Which statement about biogeochemical cycles is true?

• A. A cycle moving elements through living and nonliving systems; carbon cycle and nitrogen cycle are essential.
• B. A cycle of days and seasons; water cycle and oxygen cycle are essential.
• C. A cycle of cell division; mitotic cycle and meiotic cycle are essential.
• D. A cycle of evolutionary change; natural selection and genetic drift are essential.

Answer: (B)

Biogeochemical cycles describe how elements move through living things and the nonliving environment, creating a link between biology, chemistry, and geology. This movement keeps essential elements available for life as they cycle through ecosystems.

The statement that emphasizes a cycle moving elements through living and nonliving systems and notes carbon and nitrogen cycles as essential captures this idea. Carbon and nitrogen are fundamental to organic molecules and to energy flow, so their cycling—through processes like photosynthesis, respiration, decomposition, nitrogen fixation, and mineralization—keeps life’s chemistry in balance across air, water, soil, and organisms.

The other wording shifts focus to time, describing cycles of days and seasons rather than the movement of elements. While the water cycle is a real biogeochemical cycle and oxygen moves through ecosystems as organisms respire and photosynthesize, labeling cycles by time rather than by elemental movement is not how biogeochemical cycles are defined.