In an aquatic ecosystem, a shark has 5J of energy left in a plankton → zooplankton → small fish → large fish (shark) food chain. The energy available at the plankton level is:

5,000 J

The correct answer is Option (3) - 5,000 J

To understand the energy transfer in a food chain, we need to consider the concept of energy efficiency between trophic levels. Typically, only about 10% of the energy at one trophic level is transferred to the next level; the remaining 90% is lost as heat, used for metabolic processe.

So, Shark (top predator) has 5J.

Small fish (prey of the shark): Assuming a 10% transfer efficiency, the small fish must have had 10 times the energy the shark has:

Energy of small fish=5J×10=50J

Zooplankton (prey of the small fish): Assuming a 10% transfer efficiency, the zooplankton must have had 10 times the energy the small fish has:

Energy of zooplankton=50J×10=500J

Plankton (producers): Assuming a 10% transfer efficiency, the plankton must have had 10 times the energy the zooplankton has:

Energy of plankton=500J×10=5,000J

Therefore, the energy available at the plankton level is: 5,000 J

The 10% rule of energy transfer between trophic levels helps us estimate the energy available at each level in the food chain.