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What is the Phosphorus Cycle?

Joanna Tatomir, Kelly Robson
  • Author
    Joanna Tatomir

    Joanna holds a PhD in Biology from the University of Michigan and is currently working towards a degree in Veterinary Medicine at Michigan State University. She has taught a combination of ESL and STEM courses to secondary and university students.

  • Instructor
    Kelly Robson

    Kelly has taught High School Science and Applied Communications. She holds an Education Specialist Degree in Ed. Leadership.

Learn about the phosphorus cycle. Understand the definition and importance of the phosphorus cycle, explore the phosphorus cycle diagram, and study the steps. Updated: 01/01/2022

Phosphorus Cycle Definition

Plants and animals rely upon a variety of micronutrients, such as vitamins and minerals, in order to maintain optimal health conditions. One of these essential micronutrients is phosphorus, an element that is typically found, bound to other elements in nature. In plants, phosphorus is essential for cell division, new tissue growth, and cellular respiration. In humans, phosphorus represents an electrolyte dissolved in bodily fluids. Phosphorus also represents one of the building blocks for bones, teeth, and the genetic material found in humans, and other animals.

Phosphorus is often found as part of minerals, rocks, and soils. Due to phosphorus not usually being found in isolation in nature, access to sources of phosphorus is important for many living organisms. The phosphorus cycle constitutes the primary method for liberating phosphorus from these inorganic substances. The phosphorus cycle represents the process by which phosphorus is removed from inorganic materials, used by living organisms, and then incorporated back into waterways, such as lakes, rivers and oceans. Thus, the phosphorus cycle essentially recycles this important element between inorganic and organic sources.

The Phosphorus Cycle - Definition

Phosphorus is an essential element to all life. It is an important part of the ATP molecule that stores and gives every cell its energy. It is also found in DNA and RNA, which tell the cells how to look and act. Needless to say, phosphorus is needed for every living organism to grow and function. The phosphorus cycle is the process in which phosphorus travels from its main source of rocks through ecosystems to living organisms.

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Phosphorus Cycle Diagram and Steps

Phosphorus represents an uncombined element. An uncombined element refers to any element that is not found in its native form and is, instead, bound to other elements or compounds. On Earth, phosphorus is contained within rocks, soil, minerals, and water. So how do plants and animals obtain phosphorus if it is primarily found in these inorganic forms? The phosphorus cycle process enables phosphorus to be liberated from these sources in order to be made available to plants and animals. The phosphorus cycle steps will be further discussed below.

Weathering

Weathering represents an important step in both the phosphorus and rock cycles. The rock cycle represents the process in which rocks are recycled in order to form new minerals, sediments, and other rock types. Over time, wind and water break down and dissolve rocks, releasing their constituent elements into the surrounding soil and waterways. This process of erosion is essential for making phosphorus accessible to living organisms like plants and animals.

Plant Uptake

When phosphate ions are liberated from rocks, phosphorus is made available to plants, in particular. Plant growth is dependent upon the amount of phosphorus in the soil. As a result, farming and agriculture rely upon fertilizers containing phosphorus to help crops grow. This is especially important when plants are located in areas with little erosion and therefore no direct source of phosphorus.

If erosion provides a rich source of phosphorus for sediments and soils, then plants can access the phosphorus via direct absorption from the soil. Sometimes phosphorus becomes inaccessible when bound to soil. When this occurs, bacteria present in the soil are capable of converting phosphorus bound to soil into organic forms that are accessible to plants. Some bacteria and fungi also form symbiotic relationships with plants by attaching themselves to plant roots. When found in association with plant roots, these bacteria and fungi enhance the plant's ability to absorb nutrients, such as phosphorus and nitrogen.

The pH level of the soil also determines the accessibility of phosphorus to plants. In acidic soils, phosphorus binds to metals, making phosphorus unavailable to plants. By contrast, in basic soils, phosphorus binds to calcium and becomes available for use by plants.

The phosphorus cycle exists in both terrestrial and aquatic environments. In the phosphorus cycle example below, the diagram shows how phosphorus moves through the plants and animals living in an aquatic environment.


The phosphorus cycle in an aquatic environment.

phosphorus cycle process


Incorporation into Organic Molecules and Absorption by Animals

Once a plant has taken up phosphate compounds from the soil, animals can eat these plants and obtain phosphorus from this vegetation. Inside plants and animals, phosphorus is incorporated into a variety of organic compounds and molecules. For example, DNA and RNA both contain a phosphate backbone that is dependent upon the availability of phosphorus. Moreover, cell membranes rely upon phospholipids as integral parts of their structure. Phospholipids are formed when a phosphate group binds to a lipid.


RNA

phosphorus cycle process


Phosphorus is also essential for bone and dental health, as well as in the proper functioning of muscles and nerves. In conjunction with calcium, phosphorus helps to mineralize the structures of the skeleton and enables neurotransmission to occur within animals. Phosphorus levels are so important in the human body, that a combination of hormones helps to control the amount of phosphorus that circulates throughout the body.

Steps to the Phosphorus Cycle

The phosphorus cycle begins its journey in the crust of the Earth as phosphorous is found in rocks. Weathering causes it to break free from the rocks and wash away into the ground. At this time, the phosphorus gets mixed in the soil. Land plants are now able to soak up the phosphorus from the ground. Animals obtain the phosphorus by eating the plants.

Sometimes the phosphorus just gets washed up into the water supply. Aquatic plants and other producers are able to obtain phosphorus directly from the water. Animals, too, can get phosphorus from drinking the water.

The phosphorus is returned to the Earth in different ways. Plants and producers that are not eaten will die, and their phosphorus will be broken down when they decay. This will return the phosphorus back to the earth to mix with the soil or water. Then new producers that use the soil or water will be able to use the phosphorus. Humans and other animals return phosphorus through our waste. When our waste gets broken down, the phosphorus goes into the water system.

Even though phosphorus gets passed on from the ground to producer to animal and then returns back to the land or water, the phosphorus cycle is still not a true cycle. In a true cycle, all the phosphorus will continue to circulate through the cycle. However, in the actual phosphorus cycle, some of the phosphorus will get lost. The phosphorus that is returned to the ocean may sink to the bottom and become inaccessible and unusable. The only usable phosphorus will remain at the surface of the water.

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Video Transcript

The Phosphorus Cycle - Definition

Phosphorus is an essential element to all life. It is an important part of the ATP molecule that stores and gives every cell its energy. It is also found in DNA and RNA, which tell the cells how to look and act. Needless to say, phosphorus is needed for every living organism to grow and function. The phosphorus cycle is the process in which phosphorus travels from its main source of rocks through ecosystems to living organisms.

Steps to the Phosphorus Cycle

The phosphorus cycle begins its journey in the crust of the Earth as phosphorous is found in rocks. Weathering causes it to break free from the rocks and wash away into the ground. At this time, the phosphorus gets mixed in the soil. Land plants are now able to soak up the phosphorus from the ground. Animals obtain the phosphorus by eating the plants.

Sometimes the phosphorus just gets washed up into the water supply. Aquatic plants and other producers are able to obtain phosphorus directly from the water. Animals, too, can get phosphorus from drinking the water.

The phosphorus is returned to the Earth in different ways. Plants and producers that are not eaten will die, and their phosphorus will be broken down when they decay. This will return the phosphorus back to the earth to mix with the soil or water. Then new producers that use the soil or water will be able to use the phosphorus. Humans and other animals return phosphorus through our waste. When our waste gets broken down, the phosphorus goes into the water system.

Even though phosphorus gets passed on from the ground to producer to animal and then returns back to the land or water, the phosphorus cycle is still not a true cycle. In a true cycle, all the phosphorus will continue to circulate through the cycle. However, in the actual phosphorus cycle, some of the phosphorus will get lost. The phosphorus that is returned to the ocean may sink to the bottom and become inaccessible and unusable. The only usable phosphorus will remain at the surface of the water.

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Frequently Asked Questions

What is the role of the phosphorus cycle?

The phosphorus cycle represents an essential method for freeing phosphorus bound to inorganic materials, such as rocks, minerals, and sediments. This phosphorus is then used by living organisms to produce a variety of important organic compounds and structures, such as DNA, RNA, and ATP.

What are the processes of phosphorus cycle?

The phosphorus cycle starts with the erosion, and weathering of rocks and sediments, in order to liberate phosphate ions. Plants absorb phosphate and animals eat these plants. In both plants and animals, phosphorus is used to produce organic compounds. Phosphorus is returned to the cycle via the application of fertilizers, waste products, and the decomposition of organic matter.

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