SAT Subject Biology Practice Question 139: Answer and Explanation

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Question: 139

9. In a tropical food web, 800,000 kJ of energy are produced by autotrophic species. Approximately how much energy will exist at the level of secondary consumers?

A. 80 kJ
B. 800 kJ
C. 8,000 kJ
D. 80,000 kJ
E. 800,000 kJ

Correct Answer: C


In a trophic pyramid, primary producers form the base, creating all the energy that will travel up through the pyramid. Just above the producers are primary consumers, which are herbivores that obtain all their energy directly from producers. To obtain that energy also requires energy, and so the amount of energy created by producers is not the same amount that moves up. Approximately 10% of energy is lost for every move up the pyramid, so in this example for the 800,000 kJ of energy produced, only 80,000 kJ will be present for primary consumers, the next level. Secondary consumers are the next level up, feeding on primary consumers, so another 10% of that level's energy will be lost, putting 8,000 kJ at this trophic level.

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