G-6 glossary
compound A substance of two or more elements, whose
relative proportions never vary. Organic compounds have a
backbone of carbon atoms arranged as a chain or ring struc-
ture. The simpler, inorganic compounds do not have compa-
rable backbones.
concentration gradient A difference in the number of mol-
ecules (or ions) of a substance between two adjacent regions,
as in a volume of fluid.
conclusion In scientific reasoning, a statement that evaluates
a hypothesis based on test results.
condensation reaction Chemical reaction in which two
molecules become covalently bonded into a larger molecule,
and water often forms as a by-product.
cone cell In the retina, a type of photoreceptor that responds
to intense light and contributes to sharp daytime vision and
color perception.
connective tissue A tissue type that consists of cells in a
matrix that contains a ground substance and protein fibers.
This category includes fibrous connective tissues, cartilage,
bone tissue, blood, and adipose (fat) tissue.
consumer [L. consumere, to take completely] Of ecosystems,
a heterotrophic organism that obtains energy and raw materi-
als by feeding on the tissues of other organisms. Herbivores,
carnivores, omnivores, and parasites are examples.
continuous variation A more or less continuous range of
small differences in a given trait among all the individuals of
a population.
control group In a scientific experiment, a group that differs
from the experimental group only with respect to the variable
being studied.
core temperature The body’s internal temperature, as
opposed to temperatures of the tissues near its surface. Nor-
mal human core temperature is about 37°C (98.6°F).
cornea Transparent tissue in the outer layer of the eye,
which causes incoming light rays to bend.
coronary circulation Arteries and veins that service the
heart.
corpus luteum (core-pus loo-tee-um) A glandular structure
that develops from cells of a ruptured ovarian follicle. It
secretes progesterone and some estrogen, both of which
maintain the lining of the uterus (endometrium).
covalent bond (koe-vay-lunt) [L. con, together, and valere,
to be strong] A sharing of electrons between atoms. When
electrons are shared equally, the bond is nonpolar. When
electrons are shared unequally, the bond is polar—slightly
positive at one end and slightly negative at the other.
cranial cavity Body cavity that houses the brain.
critical thinking Objective evaluation of information;
evidence-based thinking.
crossing over During prophase I of meiosis, an interaction
between a pair of homologous chromosomes. Their nonsister
chromatids break at the same place along their length andchromosome number The number of each type of chromo-
some in all cells except dividing germ cells or gametes.
chyme (kime) The thick mixture of swallowed food boluses
and acidic gastric fluid in the stomach that enters the small
intestine during digestion.
cilia (sill-ee-uh), singular: cilium [L. cilium, eyelid] Of
eukaryotic cells, short, hairlike projections that contain
a regular array of microtubules. Cilia serve as motile struc-
tures, help create currents of fluids, or are part of sensory
structures.
clavicle Long, slender collarbone that connects the pectoral
girdle with the sternum (breastbone).
cleavage Stage of development when mitotic cell divisions
convert a zygote to the ball of cells called the blastula.
cleavage furrow Of a cell undergoing cytoplasmic division,
a shallow, ringlike depression that forms at the cell surface as
contractile microfilaments pull the plasma membrane inward.
It defines where the cytoplasm will be cut in two.
cochlea Coiled, fluid-filled chamber of the inner ear. Sound
waves striking the eardrum become converted to pressure
waves in the cochlear fluid, and the pressure waves ulti-
mately cause a membrane to vibrate and bend sensory hair
cells. Signals from bent hair cells travel to the brain, where
they may be interpreted as sound.
codominance Condition in which a pair of nonidentical
alleles are both expressed, even though they specify two dif-
ferent phenotypes.
codon One of a series of base triplets in an mRNA molecule,
most of which code for a sequence of amino acids of a specific
polypeptide chain. (Of sixty-four codons, sixty-one specify
different amino acids and three of these also serve as start
signals for translation; one other serves only as a stop signal
for translation.)
coenzyme A type of nucleotide that transfers hydrogen
atoms and electrons from one reaction site to another. NAD+
is an example.
coitus Sexual intercourse.
colon (co-lun) The large intestine.
community The populations of all species occupying a habi-
tat; also applied to groups of organisms with similar lifestyles
in a habitat.
compact bone Type of dense bone tissue that makes up the
shafts of long bones and outer regions of all bones. Narrow
channels in compact bone contain blood vessels and nerves.
comparative morphology [Gk. morph, form] Anatomical
comparisons of major evolutionary lineages.
complement system A set of about thirty proteins circulat-
ing in blood plasma with roles in nonspecific defenses and in
immune responses. Some trigger lysis of pathogens, others
promote inflammation, and others stimulate phagocytes to
engulf pathogens.
complete blood count (CBC) The number of red blood
cells, white blood cells, and platelets in a microliter of blood.
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