G12fiffGlossary
recessive genetic disorder A genetic disorder that is inherited
as a recessive trait on an autosome. Compare dominant genetic
disorder.relative species abundance How common one species is when
compared to another.reproduction The making of a new individual like oneself.
reproductive barrier A barrier that prevents two species
from interbreeding, making them reproductively isolated.reproductive isolation The condition in which barriers prevent
populations from interbreeding. Compare ecological isolation
and geographic isolation.ribonucleic acid See RNA.
ribosomal RNA (rRNA) A type of RNA that is an important
compo nent of ribosomes. Compare messenger RNA and transfer
RNA.ribosome The site of protein synthesis (translation) in the cytoplasm.
Ribosomes are embedded in the rough endoplasmic reticulum.RNA Ribonucleic acid, a single-stranded nucleic acid transcribed
from DNA and consisting of the ribonucleotides adenine,
guanine, cytosine, and uracil.RNA polymerase An enzyme that recognizes and binds a gene’s
promoter sequence and then separates the two strands of DNA
during transcription.RNA splicing Processing of mRNA in which the introns
are snipped out of a pre-mRNA and the remaining pieces of
mRNA—the exons—are joined to generate the mature mRNA.rough ER A part of the endoplasmic reticulum, having a knobby
appearance because of embedded ribosomes, where proteins are
assembled. Compare smooth ER.rRNA See ribosomal RNA.
rubisco The enzyme that catalyzes the first step in the light-
independent reactions of photosynthesis, fixing a carbon mole-
cule from CO 2.S
S phase The “synthesis” phase of the cell cycle, in which prepara-
tions for cell division begin. A critical event during this phase is
the replication of all the cell’s DNA molecules.S-shaped growth curve The type of graphical curve that
represents logistic growth. Compare J-shaped growth curve.scavenger An animal that eats dead or dying animals and
plants. Scavengers are categorized as either decomposers or
detritivores.science A body of knowledge about the natural world, and an
evidence-based process for acquiring that knowledge.scientific claim A statement about how the world works that can
be tested using the scientific method.scientific literacy An understanding of the basics of science and
the scientific process.scientific method Also called process of science. The practices
that produce scientific knowledge.scientific name The unique two-word Latin name, consisting of
the genus and species names, that is assigned to a species in the
Linnaean hierarchy.secondary consumer An organism that eats primary consumers.
Compare tertiary consumer and quaternary consumer.secondary literature Scientific literature that summarizes and
synthesizes an area of research. Compare primary literature.secondary succession Succession that occurs after a disturbance
in a community. Compare primary succession.seed In plants, the embryo and a supply of stored food, all encased
in a protective covering.selective breeding The process by which humans allow only indi-
viduals with certain inherited characteristics to mate.selective permeability The quality of plasma membranes by
which some substances are allowed to cross the membrane at all
times, others are excluded at all times, and still others can pass
through the membrane when they are aided by transport proteins.semiconservative replication The mode of replication by which
DNA is duplicated, where one “old” strand (the template strand)
is retained (conserved) in each new double helix.sense To perceive the world through a sensory system such as sight,
touch, or smell.serotype See viral strain.
sex chromosome One of the two chromosomes (X and Y) that
determine gender. Compare autosome.sex-linked Found solely on the X or Y chromosome. See also
X-linked and Y-linked.sexual dimorphism A distinct difference in appearance between
the males and females of a species.sexual reproduction The process by which genetic information
from two individuals is combined to produce offspring. It has
two steps: cell division through meiosis, followed by fertilization.
Compare asexual reproduction.sexual selection Natural selection in which a trait increases an
individual’s chance of mating even if it decreases the individual’s
chance of survival.shared derived trait A unique feature common to all members
of a group that originated in the group’s most recent common
ancestor and then were passed down in the group.simple diffusion Diffusion in which substances such as the small,
uncharged molecules of water, oxygen, or carbon dioxide, slip
between the large molecules in the phospholipid bilayer without
much hindrance. Compare facilitated diffusion.sister chromatids The two identical DNA molecules produced by
the replication of a chromosome.smooth ER A part of the endoplasmic reticulum, having a smooth
appearance, where lipids and hormones are manufactured.
Compare rough ER.soluble Able to mix completely with water.
solute A dissolved substance, such as sugar in water. Compare
solvent.