In the phosphorus cycle, where does the cycle primarily begin?

• A. With the weathering of phosphate rocks
• B. With nitrogen fixation by bacteria
• C. With the evaporation of water from oceans
• D. With the release of carbon dioxide by respiration

Answer: (A)

Verified step by step guidance

1. Understand the phosphorus cycle: The phosphorus cycle is unique compared to other biogeochemical cycles because it does not involve a gaseous phase. Phosphorus primarily cycles through rocks, soil, water, and living organisms.
2. Identify the starting point: The cycle begins with the weathering of phosphate-containing rocks. Weathering is the process where rocks break down due to environmental factors like wind, rain, and temperature changes.
3. Explain the release of phosphate: During weathering, phosphate ions (PO₄³⁻) are released into the soil and water, making them available for uptake by plants and microorganisms.
4. Clarify why other options are incorrect: Nitrogen fixation by bacteria is part of the nitrogen cycle, evaporation of water is part of the water cycle, and the release of carbon dioxide by respiration is part of the carbon cycle. These processes are unrelated to the phosphorus cycle.
5. Summarize the key point: The phosphorus cycle primarily begins with the weathering of phosphate rocks, which releases phosphate ions into the environment for biological use.