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Phosphorus Cycle

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Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The phosphorous cycle follows the movement of phosphorous through the biosphere. Phosphorous is found in many forms, both organic and inorganic, but is most commonly found in the phosphate ion. Phosphorous is essential for both plants and animals. In biotic processes, plants remove phosphorous from the soil, animals eat plants and so on. In abiotic processes, phosphate is released by rocks due to weathering, then is deposited in the soil or water through leaching or runoff.

The phosphorus cycle is how phosphorus obviously cycles its way through the environment, both through the biotic mechanisms i.e. like when plants take it from the soil and a biotic mechanisms like when rocks are withered and eroded and give off their inorganic phosphates into the water. So phosphorous typically is used in biological systems as phosphates an important ingredient and things like DNA, ATP phospholipids et cetera. Let's take a look at this diagram over here and we can see how the phosphorous cycle works. It begins when rocks which have phosphorus somehow in their makeup have water and other chemicals erode them or wither them and then by run off they wind up with phosphates in the water and ultimately can, that run off can take phosphates into the soil.

Once it's in the soil, plants can absorb the phosphate and incorporate it or simulate it into their tissues, then animals come along they eat the plants and then they gain the access to phosphates in that manner. When they die decomposers can break down the phosphates that are in the animals or in the plants and return that phosphate to the soil where it can be picked up again by plants. Now sometimes if there's sufficient run off say there's rain falling onto the soil you can wind up leeching that into the water. Well sometimes water ways can send phosphate into the soil by letting it enter into the ground water. In water bodies ultimately you'll start having sedimentation occur as you get the build up of the phosphate they'll start binding to other things and forming soil precipitates.

And this will ultimately return the phosphate into the geologic strata as you form new sedimentary rocks restarting the phosphorus cycle.