G10fiffGlossary
nucleotide pair See base pair.
nucleus (pl. nuclei) 1. The dense core of an atom, which contains
protons and neutrons. 2. The control center of the eukaryotic cell,
containing all of the cell’s DNA and occupying up to 10 percent of
the space inside the cell.nutrient A chemical element that is required by a living organism.
nutrient cycling The process by which decomposers break
down dead organisms or waste products, release the chemical
elements locked in the biological material, and return them to
the environment.O
observation A description, measurement, or record of any object
or phenomenon.omnivore An animal that eats both animals and plants. Compare
carnivore and herbivore.opposable Able to be placed opposite other digits of the hand or
foot. For example, opposable thumbs can be placed opposite each
of the other four fingers.order The unit of classification in the Linnaean hierarchy above
family and below class.organ A collection of different types of tissues that form a func-
tional unit with a distinctive shape and location in the body.organ system A network of organs that work in a closely coordi-
nated manner to perform a distinct set of functions in the body.organelle Any of the membrane-enclosed subcellular compart-
ments found in eukaryotic cells.organic molecule A molecule that includes at least one carbon-
hydrogen bond.organism An individual living thing composed of interdependent
parts.origin of replication A DNA sequence where DNA replication
is initiated.osmosis A form of simple diffusion in which water moves in and
out of cells (and compartments inside cells).ovule The egg-bearing structure in plants.
oxidative phosphorylation The third of three stages of cellular
respiration. During this process, the chemical energy of NADH
and FADH 2 is converted into the chemical energy of ATP, while
electrons and hydrogen atoms removed from NADH and FADH 2
are handed over to molecular O 2 , creating water (H 2 O). A large
amount of ATP is generated. Compare glycolysis and Krebs cycle.P
P generation The first set of parents in a series of genetic crosses.
Compare F 1 generation and F 2 generation.parasite An organism that lives in or on another species and
harms it by stealing resources. For example, some parasites
suck blood or live off the food in our intestines. Compare host.passive transport The movement of a substance without the
addition of energy. Compare active transport.PCR See polymerase chain reaction.
pedigree A chart similar to a family tree that shows genetic rela-
tionships among family members over two or more generations
of a family’s medical history.peer-reviewed publication The publishing of original research
only after it has passed the scrutiny of experts who have no direct
involvement in the research under review, or a scientific journal
that follows this standard.PGD See preimplantation genetic diagnosis.
pH scale A logarithmic scale that indicates the concentration of
hydrogen ions. The scale goes from 0 to 14, with 0 representing
an extremely high concentration of free H+ ions and 14 represent-
ing the lowest concentration.phagocytosis Literally, “cellular eating.” A large-scale version of
endocytosis in which particles considerably larger than biomole-
cules are ingested. Compare pinocytosis.phenotype The physical, biochemical, or behavioral expression of
a particular version of a trait. Compare genotype.phospholipid An organic molecule with a hydrophilic head and a
hydrophobic tail.phospholipid bilayer A double layer of phospholipids in which
the heads face out and the tails face in. Plasma membranes are
phospholipid bilayers.photoautotroph See autotroph.
photoheterotroph See heterotroph.
photosynthesis The process by which organisms capture energy
from the sun and use it to create sugars from carbon dioxide and
water, thereby transforming light energy into chemical energy
stored in the covalent bonds of sugar molecules. Compare cellu-
lar respiration.phylum (pl. phyla) The unit of classification in the Linnaean
hierarchy above class and below kingdom.physical trait An anatomical or physiological characteristic of
an individual, such as the shape of an animal’s head. Compare
behavioral trait and biochemical trait.pili (sing. pilus) Short, hairlike projections that cover the surface
of many bacteria.pinocytosis Literally, “cellular drinking.” A large-scale version of
endocytosis in which fluids are ingested. Compare phagocytosis.Plantae The plants. One of the six kingdoms of life, in the domain
Eukarya, encompassing all plants, which are multicellular photo-
synthetic autotrophs.plasma membrane A barrier consisting of a phospholipid bilayer
that separates a cell from its external environment.pleiotropy The pattern of inheritance in which a single gene influ-
ences multiple different traits. Compare polygenic trait.point mutation A mutation in which only a single base is altered.
polar molecule A molecule whose electrical charge is shared
unevenly, with some regions being electrically negative and
others electrically positive.