The movement of nutrient elements through the various components of an ecosystem is called
- (a)Bio-geo-chemical cycle
- (b)Bio-geological cycle
- (c)Ecological succession
- (d)Biological cycle
Correct — A, Bio-geo-chemical cycle. The cyclic movement of nutrient elements (such as carbon, nitrogen, phosphorus, sulphur and water) through the living (biotic) and non-living (abiotic — atmosphere, hydrosphere, lithosphere) components of an ecosystem is called a biogeochemical cycle. The name captures it exactly: 'bio' (living organisms) + 'geo' (rock, soil, air, water) + 'chemical' (the elements involved). Nutrients are continually recycled between organisms and their physical environment.
- (b)Bio-geological cycle — Not the standard term. It drops the 'chemical' element of nutrient cycling and is not the recognised name for the movement of nutrients through an ecosystem.
- (c)Ecological succession — Succession is the gradual, orderly change in the species composition of a community over time (e.g. bare rock to grassland to forest) — it is about community development, not the cycling of nutrient elements.
- (d)Biological cycle — Too narrow and vague — it implies only the living component, whereas nutrient cycling also passes through the geological and atmospheric (abiotic) reservoirs, which the term 'geo-chemical' captures.
In an ecosystem, energy flows in one direction (unidirectional, entering as sunlight and lost as heat) but nutrients are recycled. A biogeochemical cycle is the pathway by which a nutrient element moves between the biotic community and the abiotic reservoirs (atmosphere, water, soil/rock). Decomposers return elements from dead matter to the abiotic pool, closing the loop.
The phrase 'movement of nutrient elements through the components of an ecosystem' is the textbook definition of a biogeochemical cycle. Ecological succession (c) is the classic distractor because it also involves ecosystem change — but it describes changing communities, not nutrient movement.
- Biogeochemical cycle = cyclic movement of nutrients through biotic + abiotic components of an ecosystem
- The name breaks down as bio (organisms) + geo (rock/soil/air/water) + chemical (elements)
- Two types: gaseous cycles (C, N, O — reservoir in atmosphere/ocean) and sedimentary cycles (P, S — reservoir in rocks/soil)
- Energy flow through an ecosystem is one-way; nutrients are recycled, with decomposers completing the loop
Nutrients cycle from the abiotic pool through organisms and back via decomposers — this loop is the biogeochemical cycle (a).
- Confusing biogeochemical cycling (nutrients, cyclic) with energy flow (one-way)
- Picking ecological succession, which is about changing communities rather than nutrient movement
UPPSC/UPSC ask the definition, or ask you to classify gaseous vs sedimentary cycles, or to identify the cycle that lacks a gaseous phase (phosphorus).
In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?
- (a) Carbon cycle
- (b) Nitrogen cycle
- (c) Phosphorus cycle
- (d) Sulphur cycle
Answer(c) Phosphorus cycle
Same concept — biogeochemical cycles. UPSC tests the sedimentary phosphorus cycle, where weathering of rocks releases the nutrient, applying the very idea this question defines.
- practice — not a real PYQ
Which of the following is a sedimentary biogeochemical cycle with no significant gaseous (atmospheric) phase?
- (a)Phosphorus cycle
- (b)Carbon cycle
- (c)Nitrogen cycle
- (d)Oxygen cycle
Answer(a) Phosphorus cycle — its main reservoir is rock/soil (sedimentary), with no major gaseous form.
- practice — not a real PYQ
In an ecosystem, the flow of energy is ______ whereas the movement of nutrients is ______.
- (a)unidirectional; cyclic
- (b)cyclic; unidirectional
- (c)cyclic; cyclic
- (d)unidirectional; unidirectional
Answer(a) unidirectional; cyclic — energy flows one way and is lost as heat, while nutrients are recycled.