympathetic nervous system Branch of the auto-
nomic nervous system that gets the body ready to
move.
sympatric speciation Interbreeding ceases even
though no physical barrier prevents it. Can
occur as a result of polyploidy and balanced
polymorphism.
symplast pathway Movement of water and nutri-
ents through the living portion of plant cells.
synaptic knob The end of the axon. This is where
calcium gates are opened in response to the chang-
ing potential, which causes vesicles to release sub-
stances called neurotransmitters (NTs) into the
synaptic gap between the axon and the target cell.
These NTs diffuse across the gap, causing a new
impulse in the target cell.
tactile communicationCommunication that involves
the use of touch in the conveying of a message.
taiga Biome characterized by lengthy, cold, and wet
winters. This biome is found in Canada and has
gymnosperms as its prominent plant life. This
biome contains coniferous forests (pine and other
needle-bearing trees).
tapeworm Parasitic flatworm whose adult form lives
in vertebrates.
taproot system System of roots found in many
dicots that starts as one thick root and divides into
many smaller lateral roots, which serve as an
anchor for the plant.
TATA box Group of nucleotides found in the pro-
moter region that assists in binding of RNA poly-
merase to the DNA strand for transcription.
taxis The reflex movement toward or away from a
stimulus.
taxonomy The field of biology that classifies organ-
isms according to the presence or absence of
shared characteristics in an effort to discover
evolutionary relationships between species.
Tay-Sachs diseaseA fatal genetic storage disease
that renders the body unable to break down a par-
ticular type of lipid.
temperate deciduous forest A biome that is found
in regions that experience cold winters where plant
life is dormant, alternating with warm summers that
provide enough moisture to keep large trees alive.
temperate grasslandsFound in regions with cold
winter temperatures. The soil of this biome is con-
sidered to be among the most fertile of all.
termination site Region of DNA that tells the poly-
merase when transcription should conclude.
territoriality Scenario in which territorial individuals
defend their territory against other individuals.
tertiary structureThe 3D (three-dimensional) arrange-
ment of a protein caused by interaction among the
various R groups of the amino acids involved.
test cross Crossing of an organism of unknown
dominant genotype with an organism that is
homozygous recessive for the trait, resulting in off-
spring with observable phenotypes. Test crosses
are used to determine the unknown genotype.
testisThe site of sperm and testosterone production
in animals; males have two testes, located in the
scrotum.
testosterone Sex hormone produced in testes that
stimulates the growth of male sex characteristics.
thermoacidophilesArchaebacteria that live in hot,
acidic environments.
thermoregulation The process by which tempera-
ture is maintained.
thigmotropism A plant’s growth in response to
touch.
thylakoid membrane system Inner membrane that
winds through the stroma of a chloroplast. Site of
the light-dependent reactions of photosynthesis.
thymine dimersThymine nucleotides located adja-
cent to one another on the DNA strand bindhttp://www.ebook3000.com