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Difficulty: MediumEcological Functions, Nutrient Cycles and Ecological Succession

Evaluate the following statements regarding biogeochemical nutrient cycling and micro-organism functions in ecosystems:

Statement I: The primary reservoir pool for gaseous nutrient cycles resides in the atmosphere or hydrosphere, whereas for sedimentary nutrient cycles, the primary reservoir is located in the Earth's crust.
Statement II: Nitrosomonas and Nitrobacter are denitrifying bacteria responsible for returning elemental nitrogen gas to the atmosphere from soil nitrates.

Which of the statements given above is/are correct?

  1. Only Statement I is correctAnswer
  2. B
    Only Statement II is correct
  3. C
    Both Statement I and Statement II are correct
  4. D
    Neither Statement I nor Statement II is correct

Answer

Only Statement I is correct
Statement I is true because gaseous nutrient cycles maintain their major storage reservoir in the atmosphere or hydrosphere, ensuring rapid cycling and quick replacement of deficits. Sedimentary cycles store nutrients predominantly in sedimentary rocks and soil minerals, leading to much slower cycling. Statement II is false because Nitrosomonas and Nitrobacter perform nitrification (ammonia oxidation to nitrate), whereas denitrification is conducted by specialized bacteria such as Pseudomonas and Micrococcus denitrificans under anaerobic conditions.

Step-by-Step Solution

1
Analyze Statement I regarding reservoir pools of biogeochemical cycles
Gaseous nutrient cycles (e.g., Nitrogen, Carbon) have reservoirs in the atmosphere or ocean. Sedimentary nutrient cycles (e.g., Phosphorus, Calcium) have reservoirs in Earth's crustal rocks.
Statement I correctly defines the fundamental location of abiotic reservoir pools.
2
Analyze Statement II regarding the ecological role of Nitrosomonas and Nitrobacter
Nitrosomonas converts ammonia (NH3NH_3) to nitrite (NO2−NO_2^-), and Nitrobacter converts nitrite to nitrate (NO3−NO_3^-). This process is nitrification.
Statement II incorrectly classifies these organisms as denitrifying bacteria. Denitrification converts nitrates back into nitrogen gas (N2N_2) and is performed by organisms like Pseudomonas.
3
Synthesize results to select the correct evaluation
Statement I is correct and Statement II is incorrect.
Only Statement I meets scientific accuracy.

Key Concept

Classification of biogeochemical nutrient cycles (gaseous vs sedimentary) and biological steps in the nitrogen cycle.
Estimated Time:1m 15s
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Topics

Ecological Functions, Nutrient Cycles and Ecological Succession