CELL -- a usually microscopic structure containing nuclear and cytoplasmic material enclosed by a semipermeable membrane

PROTOPLASM -- a semifluid, viscous, translucent colloid (a substance made up of minute particles), the essential living matter of all animal and plant cells; it consists largely of water, proteins, lipoids, carbohydrates, and inorganic salts and is differentiated into nucleoplasm and cytoplasm

NUCLEOPLASM -- the protoplasm of the nucleus of a cell

CYTOPLASM -- the protoplasm of a cell, between the nucleus and the cell membrane

NUCLEUS -- the central, usually spherical or oval mass of protoplasm present in most plant and animal cells, containing most of the hereditary material and necessary to such functions as growth, metabolism, and reproduction

NUCLEOLUS -- a conspicuous body, mainly of protein with some RNA and usually spherical, found in the nucleus of most cells

CENTROSOME -- a very small body near the nucleus in most animal cells (as opposed to plant cells), consisting of a centriole surrounded by a centrosphere; in mitosis it divides and the two parts move to opposite poles of the dividing cell

CENTRIOLE -- a small dense structure in the middle of the centrosome; it doubles before mitosis and each part forms the center of an aster at mitosis

CENTROSPHERE -- the portion of the centrosome surrounding the centriole; center of the aster

ASTER -- a structure shaped like a star, formed around the centrosome in the cytoplasm of an animal cell during mitosis (astral rays radiating out)

MICROSOME -- any of a number of minute granules in the cytoplasm of an active cell, thought to be associated with protein synthesis

MITOSIS -- the usual method of cell division characterized typically by the resolving of the chromatin of the nucleus into a threadlike form, which condenses into chromosomes, each of which separates longitudinally into two parts, one part of each chromosome being retained in each of the two new cells resulting from the original cell

OSMOSIS -- the tendency of a fluid to pass through a semipermeable membrane (such as the wall of a living cell) into a solution where the solvent concentration is higher, thus equalizing the concentrations of materials on either side of the membrane

ENDOSMOSIS -- osmosis toward the inside of a cell or vessel

EXOSMOSIS -- osmosis toward the outside of a cell or vessel