AP Environmental Science › Phosphorus Cycle
Which biogeochemical cycle is the only one without an atmospheric component?
The phosphorus cycle
The sulfur cycle
The nitrogen cycle
The carbon cycle
All of the other cycles have at least one atmospheric component in their systems. The carbon cycle incorporates carbon dioxide in the photosynthesis portion of its cycle. The sulfur cycle incorporates gaseous sulfur dioxide when it is released by volcanic eruptions. The water cycle has the condensation of clouds in the atmosphere and the precipitation of those clouds as well. The nitrogen cycle incorporates atmospheric nitrogen gas before it is fixed by cyanobacteria. Only the phosphorus cycle does not have a phosphorus containing compound in the atmosphere that is essential for life on Earth.
The phosphorus cycle is fundamentally different from the nitrogen and sulfur cycles. How so?
The phosphorus cycle does not include a gaseous phase, resulting in no significant quantities of atmospheric phosphorus.
Phosphorus is not fixed in the atmosphere by lightning.
Phosphorus does not enter the cycle from weathering of sediments and parent material.
Phosphorus is not taken up by plants and is a strictly inorganic cycle.
Phosphorus is cycled back into the soil through precipitation.
The phosphorus cycle does not contain an atmospheric phase, while both the sulfur and nitrogen cycles do.
Which of the following is the major reservoir for phosphorus in the phosphorus cycle?
Rock
Rainwater
Plants
Animals
Soil
The reservoir of phosphorus in ecosystems is rock, where it is bound to oxygen in the form of phosphate. As phosphate-rich rocks are exposed and eroded, rainwater dissolves the phosphate. Dissolved phosphate is abosrbed through the roots of plants. Animals eat the plants and after they die decomposers return the phosphorus that remains in the dead bodies back to the soil and water. It may then be reincorporated into rock.