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Difficulty: MediumEcology and Environment

In a freshwater lake ecosystem, microscopic phytoplankton are consumed by zooplankton, which are then eaten by minnows and larger predatory fish. Which group of organisms in this food web contains the largest total amount of usable energy?

  1. A
    Minnows
  2. PhytoplanktonAnswer
  3. C
    Zooplankton
  4. D
    Larger predatory fish

Answer

Phytoplankton
Primary producers (phytoplankton) synthesize organic matter directly from solar energy and form the foundation of the ecological pyramid, retaining the greatest total biomass and usable energy in the ecosystem.

Step-by-Step Solution

1
Identify the trophic position of each organism in the freshwater food chain
Phytoplankton are primary producers, zooplankton are primary consumers, minnows are secondary consumers, and larger predatory fish are tertiary consumers.
Energy distribution across an ecosystem depends strictly on the trophic hierarchy.
2
Apply the rule of energy transfer across trophic levels
Only approximately 10% of energy transfers from one trophic level to the next, while 90% is lost through cellular respiration and heat.
The base level (producers) captures sunlight and must contain the greatest total pool of usable energy.

Key Concept

Trophic levels and energy pyramid dynamics in aquatic ecosystems
Estimated Time:45s
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Topics

Ecology and Environment

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