If grass stores 2,000 energy units received from the sun, the ecological efficiency of the ecosystems is 10% and the trophic levels are grass - cow - human, how many units of energy does the human receive of the original 2000 units?

20 units of energy

Explanation:

Given that the ecological efficiency of the ecosystem is 10%, (meaning as energy is transferred from one trophic level to another, 90% of energy is being lost), units of energy the human received of the original 2000 units can be calculated as follows:

Energy received by grass = 2000 units

Energy transferred to cow = 10% of 2000 units = 10/100 * 2000 units = 200 units (1800 units is lost)

Energy transferred from cow to the human = 10% of 200 units = 10/100 * 200 = 20 units (180 units lost)

Only 20 units of the original 2000 units is received by the human.