In a lake ecosystem the annual net primary productivity (NPP) of phytoplankton is 1500 g m⁻² yr⁻¹. Zooplankton consume 20 % of this production, small fish consume 30 % of the zooplankton production, and large fish consume 25 % of the small‑fish production.

(a) Calculate the annual production (in g m⁻² yr⁻¹) that reaches the large‑fish level.

(b) Determine the overall ecological efficiency from primary production to large fish, expressed as a percentage, and comment on how this compares with the typical 10 % rule.

Question

In a lake ecosystem the annual net primary productivity (NPP) of phytoplankton is 1500 g m⁻² yr⁻¹. Zooplankton consume 20 % of this production, small fish consume 30 % of the zooplankton production, and large fish consume 25 % of the small‑fish production.

(a) Calculate the annual production (in g m⁻² yr⁻¹) that reaches the large‑fish level.

(b) Determine the overall ecological efficiency from primary production to large fish, expressed as a percentage, and comment on how this compares with the typical 10 % rule.

Accepted Answer

22.5 g m⁻² yr⁻¹; overall efficiency 1.5 % (much lower than the 10 % rule)

Igcse Model Questions Vol1 2025 Biology Question 23

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