G4 fiffGlossary
condensation The transition from gas to liquid. Compare evap-
oration.conjugation The physical process of transferring genetic material
through direct contact.consumer An organism that obtains energy by eating all or parts
of other organisms or their remains. Compare producer.control group The group of subjects in an experiment that is
maintained under a standard set of conditions with no change in
the independent variable. Compare treatment group.controlled experiment An experiment that measures the value
of a dependent variable for two groups of subjects that are
comparable in all respects except that one group (the treatment
group) is exposed to a change in the independent variable and the
other group (the control group) is not.convection cell A large and consistent atmospheric circulation
pattern in which warm, moist air rises and cool, dry air sinks.
Earth has four giant convection cells.convergent evolution Evolution that results in organisms that
have different genetics but appear very much alike.correlation A statistical relation indicating that two or more
aspects of the natural world behave in an interrelated manner: if
one shows a particular value, we can predict a particular value for
the other aspect. Compare causation.covalent bond The sharing of electrons between two atoms.
Compare hydrogen bond and ionic bond.credentials Evidence of qualifications and competence to be
recognized as an authority on a subject. Such evidence would
include education and accomplishments.CRISPR Clustered regularly interspaced short palindromic
repeats. An RNA sequence that guides molecular machinery to a
DNA sequence through complementary base-pairing.cross See genetic cross.
crossing-over The physical exchange of chromosomal seg-
ments between homologous chromosomes. Compare genetic
recombination.CVS See chorionic villus sampling.
cyclical fluctuation A relatively predictable pattern of change in
popu lation size that occurs when at least one of two species is
stro ngly influenced by the other. Compare irregular fluctuation.cytokinesis Division of the cytoplasm, the second step of mitotic
division, resulting in two self-contained daughter cells. Compare
mitosis.cytosine (C) One of the four nucleotides that make up DNA. The
other three are adenine (A), thymine (T), and guanine (G).cytoskeleton The network of protein cylinders and filaments that
forms the framework of a cell.D
data (sing. datum) Information collected in a scientific study.
decomposer A scavenger that dissolves the dead bodies of other
organisms to consume them. Compare detritivore.deletion A mutation in which a base is deleted from the DNA
sequence of a gene. Compare insertion and substitution.density-dependent population change A change in popu-
lation size that occurs when birth and death rates change as
the population density changes. Compare density-independent
population change.density-independent population change A change in popu-
lation size that occurs when populations are held in check by
factors that are not related to the density of the population.
Compare density-dependent population change.deoxyribonucleic acid See DNA.
dependent variable Any variable that responds, or could poten-
tially respond, to changes in an independent variable.descriptive study An observational study that reports infor-
mation about what is found in nature. Compare analytical
study.desert A terrestrial biome characterized by a lack of moisture and
temperature fluctuation from very hot during the day to very cold
at night, and dominated by succulent plants such as cacti.detritivore A scavenger that mechanically breaks apart the
dead bodies of other organisms to consume them. Compare
decomposer.diffusion The movement of a substance from a region of higher
concentration to a region of lower concentration.dihybrid cross A controlled mating experiment involving organ-
isms that are heterozygous for two traits.diploid Possessing a double set of genetic information, represented
by 2n. Somatic cells are diploid. Compare haploid.directional selection The most common pattern of natural
selection, in which individuals at one extreme of an inherited
phenotypic trait have an advantage over other individuals in
the population. Compare disruptive selection and stabilizing
selection.disruptive selection The least common pattern of natural
selection, in which individuals with either extreme of an inher-
ited trait have an advantage over individuals with an interme-
diate phenotype. Compare directional selection and stabilizing
selection.DNA Deoxyribonucleic acid, the genetic code of life, consisting of
two parallel strands of nucleotides twisted into a double helix.
DNA is the genetic material that transfers information from
parents to offspring.DNA polymerase The enzyme that builds new strands of DNA in
DNA replication.DNA replication The duplication of a DNA molecule.
DNA sequence similarity The degree to which the sequences of
two different DNA molecules are the same—a measure of how
closely related two DNA molecules are to each other.domain The highest hierarchical level in the organization of life,
describing the most basic and ancient divisions among living
organisms. The three domains of life are Bacteria, Archaea, and
Eukarya.