Question

Phosphorus cycle is an example of ……. Cycle.

Answer 1

The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Phosphorus moves in a cycle through rocks, water, soil and sediments and organisms. The sedimentary rocks, as well as the other type of rocks on weathering, gives rise to the cycling of phosphorus from the abiotic to the biotic and back.

Complete answer:
The Phosphorus cycle is an excellent example of a sedimentary cycle. Phosphorus is an important element, required by organisms for their normal growth and development. It is an essential constituent of nucleic acids, energy-rich phosphates, bone, teeth etc. The principal reservoirs of phosphorus are the phosphate rocks. The fossil deposits of the bones of extinct animals and excrement deposits of fish- eating seabirds are also important reservoirs of phosphorus. Through soil erosion and running waters, some phosphorus from the reservoirs gets distributed in the soil. This forms the ‘phosphorus pool’ of the soil. Plants absorb phosphorus from this pool. From plants, phosphorus enters the food chain and reaches animals. From animals, a small amount of phosphorus is returned to the soil through their excreta. After the death and decomposition of plants and animals, a large amount of phosphorus is returned to the soil for recycling.

Additional Information:
- From the phosphorus pool of the main cycle, large amounts of dissolved phosphorus will be lost to sea through run down transport.
- They form shallow marine sediments. A small portion of them may be returned to land by fish- eating seabirds, which deposits excrement on the shores.
- A small amount may be returned to inland waters by some anadromous fishes, such as salmons, which migrate from seas to rivers for spawning.

Note:
- A considerable return of phosphorus from sea to land is affected by fish harvest. Most of the shallow marine sediments will be lost to deep sediments.
- It will not be normally recycled and hence it is lost from the living world.
- From deep marine sediments, phosphorus may be brought to terrestrial reservoirs only through major geological upheavals, which may occur once in a million years.