the bronchi, and inhibits digestion. The sympathetic
division opposes the actions of the parasympathetic
division.
sympatric speciation The creation of a new species
within a geographical area caused by reproductive iso-
lation among individuals coexisting in the area.
symplast The interconnected protoplasm between
cells in a plant due to the presence of pores between the
cells that allow cytoplasmic flow (plasmadesmata).
symplesiomorph A character state shared by two or
more taxa thought to have originated as an evolution-
ary novelty in an earlier ancestor.
symptom Asubjectively perceived problem or com-
plaint reported by an individual. For example, a rash is
a symptom that the immune system is reacting to some-
thing such as dust.
syn SeeANTI.
synapomorphy A derived or specialized character
(apomorphy) that is shared by two or more groups that
originated in their last common ancestor; used to infer
common ancestry.
synapse A gapor junction between the ends of two
neurons in a neural pathway where nerve impulses pass
from one to the other; an impulse causes the release of
a neurotransmitter at the synapse that diffuses across
the gap and triggers the next neuron’s electrical
impulse.
See alsoNEURON.
synapsis The alignment of chromosomes during
prophase of the first division in meiosis so that each
chromosome is next to its homologue; the time when
crossing over occurs.
synaptic terminal(synaptic vesicle) A membrane or
bulb at the end of an axon terminal that stores and
releases neurotransmitters.syndrome Agroup of symptoms and diseases that
together are characteristic of a specific condition.synergism The combination of two or more sub-
stances in which the sum result of this combination is
greater than the effects that would be exhibited from
each of the individual substances alone.syngamy When male and female gametes meet and
join. Same as sexual reproduction.synonyms One of several different scientific names
that are spelled differently but refer to the same species.
An example is Epilobium canum(E. Greene) Raven
and Zauschneria californicaK. Presl. The older name is
the senior synonym and is how the species thenceforth
is referred once the synonymy has been recognized. The
more recent name is the junior synonym and its use is
discontinued.synthase An ENZYME that catalyzes a reaction in
which a particular molecule is synthesized, not neces-
sarily by formation of a bond between two molecules
(contrast with synthetase).
See alsoLIGASE.synthetase SeeLIGASE.system Set of organs in the body with a common
structure or function. Examples of body systems
include the immune, gastrointestinal, respiratory, and
lymphatic systems.systematics The study of diversity, evolutionary, and
genetic relationships among organisms.systematics 319