cell division See meiosis, mitosis
cell(ular) phone Wireless telephone that permits telecommunication within a defined area that may include hundreds of square miles, using radio waves in the 800-900 megahertz (MHz) band. To implement a cell¬ phone system, a geographic area is broken into smaller areas, or cells, usually mapped as uniform hexagrams but in fact overlapping and irregu¬ larly shaped. Each cell is equipped with a low-powered radio transmitter and receiver that permit propagation of signals among cell-phone users.
rough endoplasmic reticulum
ribosomes
nucleoplasm nucleolus nuclear pore nuclear envelope _ smooth
reticulum Golgi complex apparatus)
cell membrane (plasma membrane) secretory vesicles
lysosome
peroxisome
mitochondrion
Principal structures of an animal cell. Cytoplasm surrounds the cell's specialized structures, or organelles. Ribosomes, the sites of protein synthesis, are found free in the cytoplasm or attached to the endoplasmic reticulum, through which materials are transported throughout the cell. Energy needed by the cell is released by the mitochondria. The Golgi complex, stacks of flattened sacs, processes and packages materials to be released from the cell in secretory vesicles. Digestive enzymes are contained in lysosomes. Peroxisomes contain enzymes that detoxify dangerous sub¬ stances. The centrosome contains the centrioles, which play a role in cell division. The microvilli are fingerlike extensions found on certain cells. Cilia, hairlike struc¬ tures that extend from the surface of many cells, can create movement of surround¬ ing fluid. The nuclear envelope, a double membrane surrounding the nucleus, contains pores that control the movement of substances into and out of the nucleo¬ plasm. Chromatin, a combination of DNA and proteins that coil into chromosomes, makes up much of the nucleoplasm. The dense nucleolus is the site of ribosome pro¬ duction.
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cella Vse-b\ or naos Vna-,as\ Enclosed body of a temple (as distinct from the portico), in which the image of the deity was housed. In early Greek and Roman architecture it was usually rectangular, with an entrance at one end; the side walls were often extended to form a porch. In larger temples the cella was sometimes open to the sky. In the Byzantine archi¬ tectural tradition, the naos is the area of a central-plan church where the liturgy is performed.
cellar Portion of a building beneath ground level, used for utilitarian and storage purposes. It is often called a basement, especially when con¬ structed as part of a foundation. A cellar used for food storage (e.g., a root cellar) may be beneath a house or located outdoors, partly underground, with the upper part mounded over with earth to maintain fairly constant temperature and humidity; the entire enclosure may be concrete, or the floor may be of dirt and the ceiling of timber.
Cellini Vcho-’le-neV Benvenuto (b. Nov. 1, 1500, Florence—d. Feb. 13, 1571, Florence) Italian sculptor and goldsmith active principally in Florence. Early in his career he worked in Rome, producing coins, medallions, seals, vessels, and a vari¬ ety of other objects in precious and semiprecious metals. In 1540 he began his most famous work of this type, a gold saltcellar encrusted with enamel, for Francis I at Fontaineb¬ leau; other royal commissions fol¬ lowed. For Cosimo I he produced large-scale sculpture in the round; the bronze Perseus (1545-53) in the Loggia dei Lanzi in Florence is his masterpiece. His fame owes as much to his autobiography as to his work as an artist; it achieved immediate
Saltcellar of Francis I, encrusted enamel and gold, by Benvenuto Cellini, 1540; in the Kunsthistorisches Museum, Vienna.
COURTESY OF THE KUNSTHISTORISCHES MUSEUM, VIENNA
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360 I cello ► Cennini
popularity for its lively account of his tumultuous life and its vivid pic¬ ture of Renaissance Italy.
cello \'che-,lo\ or violoncello Bowed, stringed instrument, the bass member of the violin family. Its full name means “little violone”—i.e., “little big viol.” Its proportions resemble those of the violin. Players hold its body between the legs, its weight supported by a metal spike that touches the floor. It has four strings, tuned an octave below those of the viola. The cello was developed in the early 16th century along with the violin and viola; later innovations increased its power. It gradually dis¬ placed the bass viola da gamba in the 18th century, especially as a con- tinuo instrument. It has been essential to chamber music ensembles for 250 years. The modern orchestra includes 6 to 12 cellos. In the 19th and 20th centuries it was increasingly used as a solo instrument.
cellular automata (CA) Simplest model of a spatially distributed process that can be used to simulate various real-world processes. Cellu¬ lar automata were invented in the 1940s by John von Neumann and Stanis¬ lav/ Ulam at Los Alamos National Laboratory. They consist of a two- dimensional array of cells that “evolve” step-by-step according to the state of neighbouring cells and certain rules that depend on the simulation. Though apparently simple, CAs are universal computers—that is, they can do any computer-capable computation. The best-known cellular automa¬ ton, John Conway’s “Game of Life” (1970), simulates the processes of life, death, and population dynamics.
celluloid \'sel-y3-,l6id\ Name for the first synthetic plastic material, developed in 1869. Made of a colloid of cellulose nitrate (nitrocellulose) plasticized with camphor, it is tough, cheap to produce, and resistant to water, oils, and dilute acids. It found a great variety of uses in combs, films, toys, and many other mass-produced consumer goods. Though it has been replaced in many uses by nonflammable synthetic polymers (origi¬ nally cellulose acetate and Bakelite, then a host of others), it is still manu¬ factured and used.
cellulose Complex carbohydrate (polysaccharide) consisting of 1,000- 3,000 or more glucose units in a linear chain structure that can pack into fibres of great tensile strength. The basic structural component of plant cell walls, cellulose is the most abundant of all naturally occurring organic compounds (90% of cotton and 50% of wood). Mammals (including humans) cannot digest cellulose, but bacteria in the rumens of cattle and other ruminants and protozoans in the gut of termites produce enzymes that can break it down. Soil fungi can also break down cellulose. Its most important uses are in wood, paper, and fibre products, as an ethanol and methanol source, and specialized applications. Cellulose derivatives are used in plastics, photographic films, rayon fibres, cellophane, coatings, explosives (e.g., nitrocellulose), and foods (e.g., the stabilizer and thick¬ ener carboxymethylcellulose).
Celsius Vsel-se-3s\, Anders (b. Nov. 27, 1701, Uppsala, Swed.—d. April 25, 1744, Uppsala) Swedish astronomer. He taught at the Univer¬ sity of Uppsala from 1730 to his death. In 1733 he published a collection of 316 observations of the aurora borealis. In 1744 he built the Uppsala Observatory. He is best known for his invention of the Celsius (often called centigrade) thermometer scale (1742), which set the freezing point of water at 0° and the boiling point of water at 100°.