Non-Point Source Pollution Envirothon Practice Test

The carbon cycle is about how carbon moves and is stored across Earth's major systems: the atmosphere, living things (biosphere), the oceans and freshwater (hydrosphere), and the rocks and soils (geosphere). Carbon shifts between these reservoirs through processes like photosynthesis, which pulls carbon from the air into plants; respiration and decomposition, which release CO2 back into the air; gas exchange and dissolution in ocean water; weathering of rocks that adds carbon to soils and oceans; and the long-term burial of carbon in sediments and fossil fuels. This web of exchanges keeps carbon moving rather than staying in one place, and it helps regulate atmospheric CO2 levels and climate. The other options describe different topics: nutrient movement refers to cycles of elements like nitrogen or phosphorus; water purification is about removing contaminants from water; sediment transport deals with the movement of soil and particles in water or wind. So the statement that carbon moves among the atmosphere, biosphere, hydrosphere, and geosphere best describes the carbon cycle.