stellacyanin AnELECTRON-TRANSFER PROTEIN, con-
taining a TYPE 1 COPPERsite, isolated from exudates of
the Japanese lacquer tree.
stem cell Primitive blood cells, found in the bone mar-
row, circulating bloodstream, and umbilical cord, that
are capable of reproducing and differentiating to make
all varieties of mature blood cells (white blood cells, red
blood cells, and platelets). This means that all blood cells
originate from this single type of cell. PLURIPOTENT STEM
CELLs are also usually referred to as stem cells.
stereochemical Refers to the three-dimensional view
of a molecule.
stereoisomer A special case of Isomerism created by
a difference in the spatial arrangement of atoms with-
out any difference in connectivity or bond multiplicity
between the isomers.
See alsoCONFIGURATION;CONFORMATION.
steroid hormone or drug Alarge family of struc-
turally similar chemicals. Various steroids have sex-
determining, anti-inflammatory, and growth-regulatory
roles. Examples include corticosteroid and glucocorticoid.
Stevens-Johnson syndrome Asevereallergic drug
reaction characterized by blisters breaking out on the
lining of the mouth, throat, anus, genital area, and
eyes. A severe form of erythema multiform. Drugs that
can cause this reaction include penicillin, antibiotics
containing sulfa, barbiturates, and some drugs used to
treat high blood pressure and diabetes.
stimulus The cause for making a nerve cell respond;
can be in the form of light, sounds, taste, touch, smell,
temperature, etc.
stochastic Mathematical probability; a stochastic
model takes into account variations in outcome that
are because of chance alone.
stock number SeeOXIDATION NUMBER.stoma An opening to intercellular air spaces in the
epidermis of leaves of plants, consisting of a micro-
scopic pore surrounded by guard cells that open and
close to regulate gas exchange and water loss.strand The land bordering a body of water. The term
is used in the Everglades for the isolated “islands” of
trees and shrubs.strict aerobe An organism that utilizes aerobic
respiration and can survive only in an atmosphere of
oxygen.strict anaerobe An organism that cannot survive in
an atmosphere containing any oxygen.stroma The fluid matrix of the chloroplast in which
the thylakoids are situated. Those specialized mem-
brane structures where photosynthesis takes place.
In human biology, the stroma is the thickest part of
the cornea (450–600 microns, approximately 0.5 mil-
limeters) and is located between both Bowman’s and
Decemet’s membrane.stromatolite Stromatolites are colonies of millions
of single-cell cyanobacteria (formerly known as blue-
green algae). Stromatolites are so far the oldest known
fossils, dating back well over 3 billion years. They
werethe dominant life-formfor 2 billion years and
still persist today on the west coast of Australia. One
of the largest exposures of fossilized stromatolites is
the Petrified Sea Gardens in Saratoga Springs, New
York. It is listed as one of America’s National Historic
Landmarks, designated in 1999 by the Secretary of the
U.S. Department of the Interior. It is a 500-million-
year-old ocean reef from a time when the land that is
now Saratoga Springs was at the shore of a warm
tropical sea.
Stromatolites are also known as “stone cabbage,”
based on their fossil appearance.stromatolite 315