Glossary ❮ 329obligate anaerobeOrganism that only survives in
oxygen-free environments.
observational learning The ability of an organism
to learn how to do something by watching another
individual do it first.
oilType of lipid.
Okazaki fragmentsThe lagging DNA strand con-
sists of these tiny pieces that are later connected by
an enzyme, DNA ligase, to produce the completed
double-stranded daughter DNA molecule.
ontogeny The development of an individual.
oogenesisProcess by which female gametes are
formed. Each meiotic cycle leads to the production
of a single ovum, or egg.
operant conditioning Type of associative learning
that is based on trial and error.
operator A short sequence near the promoter that
assists in transcription by interacting with regula-
tory proteins (transcription factors).
operonA promoter/operator pair that services mul-
tiple genes.
opportunistic populations R-selected organisms
that tend to appear when space in the region opens
up due to some environmental change. They grow
fast, reproduce quickly, and die quickly as well.
optimal foraging Theory that predicts that natural
selection will favor animals that choose foraging
strategies that maximize the differential between
benefits and costs.
organic compoundsCarbon-containing compounds.
Important examples include carbohydrates, pro-
teins, lipids, and nucleic acids.
osmosis The passive diffusion of water down its con-
centration gradient across selectively permeable
membranes. It will flow from a region with a lower
solute concentration (hypotonic) to a region with
a higher solute concentration (hypertonic).
outbreedingMating between unrelated individuals
of the same species.
ovary The site of egg production. In animals,
females often have two, one on either side of the
body. Plants usuallyonly have one ovary.
oviduct Known also as the fallopian tube,this is the
site of fertilization and connects the ovary to the
uterus. Eggs move through here from the ovary to
the uterus (in animals only).
ovulation Stage of menstrual cycle in which the sec-
ondary oocyte is released from the ovary.
oxaloacetateCompound that plays an important
role in C 4 photosynthesis of plants and the
Krebs cycle in animals.
oxidative phosphorylationAerobic process in which
NADH and FADH 2 pass their electrons down the
electron transport chain to produce ATP.
oxytocin Hormone that stimulates uterine contrac-
tion and milk ejection for breastfeeding.
P 1 The parent generation in a genetic cross.
palisade mesophyll Host to many chloroplasts and
much of the photosynthesis of a leaf.
parallel evolution Similar evolutionary changes
occurring in two either related or unrelated species
that respond in a similar manner to a similar
environment.
parasitism Scenario in which one organism benefits
at the other’s expense.
parasympathetic nervous systemBranch of auto-
nomicnervous system that shuts down the body to
conserve energy.
parathyroid hormone (PTH) Hormone that increases
serum concentration of Ca^2 +, assisting in the process
of bone maintenance.
parenchyma cells Plant cells that play a role in photo-
synthesis (mesophyll cells), storage, and secretion.
Patau syndromePresence of trisomy 13, which occurs
in about one out of every 12,000–16,000 live births
and causes serious brain and circulatory defects.
pedigreesFamily trees used to describe the genetic
relationships within a family. One use of a pedi-
gree is to determine whether parents will pass cer-
tain conditions to their offspring.
pepsinThe major enzyme of the stomach, which
breaks down proteins into smaller polypeptides to
be handled by the intestines.
pepsinogen The precursor to pepsin that is acti-
vated by active pepsin (a small amount of which
normally exists in the stomach).
peripheral nervous system (PNS) The PNS can be
broken down into a sensory and a motor division.
The sensory division carries information tothe
CNS while the motor division carries information
awayfrom the CNS.
peripheral proteins Proteins, such as receptor pro-
teins, not implanted in the bilayer, which are often
attached to integral proteins of the membrane.
peristalsisThe force created by the rhythmic con-
traction of the smooth muscle of the esophagus
and intestines.http://www.ebook3000.com