life table a summary of the relationship of
survivorship, mortality, fecundity, and age, for a
given population. (14.4)
lipids fats and phospholipids, such as those found
in the cellular membrane. (1.3)
locus the location of a gene on a chromosome. The
plural form is loci. (11.1)
logistic growth the type of population change that
occurs in an environment where resources are
limited. (14.2)
loop of Henle the long loop of the nephron that
extends into the medulla of the kidney between
the proximal tubule and the distal tubule. (4.2)
luteal stage the stage of the menstrual cycle that
begins with ovulation. (6.3)
lymphocyte specialized white blood cells (B cells
and T cells) formed in the bone marrow. B cells
mature in the bone marrow, while T cells mature
in the thymus gland. (4.4)macro-evolution evolution on a large scale, such as
the evolution of new species from a common
ancestor. (11.1)
macromolecules large molecules that are often
made of distinct smaller units. (1.2)
macrophage large cell that engulfs bacteria and
detritus through phagocytosis as an immune
response. (4.4)
mass extinction event in which many species
become extinct at once. (12.3)
mass number the total number of protons and
neutrons in the nucleus of one atom of an
element. (1.1)
mechanoreceptor in the ear, a sensory receptor that
translates the movement of air in the ear into a
series of nerve impulses that the brain interprets
as sound. (5.3)
medulla (renal) the inner part of the kidney, where
the loop of Henle and the collecting ducts of the
nephrons are. (4.2)
medulla oblongata structure attached to the spinal
cord at the base of the brain; has cardiac,
vasomotor, respiratory, vomiting, coughing,
hiccupping, and swallowing functions. Damage
to this part of the brain is usually fatal. (5.1)
meiosis type of cell division that occurs only in
reproductive organs producing reproductive cells
called gametes. (6.3)
memory T cell lymphocytes that remain in the
bloodstream to promote a faster response if the
same antigen appears in the body again. (4.4)
menopause period in a woman’s life during which a
decrease in estrogen and progesterone results inan end of menstrual cycles. The period usually
occurs during middle age. (6.3)
menstrual cycle in a human female, period of 20–45
days during which hormones stimulate the
development of the uterine lining, and an egg is
developed and released from an ovary. If the egg
is not fertilized, the uterine lining is shed, and
the cycle begins again. (6.3)
menstruation the last stage of the menstrual cycle,
in which the endometrium disintegrates and is
expelled from the uterus. (6.3)
messenger RNA (mRNA) strand of RNA that carries
genetic information from DNA to the protein
synthesis machinery of the cell during
transcription. (8.2)
metabolic pathway series of linked chemical
reactions that take place in the cell. (2.2)
metabolism the collective name for all the chemical
reactions that occur inside the cell. (1.1, 2.1)
micro-evolution the change in gene frequencies in a
population over time. Evolution within a species,
or evolution on a small scale. (11.1)
mimicry structural adaptation that allows one
species to resemble another species or part of
another species. (12.1)
mis-sense mutation permanent change in the
genetic material of a cell that results in slightly
altered but still functional proteins. (9.1)
modern synthesis the modern combination of
Mendel’s and Darwin’s theories on evolution.
(11.1)
monocyte white blood cell from which neutrophils
and macrophages are derived. Neutrophils and
macrophages assist in immune responses by
phagocytosis. (4.4)
monomers small repeating units that join together
to make up polymers. (1.2)
monosaccharide a carbohydrate containing three to
seven carbon atoms per molecule. (1.3)
more industrialized nation country with relatively
many industries requiring skilled workers, and
with a relatively high standard of living. (15.1)
morphological species concept classification of
organisms into species by measurable physical
characteristics. (12.2)
mortality the proportion of individuals in a
population that typically die at a given age over
a given period of time. (14.4)
motor nerves nerves that transmit commands from
the central nervous system to the muscles. (5.1)
multi-gene family in a eukaryotic cell, from a few
hundred to hundreds of thousands of copies of
the same or very similar genes. Members of these
families may be clustered together on the sameM
580 MHR • Glossary