Question: Radiation

Answer: the energy that is transferred as electromagnetic waves, such as visible light and infrared waves

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Question: recharge zone

Answer: an area in which water travels downward to become part of an aquifer

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Question: reclamation

Answer: the process of returning land to its original condition after mining is completed

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Question: recycling

Answer: the process of recovering valuable or useful materials from waste or scrap; the process of reusing some items

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Question: reforestation

Answer: the reestablishment and development of trees in a forest land

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Question: renewable energy

Answer: energy from sources that are constantly being formed

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Question: reproductive potential

Answer: the maximum number of offspring that a given organism can produce

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Question: reservoir

Answer: an artificial body of water that usually forms behind a dam

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Question: resistance

Answer: in biology, the ability of an organism to tolerate a chemical or disease-causing agent

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Question: risk

Answer: the probability of an unwanted outcome

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Question: risk assessment

Answer: the scientific assessment, study, and management of risk; a scientific estimation of the likelihood of negative effects that may result from exposure to a specific hazard

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Question: river system

Answer: a flowing network of rivers and streams draining a river basin

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Question: ruminant

Answer: a cud-chewing mammal that has a three- or four-chambered stomach; examples include sheep, goats, and cattle

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Question: rural

Answer: describes an area of open land that is often used for farming

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Question: salinity

Answer: a measure of the amount of dissolved salts in a given amount of liquid

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Question: salinization

Answer: the accumulation of salts in soil

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Question: salt marsh

Answer: a maritime habitat characterized by grasses, sedges, and other plants that have adapted to continual, periodic flooding; salt marshes are found primarily throughout the temperate and subarctic regions

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Question: sample

Answer: the group of individuals or events selected to represent a statistical population

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Question: savanna

Answer: a plain full of grasses and scattered trees and shrubs; found in tropical and subtropical habitats and mainly in regions with a dry climate, such as East Africa

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Question: secondary pollutant

Answer: a pollutant that forms in the atmosphere by chemical reaction with primary air pollutants, natural components in the air, or both

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Question: secondary succession

Answer: the process by which one community replaces another community that has been partially or totally destroyed

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Question: sick-building syndrome

Answer: a set of symptoms, such as headache, fatigue, eye irritation, and dizziness, that may affect workers in modern, airtight office buildings; believed to be caused by indoor pollutants

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Question: smelting

Answer: the melting or fusing of ore in order to separate impurities from pure metal

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Question: smog

Answer: urban air pollution composed of a mixture of smoke and fog produced from industrial pollutants and burning fuels

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Question: solid waste

Answer: a discarded solid material, such as garbage, refuse, or sludges

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Question: source reduction

Answer: any change in the design, manufacture, purchase, or use of materials or products to reduce their amount or toxicity before they become municipal solid waste; also the reuse of products or materials

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Question: species

Answer: a group of organisms that are closely related and can mate to product fertile offspring; also the level of classification below genus and above subspecies

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Question: statistics

Answer: the collection and classification of data that are in the form of numbers

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Question: stratosphere

Answer: the layer of the atmosphere that lies between the troposphere and the mesosphere and in which temperature increases as altitude increases; contains the ozone layer

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Question: subsidence

Answer: the sinking of regions of the ground surface with little or no horizontal movement

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Question: subsurface mining

Answer: a mining method in which ore is extracted from beneath the ground surface

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Question: surface impoundment

Answer: a natural depression or a human-made excavation that serves as a disposal facility that holds an accumulation of wastes

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Question: surface mining

Answer: a mining method in which soil and rocks are removed to reach underlying coal or minerals

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Question: surface water

Answer: all the bodies of fresh water, salt water, ice, and snow that are found above the ground

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Question: survivorship

Answer: the percentage of newborn individuals in a population that can be expected to survive in a given age

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Question: sustainability

Answer: the condition in which human needs are met in such a way that a human population can survive indefinitely

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Question: symbiosis

Answer: a relationship in which two different organisms live in close association with each other

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Question: taiga

Answer: a region of evergreen, coniferous forest below the arctic and subarctic tundra regions

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Question: tectonic plate

Answer: a block of lithosphere that consists of the crust and the rigid, outermost part of the mantle; also called lithospheric plate

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Question: temperate deciduous forest

Answer: a forest (or biome) that is characterized by trees that shed their leaves in the fall

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Question: temperate grassland

Answer: a community (or biome) that is dominated by grasses, has few trees, and is characterized by cold winters and rainfall that is intermediate between that of a forest and a desert

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Question: temperate rain forest

Answer: a forest community (or biome), characterized by cool, humid weather and abundant rainfall, where tree branches are draped with mosses, tree trunks are covered with lichens, and the forest floor is covered with ferns

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Question: temperature inversion

Answer: the atmospheric condition in which warm air traps cooler air near Earth's surface

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Question: thermal pollution

Answer: a temperature increase in a body of water that is caused by human activity and that has a harmful effect on water quality and on the ability of that body of water to support life

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Question: threatened species

Answer: a species that has been identified to be likely to become endangered in the foreseeable future

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Question: topsoil

Answer: the surface layer of the soil, which is usually richer in organic matter than the subsoil is

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Question: toxicology

Answer: the study of toxic substances, including their nature, effects, detection, methods of treatment, and exposure control

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Question: trophic level

Answer: one of the steps in a food chain or food pyramid; examples include producers and primary, secondary, and tertiary consumers

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Question: tropical rain forest

Answer: a forest or jungle near the equator that is characterized by large amounts of rain and little variation in temperature and that contains the greatest known diversity of organisms on Earth

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Question: troposphere

Answer: the lowest layer of the atmosphere, in which temperature drops at a constant rate as altitude increases; the part of the atmosphere where weather conditions exist

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Question: tundra

Answer: a treeless plaint that is located in the Arctic or Antarctic and that is characterized by very low winter temperatures; short, cool summers; and vegetation that consists of grasses, lichens, and perennial herbs

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Question: understory

Answer: a foliage layer that is beneath and shaded by the main canopy of a forest

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Question: urban

Answer: describes an area that contains a city

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Question: urbanization

Answer: an increase in the ratio or density of people living in urban areas rather than in rural areas

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Question: urban sprawl

Answer: the rapid spread of a city into adjoining suburbs and rural areas

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Question: value

Answer: a principle or standard that an individual considers to be important

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Question: variable

Answer: a factor that changes in an experiment in order to test a hypothesis

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Question: vector

Answer: in biology, any agent, such as a plasmid or a virus, that can incorporate foreign DNA and transfer that DNA from one organism to another, an intermediate host that transfers a pathogen or a parasite to another organism

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Question: vertebrate

Answer: an animal that has a backbone, includes mammals, birds, reptiles, amphibians, and fish

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Question: wastewater

Answer: water than contains wastes from homes or industry

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Question: water cycle

Answer: the continuous movement of water between the atmosphere, the land, and the oceans

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Question: water pollution

Answer: contamination of water by waste matter or other material that is harmful to organisms that are exposed to the water

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Question: watershed

Answer: the areas of land that is drained by a water system

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Question: weather

Answer: the short-term state of the atmosphere, including temperature, humidity, precipitation, wind, and visibility

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Question: wetland

Answer: an area of land that is periodically underwater or whose soil contains a great deal of moisture

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Question: wilderness

Answer: a region that is not cultivated and that is not inhabited by humans

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Question: yield

Answer: the amount of crops produced per unit area

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