Which process plays an important role in the biogeochemical cycles of carbon, nitrogen, and phosphorus? photosynthesis transpiration decomposition respiration

The correct answer would be decomposition.

Decomposition is a natural process by which complex organic compounds are broken down into simpler organic matter.

It plays an important role in the cycling of all the nutrients (such as nitrogen, carbon, phosphorus et cetera) or matters throughout the biosphere.

It helps in returning the nutrients to the environment (soil, water, or air) from dead plants and animals.  

For example, decomposition helps in returning the carbon contents to the soil in the form of humus which is formed by degradation or decomposition of dead organisms.

the sphincter muscles at the end of the digestive tract is the anus.