The Phosphorous Cycle

• Phosphorous is an important biological element as it is a component of ATP, phospholipids and nucleic acids, so it must be recycled.
• In the phosphorous cycle, the main reservoir is in its mineral form rather than in the atmosphere (like carbon and nitrogen).
• Phosphorous exists mainly as phosphate ions (PO4^3-) in sedimentary rock deposits. These originate in the sea but are brought to the surface by geological uplifting of rocks (as well as weathering and erosion).
• Weathering and erosion allow the phosphate ions to become dissolved and incorporated into plants and their biomass. These ions are then passed onto animals, and excess ions are released as excrement.
• On the death of plants and animals, decomposers will break them down, releasing phosphate ions into the water or soil. Some phosphate ions remain in parts of animals, such as bones, which are very slow to be broken down.
• The phosphate ions excreted by animals are transported by streams and rivers into lakes and oceans where they form sedimentary rocks, thus completing the cycle.