Phosphorus Cycle: Stages and Importance

He phosphorus cycle is the process by which phosphorus moves through rocks, water, soil and organisms. This cycle, unlike other biogeochemical cycles, does not pass through the air because there are not many gaseous compounds based on phosphorus.

The main phosphorus reserve is found in the water of rivers, lakes and oceans (hydrosphere), but also in sediments and rocks (lithosphere). Phosphorus is essential for the growth of plants and animals, as well as for the microbes that inhabit the soil, which gradually depletes over time.

Phosphorus cycle

The main biological function of phosphorus is to be part of important biomolecules such as nucleic acids (DNA and RNA), some proteins and lipids. In fact, the DNA strands are formed by phosphate ester bonds.

Calcium phosphate is also an important component for the formation of mammalian bones and teeth. Likewise, it is part of the structure of the exoskeleton of insects, the membranes of cell phospholipids and of many important metabolites such as ATP.

The phosphorus cycle is an extremely slow process, since phosphorus remains for a long time in rocks and sediments. Rain and erosion help to wash the phosphorus from the rocks, while in the soil the organic matter absorbs the phosphorus that will be used for various biological processes.

Like all biogeochemical cycles, there is no beginning or end of the phosphorus cycle, and certainly there is not a single direction of movement. Earth cycles are complex networks where resources move in multiple directions.


  • 1 Stages of the cycle
  • 2 The importance of phosphorus for living beings
    • 2.1 Limiting nutrient
    • 2.2 Conforms DNA and RNA
    • 2.3 Transport of energy
    • 2.4 Gives structure to cell membranes
    • 2.5 It is part of the bones
    • 2.6 Participation in homeostasis
    • 2.7 Regulates enzymatic activity
    • 2.8 Signal transmitter
  • 3 Impact of the human being on the phosphorus cycle
    • 3.1 Use of fertilizers
    • 3.2 Eutrophication
    • 3.3 Waste water and the use of detergents
  • 4 References

Stages of the cycle

- Over time, rain and wind erode the rocks, causing the release of phosphate ions and other minerals. This inorganic phosphate is distributed in the soil and water.

- Plants take inorganic phosphate from the soil through its roots; in this way they incorporate the phosphates to their biological molecules (nucleic acids and proteins), thus allowing their growth and development.

- Plants can be consumed by herbivorous animals. Once they enter the organism, the molecules that contain phosphorus are degraded and incorporated again into the organic molecules of the herbivorous organism.

- The herbivorous animals can be consumed by the carnivores, and in this way they transfer the phosphorus atoms to the next level of the trophic chain. The phosphates that were absorbed by these animals are returned to the soil through excretion.

- When the plant or animal dies, its tissues are decomposed by another group of organisms called decomposers. These microbes degrade the remains and, in this way, the organic phosphate is returned to the soil.

- The phosphorus in the soil can end up in different bodies of water and finally end up in the ocean. Once there, it can be incorporated into aquatic organisms or sedimented for long periods.

The importance of phosphorus for living beings

Limiting nutrient

Like carbon, oxygen, hydrogen and nitrogen, phosphorus is a limiting nutrient for all life forms, which means that the potential for the growth of an organism is limited by the availability of this vital nutrient.

Conforms DNA and RNA

Phosphorus is part of the structure of DNA and RNA. The double helix form of DNA is possible only because the phosphate molecules form a phosphate ester bridge that binds to the double helix.

Transport of energy

Phosphorus is also necessary for the transport of energy in cells, it is a fundamental part of energy storage molecules such as ATP, ADP, GDP, among others.

Gives structure to cell membranes

Phosphorus provides structure to cell membranes. The fundamental component of biological membranes are molecules called phospholipids, which are formed by different types of lipids attached to phosphate groups.

It is part of the bones

Phosphorus is found in the bones in the form of calcium phosphate and gives it its rigidity. It is also present in the enamel of the teeth of mammals and in the exoskeleton of insects.

Participation in homeostasis

Phosphorus also works in the maintenance of homeostasis. Some phosphorus-based compounds are important buffers; that is, they help maintain the balance between acids and bases (pH) in the body.

Regulates enzymatic activity

Phosphorus regulates the activity of enzymes. Many important enzymes in the metabolism are activated (or deactivated) by the addition of phosphate groups.

Signal transmitter

Phosphorus is also essential for the transmission of signals within cells.

Impact of the human being on the phosphorus cycle

The human being has interacted with its environment and has influenced many natural processes, including the phosphorus cycle. Human activities alter the phosphorus cycle mainly by adding more phosphorus to places where there was little phosphorus availability previously.

Use of fertilizers

Because phosphates are quite limited in the soil naturally, modern agricultural practices often involve the application of fertilizers containing inorganic phosphates.

When phosphorus is added to an ecosystem very frequently, much of this phosphorus is lost because it is washed quickly with rains and irrigation. Therefore, excess phosphorus ends up being transported to water bodies (rivers, seas and oceans) through a process called runoff.


Nutrients washed by runoff accumulate in water bodies, causing the exponential growth of algae and plankton. This process is known as eutrophication.

The proliferation of these organisms causes all available oxygen to be rapidly depleted, which ends up affecting all other species in the ecosystem.

This phenomenon has been observed in small ecosystems, such as the ponds of some farms, but also in huge bodies of water, such as the Baltic Sea.

Waste water and the use of detergents

Another important source of phosphorus comes from wastewater and detergents. Both end up pouring their phosphate groups into the bodies of water, thus increasing the process of eutrophication.


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