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Difficulty: MediumEcological Functions, Nutrient Cycles and Ecological Succession

In the context of ecological functions and biogeochemical nutrient cycling, consider the following statements:

1. 'Standing state' refers to the total amount of inorganic nutrients present in the abiotic component of an ecosystem at any given time.
2. In a typical pond ecosystem, the pyramid of biomass is inverted because the standing crop of phytoplankton is lower than the biomass of the consumers it supports.
3. Denitrification is an aerobic biological process that converts atmospheric nitrogen directly into soil nitrates.

Which of the statements given above are correct?

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

Answer

Statements 1 and 2 are correct, while statement 3 is incorrect.
The first statement accurately defines 'standing state' as the total quantity of inorganic nutrients (such as nitrogen, phosphorus, and calcium) present in the soil or abiotic environment at a specific time. The second statement is correct because aquatic ecosystems exhibit an inverted pyramid of biomass due to the rapid reproduction and high turnover rate of microscopic producers (phytoplankton), which support a larger standing biomass of primary and secondary consumers. The third statement is incorrect because denitrification is an anaerobic process mediated by specialized bacteria that reduces soil nitrates into elemental nitrogen gas (N2N_2), rather than an aerobic process fixing atmospheric nitrogen.

Step-by-Step Solution

1
Evaluate Statement 1 regarding standing state
Statement 1 is correct.
Standing state (or standing quality) is defined as the amount of inorganic nutrients, such as nitrogen, phosphorus, and calcium, present in the soil or abiotic environment of an ecosystem at a given time, distinct from 'standing crop' which measures living biomass.
2
Evaluate Statement 2 regarding pyramid of biomass in aquatic ecosystems
Statement 2 is correct.
In aquatic ecosystems like ponds and oceans, the pyramid of biomass is inverted because phytoplankton have very small standing crop biomass at any single moment, but high turnover rates due to rapid reproduction that support a larger standing biomass of zooplankton and fish.
3
Evaluate Statement 3 regarding denitrification process
Statement 3 is incorrect.
Denitrification is an anaerobic process carried out by specialized soil bacteria (such as Pseudomonas and Thiobacillus) that reduces nitrates (NO3−NO_3^-) back into gaseous nitrogen (N2N_2), rather than an aerobic process fixing atmospheric nitrogen.

Key Concept

Distinction between standing state and standing crop, inverted aquatic biomass pyramids, and anaerobic mechanisms of denitrification
Estimated Time:1m 30s
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Topics

Ecological Functions, Nutrient Cycles and Ecological Succession