What is carbon cycle?

• A. The series of processes by which carbon compounds are interconverted in the environment, chiefly involving the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels
• B. The movement of carbon through rocks and sediments only
• C. A cycle with no exchange with the atmosphere
• D. A cycle that occurs only in the oceans

Answer: (A)

The carbon cycle is the movement of carbon through the atmosphere, living organisms, oceans, and rocks as carbon compounds are continually interconverted. Plants fix carbon dioxide during photosynthesis, turning it into organic matter, while respiration, decay, and decomposition return carbon to the air or to the soil. Long-term storage in fossil fuels and rocks is balanced by releases when fuels are burned or rocks weather, keeping carbon circulating through major Earth reservoirs. The other options are too narrow: carbon moves beyond rocks, there is atmospheric exchange, and the cycle is not limited to the oceans.