calorie Unit of energy; amount of energy needed to raise the temperature of 1 gram of water 1 degree C (unit on Celsius temperature scale). See also kilocalorie.

Cancer Group of more than 120 different diseases, one for each type of cell in the human body. Each type of cancer produces a tumor in which cells multiply uncontrollably and invade surrounding tissue. See carcinogen, metastasis. 

capitalism See capitalist market economic system. Compare pure command economic system, pure free-market economic system.

capitalist market economic system Economic system built around controlling market prices of goods and services, global free trade, and maximizing profits for the owners or stockholders whose financial capital the company is using to do business. Compare pure command economic system, pure free-market economic system.

carbon cycle Cyclic movement of carbon in different chemical forms from the environment to organisms and then back to the environment. 

carcinogen Chemicals, ionizing radiation, and viruses that cause or promote the development of cancer. See cancer. Compare mutagen, teratogen. 

carnivore Animal that feeds on other animals. Compare herbivore, omnivore.carrying capacity (K) Maximum population of a particular species that a given habitat can support over a given period of time. See dieback. 

Cell Smallest living unit of an organism. Each cell is encased in an outer membrane or wall and contains genetic material (DNA) and other parts to perform its life function. Organisms such as bacteria consist of only one cell, but most of the organisms we are familiar with contain many cells. See eukaryotic cell, prokaryotic cell.

chain reaction Multiple nuclear fissions, taking place within a certain mass of a fissionable isotope, that release an enormous amount of energy in a short time. See nuclear.

chemical One of the millions of different elements and compounds found naturally and synthesized by humans. See compound, element. 

chemical change Interaction between chemicals in which there is a change in the chemical composition of the elements or compounds involved. Also chemical reaction is used. Compare nuclear change, physical change. 

chemical evolution Formation of the earth and its early crust and atmosphere, evolution of the biological molecules necessary for life, and evolution of systems of chemical reactions needed to produce the first living cells. These processes are believed to have occurred about 1 billion years before biological evolution. Compare biological evolution.

chemical formula Shorthand way to show the number of atoms (or ions) in the basic structural unit of a compound. Examples are H2O, NaCl, and C6H12O6.

Chemosynthesis Process in which certain organisms (mostly specialized bacteria) extract inorganic compounds from their environment and convert them into organic nutrient compounds without the presence of sunlight. Compare photosynthesis. 

chlorinated hydrocarbon Organic compound made up of atoms of carbon, hydrogen, and chlorine. Examples are DDT and PCBs. 

Chlorofluorocarbons (CFCs) Organic compounds made up of atoms of carbon, chlorine, and fluorine. An example is Freon-12 (CCl2F2), used as a refrigerant in refrigerators and air conditioners and in making plastics such as Styrofoam. Gaseous CFCs can deplete the ozone layer when they slowly rise into the stratosphere and their chlorine atoms react with ozone molecules. Also used Freons chromosome Grouping of various genes and associated proteins in plant and animal cells that carry certain types of genetic information. See genes. 

City Large group of people with a variety of specialized occupations who live in a specific area and depend on a flow of resources from other areas to meet most of their needs and wants. 

civil suit Lawsuit in which a plaintiff seeks to (1) collect damages for injuries or for economic loss or (2) have the court issue a permanent injunction against further wrongful action. Compare class action suit. 

class action suit Civil lawsuit in which a group files a suit on behalf of a larger number of citizens who allege similar damages but who need not be listed and represented individually. Compare civil suit. 

clear-cutting Method of timber harvesting in which all trees in a forested area are removed in a single cutting. Compare, seed-tree cutting, selective cutting, shelterwood cutting, strip cutting. 

Climate Physical properties of the troposphere of an area based on analysis of its weather records over a long period (at least 30 years). The two main factors determining an area's climate are temperature, with its seasonal variations, and the amount and distribution of precipitation. Compare weather. 

closed system System in which energy but not matter is exchanged between the system and its environment. Compare open system. 

Coal Solid, combustible mixture of organic compounds with 30-98% carbon by weight, mixed with various amounts of water and small amounts of sulfur and nitrogen compounds. It forms in several stages as the remains of plants are subjected to heat and pressure over millions of years. 

coal gasification Conversion of solid coal to synthetic natural gas (SNG). 

coal liquefaction Conversion of solid coal to a liquid hydrocarbon fuel such as synthetic gasoline or methanol.

coastal wetland Land along a coastline, extending inland from an estuary, that is covered with salt water all or part of the year. Examples are marshes, bays, lagoons, tidal flats, and mangrove swamps. Compare inland wetland. 

coastal zone Warm, nutrient-rich, shallow part of the ocean that extends from the high-tide mark on land to the edge of a shelflike extension of continental land masses known as the continental shelf. Compare open sea. 

Coevolution Evolution in which two or more species interact and exert selective pressures on each other that can lead each species to undergo various adaptations. See evolution, natural selection. 

cogeneration Production of two useful forms of energy, such as high-temperature heat or steam and electricity, from the same fuel source. 

cold front Leading edge of an advancing mass of cold air. Compare warm front. 

Commensalisms Interaction between organisms of different species in which one type of organism benefits and the other type is neither helped nor harmed to any great degree. Compare mutualism. 

commercial extinction Depletion of the population of a wild species used as a resource to a level at which it is no longer profitable to harvest the species. 

commercial inorganic fertilizer Commercially prepared mixture of plant nutrients such as nitrates, phosphates, and potassium applied to the soil to restore fertility and increase crop yields. Also used inorganic fertilizer. Compare organic fertilizer. 

common law Body of unwritten rules and principles derived from thousands of past legal decisions. It is based on evaluation of what is reasonable behavior in attempting to balance competing social interests. Compare statutory law. 

community Populations of all species living and interacting in an area at a particular time. 

Competition Two or more individual organisms of a single species (intraspecific competition) or two or more individuals of different species (interspecific competition) attempting to use the same scarce resources in the same ecosystem. 

competitive exclusion principle No two species can occupy exactly the same fundamental niche indefinitely in a habitat where there is not enough of a particular resource to meet the needs of both species. See ecological niche, fundamental niche, realized niche. 

compost Partially decomposed organic plant and animal matter used as a soil conditioner or fertilizer. 

Compound Combination of atoms, or oppositely charged ions, of two or more different elements held together by attractive forces called chemical bonds. Compare element. 

concentration Amount of a chemical in a particular volume or weight of air, water, soil, or other medium.

condensation nuclei Tiny particles on which droplets of water vapor can collect. 

coniferous evergreen plants Cone-bearing plants (such as spruces, pines, and firs) that keep some of their narrow, pointed leaves (needles) all year. Compare broadleaf deciduous plants, broadleaf evergreen plants. 

coniferous trees Cone-bearing trees, mostly evergreens, that have needle-shaped or scalelike leaves. They produce wood known commercially as softwood. Compare deciduous plants.

consensus science Scientific data, models, theories, and laws that are widely accepted by scientists considered experts in the area of study. These results of science are very reliable. Compare frontier science.

conservation Sensible and careful use of natural resources by humans. People with this view are called conservationists. 

conservation biologist Biologist who investigates human impacts on the diversity of life found on the earth (biodiversity) and develops practical plans for preserving such biodiversity. Compare conservationist, ecologist, environmentalist, environmental scientist, preservationist, restorationist. 

conservation biology Multidisciplinary science created to deal with the crisis of maintaining the genes, species, communities, and ecosystems that make up earth's biological diversity. Its goals are to investigate human impacts on biodiversity and to develop practical approaches to preserving biodiversity.

Conservationist Person concerned with using natural areas and wildlife in ways that sustain them for current and future generations of humans and other forms of life. Compare conservation biologist, ecologist, environmentalist, environmental scientist, preservationist, restorationist. 

conservation-tillage farming Crop cultivation in which the soil is disturbed little (minimum-tillage farming) or not at all (no-till farming) to reduce soil erosion, lower labor costs, and save energy. Also no-till farming. Compare conventional-tillage farming. 

constancy Ability of a living system, such as a population, to maintain a certain size. See homeostasis. Compare inertia, resilience.

Consumer Organism that cannot synthesize the organic nutrients it needs and gets its organic nutrients by feeding on the tissues of producers or of other consumers; generally divided into primary consumers (herbivores), secondary consumers (carnivores), tertiary (higher-level) consumers, omnivores, and detritivores (decomposers and detritus feeders). Also used heterotroph. In economics, one who uses economic goods. 

contour farming Plowing and planting across the changing slope of land, rather than in straight lines, to help retain water and reduce soil erosion. 

contour strip mining Form of surface mining used on hilly or mountainous terrain. A power shovel cuts a series of terraces into the side of a hill. An earthmover removes the overburden, and a power shovel extracts the coal, with the overburden from each new terrace dumped onto the one below. Compare area strip mining, dredging, mountaintop removal, open-pit mining, subsurface mining.

controlled burning Deliberately set, carefully controlled surface fires that reduce flammable litter and decrease the chances of damaging crown fires. See ground fire, surface fire. 

conventional-tillage farming Crop cultivation method in which a planting surface is made by plowing land, breaking up the exposed soil, and then smoothing the surface. Compare conservation-tillage farming. 

convergent plate boundary Area where earth's lithospheric plates are pushed together. See subduction zone. Compare divergent plate boundary, transform fault. 

coral reef Formation produced by massive colonies containing billions of tiny coral animals, called polyps, that secrete a stony substance (calcium carbonate) around themselves for protection. When the corals die, their empty outer skeletons form layers and cause the reef to grow. They are found in the coastal zones of warm tropical and subtropical oceans. 

core Inner zone of the earth. It consists of a solid inner core and a liquid outer core. Compare crust, mantle. 

corridors Long areas of land that connect habitat that would otherwise become fragmented. 

crop rotation Planting a field, or an area of a field, with different crops from year to year to reduce soil nutrient depletion. A plant such as corn, tobacco, or cotton, which removes large amounts of nitrogen from the soil, is planted one year. The next year a legume such as soybeans, which adds nitrogen to the soil, is planted. 

crown fire Extremely hot forest fire that burns ground vegetation and treetops. Compare controlled burning, ground fire, surface fire. 

crude birth rate Annual number of live births per 1,000 people in the population of a geographic area at the midpoint of a given year. Also birth rate is used. Compare crude death rate.

crude death rate Annual number of deaths per 1,000 people in the population of a geographic area at the midpoint of a given year. Also death rate is used. Compare crude birth rate.

crude oil Gooey liquid consisting mostly of hydrocarbon compounds and small amounts of compounds containing oxygen, sulfur, and nitrogen. Extracted from underground accumulations, it is sent to oil refineries, where it is converted to heating oil, diesel fuel, gasoline, tar, and other materials. Also oil, petroleum. 

crust Solid outer zone of the earth. It consists of oceanic crust and continental crust. Compare core, mantle.

cultural eutrophication Overnourishment of aquatic ecosystems with plant nutrients (mostly nitrates and phosphates) because of human activities such as agriculture, urbanization, and discharges from industrial plants and sewage treatment plants. See eutrophication. 

cyanobacteria Single-celled, prokaryotic, microscopic organisms. Before being reclassified as monera, they were called blue-green algae.