332 ❯ Glossary
fission and includes bacteria—both heterotrophic
and autotrophic types.
prolactinHormone that controls the production of
milk and leads to a decrease in the synthesis and
release of GnRH, thus inhibiting ovulation.
promoter region A recognition site that shows the
polymerase where transcription should begin.
prostate gland Structure whose function in the male
reproductive system is to add a basic (pH > 7)
liquid to the mix to help neutralize the acidity
of the urine that may remain in the common
urethral passage.
protein Organic compound composed of chains of
amino acids that function as structural compo-
nents, transport aids, enzymes, and cell signals,
among other things.
protein hormonesHormones too large to move
inside a cell, and which bind to receptors on the
surface of the cell instead.
protein kinase Protein that controls the activities of
other proteins through the addition of phosphate
groups.
provirusA virus genome that is integrated into the
DNA of a host cell that can be transmitted from
one generation to the next without causing lysis.
pseudocoelomate Animal that has a fluid-filled
body cavity that is not enclosed by mesoderm.
pseudopods Extensions from protists (organisms of
the kingdom Protist) that assist in collection of
nutrients.
P siteRegion in protein synthesis machinery that
holds the tRNA carrying the growing protein.
PTH Seeparathyroid hormone.
punctuated equilibria model Theorizes that evolu-
tionary change occurs in rapid bursts separated by
large periods of stasis (no change).
purineA nitrogenous base that contains a double
ring structure (adenine, guanine).
pyloric sphincterThe connection point between the
stomach and the small intestine.
pyramid of numbers Pyramid based on the number
of individuals at each level of the biomass chain.
Each box in this pyramid represents the number of
members of that level. The highest consumers in
the chain tend to be quite large, resulting in a
smaller number of those individuals spread out
over a given area.
pyrimidine A nitrogenous base that contains a single
ring structure (cytosine, thymine).
Q 10 value Statistic that shows how an increase in
temperature affects the metabolic activity of an
organism.
quaternary structure The arrangement of separate
polypeptide “subunits” into a single protein. Seen
only in proteins with more than one polypeptide
chain.
radiation The loss of heat through ejection of elec-
tromagnetic waves.
random distribution Random distribution of species
in a given geographic area.
rate of reaction Rate at which a chemical reaction
occurs.
reaction centersControl centers made up of pigments.
reciprocal altruismAltruistic behavior performed
with the expectation that the favor will be
returned.
recombinant DNA DNA that contains DNA pieces
from multiple sources.
red blood cellsCells in body that contain hemo-
globin and serve as the oxygen delivery system in
the body.
red-green colorblindness Sex-linked condition that
leaves those afflicted unable to distinguish between
red and green colors.
redox reaction A reduction–oxidation reaction
involving the transfer of electrons.
replication forkFork opened in DNA strand that
allows DNA replication to occur.
repolarization The lowering of the potential back
down to its initial level, stopping the transmission
of neural signals at that point.
repressor Protein that prevents the binding of RNA
polymerase to the promoter site.
reproductive success A measure of how many sur-
viving offspring one produces relative to how
many the other individuals in one’s population
produce.
RERSeerough endoplasmic reticulum.
respirometer Machine that can be used to calculate
the respiration rate of a reaction.
restriction enzymes Enzymes that cut DNA at spe-
cific nucleotide sequences. This results in DNA
fragments with single-stranded ends called “sticky
ends,” which find and reconnect with other DNA
fragments containing the same ends (with the
assistance of DNA ligase).
retrovirusAn RNA virus that carries an enzyme
calledreverse transcriptasethat reverse-transcribes