peptide bonds the bonds that link amino acids
together in protein molecules. (1.3)
peripheral nervous system (PNS) the nerves that
enter and leave the brain and spinal cord (the
CNS). It consists of the autonomic nervous
system and the somatic nervous system. (5.1)
perpetual resource unlimited resource such as
sunlight, wind, or tides. (15.3)
PGA 3-phosophoglycerate. (3.1)
PGAL glyceraldehyde-3-phosphate. (3.1)
PGAP 1-3-bisphosphoglycerate. (3.1, 3.3)
phagocytosis process in which a cell swallows and
devours another cell, bacterium, or detritus. (4.4)
phenotype the physical and physiological traits of
an organism. (11.1)
phospholipid bilayer the double layer of
phospholipid molecules that line up tail to tail
to create a hydrophilic cell membrane. (1.3)
phosphorylation the addition of one or more
phosphate groups to a molecule. (3.2)
photochemical smog brown or grey haze of ozone
and various nitrates formed by the reaction of
nitrogen oxides and hydrocarbons in the
atmosphere in the presence of sunlight and
water vapour. (15.3)
photolysis the splitting of water molecules by a Z
enzyme to release electrons and hydrogen ions
(H+) that are then used in a photosystem. Oxygen
is produced in this process. (3.3)
photophosphorylation the process of forming ATP
from ADP and an inorganic phosphate group by
means of chemiosmosis through the thylakoid
membrane as part of the light-dependent reaction
of photosynthesis. (3.3)
photorespiration the oxidation of RuBP (ribulose
bisphosphate) by RuBP carboxylase. (3.3)
photosynthesis the use of energy from light by cells
to produce carbohydrates (food). (3.3)
photosynthetic unit collection of several hundred
antenna pigment molecules together with the
reaction centre. (3.3)
photosystem network of chlorophyll molecules that
absorb light energy. (3.3)
phylogenetic tree pattern of descent. (10.3)
physical mutagen agent (e.g., X rays) that can
forcibly break a nucleotide sequence, causing
random changes in one or both strands of a DNA
molecule. (9.1)
physiological adaptations adaptations associated
with functions in organisms (e.g., enzymes for
blood clotting, chemical defenses of plants).
(12.1)
pineal gland a small gland located in the brain,
which produces melatonin. (6.1)
pioneer species organisms, such as lichens, that are
the very first to arrive in a barren landscape, and
that change the landscape dramatically by their
actions. (13.1)
pituitary dwarfism insufficient HGH production
during childhood results in abnormally short
stature. (6.1)
pituitary gland sometimes called the master gland.
The gland is attached to the hypothalamus in the
brain and produces hormones (e.g., TSH) that
control many of the endocrine glands. (5.1)
plasmids small, circular double-stranded DNA
molecules floating free in the cytoplasm of a
prokaryotic cell. (7.2)
point mutation chemical change that affects one or
just a few nucleotides. (9.1)
polar covalent bond chemical bond in which
electrons are shared unequally between two
bonded atoms with different electronegativities.
(1.1)
polar molecule molecule that has an unequal
distribution of charge and a net dipole, as a
result of the polar bonds within the molecule
and the shape of the molecule. (1.1)
pollutant chemical that adversely affects living
things. (15.3)
poly-A tail long series of A nucleotides added to
the 3 ′end of a pre-mRNA molecule. (8.2)
polymerase chain reaction (PCR) almost entirely
automated method of replicating DNA that
allows researchers to target and amplify a very
specific sequence within a DNA sample. The
method is used to copy and analyze minute
amounts of DNA from mummies or fossils.
(9.2, 11.1)
polymers large molecules made of many repeating
smaller molecules called monomers. (1.2)
polymorphic genetic loci that have more than one
allele. (11.1)
polypeptides long chains of amino acids (proteins).
(1.3)
polyploidy mutant condition in which errors in cell
division result in extra sets of chromosomes.
(12.3)
polyribosome a cluster of ribosomes bound to the
same mRNA molecule. Each ribosome produces a
copy of the same polypeptide. (8.3)
polysaccharide storage carbohydrate polymer made
of a long chain of monosaccharides. (1.3)
population group of individuals of the same species
living in the same geographical area. (11.1, 13.1)
porin the outer membrane of the mitochondrion.
(3.2)
positive gene regulation the process of turning on
transcription by the use of a regulatory site. TheGlossary • MHR 583