Which of the following biogeochemical cycles is correctly paired with its largest reservoir?

• A. Carbon cycle — atmosphere
• B. Water cycle — living organisms
• C. Nitrogen cycle — oceans
• D. Phosphorus cycle — sedimentary rocks

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the concept of biogeochemical cycles. These are pathways through which elements and compounds move between living organisms and the environment, including reservoirs where these elements are stored for long periods.
2. Step 2: Review the major reservoirs for each cycle. For example, the carbon cycle's largest reservoir is the atmosphere, the water cycle's largest reservoir is the oceans, the nitrogen cycle's largest reservoir is the atmosphere, and the phosphorus cycle's largest reservoir is sedimentary rocks.
3. Step 3: Analyze the options provided in the question. Compare each cycle with its stated reservoir and determine if it matches the known largest reservoir for that cycle.
4. Step 4: Focus on the phosphorus cycle. Phosphorus does not have a gaseous phase and is primarily stored in sedimentary rocks, making it unique compared to other cycles.
5. Step 5: Conclude that the correct pairing is 'Phosphorus cycle — sedimentary rocks,' as this matches the largest reservoir for phosphorus in the environment.