In a food chain, only 10% of energy is passed onto the next trophic level. The remaining energy is lost in metabolic processes and as heat released during respiration. Thus, if originally 50,000 kJ of energy is available to the producers, at the second trophic level (primary consumers), 10% of 50,000 kJ = 5000 kJ of energy will be available. At the third trophic level (secondary consumer), 10% of 5000 kJ = 500 kJ of energy will be available.Hence, 500 kJ energy is transferred from primary consumers to secondary consumers.