322 ❯ Glossary
enzymes Catalytic proteins that are picky, interact-
ing only with particular substrates. However, the
enzymes can be reused and react with more than
one copy of their substrate of choice and have a
major effect on a reaction.
epiblastDevelops into the three germ layers of the
embryo: the endoderm, the mesoderm, and the
ectoderm.
epidermis (plants) The protective outer coating of
plants.
epididymis The coiled region that extends from
the testes. This is where the sperm completes its
maturation and waits until it is called on to do
its duty.
episomesPlasmids that can be incorporated into a
bacterial chromosome.
epistasis A gene at one locus alters the phenotypic
expression of a gene at another locus. A dihybrid
cross involving epistatic genes produces a 9:4:3
phenotype ratio.
esophageal sphincter Valvelike trapdoor between
the esophagus and the stomach.
esophagusStructure that connects the throat to the
stomach.
estrogen Hormone made (secreted) in ovaries that
stimulates development of sex characteristics in
women and induces the release of luteinizing
hormone (LH) before the LH surge.
ETCSeeelectron transport chain.
ethology The study of animal behavior.
ethylene Plant hormone that initiates the ripening
of fruit and the dropping of leaves and flowers
from trees.
eubacteria One of two major prokaryotic evolution-
ary branches. Categorized according to their mode
of nutritional acquisition, mechanism of move-
ment, shape, and other characteristics.
eukaryotic cell Complex cell that contains a nucleus,
which functions as the control center of the cell,
directing DNA replication, transcription, and cell
growth. Organisms can be unicellular or multicel-
lular and contain many different membrane-bound
organelles.
evaporationProcess by which a liquid changes into
a vapor form. Functions in thermoregulation for
humans when water leaves our bodies in the form
of water vapor—sweat.
evolution Descent with modification. Evolution
happens to populations, not individuals, and
describes change in allele frequencies in popula-
tions with time.
excision repair Repair mechanism for DNA repli-
cation in which a section of DNA containing
an error is cut out and the gap is filled by DNA
polymerase.
exergonic reaction A reaction that gives offenergy as
a product. A +B→energy+C.
exocytosis Process by which substances are exported
out of the cell. A vesicle escorts the substance to
the plasma membrane, fuses with the membrane,
and ejects its contents out of the cell.
exons Coding regions produced during transcrip-
tion that are glued back together to produce the
mRNA that is translated into a protein.
exopeptidasesEnzymes that complete the digestion
of proteins by hydrolyzing all the amino acids of
any remaining fragments.
exponential growth A population grows at a rate
that creates a J-shaped curve.
extreme halophiles Archaebacteria that live in envi-
ronments with high salt concentrations.
F 1 The first generation of offspring, or the first
“filial” generation in a genetic cross.
F 2 The second generation of offspring, or the second
“filial” generation in a genetic cross.
facilitated diffusion The diffusion of particles across
a selectively permeable membrane with the assis-
tance of transport proteins that are specific in what
they will carry and have a binding site designed for
molecules of interest. This process requires no
energy.
facultative anaerobe Organisms that can survive in
oxygen-rich or oxygen-free environments.
fallopian tube Seeoviduct.
fats Lipids, made by combining glycerol and fatty
acids, used as long-term energy stores in cells.
They can be saturated or unsaturated.
fatty acidLong carbon chain that contains a car-
boxyl group on one end that combines with glyc-
erol molecules to form lipids.
fermentation Anaerobic respiration pathway that
occurs in absence of oxygen. Produces less ATP
than aerobic respiration.
ferredoxin Molecule that donates the electrons to
NADP+ to produce NADPH during the light
reactions of photosynthesis.
fibrous root system Root system found in monocots
that provides the plant with a very strong anchor
without going very deep into the soil.