Answer:
The correct answer is the sun.
The sun is the ultimate source of energy of a food chain. This energy is trapped by the green photosynthetic plants under the process of photosynthesis.
Plants only absorb 2-8% of the PAR (photosynthetically active radiation- 400 700 nm) fallen on earth.
In addition, only 10% of the energy is transferred from one trophic level to the next one and rest 90% is dissipated in metabolic process or heat.
It is the reason that earth receives 10,000 times the total energy used by human beings as we are present on I and II trophic levels in a food chain.
