Biologists classify canines as members of the carnivore (meat-eating) family Canidae. That family, made up of 30 to 35 species, includes wolves, foxes, coyotes, the dingo, jackals, and a number of species of wild dog.


Carbohydrates are compounds composed of carbon, hydrogen, and oxygen. The carbohydrate group includes sugars, starches, and cellulose.

Carbon Cycle

The carbon cycle is the process in which carbon atoms are recycled over and over again on Earth. Carbon recycling takes place within Earth's biosphere and between living things and the nonliving environment.

Carbon Dioxide

Carbon dioxide is a chemical compound consisting of one part carbon and two parts oxygen and represented by the chemical formula CO2. For a number of reasons, carbon dioxide is one of the most important gases on Earth.

Carbon Family

The carbon family consists of the five elements that make up Group 14 of the periodic table: carbon, silicon, germanium, tin, and lead. The family is particularly interesting because it consists of one nonmetal (carbon), two metals (tin and lead), and two metalloids (silicon and germanium).

Carbon Monoxide

Carbon monoxide is a compound of carbon and oxygen in which the ratio of the two elements is one atom of carbon to one atom of oxygen. Its formula is CO.


A carcinogen is a substance that causes a normal cell to change into a cancerous cell, resulting in uncontrolled cell growth. Cancer cells can multiply unchecked, forming a mass of tissue called a tumor.

Carpal Tunnel Syndrome

Carpal tunnel syndrome is a condition in which the squeezing or compressing of a nerve that passes through the wrist results in numbness, tingling, weakness, or pain in one or both hands. The hands may become so weakened that opening jars or grasping objects becomes difficult and painful.


Cartography is the art of making maps. A map is a two-dimensional (flat) drawing or chart showing the political boundaries and physical features of a geographical region.

Catalyst and Catalysis

Catalysis (pronounced cat-AL-uh-sis) is the process by which some substance is added to a reaction in order to make the reaction occur more quickly. The substance that is added to produce this result is the catalyst (pronounced CAT-uh-list).


In geology, catastrophism is the belief that Earth's features—including mountains, valleys, and lakes—were created suddenly as a result of great catastrophes, such as floods or earthquakes. This is the opposite of uniformitarianism, the view held by many present-day scientists that Earth's features developed gradually over long periods of time.


A cathode is one of the two electrodes used either in a vacuum tube or in an electrochemical cell. An electrode is the part (pole) of a vacuum tube or cell through which electricity moves into or out of the system.

Cathode-Ray Tube

A cathode-ray tube is a device that uses a beam of electrons in order to produce an image on a screen. Cathode-ray tubes, also known commonly as CRTs, are widely used in a number of electrical devices such as computer screens, television sets, radar screens, and oscilloscopes used for scientific and medical purposes.


A cave is a naturally occurring hollow area inside Earth. All caves are formed by some type of erosion process.

Celestial Mechanics

Celestial mechanics is a branch of astronomy that studies the movement of bodies in outer space. Using a mathematical theory, it explains the observed motion of the planets and allows us to predict their future movements.


The cell is the basic unit of a living organism. In multicellular organisms (organisms with more than one cell), a collection of cells that work together to perform similar functions is called a tissue.

Cell, Electrochemical

Electrochemical cells are devices for turning chemical energy into electrical energy or, alternatively, changing electrical energy into chemical energy. The first type of cell is known as a voltaic, or galvanic, cell, while the second type is an electrolytic cell.

Cellular/Digital Technology

Cellular technology is the use of wireless communication, most commonly associated with the mobile phone. The term cellular comes from the design of the system, which carries mobile phone calls from geographical service areas that are divided into smaller pockets, called cells.


Cellulose is the substance that makes up most of a plant's cell walls. Since it is made by all plants, it is probably the most abundant organic compound on Earth.


A centrifuge is a device that uses centrifugal force to separate two or more substances of different density or mass from each other. Centrifugal force is the tendency of an object traveling around a central point to fly away from that point in a straight line.


Ceramic is a hard, brittle substance that resists heat and corrosion and is made by heating a nonmetallic mineral or clay at an extremely high temperature. The word ceramic comes from the Greek word for burnt material, keramos.


Cetaceans (pronounced sih-TAY-shuns) include whales, dolphins, and porpoises. Although ancient people believed they were fish, cetaceans are aquatic mammals that bear live young, produce milk to feed their offspring, and have a bit of hair.

Chaos Theory

Chaos theory is the study of complex systems that, at first glance, appear to follow no orderly laws of mathematics or science. Chaos theory is one of the most fascinating and promising developments in late-twentieth-century mathematics and science.

Chemical Bond

A chemical bond is any force of attraction that holds two atoms or ions together. In most cases, that force of attraction is between one or more negatively charged electrons held by one of the atoms and the positively charged nucleus of the second atom.

Chemical Warfare

Chemical warfare involves the use of natural or synthetic (human-made) substances to disable or kill an enemy or to deny them the use of resources such as agricultural products or foliage in which to hide. The effects of the chemicals may last only a short time, or they may result in permanent damage and death.


Chemistry is the study of the composition of matter and the changes that take place in that composition. If you place a bar of iron outside your window, the iron will soon begin to rust.


Cholesterol is a waxy substance found in the blood and body tissues of animals. It is an important structural component of animal cell membranes.


A chromosome is a structure that occurs within cells and that contains the cell's genetic material. That genetic material, which determines how an organism develops, is a molecule of deoxyribonucleic acid (DNA).