In the following food chain, if 50 J of energy was available to the hawk, how much energy would have been present at the first and third tropic levels? Justify your answer. Grass $\longrightarrow$ Grasshopper $\longrightarrow$ Frog $\longrightarrow$ Snake $\longrightarrow$ Hawk

At the first trophic level (Grass), the energy present was $500,000\text{ J}$ (or $5 \times 10^5\text{ J}$). At the third trophic level (Frog), the energy present was $5,000\text{ J}$ (or $5 \times 10^3\text{ J}$).

Justification: According to the 10% law of energy transfer in an ecosystem, only an average of 10% of the food/energy eaten is turned into organic matter and made available for the next level of consumers. Therefore, when moving backwards from a higher trophic level to a lower trophic level, the energy available at each preceding level must be 10 times greater than the level succeeding it.