Which description correctly defines a biogeochemical cycle?

• A. It is a process that strictly occurs in the atmosphere.
• B. It moves energy, not matter, through ecosystems.
• C. It occurs only in aquatic systems.
• D. It moves elements through living and nonliving components, such as carbon and nitrogen cycles.

Answer: (D)

Biogeochemical cycles describe how elements move through both living organisms and the nonliving parts of the environment. Elements like carbon or nitrogen are taken up by plants, transformed by organisms, passed through food webs, and returned to air, water, or soil in forms that can be reused. This continual movement links atmospheric, aquatic, terrestrial, and geological reservoirs, allowing matter to be recycled rather than used up.

Energy flow is different: it travels through ecosystems and is eventually lost as heat, but it’s not recycled in a cycle. That’s why a statement that focuses on moving energy through ecosystems isn’t describing a biogeochemical cycle. Likewise, cycles aren’t limited to any single part of the environment—neither strictly the atmosphere nor only aquatic systems—since these cycles span multiple habitats and reservoirs.

So the description that fits best is the one that emphasizes moving elements through living and nonliving components, such as the carbon and nitrogen cycles.