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Difficulty: MediumEcological Functions, Nutrient Cycles and Ecological Succession

With reference to ecosystem functions and nutrient cycling, consider the following statements:

1. Gaseous cycles generally have their primary reservoir pool located in the Earth's crust, whereas sedimentary cycles have their main reservoir pool in the atmosphere or hydrosphere.
2. Nitrifying bacteria such as *Nitrosomonas* and *Nitrobacter* convert ammonia into nitrites and nitrates during the nitrogen cycle.
3. The pyramid of energy is always upright in any functional ecosystem because energy is lost as heat at each successive trophic level.

Which of the statements given above are correct?

  1. A
    1 and 2 only
  2. 2 and 3 onlyAnswer
  3. C
    1 and 3 only
  4. D
    1, 2 and 3

Answer

Statements 2 and 3 are correct.
Statement 2 accurately describes the process of nitrification carried out by nitrifying bacteria (*Nitrosomonas* and *Nitrobacter*). Statement 3 accurately describes why the pyramid of energy is always upright in functional ecosystems due to progressive energy loss across trophic levels. Statement 1 is incorrect because the reservoir pool for gaseous cycles is the atmosphere or hydrosphere, whereas for sedimentary cycles, it is the lithosphere (Earth's crust). Therefore, the correct combination includes only statements 2 and 3.

Step-by-Step Solution

1
Analyze statement 1 regarding biogeochemical reservoir pools.
Gaseous nutrient cycles (e.g., carbon, nitrogen) have their main reservoir pool in the atmosphere or hydrosphere. Sedimentary cycles (e.g., phosphorus, sulfur) have their primary reservoir pool in the lithosphere (Earth's crust/rocks). Statement 1 incorrectly swaps these definitions.
To evaluate the correct reservoir pool classifications.
2
Analyze statement 2 regarding nitrogen transformation.
Nitrification is a two-step biological oxidation process where *Nitrosomonas* converts ammonia into nitrite (NO2−NO_2^-) and *Nitrobacter* converts nitrite into nitrate (NO3−NO_3^-). Thus, statement 2 is correct.
To verify the roles of specific microbial organisms in the nitrogen cycle.
3
Analyze statement 3 regarding ecological pyramids.
Energy flows unidirectionally and diminishes at higher trophic levels (governed by the 10% law of energy transfer), making the pyramid of energy universally upright in all ecosystems without exception. Statement 3 is correct.
To confirm thermodynamic principles governing energy flow.

Key Concept

Classification of Biogeochemical Cycles and Trophic Energy Flow
Estimated Time:1m 15s
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Topics

Ecological Functions, Nutrient Cycles and Ecological Succession