Final answer:
The ecological efficiency of the lake ecosystem is calculated to be 19%. This is determined by dividing the energy at the higher trophic level by the energy at the lower trophic level and then multiplying by 100.
Step-by-step explanation:
The ecological efficiency for an ecosystem can be calculated using the following formula:
Ecological Efficiency = (Energy at higher trophic level / Energy at lower trophic level) × 100
In this case, the direct answer to the student's question is 19%, which is calculated as follows:
Ecological Efficiency = (190J / 1000J) × 100 = 19%
The ecological efficiency measures the amount of energy that is transferred from one trophic level to the next. In the context of this question, only 190 Joules of the initial 1000 Joules available at one trophic level are present in the next higher trophic level. This is a clear indication that a significant portion of energy is lost due to metabolic processes and as heat, which is consistent with the second law of thermodynamics. As a result, the overall energy transfer efficiency is quite low, in this case, only 19%. Consequently, energy pyramids in ecosystems usually demonstrate a rapid decrease in biomass and energy availability as one moves up the trophic levels, explaining why there are seldom more than four trophic levels in an ecosystem.