GLOSSARY G1
abiotic Nonliving. Compare biotic.
acid Seeacid solution.
acid deposition The falling of acids and acid-
forming compounds from the atmosphere to the
earth’s surface. Acid deposition is commonly
known as acid rain, a term that refers to the wet
deposition of droplets of acids and acid-forming
compounds.
adaptation Any genetically controlled struc-
tural, physiological, or behavioral characteristic
that helps an organism survive and reproduce
under a given set of environmental conditions.
It usually results from a benefi cial mutation.
Seebiological evolution, differential reproduction,
mutation, natural selection.
adaptive radiation Process in which numer-
ous new species evolve to fi ll vacant and new
ecological niches in changed environments,
usually after a mass extinction. Typically, this
process takes millions of years.
adaptive trait Seeadaptation.
aerobic respiration Complex process that
occurs in the cells of most living organisms,
in which nutrient organic molecules such as
glucose (C 6 H 12 O 6 ) combine with oxygen (O 2 )
to produce carbon dioxide (CO 2 ), water (H 2 O),
and energy. Compare photosynthesis.
age structure Percentage of the population
(or number of people of each sex) at each age
level in a population.
air pollution One or more chemicals in
high enough concentrations in the air to harm
humans, other animals, vegetation, or materials.
Excess heat is also considered a form of air pol-
lution. Such chemicals or physical conditions are
called air pollutants.
alien species Seenonnative species.
alpha particle Positively charged matter,
consisting of two neutrons and two protons,
which is emitted as radioactivity from the nuclei
of some radioisotopes. See also beta particle,
gamma rays.
altitude Height above sea level. Compare
latitude.
anaerobic respiration Form of cellular
respiration in which some decomposers get the
energy they need through the breakdown of
glucose (or other nutrients) in the absence of
oxygen. Compare aerobic respiration.
ancient forest Seeold-growth forest.
annual Plant that grows, sets seed, and dies in
one growing season. Compare perennial.
anthropocentric Human-centered.
applied ecology Seereconciliation ecology.
aquatic Pertaining to water. Compare
terrestrial.aquatic life zone Marine and freshwater por-
tions of the biosphere. Examples include fresh-
water life zones (such as lakes and streams) and
ocean or marine life zones (such as estuaries,
coastlines, coral reefs, and the open ocean).
aquifer Porous, water-saturated layers of
sand, gravel, or bedrock that can yield an eco-
nomically signifi cant amount of water.arid Dry. A desert or other area with an arid
climate has little precipitation.
artifi cial selection Process by which humans
select one or more desirable genetic traits in the
population of a plant or animal species and then
useselective breeding to produce populations con-
taining many individuals with the desired traits.
Comparegenetic engineering, natural selection.asexual reproduction Reproduction in which
a mother cell divides to produce two identical
daughter cells that are clones of the mother cell.
This type of reproduction is common in single-
celled organisms. Compare sexual reproduction.
atmosphere Whole mass of air surrounding
the earth. See stratosphere, troposphere. Compare
biosphere, geosphere, hydrosphere.atmospheric pressure Force or mass per unit
area of air, caused by the bombardment of a
surface by the molecules in air.
atom Minute unit made of subatomic particles
that is the basic building block of all chemical
elements and thus all matter; the smallest unit
of an element that can exist and still have the
unique characteristics of that element. Compare
ion, molecule.
atomic number Number of protons in the
nucleus of an atom. Compare mass number.
atomic theory Idea that all elements are
made up of atoms; the most widely accepted
scientifi c theory in chemistry.
autotroph Seeproducer.
background extinction Normal extinc-
tion of various species as a result of changes in
local environmental conditions. Compare mass
extinction.
bacteria Prokaryotic, one-celled organisms.
Some transmit diseases. Most act as decom-
posers and get the nutrients they need by break-
ing down complex organic compounds in thetissues of living or dead organisms into simpler
inorganic nutrient compounds.
barrier islands Long, thin, low offshore
islands of sediment that generally run parallel to
the shore along some coasts.
benthos Bottom-dwelling organisms. Com-
paredecomposer, nekton, plankton.
beta particle Swiftly moving electron emitted
by the nucleus of a radioactive isotope. See also
alpha particle, gamma ray.
biocentric Life-centered. Compare anthropo-
centric.biodegradable Capable of being broken down
by decomposers.
biodegradable pollutant Material that can
be broken down into simpler substances (ele-
ments and compounds) by bacteria or other de-
composers. Paper and most organic wastes such
as animal manure are biodegradable but can
take decades to biodegrade in modern landfi lls.
Comparenondegradable pollutant.biodiversity Variety of different species (spe-
cies diversity), genetic variability among individu-
als within each species (genetic diversity), variety
of ecosystems (ecological diversity), and functions
such as energy fl ow and matter cycling needed
for the survival of species and biological com-
munities (functional diversity).
biodiversity hot spots Areas especially rich
in plant species that are found nowhere else
and are in great danger of extinction. These
areas suffer serious ecological disruption, mostly
because of rapid human population growth and
the resulting pressure on natural resources.
biogeochemical cycle Natural processes that
recycle nutrients in various chemical forms from
the nonliving environment to living organisms
and then back to the nonliving environment.
Examples include the carbon, oxygen, nitrogen,
phosphorus, sulfur, and hydrologic cycles.
biological community Seecommunity.
biological diversity Seebiodiversity.
biological evolution Change in the genetic
makeup of a population of a species in succes-
sive generations. If continued long enough, it
can lead to the formation of a new species. Note
that populations, not individuals, evolve. See
alsoadaptation, differential reproduction, natural
selection, theory of evolution.
biological pest control Control of pest popu-
lations by natural predators, parasites, or dis-
ease-causing bacteria and viruses (pathogens).