Glossary ❮ 333the genetic information from RNA into DNA. In
the nucleus of the host, the newly transcribed
DNA incorporates into the host DNA and is tran-
scribed into RNA when the host cell undergoes
normal transcription.
reverse transcriptaseEnzyme carried by retro-
viruses that function to convert RNA to DNA.
Rf Variable that indicates the relative rate at which
one molecule migrates compared to the solvent of
a paper chromatograph.
ribosomes Host organelle for protein synthesis
composed of a large subunit and a small subunit.
Ribosomes are built in the nucleolus.
RNA polymerase Enzyme that runs transcription
and adds the appropriate nucleotides to the 3′end
of the growing strand.
RNA splicing Process that removes introns from
newly produced mRNA and then glues exons back
together to produce the final product.
rootPortion of the plant that is below the ground.
root capProtective structure found around the
apical meristem of a root that keeps it together
as it pushes through the soil.
root hairs Hairs extending off the surface of root tips
that increase the surface area for absorption of
water and nutrients from the soil.
root pressure Driving force that contributes to
the movement of water through the xylem of a
plant.
rough endoplasmic reticulum (RER)Membrane-
bound organelle with ribosomes on the cytoplas-
mic surface of the cell. Proteins produced by RER
are often secreted and carried by vesicles to the
Golgi apparatus for further modification.
rRNA Ribosomal RNA, which makes up a huge por-
tion of ribosomes.
R-selected populations Populations that experience
rapid growth of the J-curve variety. The offspring
produced by R-selected organisms are numerous,
mature quite rapidly, and require very little post-
natal care.
rubisco Enzyme that catalyzes the first step of the
Calvin cycle in C 3 plants.
saprobeOrganism that feeds off dead organisms.
saturated fat Fat that contains no double bonds. It
is associated with heart disease and atherosclerosis.
savanna Grassland that contains a spattering of trees
found all over South America, Australia, and
Africa. Savanna soil tends to be low in nutrients,
while temperatures tend to run high.
sclerenchyma cells Plant cells that function as pro-
tection and mechanical support.
search image Mental image that assists animals
during foraging. It directs them to food of interest.
secondary consumersConsumers that obtain energy
through consumption of the primary consumers.
secondary immune response Memory cells are the
basis for this efficient response to invaders.
secondary oocyte An oocyte that has half the genetic
information of the parent cell, but the majority of
its cytoplasm.
secondary plant growth Growth that leads to an
increase in plant girth.
secondary sex characteristicsThe noticeable physi-
cal characteristics that differ between males and
females such as facial hair, deepness of voice,
breasts, and muscle distribution.
secondary spermatocyte Cells formed during sper-
matogenesis that give rise to spermatids and even-
tually sperm.
secondary structureThe three-dimensional arrange-
ment of a protein caused by hydrogen bonding.
secondary succession Succession in an area that
previously had stable plant and/or animal life but
has since been disturbed by some major force such
as a forest fire.
second messenger Molecule that serves as an inter-
mediary, activating other proteins and enzymes in a
chemical reaction.
semiconservative DNA replication Before the parent
strand is copied, the DNA unzips, with each single
strand serving as a template for the creation of a
new double strand. One strand of DNA from the
parent goes to one daughter cell; the second parent
strand goes to the second daughter cell.
seminal vesicles Structures that dump fluids into the
ejaculatory duct to send along with the sperm, provid-
ing three important advantages to the sperm: energy
by adding fructose; power to progress through the
female reproductive system by adding prostaglandin
(which stimulates uterine contraction); and mucus,
which helps the sperm swim more effectively.
seminiferous tubules Actual site of sperm production.
sensory neurons Nerve cells that receive and commu-
nicate information from the sensory environment.
septae Structures that divide the hypha filaments of
fungi into different compartments.
SER Seesmooth endoplasmic reticulum.
sex pili bacterial appendage vital to process of
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