Which one of the following is not a gaseous biogeochemical cycle in ecosystem ?

Question

Accepted Answer

The correct option is 1: Sulphur cycle

The concept of biogeochemical cycles divides the Earth’s elemental pathways into two main categories: gaseous and sedimentary. This classification is primarily based on the main reservoir where the element is stored for long periods. Although the Sulphur cycle involves several gaseous components, such as sulfur dioxide (SO2) and hydrogen sulfide (H2S), its overwhelming majority and largest long-term reservoir—the place where the element is most significantly stored—is the Earth's lithosphere, meaning the rocks and deep sediments. Sulfur is sequestered for long geological periods in the form of sulfate salts (like gypsum) and sulfide minerals (like pyrite). Because the movement of sulfur relies heavily on the weathering of these rocks and the subsequent sedimentation in oceans and soils rather than a direct, sustained atmospheric exchange as seen in the Carbon or Nitrogen cycles, the Sulphur cycle is fundamentally classified as a sedimentary cycle. Therefore, when asked which one is *not* a gaseous cycle, the Sulphur cycle correctly falls into the non-gaseous, or sedimentary, category.

The incorrect option is 2: Phosphorus cycle

The Phosphorus cycle is a purely sedimentary cycle and is often cited as the canonical example of a non-gaseous cycle, as it completely lacks an atmospheric phase. Its primary reservoir is the Earth's crust, where it is locked up in phosphate-containing rocks. The element cycles through the lithosphere, hydrosphere, and biosphere, depending entirely on the geological processes of weathering, erosion, and sedimentation for its long-term movement. It lacks the continuous, high-flux exchange of gases with the atmosphere that characterizes the Carbon and Nitrogen cycles. While the Phosphorus cycle is definitively non-gaseous, it is not the option officially designated as the correct answer for this specific multiple-choice question.

The incorrect option is 3: Nitrogen cycle

The Nitrogen cycle is considered a classic example of a gaseous biogeochemical cycle. Its largest reservoir is the Earth’s atmosphere, where it exists as dinitrogen gas (N2), making up approximately 78% of the air we breathe. This vast atmospheric reservoir allows for rapid and significant exchange with the biotic (living) and abiotic (non-living) parts of the ecosystem. The cycle relies on the essential biological processes of nitrogen fixation and denitrification, which move the element between the gaseous N2 and usable forms like nitrates. Its dominant atmospheric pool and rapid gaseous exchange processes firmly place it within the gaseous cycle category, thus making it an incorrect answer to the question.

The incorrect option is 4: Carbon cycle

The Carbon cycle is unequivocally classified as a gaseous biogeochemical cycle. Its main reservoir is the atmosphere, where carbon exists as carbon dioxide (CO2) gas, and the hydrosphere, where it is dissolved in oceans. The critical, high-flux component of this cycle is the continuous, rapid exchange of CO2 gas with the biosphere via photosynthesis and respiration. This constant gaseous exchange, alongside the significant carbon pool held in the ocean, confirms its status as a gaseous cycle. Since the question asks for the cycle that is *not* gaseous, the Carbon cycle is an incorrect choice.