Biology Now, 2e

Glossary ■ (^) G9
different daughter cells. Each homologous chromosome lines up
with its partner and then separates to the two ends of the cells.
Compare meiosis II.
meiosis II The second stage of meiosis, in which sister chromatids
are separated into two new daughter cells. Compare meiosis I.
Mendelian trait A trait that is controlled by a single gene and
unaffected by environmental conditions.
messenger RNA (mRNA) A type of RNA that is complemen-
tary to a DNA template strand. Compare ribosomal RNA and
transfer RNA.
meta-analysis Work that combines results from different studies.
metabolic heat The heat released as a by-product of chemical
reactions within a cell, typically during cellular respiration.
metabolic pathway Any of various chains of linked events that
produce key biological molecules in a cell, including important
chemical building blocks like amino acids and nucleotides.
metabolism All the chemical reactions that occur inside living
cells, including those that release and store energy.
metastasis The spread of a disease from one organ to another.
methanogen An anaerobic archaean that feeds on hydrogen and
produces methane gas as a by-product of its metabolism.
microbe A microscopic, single-celled organism.
mimicry Coloration of a nonpoisonous animal that resembles the
coloration of a toxic species. Compare camouflage and warning
coloration.
mitochondrial-DNA inheritance The passing down of DNA
from the mitochondria in an egg cell to a new generation. Mito-
chondrial DNA passes virtually unchanged from mother to
child, so it can be tracked from one generation, or one species, to
another. Sequencing of mitochondrial DNA can determine how
related an individual is to its female ancestors on its mother’s
side. Compare nuclear-DNA inheritance.
mitochondrion (pl. mitochondria) An organelle that is a tiny
power plant fueling cellular activities. Mitochondria are the main
source of energy in eukaryotic cells.
mitosis Division of the nucleus, the first step of mitotic division.
Mitosis is divided into four main phases: prophase, metaphase,
anaphase, and telophase. Compare cytokinesis and meiosis.
mitotic division A type of cell division that generates two
genetically identical daughter cells from a single parent cell in
eukaryotes. It consists of two steps: mitosis and cytokinesis.
molecule An association of atoms held together by chemical bonds.
monomer A small molecule that is the repeating unit of a poly-
mer. For example, amino acids are the monomers that make up
protein polymers.
monotremes One of three main groups of mammals, whose
members lack a placenta and lay eggs. Compare eutherians and
marsupials.
morphology An organism’s physical characteristics.
most recent common ancestor The most immediate ancestor
that two lineages share.
mRNA See messenger RNA.
mutation A random change to the sequence of bases in an organ-
ism’s DNA.
mutualism A species interaction in which both species benefit.
Compare commensalism, competition, and predation.
mycelium (pl. mycelia) The entire bundle of hyphae that
composes the main body of a fungus.
mycorrhizal fungi Fungi that form mutualistic associations with
the root systems of plants, that help the plants absorb more water
and nutrients from the soil.
N
natural selection The process by which individuals with
advantageous genetic characteristics for a particular environ-
ment survive and reproduce at a higher rate than do individ-
uals with other, less useful characteristics. Compare artificial
selection.
net primary productivity (NPP) The energy acquired through
photosynthesis that is available for the growth and reproduction
of producers within an ecosystem. It is the amount of energy
captured by photosynthetic organisms, minus the amount they
expend on cellular respiration and other maintenance processes.
neutron An electrically neutral particle found in the nucleus of an
atom. Compare electron and proton.
nitrogen fixation The process, carried out by bacteria, of taking
nitrogen gas from the air and converting it to ammonia, making
it available for plants.
node The point on an evolutionary tree indicating the moment in
time when an ancestral group split, or diverged, into two separate
lineages. The node represents the most recent common ancestor
of the two lineages in question.
noncoding DNA DNA that does not code for any kind of func-
tional RNA.
notochord In chordates, a flexible yet rigid rod along the center of
the body that is critical for development.
NPP See net primary productivity.
nuclear-DNA inheritance The passing down of DNA from the
nucleus in an egg or sperm cell to a new generation. Sequencing
of nuclear DNA can determine how related an individual is to all
of its ancestors, both male and female. Compare mitochondri-
al-DNA inheritance.
nuclear envelope The boundary of a cell’s nucleus, consisting of
two concentric phospholipid bilayers.
nuclear pore Any of many small openings in the nuclear envelope
that allow chemical messages to enter and exit the nucleus.
nucleic acid Any of a major class of biomolecules, including DNA
and RNA, built of chains of nucleotides.
nucleosome DNA wrapped around histone proteins that, in multi-
ples, form the beads-on-a-string complex in a chromatin fiber.
nucleotide The basic repeating subunit of DNA, composed of the
sugar deoxyribose, a phosphate group, and one of four bases:
adenine (A), cytosine (C), guanine (G), or thymine (T).