orhydrocarbon solvents (mineral spirits). Water is the
most common solvent.
solvolysis Reaction with a solvent involving the rup-
ture of one or more bonds in the reacting solute.
somatic cell Term for any cell in the body except
gametes (sperm and egg) and their precursors.
somatic nervous system A branch of the peripheral
nervous system containing both afferent and efferent
nerves. It consists of peripheral nerve fibers that send
sensory information to the central nervous system as
well as motor nerve fibers that carry signals to skeletal
muscle, which allows the movement of arms and legs.
sonar Short for sound navigation ranging. A system
that transmits sound underwater and reads the reflected
sound received back to detect and locate underwater
objects or to measure distances. A form of echolocation.
soret band A very strong absorption band in the
blue region of the optical absorption spectrum of a
HEMEprotein.
source habitat A habitat that produces a surplus
number of individuals, i.e., where reproduction exceeds
mortality and excess individuals emigrate.
See alsoSINK HABITAT.
Southern blotting A gel technique invented by
Edward M. Southern in 1975 to locate a particular
DNA sequence within a complex mixture. DNA frag-
ments are separated by electrophoresis in an agarose
gel (involving in situ denaturation), transfer by capil-
laryaction to a nitrocellulose sheet, and hybridization
to a labeled nucleic acid probe.
spawning Sexual reproduction in the form of micro-
scopic eggs and sperm being discharged into water at
the same location; common among fish. A spawning
ground is the location where the female fish lays its
eggs and the male fertilizes them.speciation Refers to the chemical form or compound
in which an element occurs in both nonliving and living
systems. It can also refer to the quantitative distribu-
tion of an element. In biology, it refers to the origina-
tion of a new species.
See alsoBIOAVAILABILITY.species A genomically coherent group of individuals
sharing a large degree of similarity in independent fea-
tures that interbreed and are reproductively isolated
from other such groups. One of the levels of scientific
classification in a taxonomic hierarchy that includes
the genus, family, order, class, phylum, and kingdom.
There are more than 1 million named species on Earth
and millions more nameless.
See alsoTAXON.species diversity Species in a biological community
based on number and relative abundance.species richness The quantitative number of species
in a community, biome, or other defined region.species selection Based on speciation and extinction
rates, the observation that species living longer and
producing more species will determine major evolution-
ary directions.specific heat The amount of heat per unit mass
required to move the temperature by one degree Cel-
sius. Every substance has its own specific heat. Mea-
sured in joules per gram-degree Celsius (J/g°C), the
specific heat of water is 2.02 J/g°C in gas phase, 4.184
in liquid phase, and 2.06 in solid phase.specificity The property of antibodies that enables
them to react with some antigenic determinants and310 solvolysis