Q.Describe phosphorus cycle with diagram.

Phosphorus cycles between rocks, soil/water, living organisms and back to sediment, mainly through weathering, absorption, food chains, and decomposition — it is a sedimentary (not gaseous) cycle.

Phosphorus Cycle:

Reservoir: The main reservoir of phosphorus is rock (phosphate-containing minerals such as apatite), unlike carbon/nitrogen which have large atmospheric reservoirs. Hence phosphorus cycling is called a sedimentary cycle.

Steps:

1. Weathering of rocks: Phosphorus is released from phosphate rocks by weathering, entering the soil as inorganic phosphate (PO4 3-).
2. Uptake by plants: Plants absorb phosphate ions from the soil through their roots and incorporate them into organic compounds (e.g., nucleic acids, ATP, phospholipids).
3. Transfer through food chain: Herbivores obtain phosphorus by eating plants, and carnivores obtain it by eating herbivores — phosphorus thus moves up the food chain.
4. Return via decomposition: When plants and animals die, decomposers (bacteria and fungi) break down their organic matter, releasing phosphate back into the soil.
5. Loss to sediments: Some phosphate is washed by rain/rivers into the sea, where it may be deposited as sediment on the ocean floor, eventually forming new phosphate rock over geological time — completing the (very slow) cycle. …