According to the 10 per cent law of energy flow, only 10 per cent of the energy is transferred to each trophic level from the lower trophic level . If the NPP of the first trophic level (producers) is 100x, the second trophic level (primary consumers) receives 10% (10x), and the third trophic level (secondary consumers) receives 10% of that, which is x . Note: While the term Gross Primary Productivity is technically defined as the rate of production of organic matter during photosynthesis by producers , in the context of this calculation regarding energy transfer across levels, it refers to the energy assimilated at the third level.