Natural reservoir of phosphorus is

Options

A. Rock
B. Fossils
C. Sea water
D. Animal bones

Answer

### Step-by-Step Solution:

1. **Understanding Phosphorus Cycle**: The phosphorus cycle is a biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. It does not have a gaseous phase like other biogeochemical cycles.

2. **Natural Reservoir Identification**: The natural reservoir of phosphorus is primarily found in rock minerals. Phosphorus is present in the form of phosphate (PO4^3-) in these rocks.

3. **Weathering Process**: The cycle begins with the weathering of these rock minerals. Through weathering, phosphorus is released into the soil.

4. **Soil Solution**: Once released, phosphorus enters the soil solution, making it available for uptake by plants, which are the primary producers in the ecosystem.

5. **Role of Producers**: Plants absorb phosphorus from the soil solution. This phosphorus is essential for various biological processes, including energy transfer and photosynthesis.

6. **Movement through the Food Chain**: When herbivores (consumers) eat plants, they obtain phosphorus. Similarly, carnivores that eat herbivores also acquire phosphorus.

7. **Decomposition**: When organisms die, decomposers (like detritivores) break down their bodies, releasing phosphorus back into the soil, thus continuing the cycle.

8. **Conclusion**: The natural reservoir of phosphorus, therefore, is the rocks, specifically in the form of phosphate minerals.

### Final Answer:
The natural reservoir of phosphorus is **rocks**.

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