resonance Raman spectroscopy A spectroscopic
technique increasingly used in bioinorganic chemistry for
characterization and assignment of vibrations directly
connected with a CHROMOPHORE, as well for the assign-
ment of the chromophore. The excitation frequency is
applied close to the absorption maximum of the chro-
mophore. Particularly useful for deeply colored species.
resource partitioning The process whereby coexist-
ing species living in the same ecosystem each find a sep-
arate niche so that resources can be divided up and
used without having to compete. Often a few dominant
species are able to exploit most of the resources, and
the rest divide up the remainder.
respiration The process where mitochondria in the
cells of plants and animals release chemical energy
from sugar and other organic molecules through chem-
ical oxidation.
See alsoKREBS CYCLE.
respiratory system The respiratory system is the
system by which oxygen, essential for life, is taken
into the body and the waste product, carbon dioxide,
is expelled from the body. The respiratory system
consists of the mouth and nose, airways, and lungs.
Air enters through the mouth and nose and passes
down the pharynx (throat) and through the larynx
(voice box). Air then continues down through the tra-
chea (windpipe), which branches into two bronchi
(singular: bronchus) to each of the two lungs. The
inflammation of the bronchus is called bronchitis.
The bronchi branch many times until becoming much
smaller airways called “bronchioles.” At the end of
each bronchiole are tiny air-filled cavities called alve-
oli. Each alveolus is surrounded by many blood capil-
laries, which allow oxygen to move into the
bloodstream and carbon dioxide out. This exchange
of substances is the primary function of the respirato-
ry system.
resting potential The state of a neuron’s charge, the
gradient of electric potential across the membrane,
when it is in a resting state and ready to receive a nerve
impulse (the ACTION POTENTIAL); usually consists of a
negative charge on the inside of the cell relative to the
outside. At rest, the cell membrane electrical gradient
maintains a negative interior charge of –70 mv.restriction enzyme(restriction endonuclease) A DNA
cutting protein that recognizes a specific nucleotide
sequence in a DNA molecule and excises the DNA;
found in bacteria. Some sites are common and occur
every several hundred base pairs, while others are less
common. Bacteria possess several hundred restriction
enzymes that cut more than 100 different DNA
sequences. Each restriction enzyme has a single, specific
recognition sequence and cuts the DNA molecule at a
specific site. Some restriction enzymes have been used
in RECOMBINANT DNA TECHNOLOGY.restriction fragment-length polymorphisms(RFLPs)
Apolymorphism is a genetic variant that appears in
about 1 percent of the population, e.g., the human Rh
factor. An RFLP is a variation between individuals in
DNA fragment sizes cut by specific restriction
enzymes. RFLPs usually are caused by mutation at a
cutting site. The resulting polymorphic sequences in
RFLPs are used as markers on both physical and
genetic linkage maps. RFLPs are useful in screening
human DNA for the presence of potentially deleterious
genes, e.g., sickle cell anemia, and for DNA finger-
printing in forensic science.restriction site The specific site on a DNA strand
where a restriction enzyme cuts DNA.reticulate Lacelike or netlike in texture, repeating
intercrossing between lines; divided or marked to form
a network. In evolution, the lateral transfer, back and
forth, of genetic information; the complex pattern of
species origin by hybridization.retina The inner back surface, the posterior por-
tion, of the eye; composed of neural tissue and pho-
toreceptive cells that line the inner eye. The retina
converts light energy into nerve impulses and sends292 resonance Raman spectroscopy