(c) :The source of energy in all ecosystem is solar energy. About $50\%$ of the solar energy incident over earth is present in $PAR$ (Photosynthetically active radiation). About $1-5\%$ of incident solar radiation or $2 -10\%$ of $PAR$ is captured by the photosynthetic organisms in the synthesis of organic matter (gross primary productivity). Roughly $20\%$ of it is consumed in respiration so that net capture of energy (net primary productivity) is $0.8 -4\%$ of incident radiation or $1.6 -8\%$ of $PAR$.