Where is the phosphorus cycle primarily conducted?

The phosphorus cycle is primarily conducted in soil and plants, which is why this choice is correct. Phosphorus is an essential nutrient that plants require to grow and thrive. It exists in the soil as phosphate ions, which are absorbed by plant roots. This uptake is crucial for various biochemical processes, such as energy transfer (through ATP) and the formation of nucleic acids.

While animal bodies do play a role in the phosphorus cycle—through consumption of plants, excretion, and decomposition—the cycle's primary processes, including the uptake by plants and the movement of phosphorus through the soil ecosystem, take place in soil and plants. The atmosphere does not contribute significantly to the phosphorus cycle because phosphorus does not exist as a gas in the environment; it is primarily found in solid forms in rocks, soil, and biological organisms.

Although oceans and rivers can influence phosphorus distribution, they are not the main sites of the cycle, as aquatic systems primarily facilitate the transport and eventual deposition of phosphorus, rather than its primary cycling. Therefore, the correct answer highlights the fundamental role of soil and plants in this essential nutrient cycle.