The movement of nutrient elements through the various components of an ecosystem is called

The correct answer is A) Bio-geo-chemical cycle. The term describes how nutrients such as carbon, nitrogen, phosphorus and sulphur move between living organisms (biotic) and the air, water, soil and rock (abiotic) of an ecosystem, and come back into use again.

• B) Bio-geological cycle: Not the standard term. The accepted name is biogeochemical, because the chemical forms of the elements are what cycle.
• C) Ecological succession: This is the orderly change in species composition of a community over time, such as bare rock becoming forest. It does not describe nutrient movement.
• D) Biological cycle: Too vague and not the term used in ecology. Biological processes such as respiration and photosynthesis drive the cycles, but the cycles themselves are biogeochemical.

Cycles are of two broad kinds. Gaseous cycles (carbon, nitrogen, oxygen) have a large atmospheric reservoir. Sedimentary cycles (phosphorus, sulphur, calcium) have a rock and soil reservoir. For Mains, link this to nitrogen loading from fertilisers, eutrophication in water bodies, and the carbon cycle's role in climate change.

Trap: Aspirants often pick D because it sounds natural. Do not confuse nutrient cycling with energy flow, which is one-way and is not recycled.