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production, specificity, and activity of each enzyme in a metabolic pathway. Thus,
mutation of such a gene changes the ability of the cell to carry out a particular
reaction and disrupts the entire pathway.
"one gene one polypeptide hypothesis" A revision of the one gene, one
enzyme hypothesis. Some proteins are composed of different polypeptide
chains encoded by separate genes, so the hypothesis now holds that mutation in
a gene encoding a specifc polypeptide can alter the ability of the encoded
protein to function and thus produce an altered phenotype.
oocyte A cell that will/is undergo/ing development into a female gamete.
oogenesis The production of ova. The development of a diploid cell into a
haploid ovum or egg cell.
open community A community in which the populations have different density
peaks and range boundaries and are distributed more or less randomly.
opposable The capability of being placed against the remaining digits of a
hand or foot; e.g., the ability of the thumb to touch the tips of the fingers on that
hand.
opsins Molecules in cone cells that bind to pigments, creating a complex that
is sensitive to light of a given wavelength.
orders Taxonomic subcategories of classes.
Ordovician extinction Paleozoic-aged mass extinction possibly related to
glaciation in the southern-hemisphere supercontinent Gondwana.
Ordovician Period Geologic period of the Paleozoic Era after the Cambrian
Period between 500 and 435 million years ago. Major advances during this
period include the bony fish and possibly land plants (during the late
Ordovician).
organelles Cell components that carry out individual functions; e.g., the cell
nucleus and the endoplasmic reticulum. Subcellular structures (usually membrane-
bound and unique to eukaryotes) that perform some function, e.g. chloroplast,
mitochondrion, nucleus. |
organism An individual, composed of organ systems (if multicellular).
Multiple organisms make up a population.
organs Differentiated structures consisting of tissues and performing some
specific function in an organism. Structures made of two or more tissues which
function as an integrated unit. e.g. the heart, kidneys, liver, stomach.
organ systems Groups of organs that perform related functions.
orgasm Rhythmic muscular contractions of the genitals (sex organs) combined
with waves of intense pleasurable sensations; in males, results in the ejaculation
of semen.
osmoconformers Marine organisms that have no system of osmoregulation
and must change the composition of their body þuids as the composition of the
water changes; include invertebrates such as jellyÞsh, scallops, and crabs.
osmoregulation The regulation of the movement of water by osmosis into and
out of cells; the maintenance of water balance within the body.
osmoregulators Marine vertebrates whose body þuids have about one-third
the solute concentration of seawater; must therefore undergo osmoregulation.
osmosis Diffusion of water molecules across a membrane in response to
differences in solute concentration. Water moves from areas of high-water/low-
solute concentration to areas of low-water/high-solute concentration. Diffusion
of water across a semi-permeable barrier such as a cell membrane, from high
water potential (concentration) to lower water potential (concentration).
osmotic pressure Pressure generated by water moving by osmosis into or out
of a cell.
ossification The process by which embryonic cartilage is replaced with bone.
osteoarthritis A degenerative condition associated with the wearing away of
the protective cap of cartilage at the ends of bones. Bone growths or spurs
develop, restricting movement and causing pain.
osteoblasts Bone-forming cells.
osteoclasts Cells that remove material to form the central cavity in a long
bone.
osteocytes Bone cells that lay down new bone; found in the concentric layers
of compact bone. Bone cell, a type of connective tissue.
osteoporosis A disorder in which the mineral portion of bone is lost, making
the bone weak and brittle; occurs most commonly in postmenopausal women.
out of Africa hypothesis Holds that modern human populations (Homo
sapiens) are all derived from a single speciation event that took place in a
restricted region in Africa.
ovaries 1) In animals, the female gonads, which produce eggs (ova) and female
sex hormones. ) In þowers, part of the female reproductive structure in the carpel;
contain the ovules, where egg development occurs. The lower part of the carpel
that contains the ovules within which the female gametophyte develops.
overkill The shooting, trapping, or poisoning of certain populations, usually for
sport or economic reasons.
oviducts Tubes that connect the ovaries and the uterus; transport sperm to the
ova, transport the fertilized ova to the uterus, and serve as the site of fertilization;
also called the fallopian tubes or uterine tubes.
ovulation The release of the oocyte onto the surface of the ovary; occurs at the
midpoint of the ovarian cycle. The release of the ovum (egg) from the ovary [ Pobierz całość w formacie PDF ]

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