Phosphorus Cycle Notes

The Phosphorus Cycle

The phosphorus cycle is a biogeochemical cycle essential for life on Earth, alongside the water, carbon, and nitrogen cycles. A biogeochemical cycle is a pathway by which a chemical substance moves through the biotic and abiotic compartments of Earth.

Importance of Phosphorus

  • Phosphorus is crucial for plant and animal growth.
  • It is essential for the health of soil microbes.
  • It is vital for the production of DNA and RNA.
  • It helps make up cell membranes.
  • It is involved in the production of ATP (adenosine triphosphate), which is the energy currency of cells.

The Four Key Steps of the Phosphorus Cycle

The phosphorus cycle is a slow process consisting of four key steps:

Step One: Weathering
  • Phosphorus is found in rocks.
  • Weathering, along with rain, breaks down the phosphorus in rocks.
  • The broken-down phosphorus travels to the soil and into water sources.
Step Two: Absorption by Plants and Animals
  • Plants, fungi, and microorganisms in the soil absorb phosphorus allowing growth.
  • Some phosphorus makes its way to the ocean and freshwater.
  • Animals drink water and absorb the phosphorus.
  • Plants absorb water along with phosphorus.
  • Animals eat plants, allowing the phosphorus to move into the animals.
Step Three: Returning to the Environment by Decomposition
  • Animals excrete waste, and decomposers use the phosphorus in the waste material.
  • When plants and animals die, bacteria convert the organic phosphorus into inorganic phosphorus in a process called mineralization.
Step Four: Sediment to Rocks
  • Some phosphorus gets buried in sediment, which over time becomes rocks, and the cycle continues.
  • Some phosphorus in the soil gets washed to the ocean, where a similar process takes place.
  • Plants and animals in the ocean absorb the phosphorus, die, and decompose.
  • Some of the phosphorus ends up as sediments in the rock.

Human Impact on the Phosphorus Cycle

  • Fertilizers containing phosphorus are added to the soil to help plants grow.
  • However, excessive phosphorus levels can lead to an overabundance of plant nutrients, driving excessive algae growth.
  • When these algae die, they can be toxic to the plants and animals in the ecosystem.