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BotanyNEET 2024Energy flow, ecological pyramids

Ecosystem

In an ecosystem, if the Net Primary Productivity (NPP) of the first trophic level is 100x (kcal m−2) yr−1100x\ (\mathrm{kcal\,m^{-2}})\,\mathrm{yr^{-1}}, what would be the GPP (Gross Primary Productivity) of the third trophic level of the same ecosystem?

  1. A.x (kcal m−2) yr−1x\ (\mathrm{kcal\,m^{-2}})\,\mathrm{yr^{-1}}
  2. B.10x (kcal m−2) yr−110x\ (\mathrm{kcal\,m^{-2}})\,\mathrm{yr^{-1}}✓
  3. C.100x3 (kcal m−2) yr−1\dfrac{100x}{3}\ (\mathrm{kcal\,m^{-2}})\,\mathrm{yr^{-1}}
  4. D.x10 (kcal m−2) yr−1\dfrac{x}{10}\ (\mathrm{kcal\,m^{-2}})\,\mathrm{yr^{-1}}

Solution

By the 10% law each trophic level passes on about a tenth of its production. From a producer NPP of 100x100x, the second level takes in 10x10x. The official key marks 10x10x — it treats the third level's gross intake as the energy handed on by the level below it. (Applying the 10% step once more, the third level's own NPP would be xx; that is not what was marked.)

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