glossary G-9extraembryonic membranes Membranes that form along
with a developing embryo, including the yolk sac, amnion,
allantois, and chorion.
eyes Sensory organs that allow vision; they contain tissue
with a dense array of photoreceptors.
facilitated diffusion A form of passive transport where
transport proteins provide a channel through which solutes
cross a cell membrane.
fact Verifiable information, not opinion or speculation.
fat A lipid with a glycerol head and one, two, or three
fatty acid tails. The tails of saturated fats have only single
bonds between carbon atoms and hydrogen atoms attached
to all other bonding sites. Tails of unsaturated fats addi-
tionally have one or more double bonds between certain
carbon atoms.
fatty acid A long, flexible hydrocarbon chain with a
—COOH group at one end.
femur Thighbone; longest bone of the body.
fertilization [L. fertilis, to carry, to bear] Fusion of a sperm
nucleus with the nucleus of an egg, which thereupon becomes
a zygote.
fetus An embryo after it reaches the age of 8 weeks.
fever Body temperature that has climbed above the normal
set point, usually in response to infection. Mild fever pro-
motes an increase in body defense activities.
fibrous connective tissue A specialized form of connective
tissue that is strong and stretchy; the three types are loose,
dense, and elastic.
fibrous joint Type of joint in which fibrous connective tissue
unites the adjoining bones and no cavity is present.
filtration In urine formation, the process by which blood
pressure forces water and solutes out of glomerular
capillaries and into the Bowman’s capsule.
first law of thermodynamics The total amount of energy in
the universe remains constant.
flagella (fluh-jell-uh), singular: flagellum [L., whip] Tail-like
motile structures of many eukaryotic cells; they have a dis-
tinctive 9 + 2 array of microtubules. In humans only sperm
have a flagellum.
follicle (foll-ih-kul) In an ovary, a primary oocyte (imma-
ture egg) together with the surrounding layer of cells.
food chain A straight-line sequence of who eats whom in an
ecosystem.
food web A network of cross-connecting, interlinked food
chains encompassing primary producers and an array of con-
sumers, detritivores, and decomposers.
forebrain Brain region that includes the cerebrum and cere-
bral cortex, the olfactory lobes, and the hypothalamus.
fossil Physical remains or other evidence of an organism that
lived in the distant past. Most fossils are skeletons, shells,
leaves, seeds, and tracks that were buried in rock layers
before they decomposed.epidermis The outermost tissue layer of skin.
epididymis Duct where sperm mature and are stored.
epiglottis A flaplike structure at the start of the larynx, posi-
tioned to direct the movement of air into the trachea or food
into the esophagus.
epiphysis Each end of a long bone.
epithelium (ep-ih-thee-lee-um) A tissue consisting of one or
more layers of cells that covers the body’s external surfaces
and lines its internal cavities and tubes. Epithelium has one
free surface; the opposite surface rests on a basement mem-
brane between it and an underlying connective tissue. Epider-
mis is an example.
erythrocyte (eh-rith-row-site) [Gk. erythros, red, and kytos,
vessel] Red blood cell (RBC).
esophagus (ee-sof-uh-gus) Tubular portion of the diges-
tive system that receives swallowed food and leads to the
stomach.
essential amino acid Any of eight amino acids from protein
that the body cannot synthesize and must be obtained from
food.
essential fatty acid Any of the fatty acids that the body can-
not synthesize and must be obtained from food.
estrogens (ess-tro-jens) Sex hormones that help oocytes
mature, trigger changes in the uterine lining during the men-
strual cycle and pregnancy, and maintain secondary sexual
traits; also influence body growth and development.
eukaryotic cell (yew-care-ee-ah-tik) [Gk. eu, good, and
karyon, kernel] A cell that has a “true nucleus,” which con-
tains its DNA, and other membrane-bound organelles. Com-
pare prokaryotic cell.
evolution [L. evolutio, act of unrolling] Genetic change within
a line of descent over time.
excretion See urinary excretion.
exergonic reaction Chemical reaction that shows a net loss
in energy.
exocrine gland (ek-suh-krin) [Gk. ex, out of, and krinein, to
separate] Glandular structure that secretes products, usually
through ducts or tubes, to a free epithelial surface.
exocytosis (ek-so-sigh-toe-sis) Movement of a substance out
of a cell by means of a transport vesicle that fuses with the
plasma membrane and releases its contents to the outside.
exon Any of the nucleotide sequences of a pre-mRNA mol-
ecule that are spliced together to form the mature mRNA
transcript and are ultimately translated into protein.
experiment A test in which some phenomenon in the natural
world is manipulated in controlled ways to gain insight into
its function, structure, operation, or behavior.
expiration Expelling air from the lungs; exhaling.
extinction Permanent loss of a species.
extracellular fluid All the fluid not inside cells; includes
plasma (the liquid portion of blood) and tissue fluid (which
occupies the spaces between cells and tissues).
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