Phosphorus Cycle – Definition, Steps, Human Impact | Biology

Phosphorus Cycle


Phosphates are important for the growth and maintenance of animal and human bones and teeth while organic phosphates are required for cell division involving production of nuclear DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Phosphorus is not found in atmosphere .The plants obtain the phosphorus from soil either as dihydrogenophosphate (H2PO3) or hydrogenophosphate (H2PO4).Inside the plant bodies it does not undergo reduction, instead remain as phosphate as a constituent of Nucleic acid , phosphorylated carbohydrates and fats.

FIG.Phosphorus cycle

Steps Involved in Phosphorus Cycle

  • Weathering
  • Absorption by Plants
  • Absorption by Animals
  • Return of phosphorus back to the environment


Phosphate minerals present in soluble and insoluble forms in rocks and soil.The phosphate is released from these rocks by weathering process or by erosion and leaching in to the soil surface.

Absorption by Plants

Plants absorb these inorganic phosphate salts from soil and change them into organic phosphate. The absorption of phosphates by plants is greatly aided by the presence of mycorrhizae. Plants that are present in water absorb inorganic form of phosphorous from water and bottom layer of water bodies.

Absorption by Animals

Animals obtain these phosphates by eating plants parts i.e. fruit ,leaves etc. Both  the marine and terrestrial plants are eated by Plant eating  animals, birds, and fishes. The organic form of phosphorus is transferred to the next level of consumers like man. Hence, the carnivores get or obtain phosphorous by consuming herbivores.


Return of Phosphorous Back to The Ecosystem

After the death and decay of plants and animals these phosphates return  to the soil.Under suitable environmental conditions, bacteria and other microorganisms decompose or breakdown the dead organisms bodies.

During the process of decomposition, the organic form of phosphorous is converted into an inorganic form, which is then recycled to the soil and water.

After that, these element will end with rock formations or sediments, where they will remain for millions of years.

In short, phosphorous is released again in the soil by the process of weathering and absorbed by the plants. And the phosphorus cycle continue.

Large amount of the phosphate in soil is fixed or absorbed in soil particles but some part of it, is leached out into water bodies.Due to recycling of phosphorus the percentage composition of the phosphorus remains at constant or uniform.

Impact of Human  on the Phosphorus Cycle

The natural phosphate cycle is affected or disturbed by pollution, mainly from agricultural run-off containing super phosphate and also from domestic sewage.

Human activities altered the phosphorus cycle. To maintain the phosphorus levels in soils agriculturists must apply phosphorus fertilizers. A part of the phosphate that is used as fertilizers is removed in crops when harvested.

The phosphorus is released as waste when the food is processed and consumed  and added to the natural water bodies through sewage resulting in pollution.

Phosphate pollution of rivers and lakes is the major cause of algal bloom (eutrophication) which
reduces the amount of dissolved oxygen in water and disrupts the food chain.

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