Glossary ■ (^) G13
solution Any combination of a solute and a solvent.
solvent The fluid, such as water, into which a substance has
dissolved. Compare solute.
somatic cell A non–sex cell. Compare gamete.
speciation The process by which one species splits to form two
species or more.
species 1. Members of a group that can mate with one another to
produce fertile offspring.
- The smallest unit of classification in the Linnaean hierarchy.
species interaction Any of four ecological interactions—mutu-
alism, commensalism, predation, and competition—that occur
between different species.species richness The total number of different species that live in
an ecological community.spore In fungi, a reproductive structure that can survive for
long periods of time in a dormant state and will sprout under
favorable conditions to produce the body of the organism.sporulation The formation of thick-walled dormant structures
called spores.stabilizing selection The pattern of natural selection in which
individuals with intermediate values of an inherited phenotypic
trait have an advantage over other individuals in the population.
Compare directional selection and disruptive selection.start codon The codon AUG; the point on an mRNA strand at
which the ribosomes begin translation. Compare stop codon.statistics A branch of mathematics that estimates the reliability
of data.stop codon The codon UAA, UAG, or UGA; the point on an mRNA
strand at which the ribosomes end translation. Compare start codon.substitution A mutation in which one base is substituted for
another in the DNA sequence of a gene. Compare deletion and
insertion.substrate A molecule that will react to form a new product.
succession The process by which the species in a community
change over time.sustainable Able to be continued indefinitely without causing
serious damage to the environment.sympatric speciation The formation of new species in the absence
of geographic isolation. Compare allopatric speciation.T
temperate forest A terrestrial biome characterized by snowy
winters and moist, warm summers and dominated by trees and
shrubs adapted to relatively rich soil.template strand The strand of DNA that is used as a template to
make a new strand of DNA.terminator A segment of DNA that, when reached by RNA poly-
merase, stops transcription. Compare promoter.tertiary consumer An organism that eats secondary consumers.
Compare primary consumer and quaternary consumer.theory A hypothesis, or a group of related hypotheses, that has
received substantial confirmation through diverse lines of inves-
tigation by independent researchers. Compare fact.thermophile A prokaryote, usually archaean, that can live in
extremely hot environments, such as geysers, hot springs, and
hydrothermal vents.thymine (T) One of the four nucleotides that make up DNA. The
other three are adenine (A), guanine (G), and cytosine (C).tissue A group of cells that function in an integrated manner to
perform a unique set of tasks in the body.transcription The synthesis of RNA based on a DNA template.
Compare translation.transfer RNA (tRNA) A type of RNA that facilitates translation by
delivering specific amino acids to the ribosomes as codons are read
off of an mRNA. Compare messenger RNA and ribosomal RNA.translation The process by which ribosomes convert the informa-
tion in mRNA into proteins. Compare transcription.transpiration The process of plants absorbing water through
their roots and releasing this water through their leaves into the
atmosphere.transport protein A protein that acts like a gate, channel, or
pump that allows molecules to move into and out of a cell.treatment group Also called experimental group. The group
of subjects in an experiment that is maintained under the same
standard set of conditions as the control group but is subjected to
manipulation of the independent variable. Compare control group.tRNA See transfer RNA.
trophic level Each level of the energy pyramid, corresponding to
a step in a food chain.tropical forest A terrestrial biome characterized by warm
temperatures, about 12 hours of daylight, and seasonally heavy
or year-round rains, and containing a rich diversity of organisms.tumor A cell mass that results from runaway cell division.
tundra A terrestrial biome containing permafrost that is found
at the poles and on mountaintops. Tundra is dominated by
low-growing flowering plants and a lack of trees.U
up-regulation The speeding up of gene expression. Compare
down-regulation.V
vacuole An organelle in plant cells that acts as a garbage or recy-
cling center and that stores water. Compare lysosome.variable A characteristic of any object or individual organism that
can change.variable trait A trait that is different in different individuals of a
species. Compare invariant trait.vascular system In plants, a network of tissues that is made up of
tubelike structures specialized for transporting fluids.vertebrae (sing. vertebra) The strong, hollow sections of the
backbone, or vertebral column.