Which set of processes describes how elements such as carbon circulate through biological and geological components?

• A. Biogeochemical cycle
• B. Hydrologic cycle
• C. Energy pyramid
• D. Population density

Answer: (A)

Elements such as carbon move between living things and nonliving parts of Earth through processes that transform and transfer them. This pattern is described by biogeochemical cycles, which cover how atoms cycle among organisms, air, water, soils, and rocks. For carbon specifically, plants remove CO2 from the atmosphere during photosynthesis, organisms release it back through respiration and decomposition, oceans exchange carbon with the air, and carbon is stored for long times in sediments and rocks while geological processes like weathering and volcanic activity move carbon between rocks and the atmosphere or oceans. The idea of a biogeochemical cycle captures both the biological activity and the geological reservoirs involved. The other options don’t describe this cross‑component circulation: the hydrologic cycle centers on water movement, the energy pyramid on energy flow through trophic levels, and population density describes how many individuals occupy an area.