Biology Now, 2e

Glossary ■ G1

Glossary

A

abiotic Nonliving. Compare biotic.

acid A chemical compound that loses hydrogen ions (H+) in aque-

ous surroundings. Compare base (definition 1).

active site The location within an enzyme where substrates are

bound.

active transport The movement of a substance in response to an

input of energy. Compare passive transport.

adaptation 1. An evolutionary process by which a population

becomes better matched to its environment over time. 2. See

adaptive trait.

adaptive radiation The expansion of a group of organisms to

take on new ecological roles and to form new species and higher

taxonomic groups.

adaptive trait Also called an adaptation. A feature that gives

an individual improved function in a competitive environment.

adenine (A) One of the four nucleotides that make up DNA. The

other three are thymine (T), guanine (G), and cytosine (C).

ADP Adenosine diphosphate.

aerobic Requiring oxygen. Compare anaerobic.

algae One of two main groups of protists, whose members are

photosynthetic and may or may not be motile. Compare proto-

zoans.

alleles Different versions of a given gene.

allopatric speciation The formation of new species from geo-

graphically isolated populations. Compare sympatric speciation.

amino acid Any of a class of small molecules that are the building

blocks of proteins.

amniocentesis A prenatal genetic screening technique in which

amniotic fluid is extracted from the pregnancy sac that surrounds

a fetus by means of a needle that is inserted through the abdomen

into the uterus. Compare chorionic villus sampling.

anabolism Metabolic pathways that create complex biomolecules

from smaller organic compounds. Compare catabolism.

anaerobic Not requiring oxygen. Compare aerobic.

analogous trait A feature that is shared across species because

of convergent evolution, not because of modification by descent

from a recent common ancestor. Compare homologous trait.

analytical study An observational study that looks for patterns

in the information collected and addresses how or why those

patterns came to exist. Compare descriptive study.

anchorage dependence The phenomenon in which cells stop

dividing when detached from their surroundings.

angiogenesis The formation of new blood vessels.

angiosperms Flowering plants. One of two main groups of

seed-bearing plants, characterized by seeds enclosed in an ovary

and by flowers. Compare gymnosperms.

Animalia The animals. One of the six kingdoms of life, in the

domain Eukarya, encompassing all animals, including humans,

birds, and dinosaurs.

anticodon A unique sequence of three nitrogenous bases at one

end of a tRNA molecule that binds to the corresponding codon

on an mRNA molecule.

applied research Research in which scientific knowledge is

applied to human issues and often commercial applications.

Compare basic research.

Archaea One of the three domains of life (compare Bacteria and

Eukarya) and also one of the six kingdoms of life. The domain

and kingdom Archaea consists of single-celled organisms best

known for living in extremely harsh environments.

artificial selection The process by which individuals display

specific traits through selective breeding. Compare natural

selection.

ascomycetes Sac fungi, one of three main groups of fungi.

Compare basidiomycetes and zygomycetes.

asexual reproduction The process by which clones, offspring

that are genetically identical to the parent, are generated.

Compare sexual reproduction.

atom The smallest unit of an element that retains the element’s

distinctive properties. Atoms are the building blocks of all matter.

atomic mass number The sum of the number of protons and the

number of neutrons in an atom’s nucleus. Compare atomic number.

atomic number The number of protons in an atom’s nucleus.

Compare atomic mass number.

ATP Adenosine triphosphate, a small, energy-rich organic mole-

cule that is used to store energy and to move it from one part of a

cell to another. Every living cell uses ATP.