Biology Now, 2e

Glossary ■ (^) G11
pollen In plants, a microscopic structure containing sperm cells
that can be lofted into the air in massive quantities.
polygenic trait A genetic trait that is governed by the action of
more than one gene. Compare pleiotropy.
polymer A long strand of repeating units of small molecules called
monomers. For example, proteins are polymers made up of amino
acid monomers.
polymerase chain reaction (PCR) A technique for replicating
DNA that can produce millions of copies of a DNA sequence in
just a few hours from a small initial amount of DNA.
polyploidy The condition in which an individual’s somatic cells
have more than two sets of chromosomes.
population A group of individuals of the same species living and
interacting in a shared environment.
population density The number of individuals per unit of area.
population doubling time The time it takes a population
to double in size, as a measure of how fast a population is
growing.
population ecology The study of the number of organisms in a
particular place.
population size The total number of individuals in a population.
postzygotic barrier A barrier that prevents a zygote from devel-
oping into a healthy and fertile individual—that is, a reproductive
barrier that acts after a zygote exists. Compare prezygotic barrier.
predation A species interaction in which one species benefits and
the other species is harmed. Compare commensalism, competi-
tion, and mutualism.
predator A consumer that eats either plants or animals. Compare
prey.
preimplantation genetic diagnosis (PGD) The removal of
one or two cells from an embryo developing in a petri dish, usually
3 days after fertilization, followed by testing for genetic disor-
ders. One or more embryos that are free of disorders are then
implanted into a woman’s uterus.
prey An animal that is eaten by a predator.
prezygotic barrier A barrier that prevents a male gamete
and a female gamete from fusing to form a zygote—that is, a
reproductive barrier that acts before a zygote exists. Compare
postzygotic barrier.
primary consumer An organism that eats producers. Comp-
are secondary consumer, tertiary consumer, and quaternary
consumer.
primary literature Scientific literature in which research is first
published. Compare secondary literature.
primary succession Succession that occurs in a newly created
habitat, usually from bare rock or sand. Compare secondary
succession.
primates The order of mammals to which humans belong. All
primates have flexible shoulder and elbow joints, five functional
fingers and toes, opposable thumbs, flat nails, and brains that are
large in relation to the body.
primer A short stretch of RNA or DNA that is complementa-
ry-base-paired to a DNA template to provide a 3 ́-hydroxyl group
for polymerase to initiate DNA replication or the polymerase
chain reaction (PCR), respectively.
process of science See scientific method.
producer An organism at the bottom of a food chain that uses
energy from the sun to produce its own food. Compare consumer.
product A substance that results from a chemical reaction.
Compare reactant.
prokaryote An organism that belongs to either the Bacteria or the
Archaea. Compare eukaryote.
promoter A segment of DNA near the beginning of a gene that
RNA polymerase recognizes and binds to begin transcription.
Compare terminator.
protein Any of a major class of biomolecules built of amino acids.
Protista The protists. One of the six kingdoms of life, in the
domain Eukarya; a diverse group that is composed of mainly
single-celled, microscopic organisms grouped together simply
because they are not plants, animals, or fungi, and that includes
amoebas and algae.
proton A positively charged particle found in the nucleus of an
atom. Compare electron and neutron.
protozoans One of two main groups of protists, whose members
are nonphotosynthetic and motile. Compare algae.
pseudoscience Scientific-sounding statements, beliefs, or prac-
tices that are not actually based on the scientific method.
Punnett square A grid-like diagram showing all possible ways
that two alleles can be brought together through fertilization.
Q
quaternary consumer An organism that eats tertiary consum-
ers. Compare primary consumer and secondary consumer.
quorum sensing A system of cell-to-cell communication used
by prokaryotes that enables them to sense and respond to
other bacteria in the area in accordance with the density of the
population.
R
radial symmetry An animal body plan in which the body can be
sliced symmetrically along any number of vertical planes that pass
through the center of the animal. Compare bilateral symmetry.
reactant A substance that undergoes change in a chemical reac-
tion. Compare product.
receptor-mediated endocytosis A form of specific endocytosis
in which receptor proteins embedded in the membrane recognize
specific surface characteristics of substances that will be incorpo-
rated into the cell.
receptor protein A site where a molecule from another cell can
bind.
recessive allele An allele that has no effect on the phenotype
when paired with a dominant allele.