The carbon cycle is defined as

• A. The circulation of carbon atoms through organisms, the environment, and the atmosphere.
• B. The movement of water in the environment.
• C. The process of photosynthesis only.
• D. The breakdown of carbon compounds in the soil.

Answer: (A)

The carbon cycle is about how carbon moves through living things, the air, water, and soils, circulating carbon atoms among different reservoirs. Plants take in carbon dioxide during photosynthesis and store carbon in their tissues; animals obtain carbon by eating plants or other organisms, and through respiration release carbon back into the air. Decomposition returns carbon from dead organisms to the soil, while oceans exchange carbon with the atmosphere and rocks slowly over time. This continuous transfer between organisms, the environment, and the atmosphere explains why the statement about carbon atoms circulating through those parts of the system is the best description. The other options describe a different cycle (the movement of water), a single process (photosynthesis), or only one part of the cycle (decomposition), rather than the full, interconnected movement of carbon.