If grass stores 1,000 energy units received from the sun, the ecological efficiency of the ecosystem is 10%, and the trophic levels are grass → cow → human, how many units of energy does the human receive of the original 1,000 units? a. 1b.900c. 10d. 100e. 200

Answer is D

Explanation:

If we start with 1000 units of energy, according with the text, 10%  of those initial units (1000) which are contained in the grass, are passed to the next trophic level, so the cow receives 100 energy units. When tha chain continues, the 10% from the cow passes to the human, which is equal to 10 energy units.

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