Question

Which of the following is not a gaseous type of biogeochemical cycle?

• A. Carbon cycle
• B. Nitrogen cycle
• C. Phosphorus cycle
• D. Oxygen cycle

Answer 1

The correct option is C Phosphorus cycle

Unlike carbon and oxygen cycle, there is no respiratory release of phosphorus into the atmosphere. Phosphorus is a major constituent of biological membranes, nucleic acids and cellular energy transfer systems. Phosphorus is needed by many animals to make shells, bones and teeth. Rocks are the natural reservoir of phosphorus and its cycling pool is lithosphere. It contains phosphorus in the form of phosphates. When rocks are weathered, small amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants. Herbivores and other animals obtain this element from plants. Gaseous exchanges of phosphorus between organism and environment are negligible
A considerable amount of carbon returns directly to the atmosphere as ${\mathrm{CO}}_2$ (gaseous form) through the respiratory activities of the humans.
The oxygen cycle is interconnected with the carbon cycle.
All green plants during the process of photosynthesis release oxygen back into the atmosphere as a by-product. All aerobic organisms use free oxygen for respiration. Animals exhale carbon dioxide back into the atmosphere which is again used by the plants during photosynthesis. Now oxygen is balanced within the atmosphere.
In the atmosphere, nitrogen exists as a gas ($N_2$), but in the soil, it mainly exists as nitrates and nitrites.