G2 fiffGlossary
autosome Any chromosome that is not one of the sex chromosomes.
autotroph A metabolic producer, an organism that makes food on
its own. Chemoautotrophs acquire their energy from inorganic
chemicals in their environment. Photoautotrophs absorb the
energy of sunlight and take in carbon dioxide to conduct photo-
synthesis. Compare heterotroph.AV node See atrioventricular node.
B
Bacteria One of the three domains of life (compare Archaea and
Eukarya) and also one of the six kingdoms of life. The domain
and kingdom Bacteria includes familiar disease-causing
bacteria.base 1. A chemical compound that accepts hydrogen ions (H+) in
aqueous surroundings. Compare acid.- The nitrogen-containing component of nucleotides. The four
nitrogenous bases of DNA are adenine, cytosine, guanine, and
thymine. In RNA, thymine is replaced by uracil.base pair Also called nucleotide pair. Two nucleotides that form
one rung of the DNA ladder.base-pairing rules The rules that govern the pairing of nucle-
otides in DNA. Adenine (A) on one strand can pair only with
thymine (T) on the other strand, and cytosine (C) can pair only
with guanine (G).basic research Research that is intended to expand the funda-
mental knowledge base of science. Compare applied research.basidiomycetes Club fungi, one of three main groups of fungi.
Compare ascomycetes and zygomycetes.behavioral trait A characteristic of an individual’s behavior,
such as shyness or extroversion. Compare biochemical trait and
physical trait.benign Referring to a tumor, confined to one site.
bias A prejudice or opinion for or against something.
bilateral symmetry An animal body plan in which the body can
be divided by just one plane passing vertically from the top to
the bottom of the animal into two halves that mirror each other.
Compare radial symmetry.binary fission A type of cell division in which a cell simply divides
into two equal halves, resulting in daughter cells that are geneti-
cally identical to each other and to the parent cell.biochemical trait A characteristic due to specific chemical
processes of an individual, such as the level of a particular
enzyme. Compare behavioral trait and physical trait.biodiversity The variety of all the world’s life-forms, as well
as their interactions with each other and the ecosystems they
inhabit.biogeography The geographic locations where organisms or the
fossils of a particular species are found.biological hierarchy A way to visualize the breadth and
scope of life, from the smallest structures to the broadest
interactions between living and nonliving systems that we can
comprehend.biological species concept The idea that a species is defined
as a group of natural populations that can interbreed to
produce fertile offspring and cannot breed with other such
groups.biome A large region of the world defined by shared physical char-
acteristics (especially climate) and a distinctive community of
organisms.biomolecule Also called macromolecule. A large organic
molecule that is critical for living cells. Four major classes of
biomolecules are proteins, carbohydrates, nucleic acids, and
lipids.biosphere All the world’s living organisms and the physical spaces
where they live.biotic Living. Compare abiotic.
bipedal Walking upright on two legs.
boreal forest A terrestrial biome that is found in northern or
high-latitude regions, has cold, dry winters and mild summers,
and is dominated by coniferous trees.bryophytes A group of nonflowering plants that includes liver-
worts and mosses.C
Calvin cycle See light-independent reactions.Cambrian explosion The burst of evolutionary activity, occur-
ring about 540 million years ago, that resulted in a dramatic
increase in the diversity of life. Most of the major living animal
groups first appear in the fossil record during this time.camouflage Any type of coloration or appearance that makes an
organism hard to find or hard to catch. Compare mimicry and
warning coloration.cancer cell Also called malignant cell. A tumor cell gains anchor-
age independence and starts invading other tissues.capsule An additional protective layer that surrounds the cell wall
in prokaryotes.carbohydrate Any of a major class of biomolecules, including
sugars and starches, built of repeating units of carbon, hydrogen,
and oxygen.carbon cycle The movement of carbon within biotic communities,
between living organisms and their physical surroundings, and
within the abiotic world.carbon dioxide (CO 2 ) The most abundant and consequential of
the greenhouse gases.carbon fixation See light-independent reactions.
carbon sink A natural or artificial reservoir that absorbs more
carbon than it releases. Compare carbon source.carbon source A natural or artificial reservoir that releases more
carbon than it absorbs. Compare carbon sink.carnivore An animal (or, rarely, plant) that eats other animals.
Compare herbivore and omnivore.carrying capacity The maximum population size that can be
sustained in a given environment.